1 00:00:00,040 --> 00:00:01,640 Hello and welcome back to the Dee Dive. 2 00:00:02,040 --> 00:00:05,600 Today we are shifting gears. We are moving away from general 3 00:00:05,600 --> 00:00:09,720 curiosity and stepping right into the high pressure, high 4 00:00:09,720 --> 00:00:12,120 stakes environment of the medical examination hall. 5 00:00:12,200 --> 00:00:14,840 That's right. Specifically, we are simulating 6 00:00:14,840 --> 00:00:18,640 a hardcore prep session for a Gujarat University MD 7 00:00:18,640 --> 00:00:20,560 Anesthesiology student. Right. 8 00:00:20,560 --> 00:00:23,080 And if you are listening to this, you likely have the 9 00:00:23,080 --> 00:00:27,480 distinct pleasure or terror of facing a thoracic anesthesia 10 00:00:27,480 --> 00:00:31,600 case in your practicals or staring down a 20 mark long 11 00:00:31,600 --> 00:00:33,560 theory question on this exact topic. 12 00:00:33,600 --> 00:00:35,560 Exactly. So for the next hour, I'm going 13 00:00:35,560 --> 00:00:38,800 to adopt the persona of your senior faculty member, maybe 14 00:00:38,800 --> 00:00:42,080 even that slightly intimidating external examiner sitting across 15 00:00:42,080 --> 00:00:44,640 the table peering over their glasses for you to slip up. 16 00:00:44,640 --> 00:00:47,120 And I'll be the learner, the resident who has, you know, 17 00:00:47,120 --> 00:00:50,720 frantically read Miller Morgan and Mikhail and Yao and Artuzio 18 00:00:50,720 --> 00:00:54,520 the night before, but needs to synthesize all that dense text 19 00:00:54,720 --> 00:00:58,200 into a coherent, passing answer. It's a lot to bring together 20 00:00:58,200 --> 00:01:00,000 under pressure. It really is. 21 00:01:00,000 --> 00:01:02,120 Our mission today is crystal clear. 22 00:01:02,440 --> 00:01:06,520 We are cracking the code on one lung ventilation or OLV. 23 00:01:06,520 --> 00:01:10,480 We are going to cover the indications, the incredibly 24 00:01:10,480 --> 00:01:14,160 complex Physiology, the hardware and, of course, the management 25 00:01:14,160 --> 00:01:16,600 of that dreaded intraoperative hypoxia. 26 00:01:16,720 --> 00:01:20,040 It is the absolute bread and butter of thoracic anesthesia. 27 00:01:20,040 --> 00:01:23,320 I mean, if you cannot manage OLV, you simply cannot call 28 00:01:23,320 --> 00:01:26,040 yourself a thoracic anesthetist. It's that fundamental. 29 00:01:26,040 --> 00:01:29,520 It is, and from an exam perspective, this topic is a 30 00:01:29,520 --> 00:01:32,200 goldmine for examiners. It tests your Physiology, your 31 00:01:32,200 --> 00:01:34,760 pharmacology, your physics, and your crisis management all at 32 00:01:34,760 --> 00:01:36,400 once. So let's get serious. 33 00:01:36,400 --> 00:01:38,440 Let's do it. Let's jump right into Part A, 34 00:01:38,440 --> 00:01:41,720 introduction and exam framing. If I'm sitting in the exam hall 35 00:01:41,720 --> 00:01:45,160 and I get a question on OLV or the examiner asked me to define 36 00:01:45,160 --> 00:01:48,000 it, how do I set the scene? I need a definition that you 37 00:01:48,000 --> 00:01:50,680 know, screams competence. You need to be crisp and 38 00:01:50,680 --> 00:01:52,680 academic. Do not just say breathing with 39 00:01:52,680 --> 00:01:56,080 one lung, that's too simplistic. One lung ventilation is defined 40 00:01:56,080 --> 00:01:58,840 as the mechanical separation of the two lungs to allow 41 00:01:58,840 --> 00:02:01,160 ventilation of one lung while the other is allowed to 42 00:02:01,160 --> 00:02:03,200 collapse. Separation and isolation, those 43 00:02:03,200 --> 00:02:05,320 are the keywords. Those are the keywords. 44 00:02:05,320 --> 00:02:07,520 It shows you understand the core principle. 45 00:02:07,760 --> 00:02:11,480 You're not just turning 1 lung off, you're creating a physical 46 00:02:11,480 --> 00:02:14,520 barrier between the two. And strictly speaking, why do we 47 00:02:14,520 --> 00:02:16,840 do it? I mean, biologically, we're 48 00:02:16,840 --> 00:02:19,880 designed to use both lungs. Collapsing one seems completely 49 00:02:19,880 --> 00:02:22,440 counterintuitive. It is, and that's the central 50 00:02:22,440 --> 00:02:25,960 challenge, but it's the defining skill of our subspecialty 51 00:02:25,960 --> 00:02:29,080 because it achieves 2 absolutely critical things. 52 00:02:29,640 --> 00:02:32,440 First, it provides a still surgical field, the so-called 53 00:02:32,440 --> 00:02:34,600 quiet lung. Right, the surgeon needs to see 54 00:02:34,600 --> 00:02:37,120 what they're doing. They do modern thoracic surgery, 55 00:02:37,120 --> 00:02:39,040 especially video assisted techniques. 56 00:02:39,040 --> 00:02:43,400 VATS is impossible if the lung is inflating and deflating in 57 00:02:43,400 --> 00:02:45,840 the surgeon's face. They're working with long 58 00:02:45,840 --> 00:02:49,040 instruments through tiny ports. They need a motionless target. 59 00:02:49,200 --> 00:02:51,560 And the second reason. The 2nd and arguably more 60 00:02:51,560 --> 00:02:54,520 critical reason for patient safety is it protects the 61 00:02:54,520 --> 00:02:58,600 healthy lung from contamination. Contamination like from blood or 62 00:02:58,600 --> 00:02:59,960 pus? Exactly. 63 00:02:59,960 --> 00:03:02,920 We'll get into the specific indications, but imagine one 64 00:03:02,920 --> 00:03:05,600 lung is full of infectious material or is bleeding 65 00:03:05,600 --> 00:03:08,960 massively. Without isolation, that material 66 00:03:08,960 --> 00:03:12,240 would immediately spill into the healthy, dependent lung and 67 00:03:12,240 --> 00:03:14,640 you'd have an absolute catastrophe on your hands. 68 00:03:14,680 --> 00:03:17,240 But physiologically, this is a disaster, isn't it? 69 00:03:17,240 --> 00:03:19,880 I remember reading in Miller's Anesthesia that thoracic 70 00:03:19,880 --> 00:03:24,800 anesthesia is often described as a physiological trespass. 71 00:03:24,960 --> 00:03:28,000 That is the perfect phrase to use in an introduction 72 00:03:28,000 --> 00:03:31,320 physiological trespass. It shows the examiner you 73 00:03:31,320 --> 00:03:33,200 appreciate the gravity of what you're doing. 74 00:03:33,200 --> 00:03:35,120 So what does that mean exactly? Think about it. 75 00:03:35,280 --> 00:03:38,600 We are deliberately creating a massive right to left 76 00:03:38,640 --> 00:03:42,040 intrapulmonary shunt. We are collapsing a lung, so 77 00:03:42,040 --> 00:03:45,160 ventilation the V in VQ becomes 0. 78 00:03:45,160 --> 00:03:48,200 The blood flow continued. But perfusion the Q continues to 79 00:03:48,200 --> 00:03:50,520 that lung. So we are actively taking venous 80 00:03:50,520 --> 00:03:53,400 blood, running it through a lung that has no oxygen oxygen, and 81 00:03:53,400 --> 00:03:56,800 then mixing that unoxygenated blood right back into the 82 00:03:56,800 --> 00:03:59,600 arterial circulation. It's a controlled physiological 83 00:03:59,600 --> 00:04:02,120 crisis. Controlled crisis is a great way 84 00:04:02,120 --> 00:04:04,960 to put it. Our entire job during OLV is to 85 00:04:04,960 --> 00:04:07,920 manage that crisis and keep the patient safe despite the 86 00:04:07,920 --> 00:04:10,240 trespass we've committed. I like that framing. 87 00:04:10,640 --> 00:04:13,480 Before we get into the weeds of how we survive that crisis, 88 00:04:13,760 --> 00:04:17,360 let's look at the exam patterns. Looking at the DMB questions and 89 00:04:17,360 --> 00:04:20,440 some Gudrat University past papers, how does this topic 90 00:04:20,440 --> 00:04:23,120 usually appear? You need to be ready for three 91 00:04:23,120 --> 00:04:25,760 distinct formats. First, the long question. 92 00:04:26,040 --> 00:04:30,360 This is your 10 or 20 marker. Discuss indications, Physiology 93 00:04:30,360 --> 00:04:34,160 and management of hypoxia during OLV that requires A structured, 94 00:04:34,240 --> 00:04:36,760 logical essay. So a full on brain dump but 95 00:04:36,800 --> 00:04:38,440 organized. Organized is the key. 96 00:04:38,440 --> 00:04:41,160 You need headings, subheadings. You can't just ramble second, 97 00:04:41,160 --> 00:04:44,000 you'll see it as short notes. OK, like 5 markers. 98 00:04:44,000 --> 00:04:47,760 Exactly, you'll see hypoxic pulmonary vasoconstriction or 99 00:04:47,760 --> 00:04:51,680 double lumen tubes or Physiology of the lateral decubitus 100 00:04:51,680 --> 00:04:54,120 position as standalone 5 mark questions. 101 00:04:54,360 --> 00:04:56,400 They're testing specific pockets of your knowledge. 102 00:04:56,520 --> 00:04:58,520 And the Viva, that's where the nerves really kick in. 103 00:04:58,720 --> 00:05:02,120 In the Viva they will physically hand you a double lumen tube and 104 00:05:02,120 --> 00:05:04,600 say identity. Identify this, tell me about it 105 00:05:04,600 --> 00:05:07,480 or they'll give you a scenario. The dreaded scenario. 106 00:05:07,480 --> 00:05:10,160 The classic 1 you are doing a lobectomy. 107 00:05:10,160 --> 00:05:13,120 The patient is on one lung ventilation and the saturation 108 00:05:13,120 --> 00:05:16,120 drops to 85%. What do you do? 109 00:05:16,200 --> 00:05:20,200 And you need a stepwise answer. You need an algorithm, a calm, 110 00:05:20,200 --> 00:05:23,640 logical, stepwise answer. If you stumble on the management 111 00:05:23,640 --> 00:05:25,680 of hypoxia, you fail the station. 112 00:05:25,880 --> 00:05:27,840 Period. Safety is paramount. 113 00:05:27,840 --> 00:05:29,600 OK, that definitely says the stakes. 114 00:05:30,040 --> 00:05:32,240 Let's move to Part B indications. 115 00:05:32,920 --> 00:05:35,440 This seems like it could be a rote memory section, but I know 116 00:05:35,440 --> 00:05:38,400 examiners are picky about the order and classification. 117 00:05:38,800 --> 00:05:40,800 How do we present this to impress them? 118 00:05:40,800 --> 00:05:44,240 Presentation is everything. Do not just vomit a list of 119 00:05:44,240 --> 00:05:46,360 surgeries onto the page. You must classify them 120 00:05:46,360 --> 00:05:49,160 logically. The standard text Morgan, Yao, 121 00:05:49,160 --> 00:05:52,200 Miller, they all classify indications into absolute and 122 00:05:52,200 --> 00:05:54,240 relative. Absolute and relative and the 123 00:05:54,280 --> 00:05:56,560 order matters. The order matters tremendously. 124 00:05:56,640 --> 00:06:00,000 If you list a lobectomy, which is a relative indication, before 125 00:06:00,000 --> 00:06:02,640 you list a massive lung Abscess, which is absolute. 126 00:06:02,960 --> 00:06:05,960 You show the examiner you don't understand clinical priority. 127 00:06:06,000 --> 00:06:08,000 You put the life saving indications first. 128 00:06:08,040 --> 00:06:09,920 OK, so let's start with the absolute indications. 129 00:06:09,920 --> 00:06:12,320 These are the must knows the non negotiables. 130 00:06:12,520 --> 00:06:16,200 The first category of absolute indications is isolation for 131 00:06:16,200 --> 00:06:19,600 contamination control. The goal here is to prevent 132 00:06:19,600 --> 00:06:22,880 spillage from a diseased lung to a healthy. 133 00:06:22,880 --> 00:06:24,840 Lung. So protecting the good lung. 134 00:06:24,960 --> 00:06:27,080 Protecting the good lung at all costs. 135 00:06:27,320 --> 00:06:31,280 Think about infection. Imagine a patient with a massive 136 00:06:31,280 --> 00:06:33,960 lung Abscess or severe Bronchiectasis. 137 00:06:34,360 --> 00:06:36,720 We're talking about a lung cavity filled with liters of 138 00:06:36,720 --> 00:06:39,480 pus. If that pus spills into the 139 00:06:39,480 --> 00:06:42,120 healthy lung when you turn the patient lateral, you've 140 00:06:42,120 --> 00:06:44,040 essentially caused bilateral pneumonia. 141 00:06:44,280 --> 00:06:46,960 You've destroyed the patient's only means of oxygenation. 142 00:06:47,000 --> 00:06:49,440 It's catastrophic. And hemorrhage fits in here too, 143 00:06:49,440 --> 00:06:52,160 I assume. Yes, massive hemoptysis. 144 00:06:52,160 --> 00:06:55,000 If a patient is bleeding heavily from a tumor or a vessel in one 145 00:06:55,000 --> 00:06:57,240 lung, you must isolate that side. 146 00:06:57,320 --> 00:07:00,120 You have to stop the healthy lung from literally drowning in 147 00:07:00,120 --> 00:07:00,800 blood. OK. 148 00:07:00,800 --> 00:07:03,680 So infection and hemorrhage, that's category one for absolute 149 00:07:03,680 --> 00:07:04,600 indications. Yeah. 150 00:07:04,600 --> 00:07:06,440 What's the second absolute category? 151 00:07:06,840 --> 00:07:09,240 The second is called differential lung ventilation. 152 00:07:09,240 --> 00:07:11,280 This is a bit more of a physiological concept. 153 00:07:11,280 --> 00:07:13,760 It's for situations where the two lungs have such a different 154 00:07:13,760 --> 00:07:16,880 mechanical properties that they simply cannot be ventilated 155 00:07:16,880 --> 00:07:19,040 together effectively via a single tube. 156 00:07:19,160 --> 00:07:21,960 The classic example being the a bronchopleural fistula. 157 00:07:22,080 --> 00:07:24,760 Exactly a bronchopleural fistula or BPF. 158 00:07:24,760 --> 00:07:27,480 Let's walk through that. A fistula is an abnormal 159 00:07:27,480 --> 00:07:30,360 connection between the bronchus and the pleural space. 160 00:07:30,440 --> 00:07:32,680 So air is leaking out. Air is leaking out. 161 00:07:32,760 --> 00:07:35,440 If you try to ventilate that patient with a standard tube, 162 00:07:35,520 --> 00:07:38,520 all the positive pressure you apply follows the path of least 163 00:07:38,520 --> 00:07:41,400 resistance. It goes straight out the fistula 164 00:07:41,400 --> 00:07:44,800 and into the chest drain. The lung doesn't inflate the air 165 00:07:44,800 --> 00:07:47,960 just bypasses it entirely. And the patient becomes hypoxic 166 00:07:47,960 --> 00:07:49,560 and hypercarbic. Very quickly. 167 00:07:49,640 --> 00:07:52,480 So to ventilate that patient at all, you must isolate the good 168 00:07:52,480 --> 00:07:55,360 lung and ventilate it alone while the fistula side is left 169 00:07:55,360 --> 00:07:57,760 open. I also have giant unilateral 170 00:07:57,760 --> 00:08:01,320 bulla on my list here under differential ventilation. 171 00:08:01,320 --> 00:08:04,440 Correct. A bulla is a large thin walled 172 00:08:04,600 --> 00:08:07,280 air SAC. If you apply positive pressure 173 00:08:07,280 --> 00:08:10,680 ventilation to a patient with a giant bulla without isolation, 174 00:08:11,040 --> 00:08:13,200 one of two bad things can happen. 175 00:08:13,680 --> 00:08:16,640 The bullet can expand and rupture, causing attention. 176 00:08:16,640 --> 00:08:18,640 Pneumothorax. Which is an emergency. 177 00:08:18,880 --> 00:08:23,600 A life threatening emergency or the bullet can act like a 178 00:08:23,600 --> 00:08:27,040 compliance sink. It's so floppy that it steals 179 00:08:27,040 --> 00:08:29,480 all the tidal volume from the healthy parts of the lung, 180 00:08:29,760 --> 00:08:33,760 leading to poorer gas exchange. So isolation is absolute. 181 00:08:33,960 --> 00:08:36,440 And there's one more rare one that always seems to pop up in 182 00:08:36,440 --> 00:08:39,559 exams. Unilateral bronchopulmonary 183 00:08:39,559 --> 00:08:42,640 lavage. Yes, specifically for a 184 00:08:42,640 --> 00:08:45,640 condition called pulmonary alveolar proteinosis. 185 00:08:45,880 --> 00:08:49,440 It's a rare disease where the alveoli fill up with a thick, 186 00:08:49,520 --> 00:08:51,840 proteinaceous Milky fluid. Right. 187 00:08:51,920 --> 00:08:53,520 And the treatment is basically to wash it out. 188 00:08:53,600 --> 00:08:56,200 Literally, the treatment is to wash the lung out with liters 189 00:08:56,200 --> 00:08:59,520 and liters of warmed saline. Obviously you cannot drown one 190 00:08:59,520 --> 00:09:01,760 lung with saline while the other is trying to breathe unless they 191 00:09:01,760 --> 00:09:04,720 are perfectly absolutely isolated from each other. 192 00:09:04,920 --> 00:09:08,560 So to summarize for an exam answer, absolute indications are 193 00:09:08,560 --> 00:09:11,240 one, protection from contamination like infection or 194 00:09:11,240 --> 00:09:14,520 hemorrhage, and two, situations requiring differential 195 00:09:14,520 --> 00:09:17,120 ventilation, like a BPF or a giant Bola. 196 00:09:17,400 --> 00:09:18,880 Perfect. Now let's talk about relative 197 00:09:18,880 --> 00:09:20,400 indications. In the real world. 198 00:09:20,400 --> 00:09:22,360 This is actually 95% of what we do, isn't it? 199 00:09:22,560 --> 00:09:26,640 It is this category is broadly termed surgical exposure. 200 00:09:26,960 --> 00:09:29,880 We collapse the lung to make the surgeon's life easier, the 201 00:09:29,880 --> 00:09:33,640 surgery faster and often safer. How do we break this down? 202 00:09:33,760 --> 00:09:37,000 We can subdivide this into high priority and lower priority, 203 00:09:37,000 --> 00:09:39,960 though the lines are blurring. High priority would include 204 00:09:39,960 --> 00:09:43,880 major procedures like a thoracic aortic aneurysm repair, a 205 00:09:43,880 --> 00:09:47,400 pneumonectomy, removal of the entire lung, or an upper 206 00:09:47,400 --> 00:09:49,400 lobectomy. Why is an upper lobectomy 207 00:09:49,400 --> 00:09:52,920 considered high priority compared to say, a middle or 208 00:09:52,920 --> 00:09:55,760 lower lobectomy? It's purely about anatomical 209 00:09:55,760 --> 00:09:57,840 access. The upper lobes are harder for 210 00:09:57,840 --> 00:09:59,400 the surgeon to get to and manipulate. 211 00:09:59,600 --> 00:10:02,520 But let's be honest, in the modern era of minimally invasive 212 00:10:02,520 --> 00:10:05,360 surgery, this distinction is becoming a bit academic. 213 00:10:05,360 --> 00:10:08,360 You mean because of UTS? Exactly, if you are doing video 214 00:10:08,360 --> 00:10:11,200 assisted thoracoscopic surgery VATS where the surgeon is 215 00:10:11,200 --> 00:10:14,440 working through tiny keyhole ports with a camera, OLV is 216 00:10:14,440 --> 00:10:17,360 effectively mandatory. They cannot see a thing if the 217 00:10:17,360 --> 00:10:21,160 lung is inflating and deflating. So for any VATS procedure, you 218 00:10:21,160 --> 00:10:24,280 can consider it a very strong, relative, almost absolute 219 00:10:24,280 --> 00:10:27,120 indication. So for the exam, I should list 220 00:10:27,200 --> 00:10:30,240 isolation for protection first as the absolute indications, 221 00:10:30,600 --> 00:10:33,960 then list surgical exposure as the relative category. 222 00:10:34,400 --> 00:10:37,000 But be sure to mention that in modern practice, especially with 223 00:10:37,080 --> 00:10:39,760 VATS, it's essentially required. Exactly. 224 00:10:39,760 --> 00:10:42,360 That nuance shows you understand both the textbook theory and the 225 00:10:42,360 --> 00:10:44,200 reality of the modern operating theater. 226 00:10:44,200 --> 00:10:47,280 It's a high scoring approach. All right, let's dive into Part 227 00:10:47,280 --> 00:10:50,840 C Physiology. This is what you call exam gold. 228 00:10:51,760 --> 00:10:54,880 If I can explain this clearly, I passed the Physiology stage and 229 00:10:54,880 --> 00:10:56,160 we talked about the shunt earlier. 230 00:10:56,600 --> 00:11:00,080 Let's really unpack the ventilation perfusion or VQ 231 00:11:00,240 --> 00:11:02,440 changes. OK, let's visualize the switch. 232 00:11:02,640 --> 00:11:05,680 The patient is anesthetized in the lateral position and you're 233 00:11:05,680 --> 00:11:09,280 ventilating both lungs. VQ is mismatched as we'll 234 00:11:09,280 --> 00:11:11,120 discuss, but it's relatively stable. 235 00:11:11,280 --> 00:11:13,760 Then you tell your assistant to clamp the lumen to the non 236 00:11:13,760 --> 00:11:15,640 dependent lung. Let's say the left lung is up 237 00:11:15,720 --> 00:11:18,320 and you clamp it's tube. So ventilation to that lung 238 00:11:18,360 --> 00:11:23,120 instantly stops v = 0. Instantly V is 0. 239 00:11:23,520 --> 00:11:25,080 But the heart doesn't know you've done this. 240 00:11:25,080 --> 00:11:27,680 It keeps pumping blood. The right ventricle keeps 241 00:11:27,680 --> 00:11:31,000 sending unoxygenated blood to the pulmonary artery, which 242 00:11:31,000 --> 00:11:34,160 splits and sends blood to both the right and the left lung. 243 00:11:34,240 --> 00:11:37,720 So perfusion Q continues to that collapsed left. 244 00:11:37,720 --> 00:11:40,040 Lung, it continues, and so that blood goes through the 245 00:11:40,040 --> 00:11:43,600 capillaries of the collapsed lung, picks up 0 oxygen and then 246 00:11:43,600 --> 00:11:46,280 returns via the pulmonary veins to the left atrium. 247 00:11:46,520 --> 00:11:49,400 That is the definition of a right to left shunt. 248 00:11:49,480 --> 00:11:52,080 Now let's look at the math, because the textbooks like Yao 249 00:11:52,080 --> 00:11:54,840 and Artuzio love the math. What kind of numbers are we 250 00:11:54,840 --> 00:11:57,640 talking about here? In a normal healthy person, the 251 00:11:57,640 --> 00:12:00,440 physiologic shunt, the small amount of blood that bypasses 252 00:12:00,440 --> 00:12:03,080 the lungs, is less than 5%. It's negligible. 253 00:12:03,080 --> 00:12:05,720 OK. When you start OLV, assuming the 254 00:12:05,720 --> 00:12:10,080 patient is on their side, roughly 40 to 50% of the cardiac 255 00:12:10,080 --> 00:12:13,360 output is still directed to that non dependent lung, at least 256 00:12:13,360 --> 00:12:15,400 initially. So theoretically, if I just 257 00:12:15,400 --> 00:12:18,920 clamp the tube without any compensatory mechanisms, I 258 00:12:18,920 --> 00:12:22,880 should have a 40 to 50% shunt? Theoretically, yes, and a 50% 259 00:12:22,880 --> 00:12:26,280 shunt is incompatible with life. Your PO2 would plummet 260 00:12:26,280 --> 00:12:28,080 instantly. You would be profoundly cyanotic 261 00:12:28,080 --> 00:12:30,320 within minutes, but that's not what happens. 262 00:12:30,360 --> 00:12:32,960 Why not? Because the body has a powerful 263 00:12:32,960 --> 00:12:37,240 intrinsic defense mechanism, and in reality the shunt usually 264 00:12:37,240 --> 00:12:40,520 settles around 20 to 30%. Still significant, but 265 00:12:40,520 --> 00:12:43,000 manageable. And that defense mechanism is 266 00:12:43,000 --> 00:12:45,200 hypoxic pulmonary vasoconstriction. 267 00:12:45,960 --> 00:12:49,160 This brings us to .4. I see this ass as a short note 268 00:12:49,160 --> 00:12:51,760 all the time. Write short notes on HPV. 269 00:12:52,120 --> 00:12:54,360 How do I structure that answer to get full marks? 270 00:12:54,360 --> 00:12:57,200 OK for a short note on HPV you need 4 parts. 271 00:12:57,400 --> 00:13:01,240 Definition, mechanism, role in OLV and factors that inhibit it. 272 00:13:01,360 --> 00:13:04,320 Let's start with the definition. Start with a precise definition. 273 00:13:04,480 --> 00:13:08,240 HPV is a protective local physiologic reflex where 274 00:13:08,240 --> 00:13:11,720 pulmonary arterioles constrict in response to low alveolar 275 00:13:11,720 --> 00:13:14,040 oxygen tension. The emphasis is on alveolar 276 00:13:14,040 --> 00:13:15,520 oxygen. Crucial distinction. 277 00:13:15,520 --> 00:13:18,160 It is not the oxygen in the blood, the PO2, that triggers 278 00:13:18,160 --> 00:13:20,160 it. Primarily it's the lack of 279 00:13:20,160 --> 00:13:22,400 oxygen in the air SAC. The Pio 2 itself itself. 280 00:13:23,000 --> 00:13:25,920 The lung senses hypoxia locally and reacts locally. 281 00:13:26,080 --> 00:13:28,680 OK, that's the definition. Now the mechanism. 282 00:13:29,320 --> 00:13:32,320 The examiner wants to know the cellular level stuff. 283 00:13:32,720 --> 00:13:34,680 How does the lung know to constrict? 284 00:13:35,360 --> 00:13:38,200 It's incredibly complex and not fully understood, but here are 285 00:13:38,200 --> 00:13:39,760 the keywords for your answer paper. 286 00:13:40,120 --> 00:13:43,200 It involves an oxygen sensor in the smooth muscle cells of the 287 00:13:43,200 --> 00:13:46,640 pulmonary arteries. Under hypoxic conditions, this 288 00:13:46,640 --> 00:13:49,840 sensor leads to an inhibition of voltage gated potassium 289 00:13:49,840 --> 00:13:51,440 channels. OK, stick with me. 290 00:13:51,920 --> 00:13:53,200 Potassium channels are inhibited. 291 00:13:53,320 --> 00:13:55,720 What happens next? Normally, potassium leaks out of 292 00:13:55,720 --> 00:13:58,840 the cell, keeping the inside of the cell negatively charged. 293 00:13:59,080 --> 00:14:01,920 When you inhibit these channels, potassium is trapped inside the 294 00:14:01,920 --> 00:14:04,000 cell. Positive charges build up. 295 00:14:04,360 --> 00:14:07,120 This causes the cell membrane to depolarize. 296 00:14:07,120 --> 00:14:09,080 And that depolarization is the trigger. 297 00:14:09,080 --> 00:14:12,080 That's the trigger. That change in voltage opens up 298 00:14:12,160 --> 00:14:14,560 L type voltage gated calcium channels. 299 00:14:14,960 --> 00:14:17,200 Calcium then floods into the cell from the outside. 300 00:14:17,440 --> 00:14:19,760 And calcium causes contraction and smooth muscle. 301 00:14:19,880 --> 00:14:22,960 Calcium binds to comodulin, which activates myosin light 302 00:14:22,960 --> 00:14:26,720 chain kinase, the actin, myosin filament slide and boom 303 00:14:26,720 --> 00:14:29,360 vasoconstriction. Is there any other pathway 304 00:14:29,360 --> 00:14:31,320 involved? I seem to remember something 305 00:14:31,320 --> 00:14:34,200 about nitric oxide. Yes, that's another important 306 00:14:34,200 --> 00:14:37,640 piece of the puzzle. Normally healthy oxygenated lung 307 00:14:37,640 --> 00:14:41,040 tissue constantly produces vasodilators like nitric oxide 308 00:14:41,040 --> 00:14:45,120 or NO and prostacyclin. They keep the vessels relaxed. 309 00:14:45,320 --> 00:14:47,320 So when the alveolus becomes hypoxic. 310 00:14:47,320 --> 00:14:49,840 Nanosynthesis drops, so you're getting a double whammy. 311 00:14:49,840 --> 00:14:52,040 You have an active vasoconstriction process 312 00:14:52,040 --> 00:14:54,960 happening due to the calcium influx, and at the same time 313 00:14:54,960 --> 00:14:57,120 you're losing the background vasodilation. 314 00:14:57,360 --> 00:14:59,840 The balance tips heavily toward construction. 315 00:15:00,320 --> 00:15:03,000 So the vessel effectively strangles the blood flow to the 316 00:15:03,000 --> 00:15:05,320 useless collapsed lung. Exactly. 317 00:15:05,440 --> 00:15:07,680 It's an elegant auto regulation system. 318 00:15:07,680 --> 00:15:10,800 It diverts blood away from the hypoxic lung towards the 319 00:15:10,800 --> 00:15:15,120 ventilated oxygen rich lung. This is what reduces the shunt 320 00:15:15,120 --> 00:15:18,600 fraction by about 50%. So instead of that catastrophic 321 00:15:18,600 --> 00:15:22,600 50% shunt, you get a more manageable 20 to 25% shunt. 322 00:15:22,680 --> 00:15:25,440 Is this response instant? Does it happen the second I 323 00:15:25,440 --> 00:15:27,200 clamp the tube? That's a great question, and 324 00:15:27,200 --> 00:15:29,200 it's the detail that will get you extra marks. 325 00:15:29,240 --> 00:15:30,960 It's biphasic. Biphasic. 326 00:15:30,960 --> 00:15:34,600 Yes, phase one is rapid. It starts within the seconds of 327 00:15:34,600 --> 00:15:38,240 the onset of hypoxia and reaches about half its maximal effect at 328 00:15:38,240 --> 00:15:41,280 around 20 to 30 minutes. But then there's a bit of a 329 00:15:41,280 --> 00:15:42,760 lull. In Phase 2. 330 00:15:42,960 --> 00:15:46,400 Phase 2 is a slower, more sustained response that kicks in 331 00:15:46,400 --> 00:15:49,400 after about 40 minutes and continues to increase for up to 332 00:15:49,400 --> 00:15:51,480 two hours. Which implies that the most 333 00:15:51,480 --> 00:15:55,680 dangerous time for hypoxia might actually be in that first 20 to 334 00:15:55,680 --> 00:15:58,720 30 minutes right at the start, before that phase two 335 00:15:58,720 --> 00:16:02,360 reinforcement really kicks in. 100% that first half hour of one 336 00:16:02,360 --> 00:16:05,360 lung ventilation is when you are most physiologically vulnerable 337 00:16:05,600 --> 00:16:08,560 and need to be most vigilant. Now here is the classic Viva 338 00:16:08,560 --> 00:16:11,240 trap. The examiner asks what factors 339 00:16:11,240 --> 00:16:14,280 inhibit HPV? Basically, what can we as 340 00:16:14,280 --> 00:16:18,280 anaesthetists do to accidentally kill this life saving reflex and 341 00:16:18,280 --> 00:16:20,360 cause hypoxia? This is a huge topic. 342 00:16:20,440 --> 00:16:23,160 If you inhibit HPV, you increase the shunt and the patient 343 00:16:23,160 --> 00:16:25,640 saturation will fall. You need to know this list cold. 344 00:16:25,640 --> 00:16:28,320 What's at the top of the list? The biggest culprit is our own 345 00:16:28,320 --> 00:16:32,600 drugs, Volatile anaesthetics, halothane, isafluorane, 346 00:16:32,600 --> 00:16:35,360 sevafluorane, dysfluorane. They are all directed 347 00:16:35,560 --> 00:16:39,760 vasodilators and they inhibit HPV in a dose dependent manner. 348 00:16:39,760 --> 00:16:41,760 So the more gas I give, the worse the inhibition. 349 00:16:41,800 --> 00:16:44,680 Precisely the general rule of thumb, the one to quote in the 350 00:16:44,680 --> 00:16:49,560 exam, is keep the volatile concentration below 1 Ms. At 351 00:16:49,560 --> 00:16:53,200 concentrations greater than one MAS, they significantly blunt 352 00:16:53,200 --> 00:16:55,600 the HPV response. So if I'm struggling with 353 00:16:55,600 --> 00:16:58,560 oxygenation during OLV, turning up the civil thorium is the 354 00:16:58,600 --> 00:17:01,040 absolute wrong move. The worst thing you can do? 355 00:17:01,280 --> 00:17:03,960 It might deepen the anesthesia and stop the patient from 356 00:17:03,960 --> 00:17:06,920 moving, but it will worsen the and make the hypoxia more 357 00:17:06,920 --> 00:17:09,880 profound. This is a major reason why TIVA, 358 00:17:09,880 --> 00:17:13,800 or total intravenous anesthesia with propofol is so popular for 359 00:17:13,800 --> 00:17:17,079 thoracic cases. Cropofol does not inhibit HPV. 360 00:17:17,119 --> 00:17:19,680 What about other drugs? Any direct vasodilator? 361 00:17:19,839 --> 00:17:22,160 Think about drugs we might use for blood pressure control. 362 00:17:22,160 --> 00:17:25,119 Nitroglycerin, Sodium nitroproside, Hydrolazine. 363 00:17:25,240 --> 00:17:27,400 They'll dilate everything, including the vessels in the 364 00:17:27,400 --> 00:17:29,640 collapsed lung, which overrides HPV. 365 00:17:29,880 --> 00:17:32,440 Beta agonists like salbutamol can also inhibit it. 366 00:17:32,600 --> 00:17:34,600 What about physiological factors? 367 00:17:34,840 --> 00:17:38,160 Things not related to drugs. Alkalosis is a big one, both 368 00:17:38,160 --> 00:17:42,520 respiratory and metabolic. Hypocapnia, a low CO2 from 369 00:17:42,520 --> 00:17:45,880 overventilating the patient, causes pulmonary vasodilation 370 00:17:45,880 --> 00:17:48,760 and blunts HPV. So if you're hyperventilating 371 00:17:48,760 --> 00:17:51,880 the patient thinking you're helping by blowing off CF2, you 372 00:17:51,880 --> 00:17:54,320 might actually be worsening their oxygenation. 373 00:17:54,360 --> 00:17:58,200 That's a key clinical point. It is also extreme changes in 374 00:17:58,200 --> 00:18:01,200 volume status. Hypervolemia can mechanically 375 00:18:01,200 --> 00:18:04,120 force vessels open. Hypothermia inhibits the 376 00:18:04,120 --> 00:18:09,040 response and finally infection. A septic or infected lung often 377 00:18:09,040 --> 00:18:12,000 doesn't vasoconstrict well because of all the inflammatory 378 00:18:12,000 --> 00:18:14,520 mediators which are potent vasodilators. 379 00:18:14,520 --> 00:18:18,200 OK, let's move to .5, the effect of anesthesia and positioning. 380 00:18:18,640 --> 00:18:21,080 We almost always do these cases in the lateral decubitus 381 00:18:21,080 --> 00:18:23,120 position. The patient is lying on their 382 00:18:23,120 --> 00:18:25,640 side. How does that by itself mess 383 00:18:25,640 --> 00:18:28,200 with VQ matching? This is a fantastic Viva 384 00:18:28,200 --> 00:18:29,840 question. You have to explain it as a tale 385 00:18:29,840 --> 00:18:32,800 of two states, the awake patient versus the anesthetized and 386 00:18:32,800 --> 00:18:34,440 paralyzed patient. Let's start with the awake 387 00:18:34,440 --> 00:18:36,320 patient lying on their side. What's happening? 388 00:18:36,520 --> 00:18:39,480 In the awake patient, gravity pulls blood down, so the 389 00:18:39,480 --> 00:18:42,240 dependent lung, the bottom lung, gets more blood flow. 390 00:18:42,800 --> 00:18:45,040 More perfusion. OK, perfusion goes down. 391 00:18:45,040 --> 00:18:47,800 What about ventilation? You'd think ventilation might go 392 00:18:47,800 --> 00:18:50,800 to the top lung because it's less squashed, but the opposite 393 00:18:50,800 --> 00:18:53,640 is true. In the awake, spontaneously 394 00:18:53,640 --> 00:18:57,280 breathing patient, the dependent part of the diaphragm is pushed 395 00:18:57,280 --> 00:18:59,520 up into the chest by the abdominal contents. 396 00:18:59,520 --> 00:19:01,920 It's more curved. And a more curved muscle is a 397 00:19:01,920 --> 00:19:04,600 stronger muscle. By the law of la place, being 398 00:19:04,600 --> 00:19:06,760 more curved gives it a mechanical advantage. 399 00:19:06,760 --> 00:19:09,160 On contraction. It acts like a stronger piston, 400 00:19:09,600 --> 00:19:12,600 so in the await patient the bottom lung gets more blood and 401 00:19:12,600 --> 00:19:15,400 more ventilation. V&Q are pretty well matched. 402 00:19:15,400 --> 00:19:17,640 So awake lateral is actually quite efficient. 403 00:19:17,760 --> 00:19:20,960 Now, what happens when we induce anesthesia and paralysis? 404 00:19:21,040 --> 00:19:23,360 Everything falls apart. First you paralyze the 405 00:19:23,360 --> 00:19:25,680 diaphragm. It turns from an active piston 406 00:19:25,680 --> 00:19:29,360 into a floppy passive sheet. Now the weight of the abdominal 407 00:19:29,360 --> 00:19:32,520 contents, the liver on the right, the stomach and spleen on 408 00:19:32,520 --> 00:19:35,360 the left pushes up and crushes the dependent lung. 409 00:19:35,360 --> 00:19:37,800 It loses compliance. So ventilation shifts. 410 00:19:38,040 --> 00:19:41,800 Yes, air is lazy. It follows the path of least 411 00:19:41,800 --> 00:19:44,040 resistance. So with positive pressure 412 00:19:44,040 --> 00:19:47,560 ventilation the air preferentially goes to the non 413 00:19:47,560 --> 00:19:51,160 dependent or upper lung which is less compressed and more 414 00:19:51,160 --> 00:19:53,440 compliant. But gravity hasn't changed. 415 00:19:53,800 --> 00:19:55,600 Blood still goes down. Exactly. 416 00:19:55,920 --> 00:19:59,080 Gravity still pulls blood to the dependent or bottom lung. 417 00:19:59,240 --> 00:20:01,480 So now you have a massive VQ mismatch. 418 00:20:01,480 --> 00:20:03,920 The blood is going down, but the air is going. 419 00:20:03,920 --> 00:20:05,760 Up. Blood goes down, the air goes 420 00:20:05,760 --> 00:20:07,600 up. It's the worst case scenario for 421 00:20:07,600 --> 00:20:10,160 gas exchange. We call this the 4060 rule. 422 00:20:10,160 --> 00:20:12,960 As a rough guide, in the lateral position under anaesthesia, 423 00:20:12,960 --> 00:20:17,080 about 60% of blood flow goes to the dependent lung and 40% goes 424 00:20:17,080 --> 00:20:19,800 to the non dependent lung. But most of your ventilation is 425 00:20:19,800 --> 00:20:21,920 going to that non dependent lung with less blood flow. 426 00:20:22,320 --> 00:20:25,200 This is why the dependent lung is so prone to atelectasis even 427 00:20:25,200 --> 00:20:28,040 before you start OLV. That Physiology really sets the 428 00:20:28,040 --> 00:20:30,760 stage for the challenge. Now let's talk about the tools 429 00:20:30,760 --> 00:20:34,480 we use to manage this Part D techniques and devices for OLV 430 00:20:35,000 --> 00:20:39,040 .6 lung isolation techniques. You have three main weapons in 431 00:20:39,040 --> 00:20:41,240 your arsenal. Number one and the most common 432 00:20:41,240 --> 00:20:43,960 is the Double lumen Endotracheal Tube or DLT. 433 00:20:44,000 --> 00:20:46,280 That's the gold standard. What are the other options? 434 00:20:46,400 --> 00:20:49,920 #2 is the bronchial blocker and #3, which is usually reserved 435 00:20:49,920 --> 00:20:53,200 for emergencies or very small pediatric patients, is 436 00:20:53,200 --> 00:20:57,760 endobronchial intubation with a standard single lumen tube 437 00:20:57,840 --> 00:21:01,880 basically just intentionally main stemming a regular tube? 438 00:21:02,320 --> 00:21:05,880 Let's focus on the exam favorite .7, the double lumen tube. 439 00:21:06,360 --> 00:21:08,640 Describe it for the listener who can't see one right now. 440 00:21:08,840 --> 00:21:13,000 DLT is essentially 2 tubes of different lengths bonded 441 00:21:13,000 --> 00:21:15,240 together side by side. They're usually D shaped in 442 00:21:15,240 --> 00:21:18,720 cross section to save space. One tube is shorter and ends in 443 00:21:18,720 --> 00:21:20,400 the trachea. That's the tracheal lumen. 444 00:21:20,680 --> 00:21:23,840 The other tube is longer and is designed designed to extend into 445 00:21:23,840 --> 00:21:26,440 a main stem bronchus. That's the bronchial lumen. 446 00:21:26,480 --> 00:21:30,080 And they have two cuffs. It has two cuffs and two pilot 447 00:21:30,080 --> 00:21:32,480 balloons. There's a large tracheal cuff, 448 00:21:32,480 --> 00:21:35,640 usually white, which is a high volume, low pressure cuff just 449 00:21:35,640 --> 00:21:38,760 like a standard ETT. It sits in the trachea and seals 450 00:21:38,760 --> 00:21:40,480 the entire airway. And the second cuff. 451 00:21:40,760 --> 00:21:43,480 The second cuff is the bronchial cuff, which is usually blue. 452 00:21:43,800 --> 00:21:46,720 It's smaller and sits inside the bronchus to seal just that one 453 00:21:46,720 --> 00:21:49,640 lung. Traditionally these were low 454 00:21:49,640 --> 00:21:52,440 volume, high pressure cuffs which carried a risk of ischemic 455 00:21:52,440 --> 00:21:54,640 damage, but modern ones are much better. 456 00:21:54,800 --> 00:22:01,440 OK, the eternal question, left versus right DLT, the patient is 457 00:22:01,440 --> 00:22:03,360 having a right sided thoracotomy. 458 00:22:03,960 --> 00:22:06,440 Which tube do I choose? This is a classic trick 459 00:22:06,440 --> 00:22:09,800 question. In 90 to 95% of all cases, the 460 00:22:09,800 --> 00:22:13,400 answer is you choose a left DLT. Even if you are operating on the 461 00:22:13,400 --> 00:22:15,400 right lung. Even if you are operating on the 462 00:22:15,400 --> 00:22:19,000 right lung, you place a tube in the left main stem bronchus and 463 00:22:19,000 --> 00:22:21,560 ventilate the left lung while the right lung, the surgical 464 00:22:21,560 --> 00:22:23,560 lung collapses. Why? 465 00:22:23,760 --> 00:22:25,640 Why not match the tube to the bronchus? 466 00:22:25,640 --> 00:22:27,800 On the non operative side it seems more logical. 467 00:22:27,920 --> 00:22:30,240 It's all about the anatomy and the margin of safety. 468 00:22:30,560 --> 00:22:33,680 The left main bronchus in an adult is relatively long, About 469 00:22:33,680 --> 00:22:36,560 5, 5 centimeters before the 1st branch, the left upper lobe 470 00:22:36,880 --> 00:22:39,000 takes off. It's like a long safe landing 471 00:22:39,000 --> 00:22:40,760 strip. It's easy to park a tube there 472 00:22:40,760 --> 00:22:43,040 without blocking anything. And the right side is different. 473 00:22:43,360 --> 00:22:46,200 Dramatically different. The right main bronchus is 474 00:22:46,200 --> 00:22:52,000 extremely short, sometimes only 1 1/2 to 2cm before the right 475 00:22:52,000 --> 00:22:55,080 upper lobe bronchus originates. It comes off at a very sharp 476 00:22:55,080 --> 00:22:56,440 angle. So if I try to place a right 477 00:22:56,440 --> 00:22:59,560 DLTI risk blocking the right upper lobe? 478 00:22:59,760 --> 00:23:02,560 Almost guaranteed, if the tube is just a little too deep, the 479 00:23:02,560 --> 00:23:05,920 bronchial cuff will cover the RUL orifice and you'll collapse 480 00:23:05,920 --> 00:23:08,400 the entire right lung when you only meant to ventilate it. 481 00:23:08,800 --> 00:23:11,680 If it's too shallow, the cuff will herniate back into the 482 00:23:11,680 --> 00:23:13,920 trachea and you won't get good isolation. 483 00:23:14,000 --> 00:23:16,560 I've seen right DLTS have a special slot in the cuff. 484 00:23:16,720 --> 00:23:19,480 They do to solve this problem right? 485 00:23:19,480 --> 00:23:23,280 DLTS have a special ventilated slot, like a Mufi's eye on the 486 00:23:23,280 --> 00:23:26,320 side of the bronchial cuff that you must align perfectly with 487 00:23:26,320 --> 00:23:28,400 the RUL orifice using a bronchoscope. 488 00:23:28,760 --> 00:23:31,960 It is technically very difficult and the tube can easily get 489 00:23:31,960 --> 00:23:34,080 dislodged. It's a last resort. 490 00:23:34,360 --> 00:23:36,800 So when do we use a right DLT? What are the specific 491 00:23:36,800 --> 00:23:39,360 indications? Only when you absolutely cannot 492 00:23:39,360 --> 00:23:42,440 use the left bronchus. For example, if there's a large 493 00:23:42,440 --> 00:23:44,960 tumor inside the left main bronchus that you can't get 494 00:23:44,960 --> 00:23:48,160 past, or if there's been a trauma, a left sided bronchial 495 00:23:48,160 --> 00:23:51,200 rupture, or sometimes a descending thoracic aortic 496 00:23:51,200 --> 00:23:53,760 aneurysm can compress the left bronchus so much you simply 497 00:23:53,760 --> 00:23:56,440 can't pass a tube. Only then do you reach for the 498 00:23:56,440 --> 00:24:01,600 right sided tube. Got it now .8 bronchial 499 00:24:01,600 --> 00:24:03,760 blockers. These seem to be gaining 500 00:24:03,760 --> 00:24:06,040 popularity. When should I be thinking about 501 00:24:06,040 --> 00:24:09,440 using a blocker instead of DLT? The number one reason to think 502 00:24:09,440 --> 00:24:11,040 blocker is difficult? Airway. 503 00:24:11,200 --> 00:24:13,560 Why is that? DLT's are bulky, they're stiff, 504 00:24:13,560 --> 00:24:15,480 they're large, and they have an aggressive curve. 505 00:24:16,160 --> 00:24:18,720 If you have a patient with a known difficult airway, a 506 00:24:18,720 --> 00:24:22,160 Malampotti 4, limited mouth opening, poor neck extension, 507 00:24:22,520 --> 00:24:24,680 you do not want to be wrestling with the DLT. 508 00:24:24,880 --> 00:24:28,040 The risk of trauma or a failed intubation is too high. 509 00:24:28,040 --> 00:24:30,520 So what's the strategy? The strategy is you secure the 510 00:24:30,520 --> 00:24:33,400 airway first with a normal familiar single lumen tube, 511 00:24:33,400 --> 00:24:36,920 maybe over a fiber optic scope, confirm you're in, and then once 512 00:24:36,920 --> 00:24:39,680 the airway is safe, you pass the bronchial blocker through the 513 00:24:39,680 --> 00:24:41,880 single lumen tube and guide it into position. 514 00:24:42,080 --> 00:24:44,280 Or if the patient already has a tracheostomy. 515 00:24:44,560 --> 00:24:49,320 A perfect indication you can't easily put a long curved DLT 516 00:24:49,320 --> 00:24:52,080 through a short straight tracheostomy stoma. 517 00:24:52,520 --> 00:24:55,840 A blocker pass through a single lumen tract tube works great. 518 00:24:56,560 --> 00:24:59,560 Another key indication is if you anticipate the patient will need 519 00:24:59,560 --> 00:25:02,440 post operative ventilation. Right, because you can't leave a 520 00:25:02,440 --> 00:25:05,080 DLT in for long. You can't, it's uncomfortable 521 00:25:05,080 --> 00:25:07,360 and traumatic. So if you use a DLT, you have to 522 00:25:07,360 --> 00:25:10,080 exchange it for a single lumen tube at the end of the case, 523 00:25:10,360 --> 00:25:13,400 which is a high risk procedure. In a post thoracotomy patient 524 00:25:13,960 --> 00:25:16,920 with a blocker, you just deflate the balloon and pull the blocker 525 00:25:16,920 --> 00:25:19,480 out, leaving the standard ETT in place. 526 00:25:19,720 --> 00:25:22,280 What are the downsides then? Why don't we just use blockers 527 00:25:22,280 --> 00:25:25,240 for everyone? The two main problems are slow 528 00:25:25,240 --> 00:25:27,480 lung deflation and easy dislodgement. 529 00:25:27,880 --> 00:25:31,760 ADLT has a huge lumen to let air out, and for suctioning a 530 00:25:31,760 --> 00:25:35,080 blocker's central channel is tiny, maybe 2mm. 531 00:25:35,280 --> 00:25:38,000 It can take forever for the lung to collapse, which frustrates 532 00:25:38,000 --> 00:25:39,520 the surgeon. And the dislodgement issue? 533 00:25:39,680 --> 00:25:41,640 They're just not as secure as a DLT. 534 00:25:42,360 --> 00:25:45,200 A little bit of coughing or even just the surgeon manipulating 535 00:25:45,200 --> 00:25:48,720 the bronchus can easily push the blockers balloon back into the 536 00:25:48,720 --> 00:25:51,920 trachea and suddenly you lose isolation and you're ventilating 537 00:25:51,920 --> 00:25:54,920 both lungs again right in the middle of a critical part of the 538 00:25:54,920 --> 00:25:57,000 surgery. That brings us to .9 539 00:25:57,120 --> 00:25:59,960 confirmation. This is absolutely critical. 540 00:26:00,160 --> 00:26:03,400 You've placed your device, whether it's a DLT or a blocker, 541 00:26:03,880 --> 00:26:06,480 how do you know for sure that it's in the right spot? 542 00:26:06,640 --> 00:26:09,240 There are clinical methods and then there's the gold standard. 543 00:26:09,240 --> 00:26:13,160 Clinically, we use auscultation. You follow a sequence, inflate 544 00:26:13,160 --> 00:26:16,160 the tracheal cuff, confirm bilateral air entry, then 545 00:26:16,160 --> 00:26:18,600 inflate the bronchial cuff, clamp the trachealumen and 546 00:26:18,600 --> 00:26:20,680 listen. You should hear breath sounds 547 00:26:20,680 --> 00:26:23,720 only on the ventilated side and silence on the clamped side. 548 00:26:23,720 --> 00:26:26,760 But how reliable is that? Honestly, for the exam and for 549 00:26:26,760 --> 00:26:29,240 real life, clinical signs are unreliable. 550 00:26:29,280 --> 00:26:31,120 Sound can be transmitted across the media. 551 00:26:31,120 --> 00:26:34,000 Steinm the gold standard. The only acceptable answer for 552 00:26:34,000 --> 00:26:37,640 ensuring safety is fiber optic bronchoscopy FoB. 553 00:26:38,080 --> 00:26:40,840 Describe the view for a correctly placed lefty Lt. 554 00:26:41,400 --> 00:26:42,640 The examiner hands you the scope. 555 00:26:42,640 --> 00:26:44,640 What are you looking for? It's a 2 step check. 556 00:26:44,960 --> 00:26:47,520 First I pass the scope down the tracheal lumen. 557 00:26:47,840 --> 00:26:50,280 I should be able to clearly see the Karina to the right. 558 00:26:50,280 --> 00:26:53,920 I see the entrance to the right. Main bronchus is wide open and 559 00:26:53,920 --> 00:26:57,440 unobstructed to the left. I should see the top of the blue 560 00:26:57,440 --> 00:27:01,920 bronchial cuff of the DLT sitting just inside the left 561 00:27:01,920 --> 00:27:04,160 main bronchus just below the Carina. 562 00:27:04,240 --> 00:27:06,520 What are you checking for specifically with that cuff? 563 00:27:07,200 --> 00:27:09,720 I'm making sure it's not herniating out into the trachea, 564 00:27:09,720 --> 00:27:12,840 which would risk slipping, and that it's not so deep that it 565 00:27:12,840 --> 00:27:14,320 might be blocking the left upper lobe. 566 00:27:14,400 --> 00:27:16,440 You want to see just a sliver of blue? 567 00:27:16,560 --> 00:27:18,240 OK, that's step one. What's Step 2? 568 00:27:18,240 --> 00:27:22,200 Step 2 is I pull the scope out and pass it down the bronchial 569 00:27:22,200 --> 00:27:24,640 lumen. Looking through the tube, I 570 00:27:24,640 --> 00:27:27,960 should see a clear, unobstructed view down the left bronchus. 571 00:27:28,360 --> 00:27:31,720 I should be able to identify the orifices of the left upper and 572 00:27:31,720 --> 00:27:34,200 lower lobes. This confirms my tube isn't too 573 00:27:34,200 --> 00:27:35,760 deep. And when do you perform this 574 00:27:35,760 --> 00:27:37,400 check? You check immediately after 575 00:27:37,400 --> 00:27:41,040 intubation while the patient is still supine, and this is the 576 00:27:41,040 --> 00:27:44,080 Viva trap that catches everyone. You must check it again after 577 00:27:44,080 --> 00:27:46,840 you have turned the patient into the lateral decubitous position. 578 00:27:46,920 --> 00:27:48,840 Because the tube moves during positioning. 579 00:27:49,400 --> 00:27:53,040 Almost always, turning a patient from supine to lateral can move 580 00:27:53,040 --> 00:27:56,520 the Carina relative to the tube tip by a centimeter or more. 581 00:27:57,080 --> 00:28:00,400 What was a perfect position supine can become a disaster in 582 00:28:00,400 --> 00:28:03,160 the lateral position. You must reconfirm with the 583 00:28:03,160 --> 00:28:05,520 scope before the surgeon makes an incision. 584 00:28:06,160 --> 00:28:10,080 Moving on to part E Anaesthetic management .10 Preoperative 585 00:28:10,080 --> 00:28:11,760 assessment. What am I looking for? 586 00:28:12,040 --> 00:28:14,840 We use the three legged stool approach described in Miller. 587 00:28:15,040 --> 00:28:16,840 It's a framework for assessing risk. 588 00:28:17,080 --> 00:28:19,240 The first leg is respiratory mechanics. 589 00:28:19,240 --> 00:28:21,960 So PFTS, pulmonary function tests. 590 00:28:21,960 --> 00:28:23,880 Exactly. You're looking at the FEV one 591 00:28:23,880 --> 00:28:26,760 and the FTC. The key number to remember is an 592 00:28:26,760 --> 00:28:30,960 FEV one of less than two liters or less than 40% of predicted. 593 00:28:31,280 --> 00:28:34,320 If the patient is below that, they are at high risk for post 594 00:28:34,320 --> 00:28:37,440 operative complications. We also calculate a predicted 595 00:28:37,440 --> 00:28:41,600 post operative FEV one or POOFE V1 to see what they'll be left 596 00:28:41,600 --> 00:28:42,760 with. OK, that's leg one. 597 00:28:42,760 --> 00:28:45,640 What's the second leg? The second leg is gas exchange. 598 00:28:45,840 --> 00:28:48,080 You're assessing the lung parenchyma itself. 599 00:28:48,760 --> 00:28:52,280 The main test here is the DLCO, the diffusing capacity for 600 00:28:52,280 --> 00:28:56,760 carbon monoxide. ADLCO less than 40% predicted is 601 00:28:56,760 --> 00:29:00,120 another major red flag and you'll look at the baseline 602 00:29:00,120 --> 00:29:03,840 arterial blood gas. Are they retaining CO2 at rest? 603 00:29:04,160 --> 00:29:08,040 Is their PO2 low on room air? And the third leg of the stool. 604 00:29:08,040 --> 00:29:10,600 The third leg is cardio pulmonary reserve. 605 00:29:11,000 --> 00:29:13,160 This assesses the patient's overall fitness. 606 00:29:13,160 --> 00:29:16,200 It's one thing to have good lungs, but can the heart and 607 00:29:16,200 --> 00:29:18,160 muscles handle the stress of surgery? 608 00:29:18,520 --> 00:29:20,600 This is where we look at things like stair climbing. 609 00:29:20,600 --> 00:29:22,760 Can they climb two flights of stairs without stopping? 610 00:29:22,920 --> 00:29:25,920 Or more formally, A cardio pulmonary exercise test to 611 00:29:25,920 --> 00:29:28,880 measure their VO2 Max. What's the critical value for 612 00:29:28,880 --> 00:29:32,240 VO2 Max? AVO. 2 Max of less than 10 to 15 613 00:29:32,240 --> 00:29:35,320 milliliters per kilogram per minute is associated with a very 614 00:29:35,320 --> 00:29:37,520 high risk of morbidity and mortality. 615 00:29:37,680 --> 00:29:39,840 Let's talk about predictors of desaturation. 616 00:29:39,840 --> 00:29:42,840 If I'm looking at a patient's chart pre op, what tells me this 617 00:29:42,840 --> 00:29:45,000 particular patient is going to be difficult and will likely 618 00:29:45,000 --> 00:29:47,720 turn blue during OLV? There are three classic 619 00:29:47,720 --> 00:29:49,800 predictors. First right sided surgery. 620 00:29:49,840 --> 00:29:51,920 Why right sided? Because the right lung is 621 00:29:51,920 --> 00:29:54,040 bigger. The right lung has three lobes 622 00:29:54,040 --> 00:29:57,040 and accounts for about 55% of total lung function. 623 00:29:57,680 --> 00:30:00,640 The left has two lobes and accounts for 45%. 624 00:30:01,040 --> 00:30:04,240 If you collapse the bigger lung, you're creating a bigger initial 625 00:30:04,240 --> 00:30:05,240 shunt. Makes sense. 626 00:30:05,240 --> 00:30:08,560 What's the second predictor? Low preoperative pay O. 627 00:30:09,440 --> 00:30:12,440 If the patient is already struggling to oxygenate on 2 628 00:30:12,440 --> 00:30:15,160 lungs while breathing room air, they have very little 629 00:30:15,160 --> 00:30:17,880 physiological reserve. When you take one lung away, 630 00:30:17,880 --> 00:30:21,440 they are very likely to become significantly hypoxemic. 631 00:30:21,640 --> 00:30:23,960 And the third one is a bit of a paradox, isn't it? 632 00:30:23,960 --> 00:30:26,880 The VQ scan. Yes, this is a great one to 633 00:30:26,880 --> 00:30:30,840 mention in an exam. A normal VQ scan is a risk 634 00:30:30,840 --> 00:30:34,040 factor for desaturation. That sounds completely 635 00:30:34,040 --> 00:30:36,080 counterintuitive. It does, but think about it. 636 00:30:36,280 --> 00:30:39,640 A VQ scan tells you how much perfusion is going to the lung 637 00:30:39,640 --> 00:30:41,080 that you are about to operate on. 638 00:30:41,280 --> 00:30:43,680 If that lung has normal perfusion, it means you are 639 00:30:43,680 --> 00:30:46,160 about to create a huge shunt when you collapse. 640 00:30:46,160 --> 00:30:47,840 It as opposed to a patient with a big tumor. 641 00:30:47,960 --> 00:30:51,600 Exactly, if a patient has a massive tumor that has already 642 00:30:51,600 --> 00:30:54,720 destroyed the blood supply to that lung, it's perfusion on the 643 00:30:54,720 --> 00:30:57,960 VQ scan will be very low. In that case, collapsing it 644 00:30:57,960 --> 00:30:59,680 doesn't really change the Physiology much. 645 00:30:59,680 --> 00:31:03,200 The shunt is already present. So paradoxically, a healthy, 646 00:31:03,200 --> 00:31:06,800 well perfused lung is more dangerous to collapse. .11 647 00:31:06,960 --> 00:31:10,680 Induction in airway management. Any special considerations here? 648 00:31:10,840 --> 00:31:13,720 The induction itself is usually a standard 4 induction. 649 00:31:13,720 --> 00:31:16,920 The key is you need profound muscle relaxation. 650 00:31:17,080 --> 00:31:19,960 You cannot have the patient coughing or straining while you 651 00:31:19,960 --> 00:31:22,000 are trying to position a bulky DLT. 652 00:31:22,160 --> 00:31:23,840 That's a recipe for airway trauma. 653 00:31:23,880 --> 00:31:25,960 OK, what about tube sizing? It's important. 654 00:31:26,280 --> 00:31:29,080 Too small a tube gives you high resistance and makes suctioning 655 00:31:29,080 --> 00:31:32,040 difficult. Too large a tube risks trauma to 656 00:31:32,040 --> 00:31:35,240 the larynx or bronchus. As a rough guide, for adult 657 00:31:35,240 --> 00:31:40,280 females we use a 35 or 37 French tube and for males a 39 or 41 658 00:31:40,280 --> 00:31:42,680 French. You mentioned a key tip earlier, 659 00:31:42,680 --> 00:31:44,760 nitrogen washout. Can you expand on that? 660 00:31:44,920 --> 00:31:49,120 Yes, before you initiate OLV, you should ventilate the patient 661 00:31:49,120 --> 00:31:51,600 with 100% oxygen for a few minutes. 662 00:31:52,200 --> 00:31:55,200 The goal is to wash out all the nitrogen from the lung that 663 00:31:55,200 --> 00:31:57,880 you're about to collapse and replace it with oxygen. 664 00:31:58,120 --> 00:32:01,000 Why does that help? Because nitrogen is an inert 665 00:32:01,000 --> 00:32:04,160 gas, it has very low blood solubility. 666 00:32:04,560 --> 00:32:07,640 If you leave a lung full of nitrogen and air, the nitrogen 667 00:32:07,640 --> 00:32:11,200 acts like a splint holding the alveoli open, and the lung 668 00:32:11,200 --> 00:32:14,600 collapses very slowly. Whereas oxygen gets absorbed. 669 00:32:14,840 --> 00:32:17,720 Oxygen is rapidly absorbed by the blood flowing through the 670 00:32:17,720 --> 00:32:20,560 pulmonary capillaries. So if the lung is full of pure 671 00:32:20,560 --> 00:32:24,560 oxygen, this process of absorption atelectasis helps the 672 00:32:24,560 --> 00:32:28,560 lung collapse much much faster. The surgeon will thank you. .12 673 00:32:28,960 --> 00:32:31,000 Intra operative ventilation strategy. 674 00:32:31,160 --> 00:32:34,280 I said this is very high yield and that practice has changed 675 00:32:34,280 --> 00:32:35,320 significantly. It has. 676 00:32:35,320 --> 00:32:38,000 If you read an old textbook it might say use high tidal 677 00:32:38,000 --> 00:32:41,080 volumes, 10 to 12 milliliters per kilogram to prevent 678 00:32:41,080 --> 00:32:42,600 atelectasis and keep the sats up. 679 00:32:42,920 --> 00:32:44,840 Do not say this in the exam. Why not? 680 00:32:44,840 --> 00:32:47,720 Because we now know that causes volley trauma and Barrow trauma. 681 00:32:48,280 --> 00:32:51,400 You're forcing all that volume into just one lung. 682 00:32:51,720 --> 00:32:54,400 You're over distending the healthy alveoli causing 683 00:32:54,400 --> 00:32:57,680 inflammation and setting the patient up for post operative 684 00:32:57,680 --> 00:33:01,360 acute lung injury, or Ali. So what is the modern standard? 685 00:33:01,360 --> 00:33:04,280 What should I say in the Viva? You should say you will use a 686 00:33:04,280 --> 00:33:06,520 protective lung ventilation strategy. 687 00:33:06,520 --> 00:33:08,600 This has several key components. OK, what's the first one? 688 00:33:08,840 --> 00:33:11,960 First, tidal volume. We use low tidal volumes, around 689 00:33:11,960 --> 00:33:16,160 5 to 6 milliliters per kilogram of predicted body weight, not 690 00:33:16,200 --> 00:33:18,840 actual body weight. We are gentle with that one 691 00:33:18,840 --> 00:33:22,400 working lung. 2nd component. Heap positive and expiratory 692 00:33:22,400 --> 00:33:24,640 pressure. We advocate for the routine 693 00:33:24,640 --> 00:33:28,160 application of about 5 centimeters of water of PEEP to 694 00:33:28,280 --> 00:33:31,200 the dependent ventilated lung. And why is that so important? 695 00:33:31,400 --> 00:33:34,400 Remember our discussion about positioning That dependent lung 696 00:33:34,400 --> 00:33:36,920 is being crushed by the media Steinem and the abdomen. 697 00:33:37,000 --> 00:33:40,120 It is desperate to collapse. Applying a little bit of PEEP 698 00:33:40,360 --> 00:33:43,400 acts as a pneumatic splint to keep those alveoli open and 699 00:33:43,400 --> 00:33:46,400 participating in gas exchange. So low volume? 700 00:33:46,480 --> 00:33:48,560 Add peep. What about the respiratory rate? 701 00:33:48,800 --> 00:33:51,880 You adjust the respiratory rate to maintain a reasonable Paso 702 00:33:51,880 --> 00:33:54,040 two. It will likely need to be higher 703 00:33:54,040 --> 00:33:57,240 than normal, maybe 16 to 18 breaths per minute, to 704 00:33:57,240 --> 00:33:59,280 compensate for the low tidal volume. 705 00:33:59,280 --> 00:34:02,680 And what if the CO2 still climb? This is where the concept of 706 00:34:02,680 --> 00:34:06,280 permissive hypercapnia comes in. We're often willing to tolerate 707 00:34:06,280 --> 00:34:11,040 a slightly higher Paso two, say up to 50 or 60mm of mercury, as 708 00:34:11,040 --> 00:34:15,440 long as the pH is above 7.25. The priority is protecting the 709 00:34:15,440 --> 00:34:18,239 lung from high pressures, even if it means accepting a little 710 00:34:18,239 --> 00:34:20,920 bit of respiratory acidosis. OK, we are now in the thick of 711 00:34:20,920 --> 00:34:23,080 it. Part F Management of hypoxia. 712 00:34:23,440 --> 00:34:25,639 This is the big 20 mark question. 713 00:34:25,960 --> 00:34:29,080 The surgeon is working, you're on OLV and the pulse oximeter 714 00:34:29,080 --> 00:34:32,239 starts that dreaded downward alarm tone. 715 00:34:32,239 --> 00:34:37,080 De Tone De Tone 88 percent 85. First rule is don't panic. 716 00:34:37,239 --> 00:34:39,920 Panic paralyzes your thinking and kills the patient. 717 00:34:40,360 --> 00:34:42,560 You need to have a calm pre rehearsed drill. 718 00:34:43,280 --> 00:34:45,840 But first let's talk about .13 causes. 719 00:34:45,840 --> 00:34:47,600 Why is this happening? What's the most common reason? 720 00:34:47,800 --> 00:34:50,639 By far the most common cause is tube Mal position. 721 00:34:50,840 --> 00:34:54,120 The DLT has slipped, the bronchial cuff has herniated 722 00:34:54,120 --> 00:34:57,400 back into the trachea, or the tube is advanced too far and is 723 00:34:57,400 --> 00:35:00,400 now obstructing an upper lobe. Before you think of anything 724 00:35:00,400 --> 00:35:03,000 else, you think about the tube. What are some other causes? 725 00:35:03,080 --> 00:35:06,240 It could be a simple obstruction like a thick sputum plug in the 726 00:35:06,240 --> 00:35:09,800 airway, it could be bronchospasm, or it could be 727 00:35:09,800 --> 00:35:12,320 curely physiological. You have a massive shunt because 728 00:35:12,320 --> 00:35:15,400 the patient's HPV is poor, maybe because your volatile agent is 729 00:35:15,400 --> 00:35:18,720 too high, or your patient has low cardiac output leading to 730 00:35:18,720 --> 00:35:22,680 low mixed venous oxygen saturation, which makes any 731 00:35:22,680 --> 00:35:27,680 shunt much more impactful. So .14 the stepwise management 732 00:35:27,680 --> 00:35:29,840 of hypoxia. Walk me through the algorithm, 733 00:35:29,840 --> 00:35:31,520 the drill. OK, stats are falling. 734 00:35:31,760 --> 00:35:34,000 Immediately turn your Fio 2 to 100%. 735 00:35:34,280 --> 00:35:37,160 If you're using their oxygen mix, this eliminates that as a 736 00:35:37,160 --> 00:35:39,680 variable. OK, 100% oxygen, what's Step 2? 737 00:35:39,680 --> 00:35:41,560 Step 2. Check tube position. 738 00:35:41,840 --> 00:35:43,800 Announce to the surgeon that you have a problem. 739 00:35:44,080 --> 00:35:47,640 Quickly auscultate. But most importantly you must 740 00:35:47,640 --> 00:35:51,480 confirm the tubes position with your fiber optic bronchoscope. 741 00:35:51,880 --> 00:35:54,080 This is not optional. So I have to pause everything 742 00:35:54,080 --> 00:35:56,480 and get the scope out. You do pass it down the tracheal 743 00:35:56,560 --> 00:35:59,400 lumen first. Is the branchial cuff still in 744 00:35:59,400 --> 00:36:01,600 the bronchus or has it herniated out? 745 00:36:01,920 --> 00:36:04,840 If it has, fix it. That will solve 90% of your 746 00:36:04,840 --> 00:36:07,200 problems right there. What's step three if the two 747 00:36:07,200 --> 00:36:09,040 position is perfect? Step 3. 748 00:36:09,280 --> 00:36:12,160 Suction both lumens. A thick mucus plug can 749 00:36:12,160 --> 00:36:15,280 completely obstruct A lumen and cause a massive shunt. 750 00:36:15,600 --> 00:36:16,800 Clear the airway. Step. 751 00:36:16,800 --> 00:36:20,320 Four Step 4. Check and optimize hemodynamics. 752 00:36:21,200 --> 00:36:24,240 Is the patient hypotensive? Is the cardiac output low? 753 00:36:24,600 --> 00:36:27,520 If it is, the blood returning to the lungs is already very 754 00:36:27,520 --> 00:36:30,200 desaturated, which magnifies the effect of the shunt. 755 00:36:30,480 --> 00:36:32,960 Treat the hypotension with fluids or vasopressors. 756 00:36:33,200 --> 00:36:34,800 OK, so I've done all the basic checks. 757 00:36:34,800 --> 00:36:37,720 Tube is fine, airway is clear, blood pressure is good, but I'm 758 00:36:37,720 --> 00:36:40,520 still saturating at 85%. What's next? 759 00:36:40,520 --> 00:36:42,640 Now we have to start manipulating the Physiology. 760 00:36:42,880 --> 00:36:46,160 Correct Step 5. Perform a recruitment maneuver 761 00:36:46,160 --> 00:36:49,480 on the dependent lung. That bottom lung is squashed and 762 00:36:49,480 --> 00:36:51,560 likely has significant atelectasis. 763 00:36:52,040 --> 00:36:55,080 Give a sustained breath. For example, hold a pressure of 764 00:36:55,080 --> 00:36:59,200 30 to 40 centimeters of water for 20 to 30 seconds to pop open 765 00:36:59,200 --> 00:37:01,640 those collapsed alveoli. And after recruiting? 766 00:37:01,760 --> 00:37:05,080 Step 6. Apply or increase PEEP to the 767 00:37:05,080 --> 00:37:07,680 dependent lung. If you started with five, try 768 00:37:07,680 --> 00:37:10,680 increasing it to 8 or 10. This will help keep those newly 769 00:37:10,680 --> 00:37:13,360 recruited Ovioli open, but be careful. 770 00:37:13,400 --> 00:37:15,440 Why be careful? Peep is usually good for 771 00:37:15,440 --> 00:37:17,960 oxygenation. It's a delicate balance. 772 00:37:18,240 --> 00:37:20,960 If you apply too much PEEP to the pendant lung, you can over 773 00:37:20,960 --> 00:37:23,360 distend it. This increases the pulmonary 774 00:37:23,360 --> 00:37:25,120 vascular resistance in that good lung. 775 00:37:25,320 --> 00:37:27,480 And that diverts. Blood, it diverts blood flow 776 00:37:27,480 --> 00:37:30,640 away from the good ventilated lung and forces it back into the 777 00:37:30,640 --> 00:37:33,840 collapsed non ventilated lung which actually increases your 778 00:37:33,840 --> 00:37:36,080 shun fraction and makes hypoxia worse. 779 00:37:36,280 --> 00:37:39,800 You have to find the sweet spot. OK so I've tried recruitment and 780 00:37:39,800 --> 00:37:42,800 optimal peep and it didn't work. We are getting desperate. 781 00:37:43,040 --> 00:37:45,640 Sats are critically low. What's the big gun? 782 00:37:45,840 --> 00:37:49,880 Step 7 Apply C pap to the non dependent collapsed lung. 783 00:37:50,960 --> 00:37:53,680 This is probably the single most effective physiological maneuver 784 00:37:53,680 --> 00:37:56,200 you can perform. Explain that I'm applying 785 00:37:56,200 --> 00:37:58,520 pressure to the lung the surgeon is operating on. 786 00:37:58,520 --> 00:38:01,520 Yes, you connect a special circuit and apply a small amount 787 00:38:01,520 --> 00:38:05,680 of continuous positive airway pressure, just two to five, 788 00:38:05,680 --> 00:38:09,320 maybe up to 10 centimeters of water and some oxygen flow to 789 00:38:09,320 --> 00:38:11,040 the lung that is supposed to be collapsed. 790 00:38:11,440 --> 00:38:14,160 But won't that inflate the lung and completely obscure the 791 00:38:14,160 --> 00:38:16,480 surgical field? At 2:00 to 5:00 centimeters, it 792 00:38:16,480 --> 00:38:18,160 usually just puffs it up a tiny bit. 793 00:38:18,240 --> 00:38:21,200 It often doesn't interfere with the surgeon too much, but what 794 00:38:21,200 --> 00:38:25,600 it does physiologically is provide oxygen to those alveoli 795 00:38:25,600 --> 00:38:28,960 in the collapsed lung. So the blood that is inevitably 796 00:38:28,960 --> 00:38:31,680 shunting through that lung now has a chance to pick up some 797 00:38:31,680 --> 00:38:34,640 oxygen. So it converts a pure shunt into 798 00:38:34,640 --> 00:38:37,600 an area of low VQ. Precisely, it can raise the 799 00:38:37,600 --> 00:38:40,600 saturation from 80% to 95% almost instantly. 800 00:38:40,640 --> 00:38:42,360 It's a hugely powerful technique. 801 00:38:42,560 --> 00:38:45,560 And if even that fails. If that fails you have two 802 00:38:45,560 --> 00:38:48,000 options left. Step 8 is to tell the surgeon 803 00:38:48,000 --> 00:38:49,680 stop. I need to re expand the lung. 804 00:38:50,000 --> 00:38:53,680 You abandoned OLV temporarily. Go back to two lung ventilation, 805 00:38:53,960 --> 00:38:57,560 bring the sats up to 100% and then try again once the patient 806 00:38:57,560 --> 00:38:59,880 is stable. And the final ultimate step. 807 00:38:59,960 --> 00:39:02,680 Step 9, which is really a surgical maneuver, clamp the 808 00:39:02,680 --> 00:39:04,760 pulmonary artery. If the surgeon is doing a 809 00:39:04,760 --> 00:39:07,480 pneumonectomy or low the bectomy, they can temporarily or 810 00:39:07,480 --> 00:39:10,480 permanently clamp the pulmonary artery branch going to the 811 00:39:10,480 --> 00:39:13,600 collapsed lung. This mechanically eliminates the 812 00:39:13,600 --> 00:39:16,360 shunt entirely. That is the ultimate fix. 813 00:39:16,360 --> 00:39:20,200 That is a life saving algorithm. So to recap the order Fio 2 814 00:39:20,200 --> 00:39:24,200 check tube suction hemodynamics, recruit dependent lung, PEEP to 815 00:39:24,200 --> 00:39:27,120 dependent lung, CPAP to non dependent lung, then 816 00:39:27,120 --> 00:39:28,640 intermittent to lung ventilation. 817 00:39:28,640 --> 00:39:30,320 Correct. Memorize that order. 818 00:39:30,800 --> 00:39:33,520 It's logical, it's safe, and it shows the examiner you 819 00:39:33,520 --> 00:39:35,440 understand the underlying Physiology. 820 00:39:35,920 --> 00:39:38,720 Let's wrap up with Part G post operative and ICU 821 00:39:38,720 --> 00:39:40,720 considerations. Now that the surgery is over, 822 00:39:40,720 --> 00:39:43,640 what are we most worried about? .15 Post operative 823 00:39:43,640 --> 00:39:47,240 complications, the biggest fear after major lung resection is 824 00:39:47,240 --> 00:39:50,400 acute lung injury or Ali in the remaining lung. 825 00:39:50,560 --> 00:39:52,800 This is from the ventilation strategy we used. 826 00:39:52,880 --> 00:39:56,440 It can be it presents like ARDS, you see pulmonary edema, 827 00:39:56,440 --> 00:39:58,680 hypoxia. It can be caused by the volume 828 00:39:58,680 --> 00:40:02,120 trauma from over distending the dependent lung or from 829 00:40:02,120 --> 00:40:05,200 reperfusion injury when the collapsed lung is re inflated. 830 00:40:05,480 --> 00:40:07,560 This is. Exactly why we are now so 831 00:40:07,560 --> 00:40:10,360 obsessed with the protective lung ventilation strategy. 832 00:40:10,520 --> 00:40:13,680 What about other complications? Nerve injuries are common, 833 00:40:13,960 --> 00:40:17,360 brachial plexus injury from poor arm positioning during the lung 834 00:40:17,360 --> 00:40:20,800 surgery and lateral or phrenic nerve damage from the surgery 835 00:40:20,800 --> 00:40:23,480 itself, leading to a paralyzed humidiophrine which can be 836 00:40:23,480 --> 00:40:27,680 devastating after endominectomy. And .16 post operative 837 00:40:27,680 --> 00:40:29,080 management. What is the most critical 838 00:40:29,080 --> 00:40:31,400 element here? Without a doubt, pain control. 839 00:40:31,920 --> 00:40:34,800 A thoracotomy is one of the most painful incisions in all of 840 00:40:34,800 --> 00:40:37,280 surgery. If the patient is in agony, they 841 00:40:37,280 --> 00:40:40,400 won't take deep breaths, they won't cough effectively, and 842 00:40:40,400 --> 00:40:42,440 they will develop atelectasis and pneumonia. 843 00:40:42,440 --> 00:40:44,800 So what's the gold standard for analgesia? 844 00:40:44,960 --> 00:40:47,040 The thoracic epidural is the gold standard. 845 00:40:47,520 --> 00:40:49,800 A catheter placed in the epidural space, providing A 846 00:40:49,800 --> 00:40:53,120 continuous infusion of local anesthetic and opioid, provides 847 00:40:53,160 --> 00:40:55,920 excellent dynamic analgesia without sedation. 848 00:40:56,120 --> 00:40:59,160 And if an epidural is contraindicated or fails? 849 00:40:59,160 --> 00:41:01,960 A para vertebral block is a fantastic alternative. 850 00:41:02,280 --> 00:41:04,760 It involves injecting local anesthetic next to the spine 851 00:41:04,760 --> 00:41:07,760 where the intercostal nerves exit, effectively blocking the 852 00:41:07,760 --> 00:41:10,600 entire half of the chest wall. Finally, Part H Exam 853 00:41:10,600 --> 00:41:12,200 integration. Let's create some quick 854 00:41:12,200 --> 00:41:14,600 reference comparison tables and highlight the traps. 855 00:41:14,600 --> 00:41:15,880 A good idea. Table 1. 856 00:41:16,160 --> 00:41:19,800 DLT versus bronchial blocker key pros and cons. 857 00:41:19,800 --> 00:41:23,520 OK DLT pros fast and definitive isolation. 858 00:41:23,520 --> 00:41:26,840 Lung deflation is quick and you have large lumens for easy 859 00:41:26,840 --> 00:41:29,680 suctioning. DLT cons more difficult to 860 00:41:29,680 --> 00:41:32,920 place, higher risk of airway trauma and you must exchange it 861 00:41:32,920 --> 00:41:35,440 at the end of the case if post op ventilation is needed. 862 00:41:35,560 --> 00:41:38,600 And the blocker? Blocker Pros Excellent for known 863 00:41:38,600 --> 00:41:41,680 difficult airway, can be used in patients with a tracheostomy and 864 00:41:41,680 --> 00:41:43,840 no need to change the tube for post op ventilation. 865 00:41:44,280 --> 00:41:47,240 Blocker Cons Lung deflation is very slow. 866 00:41:47,400 --> 00:41:50,280 The narrow channel makes suctioning pour and it dislodges 867 00:41:50,280 --> 00:41:51,720 very easily. Table 2. 868 00:41:52,160 --> 00:41:55,240 Awake a lateral versus anesthetized lateral position. 869 00:41:55,480 --> 00:41:59,160 Simple awake lateral ventilation matches perfusion. 870 00:41:59,360 --> 00:42:01,720 Both are preferentially directed to the dependent lung. 871 00:42:02,280 --> 00:42:05,760 VQ matching is good. Anesthetized lateral A massive 872 00:42:05,760 --> 00:42:08,680 VQ mismatch. Ventilation preferentially goes 873 00:42:08,680 --> 00:42:12,360 to the non dependent upper lung, while perfusion preferentially 874 00:42:12,360 --> 00:42:13,840 goes to the dependent lower lung. 875 00:42:14,120 --> 00:42:17,080 And the Viva traps, we've mentioned a few, the need to 876 00:42:17,080 --> 00:42:20,400 recheck the tube after positioning, the danger of high 877 00:42:20,400 --> 00:42:23,400 volatile agent concentrations inhibiting HPV. 878 00:42:23,720 --> 00:42:25,360 What about nitrogen? Right. 879 00:42:25,360 --> 00:42:28,720 An examiner might ask why did you use 100% oxygen for 880 00:42:28,720 --> 00:42:30,960 induction instead of inter oxygen mix? 881 00:42:31,760 --> 00:42:35,880 The answer is not just about pre oxygenation you say I use 100% 882 00:42:35,880 --> 00:42:39,240 oxygen to facilitate a nitrogen washout as nitrogen has low 883 00:42:39,240 --> 00:42:42,320 blood solubility and acts as a splint delaying the collapse of 884 00:42:42,320 --> 00:42:44,960 the non dependent lung. Pure oxygen promotes rapid 885 00:42:44,960 --> 00:42:48,040 absorption atelectasis. That's a very slick answer. 886 00:42:48,040 --> 00:42:50,360 And if they ask you to draw a diagram in the exam. 887 00:42:50,600 --> 00:42:52,800 Be prepared. Practice drawing a simple 888 00:42:52,800 --> 00:42:55,520 diagram of the Karina with a left DLT in position. 889 00:42:55,960 --> 00:42:59,040 Practice drawing the shunt diagram showing mixed venous 890 00:42:59,040 --> 00:43:03,360 blood in a capillary bypassing an unventilated alveolus, and 891 00:43:03,360 --> 00:43:06,560 practice drawing the hypoxia management algorithm as a flow 892 00:43:06,560 --> 00:43:09,320 chart. Visuals break up text and score 893 00:43:09,320 --> 00:43:11,400 points. So let's structure a long answer 894 00:43:11,760 --> 00:43:14,280 introduction. Introduction then indications 895 00:43:14,280 --> 00:43:16,240 classified as absolute and relative. 896 00:43:16,680 --> 00:43:20,960 Then Physiology with a big section on HPV, then techniques 897 00:43:20,960 --> 00:43:24,240 comparing DLTS and blockers, then a detailed section on the 898 00:43:24,240 --> 00:43:27,640 stepwise management of hypoxia. Finished with post op 899 00:43:27,640 --> 00:43:31,000 complications and management. Let's summarize .20. 900 00:43:31,240 --> 00:43:34,200 What are the key high yield take home points for the student 901 00:43:34,200 --> 00:43:37,560 heading into that exam hall? OK, here's the rapid fire recap. 902 00:43:37,800 --> 00:43:40,920 OLV is the deliberate separation of the lungs for surgical 903 00:43:40,920 --> 00:43:43,000 exposure or protection from contamination. 904 00:43:43,120 --> 00:43:45,320 It creates a massive physiological shunt. 905 00:43:45,440 --> 00:43:48,400 Your body's primary defense against this shunt is hypoxic. 906 00:43:48,400 --> 00:43:51,280 Pulmonary vasoconstriction do not inhibit HPV with high 907 00:43:51,280 --> 00:43:55,840 concentrations of volatile agents. 4 The left DLT is the 908 00:43:55,840 --> 00:43:59,200 standard choice for lung isolation due to the anatomical 909 00:43:59,200 --> 00:44:01,880 margin of safety of the left main bronchus. 910 00:44:02,000 --> 00:44:04,640 The gold standard for confirming placement is fiber optic 911 00:44:04,640 --> 00:44:08,000 bronchoscopy, and you must recheck position after turning 912 00:44:08,000 --> 00:44:11,040 the patient lateral. Ventilate the single lung using 913 00:44:11,040 --> 00:44:14,800 a protective strategy. Low tidal volume of 5 to 6mm per 914 00:44:14,800 --> 00:44:19,560 kilodrama and add five of PEEP. Seven, if hypoxia occurs, follow 915 00:44:19,560 --> 00:44:22,160 the algorithm. First check and fix the tube. 916 00:44:22,520 --> 00:44:26,000 Last, apply CPAP to the non dependent lung or ask the 917 00:44:26,000 --> 00:44:28,520 surgeon to pause. Excellent post operative pain 918 00:44:28,520 --> 00:44:31,680 control, preferably with a thoracic epidural, is critical 919 00:44:31,680 --> 00:44:33,360 to prevent pulmonary complications. 920 00:44:33,560 --> 00:44:35,160 Fantastic to the student listening. 921 00:44:35,360 --> 00:44:37,520 You have the knowledge now. The key is structure. 922 00:44:37,680 --> 00:44:40,640 Structure your answers clearly use headings, bullet points and 923 00:44:40,640 --> 00:44:41,960 diagrams. Don't ramble. 924 00:44:42,120 --> 00:44:44,480 Be the safe, calm, knowledgeable consultant they want to hire. 925 00:44:44,480 --> 00:44:46,840 Exactly. Go draw that hypoxia algorithm 926 00:44:46,840 --> 00:44:48,640 right now. Burn it into your memory. 927 00:44:48,720 --> 00:44:51,000 Good luck. That's it for this deep dive. 928 00:44:51,000 --> 00:44:51,920 We'll see you next time.