1 00:00:00,040 --> 00:00:03,680 Welcome back to the Deep Dive. Today we are stripping away the 2 00:00:03,680 --> 00:00:05,960 safety net. We aren't just exploring a 3 00:00:05,960 --> 00:00:08,720 topic, we are entering a simulation. 4 00:00:08,880 --> 00:00:12,080 That's right, today the stakes are significantly higher than 5 00:00:12,080 --> 00:00:14,280 usual. I want you to visualize this. 6 00:00:14,720 --> 00:00:18,000 You are an MD, anesthesiology postgraduate student. 7 00:00:18,520 --> 00:00:21,520 You're sitting in the hot seat. It's the final practical exam 8 00:00:21,520 --> 00:00:24,600 for Gujarat University. The air conditioning is humming, 9 00:00:24,600 --> 00:00:27,720 your palms are sweating, and the external examiner is, you know, 10 00:00:27,720 --> 00:00:29,800 staring at you over the rim of his glasses. 11 00:00:30,120 --> 00:00:32,600 The case on the table is bronchial asthma. 12 00:00:32,600 --> 00:00:35,440 And I'm stepping into the role of that senior faculty member. 13 00:00:35,680 --> 00:00:37,600 I'm the internal examiner sitting next to you. 14 00:00:37,920 --> 00:00:41,200 My job today isn't just to teach you the facts, It's to guide you 15 00:00:41,200 --> 00:00:43,960 through the minefield. I'm here to point out the traps 16 00:00:43,960 --> 00:00:47,120 that fail candidates and the precise gold medal answers that 17 00:00:47,120 --> 00:00:49,400 distinguish the consultants from the students. 18 00:00:49,960 --> 00:00:52,320 Our mission is to take this massive stack of source 19 00:00:52,320 --> 00:00:54,480 material. We've compiled standard texts 20 00:00:54,480 --> 00:00:57,640 like Miller, Morgan and McHale Gaytan for Physiology, 21 00:00:57,720 --> 00:01:01,800 Harrison's for medicine, Robbins for pathology, and KD Tripathi 22 00:01:01,800 --> 00:01:05,560 for pharmacology and distilled them into a single, cohesive, 23 00:01:05,560 --> 00:01:08,080 exam winning narrative. We're really covering the full 24 00:01:08,080 --> 00:01:08,800 spectrum here. Oh. 25 00:01:08,840 --> 00:01:12,480 Yeah, from the cellular level of inflammation right up to the 26 00:01:12,480 --> 00:01:14,880 terrifying silence of a status asthmatic. 27 00:01:14,880 --> 00:01:16,880 His chest in the ICU. Precisely. 28 00:01:17,280 --> 00:01:19,360 But I have to issue a disclaimer before we begin. 29 00:01:19,840 --> 00:01:22,080 This is an exam preparation deep dive. 30 00:01:22,600 --> 00:01:25,800 We are basing our discussions strictly on the provided source 31 00:01:25,800 --> 00:01:28,320 texts. We all know clinical guidelines 32 00:01:28,320 --> 00:01:33,000 evolve rapidly, but in the exam hall, these standard texts are 33 00:01:33,000 --> 00:01:35,480 your Bible. So answer according to the book. 34 00:01:35,480 --> 00:01:39,320 Answer according to the book, unless you have a landmark paper 35 00:01:39,320 --> 00:01:41,960 in your back pocket to justify a deviation. 36 00:01:42,120 --> 00:01:44,200 Understood. Let's set the stage then. 37 00:01:44,440 --> 00:01:46,200 The exam usually begins with definitions. 38 00:01:46,200 --> 00:01:48,680 It sounds simple, but I've seen students stumble right out of 39 00:01:48,680 --> 00:01:50,520 the gate. We aren't just talking about 40 00:01:50,520 --> 00:01:52,520 asthma yet. We're starting with the umbrella 41 00:01:52,520 --> 00:01:55,840 category, Section 1, introduction to obstructive lung 42 00:01:55,840 --> 00:01:57,840 diseases. How do we frame this for the 43 00:01:57,840 --> 00:01:59,960 examiners to show we understand the physics of it? 44 00:02:00,200 --> 00:02:01,920 Right. If the examiner asks what is 45 00:02:01,920 --> 00:02:04,960 obstructive lung disease, do not just list diseases. 46 00:02:04,960 --> 00:02:07,720 That's a classic mistake. You must focus on the 47 00:02:07,720 --> 00:02:11,360 physiological defect. The core concept is flow 48 00:02:11,360 --> 00:02:14,240 limitation. These are diseases characterized 49 00:02:14,240 --> 00:02:18,040 by an increase in resistance to airflow due to partial or 50 00:02:18,040 --> 00:02:20,840 complete obstruction at any level of the tracheobronchial 51 00:02:20,840 --> 00:02:22,560 tree. So the problem isn't getting air 52 00:02:22,560 --> 00:02:23,560 in. Exactly. 53 00:02:23,560 --> 00:02:26,160 It's getting air out. And Robbins is very specific 54 00:02:26,160 --> 00:02:28,800 about the classification. Here we refer to the BIG4. 55 00:02:29,040 --> 00:02:31,800 Yes. In pathology, the big four are 56 00:02:31,840 --> 00:02:35,960 emphysema, chronic bronchitis, asthma, and Bronchiectasis. 57 00:02:36,320 --> 00:02:37,480 You should list these confidently. 58 00:02:37,480 --> 00:02:40,080 It shows you've read beyond just the anesthesia texts. 59 00:02:40,280 --> 00:02:43,520 But here is the pivot point for the anesthesiologist and 60 00:02:43,520 --> 00:02:45,200 specifically for this exam topic. 61 00:02:45,520 --> 00:02:49,320 We need to distinguish asthma from the rest, particularly from 62 00:02:49,320 --> 00:02:50,800 COPD. What is the single most 63 00:02:50,800 --> 00:02:54,120 important discriminator? The magic word is reversibility. 64 00:02:54,120 --> 00:02:55,800 This is an exam tip right off the bat. 65 00:02:55,800 --> 00:02:58,880 If you say asthma is airway obstruction, you're only half 66 00:02:58,880 --> 00:03:00,760 right. You must say it is reversible 67 00:03:00,760 --> 00:03:02,480 airway obstruction. So that's the keyword 68 00:03:02,560 --> 00:03:03,760 reversible. Absolutely. 69 00:03:04,360 --> 00:03:07,200 COPD, which is a clinical syndrome often comprising 70 00:03:07,200 --> 00:03:10,320 emphysema and chronic bronchitis, is characterized by 71 00:03:10,320 --> 00:03:13,560 persistent airflow limitation that is not fully reversible. 72 00:03:13,720 --> 00:03:17,800 So conceptualizing this for the Viva, asthma is a dynamic state. 73 00:03:18,000 --> 00:03:20,440 The airway clamps down, but it can open up again. 74 00:03:21,080 --> 00:03:23,560 COPD is more of a fixed structural change. 75 00:03:23,680 --> 00:03:26,680 That's a perfect way to put it, and you need to be precise with 76 00:03:26,680 --> 00:03:29,360 the definition of asthma itself. It's not just wheezing. 77 00:03:29,360 --> 00:03:30,960 That's a symptom, not a definition. 78 00:03:30,960 --> 00:03:33,160 OK, so what's the full definition we should be giving? 79 00:03:33,280 --> 00:03:36,440 Bronchial asthma is a chronic inflammatory disorder of the 80 00:03:36,440 --> 00:03:39,400 Airways. This chronic inflammation causes 81 00:03:39,400 --> 00:03:42,960 airway hyper responsiveness that leads to recurrent episodes of 82 00:03:42,960 --> 00:03:46,520 wheezing, breathlessness, chest tightness and coughing, 83 00:03:46,840 --> 00:03:49,160 particularly at night or in the early morning. 84 00:03:49,240 --> 00:03:52,800 You've used two key terms there, inflammation and hyper 85 00:03:52,800 --> 00:03:54,840 responsiveness, if we need to unpack. 86 00:03:54,840 --> 00:03:56,680 Those we will. They're central to everything. 87 00:03:56,760 --> 00:03:58,880 But first, let's touch on the epidemiology. 88 00:03:59,320 --> 00:04:01,800 Why does this matter to us as anesthesiologists? 89 00:04:01,800 --> 00:04:04,120 Is it just background noise or is there a real safety 90 00:04:04,120 --> 00:04:06,720 implication? It's a massive safety issue. 91 00:04:06,720 --> 00:04:09,920 I mean the global burden is around 300 million people. 92 00:04:10,280 --> 00:04:14,680 It is likely the most common pulmonary comorbidity you will 93 00:04:14,680 --> 00:04:16,480 encounter in your day-to-day practice. 94 00:04:16,480 --> 00:04:18,000 So we're going to see it all the time. 95 00:04:18,160 --> 00:04:21,160 All the time. And Miller explicitly points out 96 00:04:21,160 --> 00:04:24,520 that about 9% of asthmatics may develop bronchospasm 97 00:04:24,520 --> 00:04:27,520 perioperatively. 9% That's nearly one in 10. 98 00:04:27,800 --> 00:04:30,640 That is a statistically significant risk for every 99 00:04:30,640 --> 00:04:31,960 single list we run. Correct. 100 00:04:32,360 --> 00:04:35,680 And intraoperative bronchospasm isn't a minor annoying it's not 101 00:04:35,680 --> 00:04:38,880 just a bitter wheezing. In severe cases, it leads to 102 00:04:38,880 --> 00:04:42,560 inability to ventilate, severe hypoxia, and potentially brain 103 00:04:42,560 --> 00:04:46,080 damage or death. So this can be a true anesthetic 104 00:04:46,080 --> 00:04:48,520 catastrophe. It can be, and you also need to 105 00:04:48,520 --> 00:04:51,840 be attuned to the concept of the silent chest, which signifies 106 00:04:51,840 --> 00:04:54,520 obstructions so severe that air movement is minimal. 107 00:04:55,040 --> 00:04:58,400 If you're waiting for a wheeze to diagnose severity, you might 108 00:04:58,400 --> 00:05:00,160 miss the patient who is about to arrest. 109 00:05:00,320 --> 00:05:02,320 That is a terrifying concept to Silent Chest. 110 00:05:02,320 --> 00:05:04,200 We will absolutely drill down into that later. 111 00:05:04,440 --> 00:05:06,560 But first, let's look at the exam paper itself. 112 00:05:07,160 --> 00:05:10,120 If I'm the student, what kind of questions am I anticipating? 113 00:05:10,120 --> 00:05:12,200 You will see patterns for short notes. 114 00:05:12,200 --> 00:05:15,240 They love mechanism based questions like pathophysiology 115 00:05:15,240 --> 00:05:18,240 of asthma or equipment based ones like capnography and 116 00:05:18,240 --> 00:05:19,960 bronchospasm. OK, short and focus. 117 00:05:20,040 --> 00:05:25,080 Exactly for the long 10 to 20 mark questions, expect a high 118 00:05:25,080 --> 00:05:28,280 stakes clinical scenario. Discuss the anesthetic 119 00:05:28,280 --> 00:05:31,120 management of a case of status asthmaticus for emergency 120 00:05:31,120 --> 00:05:32,920 surgery. The nightmare scenario. 121 00:05:32,920 --> 00:05:36,720 The one that tests everything. And for the Viva or OSCE, be 122 00:05:37,120 --> 00:05:41,080 ready to interpret flow volume loops or arterial blood gases on 123 00:05:41,080 --> 00:05:42,960 the spot. OK, let's tackle that first 124 00:05:42,960 --> 00:05:46,920 short note topic, Section 2, the pathophysiological basis of 125 00:05:46,920 --> 00:05:48,880 asthma. This is the core of the exam, 126 00:05:48,880 --> 00:05:50,160 isn't it? If you don't understand the 127 00:05:50,160 --> 00:05:53,080 pathology, you can't justify your pharmacological choices 128 00:05:53,080 --> 00:05:54,120 later. Absolutely. 129 00:05:54,200 --> 00:05:57,160 The most common mistake students make is thinking asthma is just 130 00:05:57,280 --> 00:05:59,240 bronchospasm, just muscle tightening. 131 00:05:59,240 --> 00:06:01,520 It's not. It is fundamentally a disease of 132 00:06:01,520 --> 00:06:04,520 chronic airway inflammation. So the muscle spasm is just the 133 00:06:04,520 --> 00:06:07,440 symptom, the disease is the angry inflamed tissue 134 00:06:07,440 --> 00:06:08,720 underneath. Exactly. 135 00:06:08,720 --> 00:06:11,200 Even when the patient is asymptomatic, walking around 136 00:06:11,200 --> 00:06:14,280 feeling fine, their airway is infiltrated with mast cells, 137 00:06:14,280 --> 00:06:18,040 eosinophils, and T lymphocytes. This chronic state leads to what 138 00:06:18,040 --> 00:06:20,600 we call airway remodeling. Remodeling sounds like a 139 00:06:20,600 --> 00:06:23,040 construction project, but in this context I assume it's 140 00:06:23,040 --> 00:06:25,400 destructive. It is maladaptive. 141 00:06:25,400 --> 00:06:28,920 It's the body trying to repair pair itself but doing a bad job. 142 00:06:29,240 --> 00:06:32,720 We see thickening of the sub basement membrane, hypertrophy 143 00:06:32,720 --> 00:06:35,800 of the smooth muscle, and hyperplasia of the mucus glands. 144 00:06:35,800 --> 00:06:38,240 So the airway is literally changing its structure for the 145 00:06:38,240 --> 00:06:40,600 work. Precisely this structural change 146 00:06:40,600 --> 00:06:42,760 makes the airway hyper responsive. 147 00:06:42,760 --> 00:06:45,760 Define hyper responsiveness for me in an exam context. 148 00:06:45,840 --> 00:06:47,200 Yeah. How do I explain that to a 149 00:06:47,200 --> 00:06:49,560 junior colleague? It is the tendency of the 150 00:06:49,560 --> 00:06:53,520 Airways to narrow excessively in response to triggers that 151 00:06:53,520 --> 00:06:56,600 wouldn't affect a normal person. A little bit of cold air, a 152 00:06:56,600 --> 00:07:01,200 specific or the mechanical touch of a laryngoscope blade that you 153 00:07:01,200 --> 00:07:04,200 or I would ignore causes a massive disproportionate 154 00:07:04,200 --> 00:07:06,960 reaction in an asthmatic A. Real overreaction of the area. 155 00:07:06,960 --> 00:07:09,200 A huge overreaction and then we have the mucus. 156 00:07:09,200 --> 00:07:10,840 This isn't just normal secretions, is it? 157 00:07:10,880 --> 00:07:13,440 No, not at all. The mucus plugging in asthma is 158 00:07:13,440 --> 00:07:16,160 nasty. It's thick, tenacious, and 159 00:07:16,160 --> 00:07:20,120 incredibly difficult to suction. Pathology texts like Robbins 160 00:07:20,120 --> 00:07:23,640 describes specific microscopic findings within this mucus. 161 00:07:23,640 --> 00:07:25,440 Oh, this sounds like bonus points territory. 162 00:07:25,600 --> 00:07:27,880 It is. You have Kirchman spirals, which 163 00:07:27,880 --> 00:07:32,040 are these little whirls of shed epithelium, and charcoal Leiden 164 00:07:32,040 --> 00:07:34,840 crystals which are composed of Eucenophil proteins. 165 00:07:35,200 --> 00:07:37,520 Those sound like incredible buzzwords for a pathology 166 00:07:37,520 --> 00:07:39,720 question. They are gold medal details. 167 00:07:40,120 --> 00:07:43,440 Dropping charcoal Leiden crystals into your answer tells 168 00:07:43,440 --> 00:07:45,520 the examiner you've read the pathology text. 169 00:07:45,520 --> 00:07:47,000 It's not just the anesthesia summary. 170 00:07:47,240 --> 00:07:51,200 OK, so Kirchman's spirals and charcoal Leiden crystals, but 171 00:07:51,200 --> 00:07:54,840 what's the anesthetic relevance? The clinical relevance is this, 172 00:07:55,240 --> 00:07:58,760 that inflammation makes the airway incredibly twitchy. 173 00:07:59,080 --> 00:08:02,960 Instrumentation like putting in an endotracheal tube is a potent 174 00:08:02,960 --> 00:08:05,040 trigger. You are essentially poking an 175 00:08:05,040 --> 00:08:07,080 angry bear. An excellent analogy. 176 00:08:07,400 --> 00:08:10,680 Moving on to Section 3, immunological mechanisms, this 177 00:08:10,680 --> 00:08:13,640 is often labeled as exam gold. We need to understand the 178 00:08:13,640 --> 00:08:15,800 mechanism to understand the drugs we use. 179 00:08:15,920 --> 00:08:18,680 You need to know that it is predominantly an IG mediated 180 00:08:18,680 --> 00:08:21,680 hypersensitivity or type hypersensitivity. 181 00:08:21,720 --> 00:08:23,160 Walk us through the cellular level. 182 00:08:23,160 --> 00:08:25,840 Who are the players? The star of the show is the mast 183 00:08:25,840 --> 00:08:27,760 cell. Think of them as Sentinel cells 184 00:08:27,760 --> 00:08:32,360 embedded in the submucosa, just waiting exactly in an atopic 185 00:08:32,360 --> 00:08:34,559 individual, someone prone to allergies. 186 00:08:34,880 --> 00:08:37,480 These cells are coated with Ige antibodies. 187 00:08:38,280 --> 00:08:42,440 When an antigen, say pollen or a specific drug binds to that Ige, 188 00:08:42,559 --> 00:08:45,600 it causes crosslinking. And crosslinking acts as the 189 00:08:45,600 --> 00:08:47,760 trigger, like turning a key in a lock. 190 00:08:47,920 --> 00:08:50,640 A perfect analogy. It triggers degranulation. 191 00:08:50,920 --> 00:08:54,720 The mast cell essentially explodes, releasing a cocktail 192 00:08:54,720 --> 00:08:57,000 of preformed inflammatory mediators. 193 00:08:57,280 --> 00:08:58,920 The big one, of course, is histamine. 194 00:08:59,000 --> 00:09:01,600 Which causes the immediate reaction we see on the table, 195 00:09:01,640 --> 00:09:03,040 the wheezing, the pressure going. 196 00:09:03,040 --> 00:09:06,720 Up right histamine causes rapid bronchoconstriction and mucosal 197 00:09:06,720 --> 00:09:08,960 edema. That's the early phase, but you 198 00:09:08,960 --> 00:09:11,800 also have the synthesis of new mediators like the leukotrienes, 199 00:09:11,800 --> 00:09:14,520 which were formerly known as the slow reacting substance of 200 00:09:14,520 --> 00:09:16,400 anaphylaxis. That's a great piece of medical 201 00:09:16,400 --> 00:09:18,440 trivia. Slow reacting substance of 202 00:09:18,440 --> 00:09:20,760 anaphylaxis. It is, and it tells you what it 203 00:09:20,760 --> 00:09:22,960 does. Leukotrienes cause prolonged, 204 00:09:22,960 --> 00:09:26,400 sustained bronchospasm. They are much more potent and 205 00:09:26,400 --> 00:09:27,920 longer lasting than histamine. OK. 206 00:09:27,920 --> 00:09:30,560 So that's the immediate problem, but you mentioned early versus 207 00:09:30,560 --> 00:09:32,360 late phase reactions. Yes. 208 00:09:32,360 --> 00:09:35,600 And this is a crucial conceptual leap for the anesthesiologist, 209 00:09:35,600 --> 00:09:37,520 the early versus late phase reaction. 210 00:09:37,520 --> 00:09:39,680 Why is this so clinically relevant for us? 211 00:09:40,280 --> 00:09:41,920 The early phase happens in minutes. 212 00:09:41,920 --> 00:09:44,400 That's the immediate bronchospasm you fight during 213 00:09:44,400 --> 00:09:47,920 induction, but the late phase happens 2 to 8 hours later. 214 00:09:48,080 --> 00:09:50,320 This is caused by the recruitment of inflammatory 215 00:09:50,320 --> 00:09:52,960 cells like neutrophils and eosinophils into the Airways. 216 00:09:52,960 --> 00:09:55,400 So. A patient could have a reaction 217 00:09:55,400 --> 00:09:58,160 in the OT, You stabilize them, everything looks good, you send 218 00:09:58,160 --> 00:10:01,480 them to the ward and then. And then six hours later in the 219 00:10:01,480 --> 00:10:04,280 pay CU or on the floor they deteriorate. 220 00:10:04,440 --> 00:10:07,640 They might look fine initially but crash post op because of 221 00:10:07,640 --> 00:10:09,400 this late phase inflammatory bloom. 222 00:10:09,600 --> 00:10:11,560 That is a Viva trap right there. Yeah. 223 00:10:11,680 --> 00:10:14,640 Why did the patient deteriorate in the PCU despite a smooth 224 00:10:14,640 --> 00:10:17,520 emergence? Exactly, if you can answer late 225 00:10:17,520 --> 00:10:20,280 phase reaction due to inflammatory cell recruitment 226 00:10:20,280 --> 00:10:22,760 you get full marks. It shows you're thinking beyond 227 00:10:22,760 --> 00:10:25,240 the immediate crisis. Now let's connect this to 228 00:10:25,240 --> 00:10:27,640 Section 4 effects on lung mechanics. 229 00:10:27,640 --> 00:10:31,200 We talked about flow limitation. When the Airways narrow, what 230 00:10:31,200 --> 00:10:34,040 happens to resistance? It's skyrockets and for the exam 231 00:10:34,040 --> 00:10:36,360 you need to quote Kwizu's law. Oh, physics. 232 00:10:36,360 --> 00:10:38,600 OK. It's simple but powerful. 233 00:10:38,960 --> 00:10:42,040 Resistance is inversely proportional to the radius to 234 00:10:42,040 --> 00:10:44,320 the power of 4. For laminar flow, the. 235 00:10:44,360 --> 00:10:46,800 Power of four. Let's do the math on that if the 236 00:10:46,800 --> 00:10:49,880 radius is halved. The resistance increases 16 237 00:10:49,880 --> 00:10:52,640 fold. It's not a linear relationship, 238 00:10:52,680 --> 00:10:55,520 it's exponential. 16 times harder to breathe. 239 00:10:55,600 --> 00:10:58,720 Exactly. And if flow becomes turbulent, 240 00:10:58,720 --> 00:11:01,960 which it often does in narrowed Airways, the dependence is on 241 00:11:01,960 --> 00:11:05,800 the radius to the power of 5. This explains why breathing 242 00:11:05,800 --> 00:11:07,520 becomes such incredibly hard work. 243 00:11:07,800 --> 00:11:10,280 The patient has to generate massive negative pressure to 244 00:11:10,280 --> 00:11:13,560 pull air in and massive positive pressure to push it out. 245 00:11:13,680 --> 00:11:16,680 And specifically, expiration is affected more than inspiration, 246 00:11:16,680 --> 00:11:17,600 correct? Why is that? 247 00:11:17,760 --> 00:11:20,520 Yes, inspiration is an active process. 248 00:11:20,680 --> 00:11:23,600 The chest wall expands and pulls the Airways open through 249 00:11:23,600 --> 00:11:25,160 something called radial traction. 250 00:11:25,360 --> 00:11:27,320 Expiration, however, is normally passive. 251 00:11:27,680 --> 00:11:30,720 As the lung empties, the Airways naturally narrow a bit. 252 00:11:31,080 --> 00:11:33,640 In asthma, this natural narrowing combined with the 253 00:11:33,640 --> 00:11:36,800 pathology, the swelling, the mucus, the spasm leads to 254 00:11:36,800 --> 00:11:39,160 premature airway closure. So the air gets trapped. 255 00:11:39,360 --> 00:11:42,880 The air gets trapped. And this brings us to a critical 256 00:11:42,880 --> 00:11:47,560 concept, dynamic hyperinflation or what we call auto peep. 257 00:11:47,800 --> 00:11:50,880 Let's unpack auto peep. This is the term we hear in the 258 00:11:50,880 --> 00:11:54,160 ICU all the time, but explaining it physically can be tricky. 259 00:11:54,600 --> 00:11:57,040 Imagine breathing in through a very thin straw. 260 00:11:57,400 --> 00:11:59,480 It's hard. Now imagine trying to breathe 261 00:11:59,560 --> 00:12:02,080 out through that same straw, but before you have finished 262 00:12:02,080 --> 00:12:05,160 exhaling, you are forced to take another breath in. 263 00:12:05,280 --> 00:12:07,880 I'd still have air left in my lungs from the first breath. 264 00:12:07,880 --> 00:12:09,680 I wouldn't have time to empty them completely. 265 00:12:09,680 --> 00:12:11,960 Exactly. Air goes in, but it cannot get 266 00:12:11,960 --> 00:12:14,000 out completely before the next breath starts. 267 00:12:14,080 --> 00:12:17,080 This is air trapping. The lungs get bigger and bigger 268 00:12:17,080 --> 00:12:19,160 with each breath. The functional residual 269 00:12:19,160 --> 00:12:21,920 capacity, or FRC just keeps rising. 270 00:12:21,920 --> 00:12:24,520 It sounds like it would increase pressure inside the chest quite 271 00:12:24,520 --> 00:12:25,480 a bit. It does. 272 00:12:25,560 --> 00:12:27,600 It increases intrathoracic pressure. 273 00:12:27,960 --> 00:12:29,680 Now think about the hemodynamics. 274 00:12:29,760 --> 00:12:32,800 What does high intrathoracic pressure do to the heart? 275 00:12:33,120 --> 00:12:37,040 It acts like a tamponade. It squashes the great veins, 276 00:12:37,400 --> 00:12:39,560 reducing venous return to the right heart. 277 00:12:39,840 --> 00:12:43,120 Correct, it decreases venous return which decreases preload 278 00:12:43,240 --> 00:12:47,520 which leads to hypotension. So here is the clinical Pearl. 279 00:12:47,880 --> 00:12:50,240 If you are ventilating an asthmatic and their blood 280 00:12:50,240 --> 00:12:53,440 pressure suddenly drops, you must immediately think of auto 281 00:12:53,440 --> 00:12:55,840 peep. And the fix isn't fluids or 282 00:12:55,840 --> 00:12:58,680 pressors initially. No, the immediate fix is to 283 00:12:58,680 --> 00:13:02,640 treat the cause the trapped air. You disconnect the ventilator 284 00:13:02,640 --> 00:13:06,040 from the endotracheal tube, you allow a long apnea period. 285 00:13:06,400 --> 00:13:09,280 You might even gently push on the chest to help them exhale 286 00:13:09,280 --> 00:13:11,400 that trapped gas. What happens when you do that? 287 00:13:11,440 --> 00:13:14,000 You will hear a long hiss of air escaping and you'll see the 288 00:13:14,000 --> 00:13:15,440 blood pressure come right back up. 289 00:13:15,480 --> 00:13:18,480 It's dramatic and life saving. That's a practical save a life 290 00:13:18,480 --> 00:13:20,920 tip disconnect and let them exhale. 291 00:13:21,560 --> 00:13:24,760 Now Section 5 clinical features of asthma. 292 00:13:24,760 --> 00:13:27,800 We know the classic triad, dyspnea, cough, wheezing, but 293 00:13:27,800 --> 00:13:29,960 you mentioned the silent chest earlier. 294 00:13:29,960 --> 00:13:32,280 Yes. In the exam, they will ask, is 295 00:13:32,280 --> 00:13:34,280 the loudness of the wheeze a sign of severity? 296 00:13:34,440 --> 00:13:37,720 The answer is an emphatic NO. Explain why that seems 297 00:13:37,720 --> 00:13:40,520 counterintuitive. Because to make a wheeze, which 298 00:13:40,520 --> 00:13:43,600 is a musical sound produced by turbulent flow through a narrow 299 00:13:43,600 --> 00:13:47,520 tube, you need airflow. In severe obstruction there is 300 00:13:47,520 --> 00:13:50,440 so little air moving that there is no sand generation. 301 00:13:50,800 --> 00:13:54,400 A silent chest in a distressed tachypneic patient is a pre 302 00:13:54,400 --> 00:13:56,760 terminal sign. So silence is worse than noise. 303 00:13:56,760 --> 00:13:59,960 Silence is terrifying. It means imminent respiratory 304 00:13:59,960 --> 00:14:02,240 arrest. What about triggers? 305 00:14:02,600 --> 00:14:05,160 We know about pollen and dust. What about drugs? 306 00:14:05,720 --> 00:14:07,440 This is crucial for our history taking. 307 00:14:07,520 --> 00:14:10,160 Aspirin and other NSIS are classic triggers. 308 00:14:10,360 --> 00:14:13,560 About 1% to 5% of asthmatics are sensitive. 309 00:14:13,880 --> 00:14:16,280 This is sometimes known as Sampter's triad, which is 310 00:14:16,280 --> 00:14:18,680 asthma. Aspirin sensitivity in nasal 311 00:14:18,680 --> 00:14:20,600 polyps. What is the mechanism there? 312 00:14:20,600 --> 00:14:23,640 It's not IG E mediated is it? No, it's not a true allergy. 313 00:14:23,640 --> 00:14:27,280 It's biochemical. Nsiis inhibit the cyclooxygenase 314 00:14:27,280 --> 00:14:30,160 or Cox enzyme. This blocks the production of 315 00:14:30,160 --> 00:14:32,440 prostaglandins. However, the arachidonic acid 316 00:14:32,440 --> 00:14:34,680 precursor has to go somewhere. So it gets diverted. 317 00:14:34,720 --> 00:14:37,040 It gets shunted down the lipoxygenase pathway. 318 00:14:37,040 --> 00:14:40,000 Which produces more? Leukotrienes and as we know from 319 00:14:40,000 --> 00:14:42,520 our earlier discussion, leukotrienes cause potent 320 00:14:42,520 --> 00:14:46,360 prolonged bronchospasm. So as a rule, avoid Toradol or 321 00:14:46,360 --> 00:14:49,320 diclofenac in these patients unless you are absolutely 322 00:14:49,320 --> 00:14:51,080 certain they are not aspirin sensitive. 323 00:14:51,160 --> 00:14:54,520 In any asthmatic with a history of nasal polyps or known aspirin 324 00:14:54,520 --> 00:14:56,280 sensitivity, absolutely avoid them. 325 00:14:56,360 --> 00:14:58,680 It's not worth the risk. Let's talk investigations, 326 00:14:58,680 --> 00:15:01,760 Section 6, pulmonary function tests, or PFTS. 327 00:15:01,800 --> 00:15:04,520 This is absolutely essential for the exam. 328 00:15:04,640 --> 00:15:06,720 You must know the spiromet findings cold. 329 00:15:06,800 --> 00:15:09,880 The hallmark of any obstructive disease is a reduction in FEV 330 00:15:09,920 --> 00:15:12,440 one the forced expiratory volume in one second. 331 00:15:12,960 --> 00:15:15,840 The flow is slow. And the FVC, the forced vital 332 00:15:15,840 --> 00:15:18,360 capacity, the total amount of air they can blow out. 333 00:15:18,840 --> 00:15:21,960 It's usually normal or might be slightly reduced due to the air 334 00:15:21,960 --> 00:15:24,400 trapping we talked about. But the key number, the one the 335 00:15:24,400 --> 00:15:28,080 examiner wants to hear, is the FEV 1 FVC ratio. 336 00:15:28,400 --> 00:15:32,920 In asthma and COPD this ratio is reduced, typically less than .7 337 00:15:32,920 --> 00:15:35,720 or 70%. A normal person can blow out 338 00:15:35,720 --> 00:15:37,720 most of their air in the first second and obstruct. 339 00:15:37,720 --> 00:15:39,840 A person can't. And how do we prove it's asthma 340 00:15:39,840 --> 00:15:43,960 and not COPD using just the PFT? Reversibility testing. 341 00:15:44,160 --> 00:15:46,560 This is the gold standard for diagnosis. 342 00:15:47,080 --> 00:15:50,200 You do the spirometry, then you give a bronchodilator like 343 00:15:50,200 --> 00:15:53,360 cellbutamol, wait 15 minutes and repeat the test. 344 00:15:53,680 --> 00:15:56,680 And what are we looking for? If the FEV 1 increases by more 345 00:15:56,680 --> 00:15:59,960 than 12% ND more than 200 milliliters from the baseline, 346 00:16:00,120 --> 00:16:03,040 that is a positive test. It confirms reversible 347 00:16:03,040 --> 00:16:04,960 obstruction, which is the hallmark of asthma. 348 00:16:05,120 --> 00:16:07,800 OK, 12% and 200 milliliters. Got it. 349 00:16:08,160 --> 00:16:11,040 Now for the visual learners, imagine the flow volume loop you 350 00:16:11,040 --> 00:16:12,480 are at the whiteboard and the Viva. 351 00:16:12,520 --> 00:16:15,800 What are you drawing? You draw the axis with flow on 352 00:16:15,800 --> 00:16:18,080 the axis and volume on the X axis. 353 00:16:18,080 --> 00:16:20,440 You draw the inspiratory limb, which is usually a nice 354 00:16:20,440 --> 00:16:22,720 symmetrical semicircle on the bottom. 355 00:16:23,080 --> 00:16:25,160 Then you draw the expertory limb on top. 356 00:16:25,280 --> 00:16:27,640 And for asthma? The expertory limb looks scooped 357 00:16:27,640 --> 00:16:29,480 out. It has a concave appearance. 358 00:16:29,480 --> 00:16:32,600 It starts with a sharp peak, but then the flow drops off very 359 00:16:32,600 --> 00:16:35,240 quickly and tails off as the Airways collapse. 360 00:16:35,360 --> 00:16:38,360 Unlike A restrictive disease. Right, A restrictive disease 361 00:16:38,360 --> 00:16:40,840 like pulmonary fibrosis looks like a witch's hat. 362 00:16:41,120 --> 00:16:44,520 It's narrow because the volumes are small, but the is preserved 363 00:16:44,760 --> 00:16:47,440 and it's tall because the flows can be high relative to the 364 00:16:47,440 --> 00:16:49,480 volume. Obstructive is scooped out. 365 00:16:49,840 --> 00:16:52,600 Section 7. ABG changes in asthma. 366 00:16:52,800 --> 00:16:56,200 This is an exam favorite. How does the ABG change as an 367 00:16:56,200 --> 00:16:58,640 asthma attack progresses from mild to severe? 368 00:16:58,800 --> 00:17:02,320 This is a classic progression that you must know in early or 369 00:17:02,320 --> 00:17:04,240 mild asthma, the patient is anxious. 370 00:17:04,240 --> 00:17:06,240 They feel short of breath, so they hyperventilate. 371 00:17:06,520 --> 00:17:09,280 They're breathing fast. So what happens to their CO2? 372 00:17:09,359 --> 00:17:12,440 They blow it off. So hypocapnia, which leads to a 373 00:17:12,440 --> 00:17:15,440 respiratory alkalosis. Correct and usually mild 374 00:17:15,440 --> 00:17:17,599 hypoxemia because of some VQ mismatch. 375 00:17:18,000 --> 00:17:20,480 Now, as the attack gets more severe and the patient gets 376 00:17:20,480 --> 00:17:23,200 tired, remember breathing through a straw is exhausting 377 00:17:23,200 --> 00:17:25,760 work, The respiratory muscles begin to fatigue. 378 00:17:26,119 --> 00:17:29,120 The rate might stay high, but the tidal volume drops. 379 00:17:29,320 --> 00:17:31,920 The CO2 starts to rise. It returns to normal. 380 00:17:31,920 --> 00:17:35,400 Wait, normal CO2 sounds good? If I see a PECO 2 of 40 milli 381 00:17:35,400 --> 00:17:37,440 milli HG on an ABG, I'm usually pretty. 382 00:17:37,440 --> 00:17:37,800 Happy. No. 383 00:17:37,920 --> 00:17:41,840 That is the trap. A normal Peco 2, say 35 to 45 384 00:17:41,840 --> 00:17:45,480 milli milli HG in a tachypneic, panting, distressed, asthmatic 385 00:17:45,480 --> 00:17:47,000 is a huge danger sign. Why? 386 00:17:47,200 --> 00:17:49,720 It implies that they can no longer maintain the work of 387 00:17:49,720 --> 00:17:51,480 breathing needed to clear the CO2. 388 00:17:51,560 --> 00:17:53,240 They are tiring out. They are failing. 389 00:17:53,240 --> 00:17:56,200 So if I see a normal CO2 two in a distressed asthmatic, I 390 00:17:56,200 --> 00:17:58,040 shouldn't be reassured, I should be worried. 391 00:17:58,200 --> 00:18:00,200 You should be preparing for intubation. 392 00:18:00,200 --> 00:18:02,560 It signals impending respiratory failure. 393 00:18:03,080 --> 00:18:07,040 The next stage is hypercapnia, a high CO2 which causes a 394 00:18:07,040 --> 00:18:09,960 respiratory acidosis and severe hypoxemia. 395 00:18:10,240 --> 00:18:14,080 If you wait for the CO2 to be high, you have waited too long. 396 00:18:14,360 --> 00:18:17,040 Let's move to Section 8, preoperative evaluation. 397 00:18:17,840 --> 00:18:20,640 A patient comes to your clinic with a history of asthma, 398 00:18:20,800 --> 00:18:23,360 scheduled for elective surgery. What are the high yield 399 00:18:23,360 --> 00:18:25,760 questions? History is absolutely key. 400 00:18:25,760 --> 00:18:27,840 You want to know the frequency of their inhaler use. 401 00:18:27,840 --> 00:18:29,880 Are they using their rescue inhaler daily? 402 00:18:30,040 --> 00:18:32,400 That's a bad sign. What else you need to know about 403 00:18:32,400 --> 00:18:33,920 their history of hospitalizations? 404 00:18:33,920 --> 00:18:35,720 Have they ever been admitted for asthma? 405 00:18:35,720 --> 00:18:39,040 Ever been in the ICU? And the most critical question 406 00:18:39,520 --> 00:18:42,200 Have they ever been intubated for their asthma? 407 00:18:42,200 --> 00:18:44,360 Why is the intubation history so important? 408 00:18:44,400 --> 00:18:47,000 If they've been intubated for asthma before, they are by 409 00:18:47,000 --> 00:18:50,240 definition a high risk patient. It suggests their disease is 410 00:18:50,240 --> 00:18:52,720 capable of becoming life threatening very quickly. 411 00:18:53,200 --> 00:18:57,080 Also ask about recent upper respiratory infections or Uris. 412 00:18:57,080 --> 00:18:58,680 Common cold. Exactly. 413 00:18:58,960 --> 00:19:02,240 A Uri increases airway reactivity for weeks. 414 00:19:02,240 --> 00:19:04,920 Some texts say up to six weeks post infection. 415 00:19:05,120 --> 00:19:07,480 That's a long time. If they have a cold, do we 416 00:19:07,480 --> 00:19:10,240 cancel the surgery? For elective surgery, yes. 417 00:19:10,320 --> 00:19:12,920 The rule of thumb is that elective surgery should be done 418 00:19:12,920 --> 00:19:15,560 when the patient is at their baseline symptom free. 419 00:19:15,840 --> 00:19:18,800 If they are actively wheezing in the pre op Bay, you do not 420 00:19:18,800 --> 00:19:22,280 induce, you postpone. If they had a Uri last week, you 421 00:19:22,280 --> 00:19:24,920 postpone if possible. What about smoking cessation? 422 00:19:25,160 --> 00:19:26,800 Always a good idea, but what's the timeline? 423 00:19:27,000 --> 00:19:29,680 The longer the better, ideally 4 to 8 weeks. 424 00:19:30,360 --> 00:19:32,600 What if they stopped just 48 hours before? 425 00:19:33,040 --> 00:19:36,280 Does that do anything? It helps with carboxyhemoglobin 426 00:19:36,280 --> 00:19:38,160 levels. It shifts the oxygen 427 00:19:38,160 --> 00:19:41,800 dissociation curve back to the right, which improves oxygen 428 00:19:41,800 --> 00:19:44,960 delivery to the tissues, but it doesn't do much for airway 429 00:19:44,960 --> 00:19:49,120 reactivity or mucus claimants. In fact, sputum production might 430 00:19:49,120 --> 00:19:52,000 increase initially as the cilia start to wake up and clear out 431 00:19:52,000 --> 00:19:54,280 the gunk. So 4 to 8 weeks is the real 432 00:19:54,280 --> 00:19:57,600 target for pulmonary benefit. Yes, that's when you start to 433 00:19:57,600 --> 00:20:00,960 see restoration of mucosciliary transport and a reduction in 434 00:20:00,960 --> 00:20:04,840 post op pulmonary complications. Let's look at Section 9, risk 435 00:20:04,840 --> 00:20:06,800 stratification. How do we put all that 436 00:20:06,800 --> 00:20:09,160 information together to decide who is going to have 437 00:20:09,160 --> 00:20:12,600 bronchospasm on the table? The main predictors are a recent 438 00:20:12,640 --> 00:20:17,320 Uri as we just discussed, active smoking and the type of surgery 439 00:20:17,320 --> 00:20:20,040 and airway device. So instrumentation of the airway 440 00:20:20,040 --> 00:20:22,040 matters a lot. It's a huge factor. 441 00:20:22,360 --> 00:20:27,200 An endotracheal tube ETT is much more stimulating to the trachea 442 00:20:27,200 --> 00:20:29,920 than a laryngeal mask, airway or LMA. 443 00:20:30,680 --> 00:20:33,760 Also be aware that well controlled asthma carries a risk 444 00:20:33,760 --> 00:20:36,120 that's pretty similar to non asthmatics. 445 00:20:36,360 --> 00:20:39,440 It's the poorly controlled or symptomatic patient who is in 446 00:20:39,440 --> 00:20:41,240 the danger zone. That leads us perfectly to 447 00:20:41,240 --> 00:20:45,080 Section 10 choice of anesthesia. If you have a choice, regional 448 00:20:45,080 --> 00:20:47,920 anesthesia is the gold standard for an asthmatic patient. 449 00:20:48,160 --> 00:20:49,480 Why? What's the advantage? 450 00:20:49,480 --> 00:20:51,600 It's simple. You avoid putting a tube in the 451 00:20:51,600 --> 00:20:53,840 trachea. You avoid that direct mechanical 452 00:20:53,840 --> 00:20:55,760 stimulation of the twitchy airway. 453 00:20:55,920 --> 00:20:58,040 You bypass the main trigger entirely. 454 00:20:58,160 --> 00:21:00,920 But there's a caveat, right? We can't just do a high spinal 455 00:21:00,920 --> 00:21:02,240 block and relax. Correct. 456 00:21:02,240 --> 00:21:05,160 You have to be careful. Avoid high blocks generally 457 00:21:05,160 --> 00:21:08,760 above the T4 dermatome that might compromise the accessory 458 00:21:08,760 --> 00:21:12,160 muscles of respiration, and asthmatic needs their 459 00:21:12,160 --> 00:21:15,240 intercostals and abdominal muscles to actively exhale 460 00:21:15,240 --> 00:21:17,640 against resistance. If you knock out their 461 00:21:17,640 --> 00:21:21,080 intercostals with a high spinal, they might feel dysmayic even if 462 00:21:21,080 --> 00:21:23,400 their oxygenation is perfectly fine. 463 00:21:23,400 --> 00:21:26,200 But sometimes we have to do general anesthesia, laparoscopy 464 00:21:26,200 --> 00:21:28,080 for instance, or major abdominal surgery. 465 00:21:28,120 --> 00:21:31,120 Right. And if you must do GA, the goal 466 00:21:31,120 --> 00:21:34,360 is deep anesthesia. You need to completely suppress 467 00:21:34,360 --> 00:21:37,360 those airway reflexes before you touch the airway with a 468 00:21:37,360 --> 00:21:40,600 laryngoscope or a tube. OK, let's talk about Section 11 469 00:21:40,880 --> 00:21:43,600 premedication strategies. How do we set them up for 470 00:21:43,600 --> 00:21:45,400 success before they even get to the OR? 471 00:21:45,560 --> 00:21:47,840 First, anxiety triggers bronchospasm. 472 00:21:48,360 --> 00:21:51,400 It's a physiological response via the parasympathetic system. 473 00:21:51,400 --> 00:21:54,280 So anxiolysis with something like a small dose of midazolam 474 00:21:54,320 --> 00:21:56,400 is very useful. And their inhalers, do they take 475 00:21:56,400 --> 00:21:59,360 them on the day of surgery? Absolutely, they should continue 476 00:21:59,360 --> 00:22:02,080 all their regular inhalers including their steroids and 477 00:22:02,080 --> 00:22:04,800 long acting bronchodilators right up to the morning of 478 00:22:04,800 --> 00:22:07,200 surgery. We often give a prophylactic 479 00:22:07,200 --> 00:22:10,160 nebulization with cell butamol in the pre op area as well. 480 00:22:10,160 --> 00:22:11,600 And. What about steroids? 481 00:22:11,680 --> 00:22:13,480 The systemic ones. This is key. 482 00:22:13,800 --> 00:22:17,480 If they are on chronic systemic steroids, their own adrenal axis 483 00:22:17,480 --> 00:22:20,240 is suppressed. You must give them a stress dose 484 00:22:20,240 --> 00:22:23,400 of steroids, usually hydrocortisone 100 milligram IV 485 00:22:23,480 --> 00:22:26,200 at induction and then continue at post op and. 486 00:22:26,280 --> 00:22:29,240 What if they're not on chronic steroids, but they're actively 487 00:22:29,240 --> 00:22:31,040 wheezing before an urgent surgery? 488 00:22:31,120 --> 00:22:33,920 In that case we might start a short course of oral steroids 489 00:22:33,920 --> 00:22:37,040 for three to five days pre op to really calm the inflammation 490 00:22:37,040 --> 00:22:39,920 down before the surgery date. Now the moment of truth. 491 00:22:40,360 --> 00:22:43,040 Section 12. Induction in airway management. 492 00:22:43,520 --> 00:22:45,360 We want a smooth, gentle induction. 493 00:22:45,360 --> 00:22:48,240 What drugs are we reaching for? Propofol is a great choice. 494 00:22:48,320 --> 00:22:51,720 It has mild bronchodilating properties and it suppresses the 495 00:22:51,720 --> 00:22:54,800 laryngeal reflexes very well. It's a very smooth induction. 496 00:22:54,800 --> 00:22:56,880 What about ketamine? I always hear about ketamine for 497 00:22:56,880 --> 00:22:59,320 asthmatics. Ketamine is the theoretical 498 00:22:59,320 --> 00:23:02,160 exeriencer for the actively wheezing patient. 499 00:23:02,600 --> 00:23:04,680 It is an excellent bronchodilator. 500 00:23:05,080 --> 00:23:07,800 It works via a sympathomimetic action. 501 00:23:08,320 --> 00:23:11,560 It increases circulating catecholamines, which relax the 502 00:23:11,560 --> 00:23:14,960 bronchial smooth muscle. It's the agent of choice and a 503 00:23:14,960 --> 00:23:17,960 hypotensive asthmatic or someone in the middle of a severe 504 00:23:17,960 --> 00:23:20,280 bronchospasm. Were there any downside to 505 00:23:20,280 --> 00:23:23,120 ketamine? Yes, the big one is increased 506 00:23:23,120 --> 00:23:25,440 secretions. You might need to give an 507 00:23:25,440 --> 00:23:29,480 antisalagon like glycopyrrolate alongside it to keep the airway 508 00:23:29,480 --> 00:23:31,080 dry. And what do we avoid for 509 00:23:31,080 --> 00:23:33,360 induction? The classic one to avoid is 510 00:23:33,520 --> 00:23:35,800 thiopentone. Historically it's associated 511 00:23:35,800 --> 00:23:38,120 with histamine release in an exam. 512 00:23:38,120 --> 00:23:41,040 If you suggest thiopentone for an asthmatic, you might get a 513 00:23:41,040 --> 00:23:43,520 frown from the examiner. Even if the evidence is a bit 514 00:23:43,520 --> 00:23:45,680 weak. Even then, why take the risk 515 00:23:45,680 --> 00:23:48,280 when propofol exists? It's about choosing the safest 516 00:23:48,280 --> 00:23:50,720 possible option. Airway device you mentioned an 517 00:23:50,720 --> 00:23:53,480 LMA is better. An LMA sits above the glottis. 518 00:23:53,480 --> 00:23:56,080 It doesn't stimulate the trachea itself, so it is much less 519 00:23:56,080 --> 00:23:59,120 stimulating and preferred if there is no contraindication 520 00:23:59,120 --> 00:24:03,080 like a high risk of aspiration or if you need high ventilatory 521 00:24:03,080 --> 00:24:05,320 pressures. But if we need an ETT for a lap 522 00:24:05,320 --> 00:24:07,800 coal for example. Then you must ensure the patient 523 00:24:07,800 --> 00:24:10,040 is deep. I can't stress this enough. 524 00:24:10,480 --> 00:24:14,080 Deep volatile anesthesia. Or you can use IV lidocaine, 525 00:24:14,080 --> 00:24:18,440 about 1.5 milligrams given 90 seconds before you intubate to 526 00:24:18,440 --> 00:24:19,800 blunt the airway. Reflexes. 527 00:24:20,200 --> 00:24:22,000 Do not intubate a light asthmatic. 528 00:24:22,080 --> 00:24:25,320 That is asking for disaster. Once the tube is in, we have to 529 00:24:25,320 --> 00:24:28,360 ventilate them. Section 13 Interoperative 530 00:24:28,360 --> 00:24:30,960 ventilation strategy. This is marked as very high 531 00:24:30,960 --> 00:24:32,200 yield. It is. 532 00:24:32,240 --> 00:24:34,720 The entire strategy can be summed up in 3 words. 533 00:24:34,920 --> 00:24:38,120 Avoid air trapping. Prevent that auto peep we talked 534 00:24:38,120 --> 00:24:39,520 about. So how do we set the ventilator 535 00:24:39,520 --> 00:24:41,360 to do that? We need to give them a long time 536 00:24:41,360 --> 00:24:43,520 to exhale. Remember, their expiration is 537 00:24:43,520 --> 00:24:46,480 prolonged and difficult, so we use a low respiratory rate, 538 00:24:46,960 --> 00:24:49,800 maybe 6 to 10 breaths per minute, and we deliberately 539 00:24:49,800 --> 00:24:52,320 prolong the expiratory time. So the IE ratio. 540 00:24:52,400 --> 00:24:57,040 Instead of the usual 1.2, we go for 1.2.51.3 or even 1.4. 541 00:24:57,040 --> 00:24:59,560 In severe cases. We want the expiratory phase to 542 00:24:59,560 --> 00:25:01,920 be long enough for the expiratory flow to return to 0 543 00:25:01,920 --> 00:25:03,280 before the next breath is delivered. 544 00:25:03,400 --> 00:25:06,680 But if we breathe them that slowly, their CO2 will rise. 545 00:25:06,840 --> 00:25:09,560 And that is OK. That is the concept of 546 00:25:09,560 --> 00:25:13,720 permissive hypercapnia. We accept a higher CO2 as long 547 00:25:13,720 --> 00:25:18,000 as the pH say is above roughly 7.2 in exchange for lower airway 548 00:25:18,000 --> 00:25:21,040 pressures and avoiding Barra trauma or the hemodynamic 549 00:25:21,040 --> 00:25:24,160 collapse from auto PEEP. We prioritize lung mechanics 550 00:25:24,160 --> 00:25:26,840 over blood gas chemistry. And the tidal volume? 551 00:25:27,080 --> 00:25:29,960 Moderate 6 to 8 milligrams of ideal body rate. 552 00:25:29,960 --> 00:25:32,600 Don't use large tidal volumes that could over distend the 553 00:25:32,600 --> 00:25:34,280 lungs. Section 14. 554 00:25:34,600 --> 00:25:37,720 Anesthetic drug considerations. We're in the maintenance phase 555 00:25:37,720 --> 00:25:40,080 of anesthesia. Which gas are we using? 556 00:25:40,200 --> 00:25:43,120 Civil fluorine. It's an excellent bronchodilator 557 00:25:43,120 --> 00:25:45,480 and it's non irritant. It's sweet smelling. 558 00:25:45,680 --> 00:25:47,680 It is the agent of choice for maintenance. 559 00:25:48,120 --> 00:25:50,160 What about dysplorine? Absolutely not. 560 00:25:50,160 --> 00:25:52,600 Dysplorine is pungent. It irritates the airway and can 561 00:25:52,600 --> 00:25:55,360 cause coughing, laryngospasm and bronchospasm. 562 00:25:55,600 --> 00:25:58,240 Avoided in asthmatics. It's a key drug to avoid. 563 00:25:58,360 --> 00:26:01,120 And muscle relaxants we've induced, now we need to keep 564 00:26:01,120 --> 00:26:02,920 them relaxed. Avoid the histamine releases. 565 00:26:02,920 --> 00:26:05,880 That means Actrocurium and its cousin Mevacurium are out. 566 00:26:05,880 --> 00:26:09,040 So what are the safe choices? Rocuronium, vecuronium or 567 00:26:09,040 --> 00:26:11,520 sesatrocurium. They are historically very safe. 568 00:26:11,520 --> 00:26:13,320 Regarding histamine release, stick to those. 569 00:26:13,600 --> 00:26:16,320 Analgesics. Fentanyl versus morphine. 570 00:26:16,360 --> 00:26:18,320 Fentanyl and its derivatives are safe. 571 00:26:18,680 --> 00:26:21,040 Morphine is a known histamine releaser. 572 00:26:21,040 --> 00:26:24,120 So in the exam you say you will avoid morphine. 573 00:26:24,120 --> 00:26:25,800 OK, we're in the middle of surgery. 574 00:26:26,040 --> 00:26:29,040 We've done everything right, but suddenly the peak pressures go 575 00:26:29,040 --> 00:26:32,200 up, The alarms are blaring. Section 15. 576 00:26:32,600 --> 00:26:35,520 Recognition of intraoperative bronchospasm. 577 00:26:36,120 --> 00:26:39,080 Clinically, you might hear a wheeze with your stethoscope, 578 00:26:39,480 --> 00:26:42,760 but remember with the noise of the OT and the surgical drapes, 579 00:26:42,880 --> 00:26:45,680 you might miss it. The most reliable sign is on 580 00:26:45,680 --> 00:26:47,840 your monitor. Look at the Capna graph. 581 00:26:47,840 --> 00:26:50,200 The waveform. Yes, you will see a classic 582 00:26:50,200 --> 00:26:53,200 shark fin pattern. Describe that for the listener 583 00:26:53,200 --> 00:26:56,240 who has to draw it in an exam. Normally the expertory waveform 584 00:26:56,240 --> 00:26:58,920 is a nice square box. You have a shop up stroke, a 585 00:26:58,920 --> 00:27:00,840 flat plateau and a sharp down stroke. 586 00:27:01,120 --> 00:27:03,520 In bronchospasm. The up stroke, which is phase 587 00:27:03,520 --> 00:27:07,040 two, becomes slow and slurred because of the obstruction and 588 00:27:07,040 --> 00:27:10,080 the alveolar plateau phase three slopes steeply upward because 589 00:27:10,080 --> 00:27:12,240 the alveoli are emptying at different rates. 590 00:27:12,360 --> 00:27:13,800 So it looks like a shark's dorsal fin. 591 00:27:14,240 --> 00:27:16,120 Exactly. Pointing to the left on most 592 00:27:16,120 --> 00:27:19,480 monitors, it's an unmistakable sign of expiratory airflow 593 00:27:19,480 --> 00:27:21,920 obstruction. And we need to verify this with 594 00:27:21,920 --> 00:27:25,360 the vimilator pressures. Yes, you will see a High Peak 595 00:27:25,360 --> 00:27:29,160 inspiratory pressure PIP but, and here is the key 596 00:27:29,160 --> 00:27:33,000 discriminator for the Viva, the plateau pressure P plat will be 597 00:27:33,000 --> 00:27:35,360 normal or only slightly elevated. 598 00:27:35,520 --> 00:27:37,280 Why is the plateau pressure normal? 599 00:27:37,720 --> 00:27:40,480 Because plateau pressure reflects the compliance of the 600 00:27:40,480 --> 00:27:44,960 lung parenchyma and the chest wall, the static compliance in 601 00:27:44,960 --> 00:27:47,840 asthma, the compliance of the lungs themselves is generally 602 00:27:47,840 --> 00:27:50,280 OK. The problem is the resistance in 603 00:27:50,280 --> 00:27:53,400 the conducting Airways. So to summarize for the exam. 604 00:27:53,560 --> 00:27:56,360 A High Peak pressure with a normal plateau pressure means a 605 00:27:56,360 --> 00:28:00,000 resistance problem. Think asthma, A kinked tube or a 606 00:28:00,000 --> 00:28:02,880 mucus plug. A High Peak pressure with a high 607 00:28:02,880 --> 00:28:05,120 plateau pressure means a compliance problem. 608 00:28:05,520 --> 00:28:08,720 Think pneumothorax, pulmonary edema, or abdominal 609 00:28:08,720 --> 00:28:11,040 insufflation. That is a crucial distinction. 610 00:28:11,040 --> 00:28:13,000 It helps you build a differential diagnosis in 611 00:28:13,000 --> 00:28:14,880 seconds. It helps you rule out a life 612 00:28:14,880 --> 00:28:16,720 threatening pneumothorax very quickly. 613 00:28:16,720 --> 00:28:18,560 So we have identified bronchospasm. 614 00:28:18,560 --> 00:28:20,320 The shark fin is there, the pressures are up. 615 00:28:20,520 --> 00:28:23,200 Section 16. Management of acute bronchospasm 616 00:28:23,200 --> 00:28:26,000 give us the examiner safe algorithm step by step. 617 00:28:26,240 --> 00:28:31,480 OK Step 1 deepen anesthesia. Light anesthesia is the most 618 00:28:31,480 --> 00:28:33,920 common cause of bronchospasm under GA. 619 00:28:34,480 --> 00:28:38,560 Turn up the CEVA flaring to 3 or 4% or give a bolus of propofol 620 00:28:38,560 --> 00:28:42,920 step 200% oxygen and switch to manual ventilation. 621 00:28:43,240 --> 00:28:45,960 Get your hand on the bag. You can feel the compliance and 622 00:28:45,960 --> 00:28:48,280 resistance much better than the machine can tell you. 623 00:28:48,600 --> 00:28:51,040 It also helps you rule out a ventilator malfunction. 624 00:28:51,040 --> 00:28:52,320 Step 3. Pharmacology. 625 00:28:52,600 --> 00:28:54,920 Beta 2 agonists. You have cellbutamol. 626 00:28:54,920 --> 00:28:58,120 You can puff it directly down the ETT using a specific adapter 627 00:28:58,280 --> 00:29:00,880 or use a nebulizer. In the breathing circuit, give 6 628 00:29:00,880 --> 00:29:02,600 to 8 puffs and assess the response. 629 00:29:02,600 --> 00:29:04,960 Step 4. Add anticholinergics like 630 00:29:05,040 --> 00:29:07,600 ipratropium bromide. It's often given together with 631 00:29:07,600 --> 00:29:09,560 the cellbutamol for a synergistic effect on 632 00:29:09,560 --> 00:29:12,360 bronchodilation step. Five if things aren't improving. 633 00:29:12,800 --> 00:29:16,080 4 Steroids hydrocortisone hundred 200 milligram or 634 00:29:16,080 --> 00:29:18,480 dexamethasone. Remember this takes hours to 635 00:29:18,480 --> 00:29:21,160 work so it won't fix the spasm now, but you must give it early 636 00:29:21,160 --> 00:29:23,360 to treat the underlying inflammation and prevent that 637 00:29:23,360 --> 00:29:27,680 late phase reaction. Step 6. 5V Magnesium sulfate 2G 638 00:29:27,680 --> 00:29:29,960 infused intravenously over about 20 minutes. 639 00:29:30,120 --> 00:29:33,440 How does magnesium work here? It acts as a smooth muscle 640 00:29:33,440 --> 00:29:36,120 relaxant. It interferes with calcium 641 00:29:36,120 --> 00:29:39,320 uptake and signaling in the bronchial smooth muscle cells, 642 00:29:39,560 --> 00:29:42,960 causing them to relax. It's very effective in severe 643 00:29:42,960 --> 00:29:45,720 refractory cases. Is there a role for epinephrine? 644 00:29:46,200 --> 00:29:50,080 Yes, in refractory life threatening cases, if the blood 645 00:29:50,080 --> 00:29:53,160 pressure is dropping and you can't break the spasm, give low 646 00:29:53,160 --> 00:29:56,440 dose IV epinephrine. You can give it in small boluses 647 00:29:56,440 --> 00:30:00,480 of say 10 to 20 micrograms at a time, or as a continuous 648 00:30:00,480 --> 00:30:01,680 infusion. In ketamine. 649 00:30:02,000 --> 00:30:04,120 If you haven't already used it for induction, a bolus of 650 00:30:04,120 --> 00:30:07,120 ketamine, say .5 milligram, can also help break the. 651 00:30:07,120 --> 00:30:08,800 Spasm. The surgery is done, you've 652 00:30:08,800 --> 00:30:10,760 managed the spasm. Time to wake them up. 653 00:30:10,920 --> 00:30:13,960 Section 17 and 18. Post operative complications in 654 00:30:13,960 --> 00:30:16,320 management. The main post op complications 655 00:30:16,320 --> 00:30:19,000 are a recurrence of bronchospasm, especially during 656 00:30:19,000 --> 00:30:22,720 extubation, hypoxia due to ongoing VQ mismatch, and 657 00:30:22,720 --> 00:30:25,720 atelactasis. Those mucus plugs can easily 658 00:30:25,720 --> 00:30:28,200 collapse segments of the lung. And the extubation itself. 659 00:30:28,200 --> 00:30:30,880 This is always a tense moment. It is This is the great debate. 660 00:30:30,880 --> 00:30:35,240 Deep versus awake extubation. So deep extubation means taking 661 00:30:35,240 --> 00:30:38,120 the tube out while they are still deeply anesthetized? 662 00:30:38,120 --> 00:30:40,840 Yeah, and Gwettel's stage 3 so they don't cough on the tube. 663 00:30:40,960 --> 00:30:42,760 Right, it's elegant when it works. 664 00:30:42,960 --> 00:30:45,960 No coughing, no bucking, no bronchospasm triggered by the 665 00:30:45,960 --> 00:30:48,520 tube. But you lose your airway 666 00:30:48,520 --> 00:30:51,240 protection immediately If they vomit or have a lot of 667 00:30:51,240 --> 00:30:55,000 secretions they can aspirate. It requires an expert hand and a 668 00:30:55,000 --> 00:30:58,240 guaranteed easy airway. And awake extubation. 669 00:30:58,320 --> 00:31:01,160 This is safer from an aspiration point of view, but they will 670 00:31:01,160 --> 00:31:03,960 almost certainly cough on the tube, and that coughing is a 671 00:31:03,960 --> 00:31:06,080 powerful trigger for bronchospasm. 672 00:31:06,080 --> 00:31:08,760 So what's the exam answer? There's no perfect choice. 673 00:31:08,920 --> 00:31:12,680 The safe answer for a generalist and for the exam is usually 674 00:31:12,720 --> 00:31:15,400 awake but smooth. This is the middle ground. 675 00:31:15,760 --> 00:31:19,520 You utilize Ivy to cane or small doses of opioids to suppress the 676 00:31:19,520 --> 00:31:22,840 cough reflex, but you ensure they are fully awake, following 677 00:31:22,840 --> 00:31:25,040 commands and breathing adequately before you pull the 678 00:31:25,040 --> 00:31:27,040 tube. However, you should mention that 679 00:31:27,040 --> 00:31:30,800 deep extubation is an option in carefully selected patients. 680 00:31:30,840 --> 00:31:32,800 Post op pain control matters too I assume. 681 00:31:32,880 --> 00:31:34,800 Absolutely. If they are in pain, they 682 00:31:34,800 --> 00:31:36,680 splint. They don't take deep breaths. 683 00:31:36,680 --> 00:31:39,000 That worsens atelectasis and mucus plugging. 684 00:31:39,240 --> 00:31:42,760 Epidurals are fantastic for thoracic or major abdominal 685 00:31:42,760 --> 00:31:45,800 surgery and asthmatics because they provide excellent pain 686 00:31:45,800 --> 00:31:47,480 relief without respiratory depression. 687 00:31:47,760 --> 00:31:51,560 Let's briefly touch on Section 19 ICU management for severe 688 00:31:51,560 --> 00:31:55,400 asthma or status asthmaticus. When do we decide to intubate a 689 00:31:55,400 --> 00:31:57,400 patient with severe asthma in the ICU? 690 00:31:57,440 --> 00:31:59,680 It's a last resort. We try everything else first. 691 00:31:59,800 --> 00:32:02,560 Bipap, high flow oxygen, continuous nibs. 692 00:32:02,960 --> 00:32:06,960 The indications for intubation are a rising Paco 2 indicating 693 00:32:06,960 --> 00:32:10,920 fatigue, a deteriorating level of consciousness, or of course, 694 00:32:11,080 --> 00:32:13,640 cardiorespiratory arrest. But ventilation and status 695 00:32:13,640 --> 00:32:15,480 asthmaticus is famously dangerous. 696 00:32:15,480 --> 00:32:18,480 Extremely, the risk of barotrauma like causing a 697 00:32:18,480 --> 00:32:21,240 pneumothorax and severe hypotension from auto PEEP is 698 00:32:21,240 --> 00:32:23,160 very high. We use the strategy of 699 00:32:23,160 --> 00:32:26,400 controlled hypovilation. We deliberately allow the CO2 to 700 00:32:26,400 --> 00:32:29,920 rise permissive hypercapnia to keep the airway pressures down. 701 00:32:30,120 --> 00:32:32,880 We prioritize keeping the plateau pressure below 30 702 00:32:33,000 --> 00:32:36,040 centimeter HA2O overachieving a normal pH. 703 00:32:36,160 --> 00:32:37,880 And constantly watching for that auto P. 704 00:32:37,880 --> 00:32:39,800 Constantly. If they suddenly become 705 00:32:39,800 --> 00:32:42,800 hypotensive on the ventilator, your first move is to disconnect 706 00:32:42,800 --> 00:32:45,080 the circuit and manually decompress the chest. 707 00:32:45,240 --> 00:32:48,080 Before we wrap up, let's hit Section 20 comparison tables. 708 00:32:48,080 --> 00:32:49,400 These are high yield for the Viva voce. 709 00:32:49,680 --> 00:32:52,400 Let's do a quick fire round. Asthma versus COPD. 710 00:32:52,600 --> 00:32:56,080 Age of onset asthma is usually childhood or early adulthood. 711 00:32:56,640 --> 00:32:59,400 COPD is midlife or later. Asthma is associated with 712 00:32:59,400 --> 00:33:03,720 allergy, atopy, eczema. COPD is overwhelmingly 713 00:33:03,720 --> 00:33:06,640 associated with smoking. Asthma shows significant 714 00:33:06,640 --> 00:33:08,680 reversibility with bronchodilators. 715 00:33:08,880 --> 00:33:11,760 COPD shows minimal or only partial reversibility. 716 00:33:12,040 --> 00:33:15,800 DLCO, diffusion capacity. This is a key differentiator. 717 00:33:16,080 --> 00:33:19,320 It is normal and pure asthma because the lung parenthema, the 718 00:33:19,320 --> 00:33:23,120 alveoli are intact. It is decreased in emphysema 719 00:33:23,120 --> 00:33:25,840 predominant COPD because the parenchema is destroyed. 720 00:33:26,160 --> 00:33:28,760 That DLCO point is a great Viva nugget. 721 00:33:28,760 --> 00:33:30,960 It shows a deep physiological understanding. 722 00:33:31,040 --> 00:33:33,320 It separates the students who've read deeply from those who have 723 00:33:33,320 --> 00:33:35,400 just skimmed the summary chapter. 724 00:33:35,600 --> 00:33:39,000 Let's review Section 21 common exam questions in Viva drafts. 725 00:33:39,000 --> 00:33:43,240 We've covered a few trap one. Is wheezing a sign of severity? 726 00:33:43,240 --> 00:33:47,920 No, a silent chest is far worse. Trap 2A normal ABG in a panting 727 00:33:47,920 --> 00:33:49,560 asthmatic. It's a sign of impending 728 00:33:49,560 --> 00:33:53,080 failure, not stability. Trap 3 Using Atrocurium for 729 00:33:53,080 --> 00:33:54,600 muscle relaxation. Don't say it. 730 00:33:54,600 --> 00:33:57,520 It's a known histamine releaser. Stick to rocaronium or 731 00:33:57,520 --> 00:33:59,840 vecaronium. And the Examiner's favorite 732 00:33:59,840 --> 00:34:01,920 waveform? The Kapnograph in bronchospasm, 733 00:34:02,080 --> 00:34:05,760 the shark fin be able to draw it and explain why Phase 2 is 734 00:34:05,760 --> 00:34:09,199 prolonged and phase 3 is upsloping due to uneven alveolar 735 00:34:09,199 --> 00:34:12,639 emptying. Section 22 Diagrams In a written 736 00:34:12,639 --> 00:34:14,960 exam, what should we definitely draw? 737 00:34:15,159 --> 00:34:17,639 Definitely draw the flow volume loop showing this scooped out 738 00:34:17,639 --> 00:34:20,639 appearance of obstruction. And for a management question, 739 00:34:20,639 --> 00:34:23,560 draw the bronchospasm management algorithm as a flow chart. 740 00:34:23,840 --> 00:34:26,440 It saves time, it's clear and it looks professional. 741 00:34:26,440 --> 00:34:29,760 Let's summarize Section 23 summary and exam conclusion. 742 00:34:29,920 --> 00:34:32,960 Give us the final high yield. Recap the take home points. 743 00:34:32,960 --> 00:34:36,760 OK one, asthma is fundamentally a disease of inflammation and 744 00:34:36,760 --> 00:34:38,840 hyper reactivity. It's not just about muscle 745 00:34:38,840 --> 00:34:42,800 spasm. 2 Preoperative optimization is mandatory before 746 00:34:42,800 --> 00:34:45,360 any elective surgery. Symptom free is the goal. 747 00:34:45,880 --> 00:34:48,920 Three avoid histamine releasing drugs like thiopentone, 748 00:34:48,920 --> 00:34:52,880 atrocurium, and morphine 4. Deep anesthesia before any 749 00:34:52,880 --> 00:34:54,880 airway manipulation is non negotiable. 750 00:34:55,040 --> 00:34:58,640 Light anesthesia is your enemy. 5 And finally, permissive 751 00:34:58,640 --> 00:35:01,240 hypercapnia is your friend. When ventilating a severe 752 00:35:01,240 --> 00:35:04,920 asthmatic, prioritize low pressures over a normal CO2. 753 00:35:05,200 --> 00:35:07,680 That is a solid foundation if you can articulate those five 754 00:35:07,680 --> 00:35:09,280 points clearly in a very good position. 755 00:35:09,400 --> 00:35:11,440 Mastering this topic gives you confidence. 756 00:35:11,800 --> 00:35:14,520 It's a common clinical case, but when managed poorly, it's a 757 00:35:14,520 --> 00:35:16,960 nightmare. When you manage it well, it's 758 00:35:16,960 --> 00:35:19,680 smooth sailing. Good luck to everyone preparing 759 00:35:19,680 --> 00:35:23,720 for the Gujarat University exams or for any anesthesiology board 760 00:35:23,720 --> 00:35:25,560 exam for that matter. You have the tools now. 761 00:35:25,560 --> 00:35:28,360 My advice? Go practice drawing those flow 762 00:35:28,360 --> 00:35:31,040 volume loops in the shark fin capnograph right now. 763 00:35:31,480 --> 00:35:33,760 Don't wait. Get it into your muscle memory. 764 00:35:33,800 --> 00:35:36,200 Next time, we tackled the Cardiac Risk Index. 765 00:35:36,480 --> 00:35:38,320 Until then, keep diving deep.