Clinical Management of Acute Contrast Media Reactions

Decoding Acute Contrast Reactions in Real Time Picture this, you're reading a routine outpatient abdomen CT. It's it's like 2.0 AM. Speaker 2 Prime time for things to go wrong. Speaker 1 Exactly. You're the only resident in the reading room and suddenly the door just flies open. The technologist looks at you panicking and says doc. The patient in scanner too is dropping their pressure. Speaker 2 And your heart just drops. Speaker 1 Oh, totally. Because in the next 30 seconds you have to run into that room, look at a monitor and decide, you know, between pushing up and nephrine or pushing atropine. Speaker 2 Which is a terrifying choice if you aren't prepared. Speaker 1 Right, because if you choose wrong, I mean if you mix up the hemodynamics for even a second, you could basically pour absolute pharmacological rocket fuel onto a failing heart. Speaker 2 Yeah. And that's exactly why we're doing this is the ultimate test of clinical triage under pressure. Speaker 1 It really is. Speaker 2 Because when an acute reaction to intravenous contrast starts evolving right there on the scanner table, I mean, the patient doesn't come with a diagnostic label. Speaker 1 Right, there's no chart telling you what's happening. Speaker 2 No, you don't get a clean lab report. You just get this rapid sequence of physiological failures and you have to decode them in real time. Speaker 1 Which is exactly our mission for this deep dive. For everyone listening, especially you radiology residents prepping for the ABR Core exam, we are taking a highly structured, honestly pretty dense clinical reference document detailing acute reactions to iodinated and gadolinium based IV contrast media and we're breaking it down. Speaker 2 Yeah, if you've looked at the source text, you know it's essentially a Dictionary of worst case scenario. Speaker 1 Oh 100%, it's incredibly dry. It's just packed with lists and rigid algorithms. Speaker 2 Right. So our goal today is to translate those algorithms into a seamless logical framework for you. Speaker 1 Because by the time we're done, the pathophysiology should make so much sense that the drug dosages will just like feel intuitive rather than memorized. Speaker 2 Absolutely, and I think the best way to build that intuition is to start at the absolute baseline. Speaker 1 Let's do it. Two Distinct Contrast Reaction Pathways Explained So the source document makes this critical distinction right out of the gate regarding how these reactions fundamentally originate. We are dealing with two entirely distinct mechanistic pathways. On one side we have your allergic type reactions and on the other side we have non allergic type reactions which historically are referred to as physiochemotoxic reaction. Speaker 1 Oh, physiochemotoxic. It's a mouthful. Speaker 2 It really is, but the text emphasizes A crucial caveat here, which is that both of these pathways can manifest across the entire spectrum of severity. Speaker 1 Right from a totally self limited annoyance to a lethal emergency. Exactly. OK, so let's unpack this divide. Because understanding the difference between an allergic cascade and a physiochemotoxic event completely changes how you manage the patient. Oh, absolutely. I want to start with the physiochemotoxic side, because the source points out that many of these adverse effects are driven purely by the physical properties of the contrast solution itself. Specifically, it's hyperosmolarity. Speaker 2 Yeah. And the physics here are they're really fascinating when you look at what happens at the endothelial layer. Speaker 1 Let's get into that. Speaker 2 So human plasma operates at a very tightly regulated osmolarity, usually around like 285 to 295 millius moles per kilogram. Speaker 1 OK, so a very narrow window. Speaker 2 Very narrow now when you slam 100 CCS of a contrast agent into a peripheral vein at 4 milliliters a second. Speaker 1 Just standard. Speaker 2 Right, standard injection. You are introducing a fluid that, depending on the generation of the agent, can have an osmolarity anywhere from two to three times that of normal blood. Speaker 1 Wow. Two to three times. Speaker 2 Yeah. So you're creating this massive instantaneous osmotic gradient across the vascular endothelium. Speaker 1 Right. And nature abhors a vacuum and it abhors A concentration gradient. Exactly. So because the contrast is hyperosmolar, it's physically pulling water out of the surrounding interstitial space and the intracellular fluid compartment directly into the intravascular space to dilute itself. Speaker 2 Precisely, you get this rapid transient expansion of the the intravascular volume, but it's not just the volume shift you. Speaker 1 Know what else is happening? Speaker 2 It's a sheer chemical toxicity and the physical weight of these large iodine or gadolinium based molecules. They're literally scraping along the glycoccalyx of the endothelium, and that physical stress combined with the sudden volume expansion and the altered blib viscosity, it just triggers a cascade of physiological responses. Speaker 1 So the body is essentially reacting to the mechanical and chemical trauma of the fluid dynamics, Yes. It's not fighting off a foreign biological invader at all. Speaker 2 Exactly. There is no Ige antibody involved. Speaker 1 Here, no mast cell degranulation. None. Speaker 2 Just raw hemodynamics and cellular stress. Speaker 1 Which sets up a perfect contrast, no pun intended, to the allergic type reaction. Speaker 2 Right, which are entirely immune mediated. Why Seafood Allergy Doesn't Predict Contrast Risk Yeah, and this actually brings us to a concept I really want to synthesize for you listening, because the source tackles a really pervasive piece of medical dogma head on. Speaker 2 Oh, the classic board exam. Speaker 1 Fodder it is, but it also dictates how we triage out patients every single day. Let's talk about the myth of the seafood allergy. Speaker 2 It is the ultimate trap. Speaker 1 It really is. Speaker 2 For decades, the medical community perpetuated this this idea that an allergy to shellfish or seafood, or like topical povidone iodine, meant a patient was at a massively elevated risk for severe reaction to iodinated IV contrast. Speaker 1 I mean, I see this on the screening questionnaires all the time. Oh yeah, the patient checks yes for a shrimp allergy, and suddenly the technologist is treating the contrast injection like it's a loaded weapon. Speaker 2 Right, everyone freaks out. Speaker 1 But the text is explicit. Having an allergy to seafood or shellfish does not increase your risk of a contrast reaction any more than having an allergy to peanuts or strawberries or pollen. Speaker 2 Right, because it is a fundamental misunderstanding of biochemistry. Speaker 1 Break that down for us. Speaker 2 So if we look closely at what actually causes anaphylaxis in a patient eating shrimp, the culprit is almost always a muscle protein called tropomyosin. Speaker 1 Tropomyosin. Speaker 2 Tropomyosin has absolutely 0 structural relationship to the triadinated benzene ring structure of modern contrast media. Speaker 1 They look nothing alike. Speaker 2 Nothing alike. The persistent myth originated because shelters contain trace amounts of elemental iodine from the ocean right and contrast contains iodine. Therefore people assume the allergy was to the iodine itself. Speaker 1 Which is wild because you literally cannot be allergic to the iodine atom. Speaker 2 No, you can't. Speaker 1 It's an essential element. Your thyroid gland requires it to synthesize nyroxine, right? If you are allergic to iodine, your own endocrine system would send you into anaphylaxis. Speaker 2 Exactly. So when a patient says they haven't quote iodine allergy, what they are actually communicating is that they had a prior hypersensitivity reaction to a specific molecular structure that just happened to contain iodine. Speaker 1 I see. Speaker 2 But the immune system recognized the complex molecule, right? Not the elemental halogen. Got it. So a shellfish allergy is really just a marker of general atopy. Speaker 1 Meaning they just have a sensitive immune system. Speaker 2 Exactly. It tells you the patient has a hyperactive immune system in general, which sure slightly elevates their risk for any allergic reaction, but it is absolutely not a direct cross reactivity. Speaker 1 OK, However, the source text does highlight a different comorbidity. That is a major red flag. Speaker 2 Yes it does. Speaker 1 Asthma, right? A patient with a history of asthma is at a significantly increased risk for an allergic like contrast reaction. Speaker 2 And if we think about the pathophysiology of asthma, I mean, that makes perfect sense. Speaker 1 Yeah, because asthma is characterized by chronic inflammation, right? Speaker 2 Chronic inflammation and hyper reactivity of the tracheobronchial tree. Their mast cells and basophils are already primed. Speaker 1 They're on a hair trigger. Speaker 2 Exactly. So when an allergic type contrast reaction triggers the release of histamine and leukotrienes and asthmatics, Airways are going to respond much more violently than a healthy patient's. Speaker 1 Their threshold for severe bronchospasm is just drastically lower. Speaker 2 Precisely. Speaker 1 So understanding true risk factors like asthma versus mythical risk factors like the shrimp allergy is really the first step in clinical triage. It is. Understanding Expected vs. Anomalous Contrast Responses But before we can manage a crisis, we have to recognize when a reaction is actually occurring. So let's look at the immediate moments right after the injection. The. Speaker 2 Crucial window. Speaker 1 The contrast goes in and the patient and almost immediately complaints of feeling strange. The source details a specific set of sensations. Here. It lists mild nausea, a sudden sensation of systemic warmth and flushing of the skin. Speaker 2 So the critical take away from the text regarding these specific symptoms is that they are considered purely physiologic. Speaker 1 OK, Physiologic. Speaker 2 Right. They are not adverse reactions. They are expected physiological responses to the pharmacological and physical properties of the drug. Speaker 1 It's sort of like the physical forces of a roller coaster, right? Speaker 2 What do you mean? Speaker 1 Well, when you drop down a massive hill at 60 miles an hour, you feel the G forces in your chest and the wind hits your face. That isn't a malfunction of the ride, it's just the required physical consequence of the kinetic energy. I like that. So if you inject a highly concentrated hyperos molar fluid into a vein, the body is going to respond to that physical force. Speaker 2 And the mechanism behind that response is really well documented. Speaker 1 What's happening in the vessels? Speaker 2 That hyperosmolar fluid shift we discussed earlier causes an immediate transient vasodilation. OK, the smooth muscle and the vascular walls relaxes, the capillary beds open up and you get this certain rush of blood flow, usually starting in the pelvis and rushing upward. Speaker 1 And that's what causes that intense feeling of warmth and the visible cutaneous flush. Speaker 2 Exactly and simultaneously, that osmotic shift and the chemical presence of the contrast molecules can directly stimulate the chemoreceptor trigger zone. Speaker 1 Right in the area post Streama of the medulla. Speaker 2 Yes, which triggers that brief wave of nausea. Speaker 1 Which is why clinically, we do absolutely nothing. Nothing at all. You don't stop the scan, you don't reach for the crash cart. You just reassure the patient that their anatomy is working exactly as it should. Right, But what happens when the symptoms cross the line from a physiologic expectation to a true anomaly? How do we define a mild reaction? Speaker 2 So the source provides A strict 2 part clinical definition for a mild reaction. Recognizing Self-Limited Contrast Reaction Symptoms OK, what's Part 1? Speaker 2 First, it must be self limited. The symptoms arise, they plateau, and they resolve on their own. Speaker 1 And Part 2. Speaker 2 2nd, and most importantly for you as the physician, it does not require medical management. Speaker 1 So sticking with the roller coaster analogy. Speaker 2 Yeah, let's keep it going. Speaker 1 A mild reaction is like boarding the ride, pulling down the shoulder harness and realizing it's a little bit loose. Speaker 2 Oh, that's a terrifying. Speaker 1 Right, It's definitely an anomaly. It's not supposed to happen, but it clicks into place on its own before the ride starts, and you don't need to call the maintenance crew to shut down the park. Speaker 2 Exactly. You observe it, but your hands stay in your pockets. Speaker 1 So let's break down the specific clinical presentations here, starting with the mild, non allergic, the physiochemotoxic side. Speaker 2 OK, so the text lists headache, dizziness, mild hypertension, anxiety, altered taste which is usually described as a metallic taste, limited nausea or vomiting, and transient flushing, warmth or chills. Speaker 1 You know what stands out to me? Here are all those modifiers. Speaker 2 What do you mean? Speaker 1 Well, it says mild hypertension, limited nausea, transient chills. It really suggests a system that's under stress, but one that is successfully compensating. Speaker 2 That's a great way to put it. The body is being pushed out of its homeostatic baseline by that hyperosmolar fluid shift and the chemical toxicity, right? So maybe the transient volume expansion causes the blood pressure to spike briefly, which registers as mild hypertension. Or maybe. Speaker 1 The stimulation of the chemo receptor trigger zone is strong enough to cause a single episode of emesis rather than just nausea. Exactly. Speaker 2 But then the autonomic nervous system and the renal system step in, balance is restored and the symptom fades entirely without pharmacological intervention. But. Speaker 1 There is one mild non allergic reaction that requires specific attention because it mimics something much more dangerous. Speaker 2 Ah yes, the mild vasovagal reaction, right? Speaker 1 The source defines this strictly by the presence of bradycardia and hypotension. Low heart rate, low blood pressure. Yes, it resolves spontaneously and it is firmly non allergic. This is a. Speaker 2 Critical hemodynamic profile for residents to master because it. Speaker 1 Looks so scary because a lot. Speaker 2 Of practitioners see a patient get pale, diaphoretic and suddenly drop their blood pressure and their brain just immediately screens anaphylaxis right they. Speaker 1 Want to reach for the EPI but the. Speaker 2 Vasovagal response is purely neurological. The contrast injection, the sudden heat or honestly even just the severe anxiety of being in the scanner. It stimulates the vagus nerve and the. Speaker 1 Vagus nerve is the main superhighway of the parasympathetic nervous system, right? So when it fires aggressively, it releases acetylcholine directly onto the muscarinic M2 receptors of the sinoatrial and atrioventricular nodes in the heart Which? Speaker 2 Increases potassium conductance, hyperpolarizes the pacemaker cells, and drastically decreases the heart rate. Bradycardia, and simultaneously that parasympathetic surge withdraws sympathetic tone to the peripheral vasculature, leading to profound vasodilation. Hypertension. Speaker 1 Exactly. Speaker 2 The cardiac output drops, blood pools in the splash neck and lower extremity venous beds and cerebral perfusion pressure falls and the. Speaker 1 Patient feels dizzy or experiences syncope right? But because we are still in the mild category, this is self limited right it? Speaker 2 Fixes itself because. Speaker 1 The baroreceptors and the carotid sinus and aortic arch detect the drop in pressure, the brain realizes it's starting for oxygen, and it forcibly dials back the vagal tone. You literally. Speaker 2 Just lay the patient flat. Gravity restores venous return, the brain gets perfused and the system resets. No. Speaker 1 Drugs required, No. Speaker 2 Drugs. Yeah. Now compare that to the mild allergic side. OK, here we are looking at histamine release, but it is strictly localized. Localized. Yeah, the mast cells are degranulating, releasing histamine which binds to H1 and H2 receptors, but it hasn't become a systemic cascade yet. So the. Speaker 1 Source lists conjunctivitis like red watery eyes, vinorrhea, sneezing and nasal congestion. It also lists limited urticaria or puritis and localized cutaneous edema. So like a. Speaker 2 Few hives on the arm where the IV is or just localized itching, right? Speaker 1 And the underlying mechanism for all of these is basically the same, right? Histamine increases capillary permeability and causes local vasodilation. Exactly. Speaker 2 Fluid leaks out of the capillaries into the interstitial, so in. Speaker 1 The skin that creates a wheel, a hive in the nasal mucosa. It creates congestion and rhinorrhea. Correct, but the text also includes mild angioedema in this category. It describes symptoms like a scratchy or itchy throat and slight tongue or facial swelling. Yes, it. Speaker 2 Does and I. Speaker 1 Have to synthesize this from the perspective of a resident on call. Speaker 2 OK, put yourself in their shoes if a. Speaker 1 Nurse calls me into the CT room and says the patient's tongue is swelling and their throat is itchy. My sympathetic nervous system is going to kick into OverDrive, of course, because airway compromises the ultimate nightmare. Yes, it. Speaker 2 Is so. Speaker 1 How does a resident know when to just watch the patient versus when to intervene? I mean, how do you not panic the clinical? Speaker 2 Restraint required in that moment is immense. It really is I bet. But the guideline is drawn cleanly at progression and the need for medical management. OK. Speaker 1 If you. Speaker 2 Examine the patient right and their tongue is slightly edematous and they report a scratchy throat, but their phonation is perfect, they are moving air without effort, their oxygen saturation is 100%, and most importantly, 5 minutes later it hasn't worsened. Then what? That is by definition mild angioedema. It is a localized histamine response that is plateaued. Speaker 1 So you don't immediately slam them with epinephrine just because the word throat is used, correct? Speaker 2 You monitor them continuously. I mean, obviously you keep the crash cart right outside the door, but you don't intervene medically unless the pathology dictates it. However, if that loose seat belt doesn't catch itself if things. Speaker 1 Start slipping Yeah, if the. Speaker 2 Patient's voice starts to change. If the scratchiness turns into a real feeling of tightness, the Physiology is tipping over the self. Speaker 1 Limitation is gone exactly. Speaker 2 And we cross into the moderate category which. Managing Stable But Symptomatic Contrast Events Fundamentally shifts the definition. The source states that moderate reactions are not immediately life threatening and vital signs are stable, but they are pronounced enough that they may require medical management. The. Speaker 2 Absolute anchor of that definition is stable. Vital signs stable. Speaker 1 Vitals, yes. Speaker 2 The patient might be in severe distress, they might be incredibly uncomfortable, but their compensatory mechanisms are holding the line right. Speaker 1 Their cardiovascular and respiratory systems are successfully maintaining perfusion and oxygenation. Exactly. So let's track the non allergic reactions into this moderate territory. We discussed the mild vasovagal reaction resolving on its own right. The moderate vasovagal reaction is defined by the fact that it requires and is responsive to treatment the vagal. Speaker 2 Surge doesn't self correct here, so the. Speaker 1 Bradycardia persists. Yes, the. Speaker 2 Bradycardia persists, the hypotension remains, and cerebral profusion just isn't recovering just by lying them flat. So you have to. Speaker 1 Actively intervene you do. Speaker 2 By elevating the lower extremities to force a fluid shift back to the heart, or by running wide open IV normal saline to increase preload and cardiac output. Speaker 1 And the key is that once you provide that mechanical or volume support, the hemodynamics stabilize. Now the text also lists protracted nausea and vomiting in this category, so an ongoing vaguely mediated emetic response rather than a single event. But then it lists 2 specific non allergic presentations that feel honestly highly counterintuitive to classify as moderate. Which ones Isolated chest pain and hypertensive urgency. And if a patient clutches their chest in the scanner or their blood pressure shoots up to 200 systolic, it's really hard to convince yourself that this is just a moderate event. Oh it. Speaker 2 Absolutely feels like a Code Blue scenario. It does. Speaker 1 But we have. Speaker 2 To evaluate the clinical definitions, let's take isolated chest pain. OK, The hyperosmolar load of the contrast can trigger transient coronary vasospasm, so it's. Speaker 1 Temporarily mismatching myocardial oxygen supply and demand. Exactly. Speaker 2 It causes angina. It's terrifying for the patient but if you look at the monitor and their heart rate is 80 and regular, their blood pressure is 130 / 80 and their pulse oximetry is 99% their. Speaker 1 Vital signs are stable. They are. Speaker 2 Stable. They are not in cardiogenic shock. They're in the moderate category. And I. Speaker 1 Assume the exact same logic applies to hypertensive urgency exactly. Speaker 2 Hypertensive urgency is a very specific medical term. It means the systemic vascular resistance has spiked and the blood pressure is critically high, perhaps 210 / 110, which is. Speaker 1 Sky high it is. Speaker 2 But the word urgency implies that the body's auto regulatory mechanisms in the brain, kidneys and heart are still successfully protecting those organs from the high pressure. Speaker 1 So there is no acute end organ damage, right? Speaker 2 They are not actively dissecting their aorta, they aren't having a hemorrhagic stroke, and they aren't in acute renal failure. So in. Speaker 1 Emergency triage Moderate doesn't mean not scary not. Speaker 2 At all it means not. Speaker 1 Actively dying in the next 60 seconds. It means you have a clinical window to institute medical management, like giving an antihypertensive or an antiimetic in a controlled manner rather than having to execute chaotic immediate resuscitation. Exactly. When Allergic Symptoms Require Intervention You have the luxury of a few minutes. OK, so. Speaker 1 Let's track the allergic cascade into the moderate zone, OK? Speaker 2 So the localized histamine release becomes systemic meaning. Speaker 1 Mild limited urticaria becomes diffuse urticaria paratus and erythema right the. Speaker 2 Highest and redness are spreading across the entire body, but the. Speaker 1 True high yield distinctions for the boards and for clinical practice involve the respiratory system. Here they do. Speaker 2 The source is very precise. Here it says. Speaker 1 Bronchospasm or wheezing is considered moderate if it occurs with mild or no hypoxia. Yes, and facial edema, hoarseness or throat tightness is moderate if there is no dyspnea. This is where. Speaker 2 Understanding physiological compensation is just paramount. Break it down. Speaker 1 South. Speaker 2 Bronch spasm means the smooth muscle wrapped around the bronchioles is constricting due to leukotrene and histamine activity, right the. Speaker 1 Airway resistance is increasing you're. Speaker 2 Wheezing on auscultation. But if you look at the pulse oximeter and it reads 95%, the patient's respiratory Dr. and alveolar gas exchange are successfully compensating for the narrowed Airways. Oh, I. Speaker 1 See. So they might be working harder to breathe, but they are maintaining oxygenation. Exactly. And the same goes for the upper airway if their voice gets worse. You know the laryngeal tissues are edematous, right? But if there is no dyspnea, no subjective feeling of shortness of breath, no accessory muscle use, the airway is still patent enough to meet the metabolic demands of the body and these. Speaker 2 Patients require medical management. You need to give an albuterol inhaler for the bronchospasm or IV diphenhydramine for the diffuse hives. But. Speaker 1 Because the vitals are stable, you can draw up the medications calmly, but the moderate category is essentially A tightrope walk. You have that window of time, but you are watching the monitors continuously because the pathology is active, very active. And if those compensatory mechanisms fail, if the histamine cascade overwhelms the respiratory drive or the vasodilation outcases, the heart's ability to pump the patient falls off the tightrope, the window. Speaker 2 Of time just vanishes and. Speaker 1 We enter the severe category, the danger zone, the core. Speaker 2 Definition here strips away all ambiguity the source. Speaker 1 Says signs and symptoms are often life threatening and vital signs are unstable. Speaker 2 Instability is the absolute hallmark here. Yeah, the body's homeostatic mechanisms have completely surrendered the. Speaker 1 Physiological Baseline line is actively collapsing. Catastrophic Physiochemotoxic Contrast Reactions Yes, let's follow the non allergic physiochemotoxic side to its absolute extreme. First. We watched the vasovagal response go from mild to moderate right? A severe vasovagal reaction is one that is refractory to treatment, meaning. Speaker 2 You elevate the legs, you push a liter of normal saline, but the vagus nerve simply will not let go. So the. Speaker 1 Profound bradycardia persists and the hypotension deepens to the point of critical hypoperfusion and that. Speaker 2 Extreme cardiovascular stress can fracture the electrical pathways to the heart entirely. Yeah. Speaker 1 The text lists clinically manifest arrhythmias as a severe non allergic reaction and we. Speaker 2 Aren't just talking about a few premature ventricular contractions here. No, we are talking about the hyperosmolar stress and the resulting ischemia disrupting the ion channels, prolonging the action potentials and throwing the heart into ventricular tachycardia or ventricular fibrillation, which is. Speaker 1 Terrifying. The source also lists hypertensive emergency, which is the catastrophic evolution of the moderate hypertensive urgency we discussed earlier right in. Speaker 2 An emergency the auto regulation we talked about has failed so the. Speaker 1 Blood pressure is so high that it is physically tearing through the microvasculature of the organs you are now. Speaker 2 Looking at acute intracranial hemorrhage, myocardial infarction or flash acute kidney injury. The stability. Speaker 1 Is gone completely. Speaker 2 Gone and the. Speaker 1 Final severe non allergic presentation is to me honestly the most terrifying pulm pulmonary edema. It's the. Speaker 2 Ultimate manifestation of the physiochemotoxic mechanism. Why does? Speaker 1 It happen. Think back. Speaker 2 To the hyperosmolar fluid shift, pulling massive amounts of water into the vascular space, right? Speaker 1 Diluting the contrast if the. Speaker 2 Patient has underlying poor left ventricular function. Or if the sheer volume of the fluid shift is just too rapid, the hydrostatic pressure inside the pulmonary capillaries skyrockets. OK, so. Speaker 1 The Starling forces are completely disrupted. Speaker 2 Completely. The hydrostatic pressure physically overwhelms the oncotic pressure and the lymphatic drainage, chastity and fluid is violently pushed out of the capillaries, across the alveolar capillary membrane and directly into the air sacs of the lungs. Speaker 1 Wow, the patient is literally drowning in an internal flood. VR. And again, this is purely mechanical and physical. There is no allergy involved, but the. Recognizing Life-Threatening Allergic Contrast Shock Severe allergic side is equally catastrophic, right? Speaker 1 Let's look at that. The text lists anaphylactic shark, the fuse erythema, the massive red flush we saw in the moderate category, but now it is paired with hypotension that is the. Speaker 2 Dividing line right? Speaker 1 If you are red and itchy from head to toe but your blood pressure is normal, you are moderate. But the second your systemic vascular resistance drops so low that your blood pressure crashes, you cross into severe you are in distributive shock the mast. Speaker 2 Cells have dumped so much histamine systemically that the smooth muscle in the arterioles has completely relaxed, so the. Speaker 1 Vascular bed has massively expanded, yes. Speaker 2 And the total blood volume is no longer sufficient to fill the pipes venous. Speaker 1 Return plummets, cardiac output crashes, and the brain and organs are starved of oxygen and the. Speaker 2 Respiratory symptoms follow the exact same catastrophic trajectory the. Speaker 1 Moderate hoarseness becomes laryngeal edema with stridor and or hypoxia and. Speaker 2 Stridor is that high pitched terrifying whistling sound when the patient twins to inspire it means. Speaker 1 The glottic opening is physically swelling shut, yes. Speaker 2 And the moderate bronchospasm becomes wheezing with significant hypoxia the airway. Speaker 1 Resistance is now so high that alveolar ventilation has failed entirely. The oxygen saturation plummets the text. Speaker 2 Also notes altered mental status and cardiac arrest as varied symptoms of a severe allergic reaction, which is. Speaker 1 The logical endpoint of untreated hypoxia and profound hypotension, right? Speaker 2 The brain fails, manifesting as confusion, combativeness or unresponsiveness and. Speaker 1 Eventually, the hypoxic myocardium simply stops. Yeah. What's striking when you lay all these severe symptoms out side by side? The arrhythmias, the pulmonary edema, the anaphylactic shock, the stride or is that the endpoint is identical loss? Speaker 2 Of physiological compensation resulting in hypoperfusion or hypoxia, right? Speaker 1 But how you reverse that endpoint depends entirely on whether the root cause is allergic or non allergic. The. Speaker 2 Resuscitation pathways diverge dramatically based on that initial classification, because if you. Speaker 1 Treat non allergic pulmonary edema with the the aggressive IV fluid required for anaphylactic shock. You will flood their lungs faster and kill them. Exactly. Speaker 2 And if you treat the severe bradycardia of a vasovagal reaction with the epinephrine required for anaphylaxis, you create a fatal autonomic conflict. We are going. Speaker 1 To break down the exact step by step algorithms for those divergent pathways shortly. OK, but before we discuss how to pull a patient back from the brink of death, we have to discuss how we try to prevent them from getting there in the 1st place. Strategic Rules for Preventing Contrast Reactions Which. Speaker 2 Brings us to the rules of pre medication, right? Speaker 1 If a patient has a documented history of a prior contrast reaction, what is our defense strategy So. Speaker 2 The source outlines several foundational rules for pre medication the 1st. Speaker 1 Rule sets the baseline for risk. If a patient has a known contrast allergy, their next reaction will likely be similar in nature to the prior one, but it could be more or less severe. Right you. Speaker 2 Cannot assume a mild reaction in the past guarantees A mild reaction today because. Speaker 1 Biology is dynamic, the immune. Speaker 2 System's memory and reactivity fluctuate based on 1000 different variables. Now the. Speaker 1 Second rule is incredibly high yield for the core exam. Pre medication is only indicated for allergic type prior reactions. It is not indicated for physiochemotoxic non allergic prior reactions and if you. Speaker 2 Understand the mechanisms we've spent the last half hour discussing. This rule is completely intuitive. Break it down. Speaker 1 Pre. Speaker 2 Medication involves giving corticostroids and antihistamines to preemptively blockade the H1 and H2 receptors and suppress the inflammatory leukotriene cascade. But if a patient's prior reaction was a Vasovagar swoon caused by the physical stretching of the vessels or. Speaker 1 Mild nausea driven by osmolarity stimulating the area. Postrema steroids. Speaker 2 Are pharmacologically useless. They do not alter the physics of osmolarity or the neuroanatomy of the vagus nerve giving. Speaker 1 Steroids to prevent a physio or chemotoxic reaction is like taking an antibiotic to prevent a sunburn. That's a great. Speaker 2 Analogy. You're deploying the wrong chemical weapon for the underlying mechanism. Exactly. Speaker 1 Now the third rule is a reality check. Premedication does not guarantee a reaction won't happen. Breakthrough. Speaker 2 Reactions occur regularly. It mitigates the risk, it does not eliminate it and the. Speaker 1 Final rule is the absolute contraindication. Intravenous contrast is generally contraindicated if the patient has had a prior severe allergic type reaction. Yes. Let's construct A mechanism based analogy for this premedication strategy. Think of a contrast injection like a hurricane bearing down on a coastal house. OK, I'm with you. Your prior reaction history tells you the likelihood of the storm hitting. Pre medication, the steroids and antihistamines is like boarding up the windows and throwing sandbags against the doors, right? If you've had a mild or moderate allergic reaction in the past, you absolutely want those boards up. It will likely block the winds and the rain, the histamine release and keep the house safe. But. Speaker 2 Boarding up the windows doesn't change the fact that a hurricane is hitting exactly. Speaker 1 Breakthrough damage can still occur if the storm is strong enough and if the. Speaker 2 Last time a hurricane hit this house, it was a category five that ripped the roof off and leveled the foundation. That's. Speaker 1 Your prior severe anaphylactic reaction, all right. Speaker 2 Well, a few sheets of plywood aren't going to save you. We aren't going to let you stay in the house. The contrast is contraindicated. We. Speaker 1 Find a different way to image you like a non contrast MRI or an ultrasound that. Speaker 2 Captures the clinical risk benefit analysis perfectly. Speaker 1 So what are the actual plywood and sandbags? Understanding the 4-Hour Corticosteroid Efficacy Window What are the specific pharmacological regimens? Well, the core. Speaker 2 Exam will test these exact numbers. First. Is the elective regimen used when you have an outpatient scan and plenty of time. OK, what? Speaker 1 Is it the? Speaker 2 Standard elective schedule is Prednisone 50 milligrams taken by mouth and it must be administered at 3 specific intervals. Speaker 1 Which are 13. Speaker 2 Hours, 7 hours and 1 hour before the contrast injection. Speaker 1 13, seven and one, Those are the magic numbers and you. Speaker 2 Pair that long acting steroid coverage with a rapid acting antihistamine, aphenhydrine, commonly known as Benadryl. 50 milligrams given either IV or by mouth one hour before the exam. So you have a. Speaker 1 Dual blockade The Cortico Strides have been suppressing the immune machinery overnight and the diphenhydramine provides a direct H1 receptor blockade right at the moment of injection. Exactly. But what if you don't have 13 hours? What if a trauma patient rolls in from a motor vehicle accident? They need ACT right now to rule out an aortic injury, but they have a documented moderate contrast allergy. Then you. Speaker 2 Pivot to the emergent regimen. You switch from oral Prednisone to intravenous hydrocortisone. The The dose is 200 milligrams to V given at five hours and one hour before administration and the. Speaker 1 Benadryl you include. Speaker 2 The 50 milligrams of diphenhydramine one hour prior now. Speaker 1 Here is the critical massive caveat that the source explicitly highlights. Varvi steroids have not been shown to be effective if given sooner than 4 hours before contrast administration. This is. Speaker 2 A point of immense frustration for residents. I can. Speaker 1 Imagine a patient needs a scan right now. The resident thinks I'll just push a massive dose of Ivy hydrocortisone right now, wait 15 minutes and stand them. At least I'm doing something but doing. Speaker 2 Something doesn't mean doing something effective, right? Speaker 1 Why doesn't a massive IV dose of steroids work immediately to understand? Speaker 2 The four hour rule, you really have to understand the pharmacodynamics of corticosteroids at the molecular. Speaker 1 Level Let's do it steroids. Speaker 2 Do not work like epinephrine or diphenhydramine. When you push Benadryl, it flows to the blood, physically binds to the H1 receptor on the cell surface, and instantly blocks histamine from attacking. It's an. Speaker 1 Immediate direct receptor antagonism, but. Speaker 2 Corticosteroids are lipophilic, meaning. Speaker 1 They pass right through the cell membrane. Exactly. Speaker 2 They pass right through and bind to glucocorticoid receptors located inside the cytoplasm. OK. Speaker 1 Inside the cell and that. Speaker 2 Steroid receptor complex then has to physically translocate into the nucleus of the cell that's. Speaker 1 Quite a journey once. Speaker 2 Inside the nucleus, it binds to specific DNA sequences, glucocorticoid response elements, and alters the actual transcription of message your RNA. Wow. Speaker 1 So it forces the cell to synthesize completely new anti-inflammatory proteins right? Like. Speaker 2 Leucocortin one, which then go out and inhibit fossilipase A2, thereby shutting down the entire arachidonic acid cascade that produces leukotrains and prostaglandins. You are. Speaker 1 Literally waiting on the central dogma of biology. DNA to RNA to protein and genetic. Speaker 2 Transcription and protein synthesis take time. They take hours, so pushing. Speaker 1 An IV steroid 30 minutes before a scan does absolutely nothing to prevent an acute reaction. Nothing. Speaker 2 Because the drug has not had the physical time required to alter the cell's inflammatory machinery, the. Speaker 1 4 hour mark is the absolute minimum pharmacokinetic floor for efficacy, Yes. Speaker 2 If you can't wait 4 hours, the steroids will not protect your patient. Speaker 1 The molecular biology dictates the clinical protocol perfectly, but as we've established, even if you follow the 1371 regimen perfectly, breakthrough reactions happen. They do. You can do everything right and the patient can still crash on the scanner table. Critical Epinephrine Administration for Allergic Reactions Which brings us to the final and honestly most critical section, the action plan. Speaker 2 This is where theory is abandoned and muscle memory must take over. These are. Speaker 1 The exact step by step treatment algorithms you need to execute Florida State. Let's start with what the source document calls the universal first steps, right? Speaker 2 Almost every severe reaction algorithm begins with the same vital baseline action. Step one. Monitor vital signs continuously. ECG, pulse oximetry, blood pressure. You cannot treat what you are not measuring. Step 2. Speaker 1 Administer. Speaker 2 Oxygen via face mask because. Speaker 1 As we noted earlier, the end point of almost all all these severe reactions is hypoxia or hypoperfusion exactly. Speaker 2 And then there is a step explicitly highlighted across all algorithms call for assistance, and the text specifically notes this can and should be done at any point. This is a. Speaker 1 Massive human factors issue. Do not be a hero. Please don't. When a patient's airway is swelling shut in a dark MRI suite, your cognitive load is maxed out. You need hands. You need the. Speaker 2 Code team. You need anesthesia. You need ICU doctors. Get help early, OK? Speaker 1 Let's breakdown the specific algorithm, scaling up the severity of allergic reactions. First, we start with urticaria hives, the universal. Speaker 2 First step here, before drugs, is always to discontinue the contrast injection. If it is still actively pumping, stop the trigger and if the. Speaker 1 Hives are mild and localized. The source. Speaker 2 Says no treatment required. Observe the patient if the hives. Speaker 1 Cross into moderate, meaning they're diffuse spreading and causing significant puritus you administer. Speaker 2 Diphenhydramine 25 to 50 milligrams. It can be given orally I am or IV depending on the IV axis you are. Speaker 1 Providing direct H1 receptor blockade. But if the hives are categorized as severe, and this is a fascinating nuance, the text bypasses the antihistamine entirely and goes straight to epinephrine. Yes. Speaker 2 Intramuscular route one to 1000 concentration .3 milliliters, which equates to .3 milligrams notice. Speaker 1 That oxygen via face mask is not universally listed as Step 2 for isolated hives, unlike the respiratory or hemodynamic reactions right isolated. Speaker 2 Severe urticaria is a profound cutaneous manifestation, but unless it is paired with airway compromise or hypotension, oxygen isn't the primary lever you need to pull epinephrine. Speaker 1 Is because it. Speaker 2 Provides profound mast cell stabilization via its beta 2 agonist effects, rapidly halting the histamine release at the source. OK, moving. Speaker 1 Up the ladder of severity, facial or laryngeal edema and bronchospasm. The airway is now under attack. Now the. Speaker 2 Oxygen mask comes on immediately. Step 2 for bronchospasm. Speaker 1 Wheezing with intact oxygenation. The source lists a specific first line medical step before you reach for the epinephrine step. Speaker 2 3 is a beta agonist inhaler specific which? Speaker 1 Makes pharmacological sense if the problem is localized smooth muscle constriction in the bronchioles, you deliver a targeted beta 2 agonist directly to the lungs via inhalation to relax that specific smooth muscle without exposing the entire cardiovascular system to systemic epinephrine. But. Speaker 2 If the patient is poorly responsive to the albuterol, or if you are dealing with facial and laryngeal edema where the upper airway tissue is physically swelling shut and an inhaler can't reach the pathology, you escalate immediately to systemic epinephrine and. Speaker 1 We need to stop here and dissect epinephrine dosing. This is arguably the highest yield, most heavily tested, and most practically dangerous area of confusion in all of emergency medicine. The source. Speaker 2 Lists two different routes of administration, and crucially, 2 entirely different concentrations. Mixing these up is a fatal error route. Speaker 1 One is intramuscular or IM. You inject it deep into the anterolateral aspect of the thigh. Because it has to absorb through the muscle tissue into the central circulation, the concentration must be highly concentrated, right? Speaker 2 The IM concentration is 1 to 1000. The standard dose is Ala .3 milliliters, which delivers .3 milligrams of epinephrine route. Speaker 1 2 is intravenous or eiffeli. You are pushing the drug directly into the central venous circulation. It is going to hit the right atrium of the heart in seconds. Therefore, the concentration must be significantly more dilute the IV. Speaker 2 Concentration is 1 to 10,000 this. Speaker 1 Is the nightmare scenario. If a panic resident grabs the highly concentrated one to 1000 IM formulation and pushes it directly into an IV, what happens? We deliver. Speaker 2 A massive instantaneous shock of A1 and beta one stimulation directly to the myocardium. The systemic vascular resistance skyrockets while the heart is whipped into a frenzy. Wow. You will almost certainly induce A lethal ventricular arrhythmia or a myocardial infarction. Dilute. Speaker 1 For the vein concentrated for the muscle exactly so using the dilute 4 route the one to 10,000. The dose listed for severe edema or brompospasm is 1 to 3 milliliters, which delivers .1 to .3 milligrams of epinephrine and for. Speaker 2 Both the IM and IV routes, the text notes you may repeat the dose up to a maximum of 1 milligram total depending on clinical response. But here. Speaker 1 Is a critical granular distinction. When we look at the algorithm for full blown anaphylaxis, meaning distributive shock, hypotension and tachycardia are present, the four epinephrine dose changes slightly. It does for anaphylactic shock. The four dose is strictly listed as one milliliter or 0.1kg at a time, not the one to three milliliter range. The. Speaker 2 Pharmacological threshold for pushing 4 epinephrine in profound anaphylaxis is incredibly tight because the hemodynamics are already an absolute chaos. The heart is racing trying to compensate for the vasodilation. So you give. Speaker 1 The smaller exact .1 milligram dose monitor the blood pressure response and repeat heat if necessary, carefully titrating up to that 1 milligram maximum exactly. Epinephrine vs. Atropine for Hypotensive Crisis Let's focus entirely on those hemodynamics because this is the absolute crux of the entire deep dive. It's the tachycardia versus bradycardia split. This is the. Speaker 2 Scenario from our introduction. The door flies open. The patient is hypotensive. You run. Speaker 1 In, you slap the leads on the patient's chest. You look at the monitor, the blood pressure is 70 / 40. They are in shock. The single most important piece of data you need in that exact second is the heart rate. Are they tachycardic? Is the heart racing at 130 beats per minute or are they bradycardic? Is the heart slugging along at 40 beats per minute? Both. Speaker 2 Patients have profound hypotension, but the underlying pathophysiology requires diametrically opposed treatments. If you. Speaker 1 See hypertension plus tachycardia. You are diagnosing severe anaphylaxis. It is an allergic distributive shock. The. Speaker 2 Systemic histamine release has caused massive vasodilation, the blood pressure has crashed because the vascular container has expanded too much, and the heart is. Speaker 1 Tachycardic because the baroreceptors are screaming at the sympathetic nervous system to beat faster to try and maintain cardiac output the. Speaker 2 Treatment algorithm here is aggressive volume and vasoconstriction oxygen. Elevate the patient's legs or place them in the Trendolinbrier position so you. Speaker 1 Are using gravity to physically drain blood from the lower extremities back into the central circulation to increase preload. You start. Speaker 2 A rapid IV fluid bolus running normal saline wide open to fill up those dilated pipes and then. Speaker 1 You administer epinephrine. I am or iffy. The epinephrine acts on the A1 receptors in the peripheral vasculature causing intense vasoconstriction, shrinking the container back down and reversing the shock. But. Speaker 2 If you look at the monitor and you see hypotension plus bradycardia, you are diagnosing a severe vasovagal reaction, which is. Speaker 1 Firmly non allergic the. Speaker 2 Vagus nerve is dumping acetylcholine onto the heart, suppressing the heart rate while simultaneously withdrawing sympathetic tone to dilate the blood vessels. The. Speaker 1 Treatment algorithm starts with the same mechanical steps to improve preload oxygen, elevate the legs or Trendelenburg administer wide open IV fluids, but here. Speaker 2 Is the massive life or death divergent if the patient is poorly responsive to fluids and positioning? You do not give epinephrine, you give. Speaker 1 Atropine the dose. Speaker 2 Is .5 milligrams of fee and you may repeat it up to a total of 3 milligrams. I want to. Speaker 1 Breakdown Exactly why giving epinephrine to a severe vasovigal patient is pouring rocket fuel on a disorganized system. It comes. Speaker 2 Down to autonomic conflict. If you give epinephrine, you are violently stimulating the alpha and beta receptors. You were telling the peripheral vessels to clamp down and the heart to beat furiously, but the. Speaker 1 Vagus Nerve is still actively firing, slamming the brakes on the AV node you have. Speaker 2 Maximum sympathetic Dr. fighting, maximum parasympathetic Dr. Simultaneously, the heart cannot handle that electrical conflict and you can induce profound lethal arrhythmias. You have to. Speaker 1 Turn off the brakes before you hit the gas and that is what atropine does. Atropine. Speaker 2 Is a competitive muscarinic receptor antagonist. It physically blocks the acetylcholine released by the vagus nerve from binding to the receptors on the heart by. Speaker 1 Blocking that parasympathetic signal, you take the brakes off, allowing the heart's intrinsic pacemaker to naturally increase the heart rate and restore the blood pressure. Conversely. Speaker 2 If you panicked and gave atropine to an anaphylactic patient, you've done absolutely nothing to stop the histamine cascade and nothing to constrict the violently dilating blood vessels. The distributive shock will continue to worsen and the patient will code that is. Treating Severe Non-Allergic Contrast Complications Why looking at the heart rate is the single most important action in the room Tachycardia means epinephrine. Bradycardia means atropine. We have. Speaker 2 Two final severe non allergic events to cover the 1st. Speaker 1 Is pulmonary edema this is. Speaker 2 The hydrostatic pressure failure we discussed where the fluid overloads the lungs, the. Speaker 1 Algorithm starts with the universal steps monitor vitals, oxygen via face mask. But then Step 3 is a physical positioning maneuver. Elevate torso. Think about. Speaker 2 The physics of what we just did for hypotension For hypotension, we elevated the legs to dump fluid into the central circulation, but in. Speaker 1 Pulmonary edema The central circulation is already catastrophically overloaded if you. Speaker 2 Elevate the legs of a patient in pulmonary edema. You dump even more venous return into a failing heart, pushing even more fluid into the flooded lungs. You will drown them faster. Exactly. Speaker 1 You sit them up, you elevate the torso, You use gravity to pull the fluid volume down to the lower extremities, reducing the preload on the heart and allowing the fluid in the lungs to settle into the lung bases, freeing up the upper Airways for ventilation. It is. Speaker 2 Diametrically opposed physical positioning based entirely on the underlying mechanism of the failure and then? Speaker 1 Step 4 is pharmacological intervention furosemide 20 to 40 milligrams the fee furosemide. Speaker 2 Is a potent loop diuretic it targets the sodium potassium chlorides importer in the thick ascending limb of the loop of Hamlet in the kidneys it. Speaker 1 Forcibly blocks the reabsorption of sodium, dragging massive amounts of water with it into the urine. You are rapidly Diaries in the excess fluid out of the body, relieving the hydrostatic pressure on the pulmonary capillaries and. Speaker 2 Finally, the algorithm for seizures the. Speaker 1 Hyperes, molar or hypoxic stress has caused a chaotic electrical storm in the cortex of the brain. The universal steps apply monitor vitals oxygen via face mask to protect against the massive oxygen consumption of the seizing brain and then. Speaker 2 Step three, consider diazepam 5 milligrams the faith or mendazolam 2.5 milligrams the faith. These are. Speaker 1 Benzodiazepines. They bind to an allosteric site on the GABA A receptors in the brain, enhancing the inhibitory effect of GABA, allowing chloride ions to flood into the neurons, hyperpolarizing them, and physically halting the electrical storm. But step. Speaker 2 4 specifically reminds you to continue to monitor vitals and pulse ox meticulously because while benzodiazepines stop the seizure they are profound central nervous system depressants, they can. Speaker 1 Easily cause respiratory depression or apnea. You might stop the seizure, but you might stop their breathing too. Which? Speaker 2 Brings us right back to the most important universal step of all. Call for assistance early. You need an airway expert in the room if you are pushing benzodiazepines. Mastering Pathophysiology for Patient Safety and Innovation We have. Speaker 1 Covered an immense amount of complex pathophysiology and pharmacology today, let's. Speaker 2 Summarize the framework we've built. We started by recognizing the sheer physical force of hyperosmolar contrast, distinguishing between a physiologic expected flush of transient vasodilation and a mild reaction that is a true clinical anomaly but successfully self limits we track. Speaker 1 The tipping point of physiological compensation entering the moderate territory where stable vital signs give you a window of time to institute targeted medical management, like albuterol for wheezing or fluid for a persistent vagal response, we. Speaker 2 Identified the catastrophic loss of that compensation in severe reactions marked by unstable vital signs, hypoxia, and shock we. Speaker 1 Dissected the molecular biology of pre medication, proving why corticosteroids require 4 hours of gene transcription to be effective and why they only work against immune mediated allergic cascades and. Speaker 2 We executed the precise, mechanistically driven treatment algorithms. We contrasted the alpha and beta agonism of epinephrine with the muscarinic antagonism of atropine, and we mapped out the diametrically opposed physical positioning required for distributive shock versus hydrostatic pulmonary edema. You are. Speaker 1 Now armed with the physiological intuition to navigate the most chaotic moments in the reading room. But I want to. Speaker 2 Leave you with a final thought to ponder, a thought that builds on everything we've discussed about the physics of these agents stretching into the future of our specialty. Let's hear. Speaker 1 It the source. Speaker 2 Documents make it incredibly clear that hyperosmolarity, the physical weight and concentration of the fluid, drives almost the entirety of the non allergic physiochemotoxic reactions. It triggers the vagus nerve. It pulls the fluid that causes the pulmonary edema. It stimulates the chemoreceptor trigger zone. We currently use low osmolar agents, but they are still not perfectly matched to human blood. They still exert a. Speaker 1 Pathological osmotic gradient, right? Speaker 2 So challenge yourself to think about the future of biochemical engineering. What if we could design A contrast agent that completely perfectly mimics the exact osmolarity of human plasma? A. Speaker 1 True ISO osmolar ideal that still provides the necessary electron density to attenuate X-rays, but exerts absolutely 0 osmotic pressure on the endothelium if you. Speaker 2 Completely remove the mechanical stress of the fluid shift. You radically eradicate the entire physiochemotoxic pathway. No more. Speaker 1 Visovagal swoons. No more contrast induced pulmonary edema, no more transient flushing or nausea. Exactly. Speaker 2 You would only be left managing true Ige mediated or direct histamine release allergic reactions. It would fundamentally alter the safety profile and the triage algorithms of daily radiological practice. It's. Speaker 1 Something to think about as you study these current pathways. The algorithms we memorized today are just a reflection of the limitations of the molecules we currently inject the. Speaker 2 Diagnostic landscape might not always be this physically traumatic for the patient I. Speaker 1 Love that perspective. Think back to the very beginning of our dive. We talked about the terrifying moment when the CT door flies open and you are faced with a crashing patient. Acute contrast reactions strip away the comfort of a clean binary diagnosis. They force you to read the subtle hemodynamics, the shifting heart rate, the respiratory drive. It is. Speaker 2 Messy. It is high stakes, and it requires you to be an absolute expert in the pathophysiology of failure. But. Speaker 1 By understanding the deep molecular and mechanical why behind the algorithms, you bring clarity and control back into that room. You become the precision instrument beautifully. Speaker 2 Said thank you. Speaker 1 For joining us on this deep dive, you are now armed with the exact pharmacological mechanisms and the underlying hemodynamic logic needed to dominate this section of the ABR core exam and infinitely more importantly, to keep your patients safe when the unexpected happens on the scanner table. Study hard, trust your training, and we will catch you next time.