NBME 20 Early septic shock (NBME Answers)

Retired NBME 20 Answers

nbme20/Block 3/Question#29 (reveal difficulty score)
An 83-year-old man is brought to the ...
Early septic shock 🔍 / 📺 / 🌳 / 📖
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submitted by ∗hayayah(1212)

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Septic shock is a type of distributive shock which is marked by massive vasodilation (d/t inflammatory response) causing decreased SVR, decreased preload / PCWP, and increased CO.

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smc213 Septic shock can also present with hypothermia <36C +3

bethune Why is it not gastrointestinal bleeding? +4

beanie368 GI bleeding would present with increased SVR as a response to hypovolemia +10

mysteriousmantyping Why would this not be pulmonary embolism? +1

step1passfail Pulmonary embolism would cause a decrease in cardiac output. There is increased pressure in the high compliant RV which can bulge and compress the LV, decreasing its preload. CO=Heart rate x stroke volume and stroke volume is partially determined by preload. If the pulmonary embolism is large enough, it can also obstruct the pulmonary vessels and subsequently not have enough blood going to the LA and LV, ultimately making the cardiac output near 0. +3

chj7 Out of all the different types of shock, cardiac output is increased only in distributive shock (ie. anaphylactic, septic). +1

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submitted by ∗bfinard1(3)

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Can someone explain why cardiac output is high in septic shock?

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drdoom Bacteria and bacterial components (like LPS) in circulation trigger massive release of cytokines (Interleukin-1, Interleukin-6 and TNFa), resulting vasodilation. Heart rate increases to maintain decent BP. +1

bfinard1 Is stroke volume not affected by that massive vasodilation? I would think if venous system is vasodilated then you'd have reduced EDV from reduced blood flow to heart +

zedora Both of you are correct. In septic shock there is a massive vasodilation. In order to compensate for the reduced blood pressure, there is an increased heart rate. Now, keeping this in mind, what is the CO formula? CO = HR x SV Right? Lets say under normal conditions HR is 60 & Stroke volume is 50. Your cardiac output = 60 x 50 = 3000. Now in septic shock, your heart rate is massivly increased but your stroke volume is decreased minimally. So lets plug in the numbers. Lets say, under septic shock, HR = 150 & stroke volume is now 30. The cardiac output is now gonna be = 150 x 30 = 4500, hence your CO is increased. In Septic Shock, the heart rate is massively increased compared to the amount of SV decreased. +

drdoom @bfinard1 By vasodilation, I almost exclusively mean arterial vasodilation. When it comes to CV, I always work backward from “first principles”, and in my view the first principle of the CV system is, “Maintain pressures to maintain good flow.” All other accommodations of the CV system (changes in inotropy[strength], chronotropy[time], vasoconstriction and vasodilation) are in *service* to maintaining flows. Without good flows, you get the thing human tissues like the least: not lack of oxygen but accumulation of CO2 (and the acidity that goes with it). +

drdoom So, all that was a long-winded way of saying that Cardiac Output will remain high when the body is producing higher-than-desired levels of CO2 (when organs and the immune system have gone into overdrive to respond to a threat or to address decompensation in some other part of the system); the plummeting of Cardiac Output heralds the beginning of the end. It signifies that the stresses being imposed on the body exceed the capabilities of the system. +

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submitted by ∗calvin_and_hobbes(2)

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Why is the T normal in this patient? I would have predicted underlying infection — ie, fever — before even "early" septic shock. I selected septic shock purely for the intractable low SVR despite fluids but want to understand more about the absence of fever... Thanks!

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drdoom Elderly (and immunocompromised, generally) do not mount robust fever responses to bacteria and other microorganisms; in elderly, this probably has to do with “declines” of the innate immune system (your macrophages, dendritic cells, monocytes, &c., just don't function as well as they used to). In other words, if you (1) wiped out someone's immune system and then (2) injected bacteria into their bloodstream, you wouldn't observe any fever either. The presence of a “typical” (normal) fever in an elderly or immunocompromised patient can be a super concerning sign: they might have a raging infection on the inside. +

drdoom For more: https://academic.oup.com/cid/article/31/1/148/318030 +

drdoom ^from the article: “Absent or blunted fever response in the elderly. There is ample evidence that a blunted fever response to a serious bacterial, viral, or fungal infection suggests a poorer prognosis than does a robust fever response [13]. In addition, there is a substantial body of data, mostly from animal models, that fever—through its effects on immune function—may be an important host defense mechanism [14]. Roughly 20%–30% of elderly persons with serious bacterial or viral infections will present with a blunted or entirely absent fever response [2,3,15].” +

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submitted by ∗spaceboy98(22)

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The way i look at this is the temperature.

A hypothermic patient will almost always present with septic shock because septic shock can present as both hyperthermia or hypothermia

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athenathefirst Doesn't sound accurate. This patient had a normal temperature. +

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