Recognising and Treating Intraoperative Hypotension
CA-1 · draft
CA-1 Bootcamp day 3. Authored from cited abstracts; every claim carries a PMID.
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Before induction
Cardiac output is the product of stroke volume and heart rate, and it can only be altered through heart rate or rhythm, preload, contractility or afterload - which is the whole list you have to walk before you reach for a drug.
The Perioperative Quality Initiative consensus is that intraoperative mean arterial pressures below 60 to 70 mmHg are associated with myocardial injury, acute kidney injury and death, and that the injury is a function of both how far the pressure falls and how long it stays down.
Reported definitions of intraoperative hypotension are wildly inconsistent across the literature, and the recommendation from that review is to use the Perioperative Quality Initiative absolute values - a mean arterial pressure below 60 to 70 mmHg or a systolic below 100 mmHg - and to report how long the patient spent there.
In the VISION cohort a minimum systolic pressure below 100 mmHg together with a maximum heart rate above 100 bpm was more strongly associated with myocardial injury (odds ratio 1.42) than a systolic below 100 mmHg on its own (odds ratio 1.20), so the heart rate is part of the problem and not a bystander.
Across 42 studies, organ injury was reported after 10 minutes or more below a mean arterial pressure of 80 mmHg, after shorter periods below 70 mmHg, and at any exposure below 55 to 50 mmHg - depth and duration multiply rather than act separately.
Randomising cardiovascular-risk patients to a mean arterial pressure target of at least 75 mmHg instead of at least 60 mmHg cut time spent below 65 mmHg by about 60% but did not reduce acute myocardial injury or 30-day major cardiac and kidney events, so chasing a higher number is not automatically treatment.
Questions in the room
Say the equation out loud - which of its terms has actually changed in this patient?
Is this rhythm sinus, and at this rate is the rhythm itself the problem?
How would you decide whether he needs volume rather than a pressor?
What is your mean arterial pressure target here, and where does that number come from?
Oral boards stem
You are at the head of the bed on your own for the first time. Forty minutes into a hemicolectomy in a 70-year-old, the cuff cycles and reads 72/38, mean 49. Your attending walks in, does not touch anything, and asks you to talk out loud through why the pressure is low before you treat it - naming the parts of the equation rather than naming a drug.
Sources
Mehta et al., World Journal of Cardiology 2014
PMID 25276302
Sessler et al., British Journal of Anaesthesia 2019
PMID 30916004
Weinberg et al., BMC Anesthesiology 2022
PMID 35277122
Abbott et al., Anesthesia and Analgesia 2018
PMID 29077608
Wesselink et al., British Journal of Anaesthesia 2018
PMID 30236233
Wanner et al., Journal of the American College of Cardiology 2021
PMID 34711333
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