Intraoperative Hypotension and Adverse Outcomes

Intraoperative hypotension is a known complication of general anesthesia and is thought to raise the risk of inadequate organ perfusion during surgery and thus cause complications. The extent of these complications is unclear, in part because there is no widely accepted, operational definition of intraoperative hypotension³.

The potential association between intraoperative hypotension and adverse outcomes is well documented, and it seems that both the magnitude and the duration of the hypotensive event contribute to the risk of complications³. In 2018, a systematic review in the British Journal of Anesthesia aggregated all the existing literature surrounding postoperative complications secondary to intraoperative hypotension³. It found first and foremost that, while long durations of time when a patient’s MAP fell below 80 mmHg presented a mild risk of inadequate organ perfusion, any incidence of a MAP between 50-55 mmHg presented a high risk of complication³. Possible adverse outcomes include stroke, myocardial infarction, acute kidney injury, mortality and increased length of stay³. Two studies looking at outcomes in non-cardiac surgery patients found that in both, intraoperative hypotension was linked to 30-day mortality³. A 2003 study focus looked at the relationship between intraoperative hypotension in orthoscopic liver transplant patients¹. An earlier study defined a hemodynamically successful orthoscopic liver transplant as one in which there is a rapid increase in systemic vascular resistance, fall in cardiac output and no change in systolic blood pressure¹. Most cases of severe, systemic hypotension seemed to happen during donor organ reperfusion¹. When severe hypotension was prolonged, patients were documented to develop further hemodynamic instability, along with cardiac arrythmias, and cardiac arrest¹. However, these relationships could not be determined to be causal, nor was any positive effect of early intervention on such outcomes recorded³.

Despite the fact that the link between intraoperative hypotension and adverse outcomes has not been fully delineated, many experts do believe that there is indeed some value in predicting when intraoperative hypotension will occur and intervening in order to prevent it². Two machine learning algorithms for predicting the risk of intraoperative hypotension have been discussed; one predicts post-induction hypotension after general anesthesia, and the other calculates the Hypotension Prediction Index². The HPI algorithm is the only one that is commercially available, and it indicates the likelihood that a hypotensive event will happen in the next 15 minutes, using a number between 0-100². The algorithm has set the threshold to be about 85, and at this number the system will warn providers that the patient is getting dangerously hypotensive². The sensitivity was 62%, the specificity was 78%, and the positive predictive value was only 13%, showing that there is still a good amount of work to be done in developing a more accurate and precise predictive algorithm². However, this kind of high-fidelity data analysis, when refined, can provide a clinically relevant output for clinicians to use when making decisions about their patients².

While the conclusions in the literature surrounding intraoperative hypotension as a risk factor for postoperative adverse outcomes are not conclusive, many experts believe that there is some clinical benefit in minimizing its occurrence. If there is in fact an impact on patient outcomes, it is worth delineating this relationship in future research.

References 

1. Reich DL, Wood RK, Emre S, Bodian CA, Hossain S, Krol M, Feierman D. Association of Intraoperative Hypotension and Pulmonary Hypertension with Adverse Outcomes after Orthotopic Liver Transplantation. Journal of Cardiothoracic and Vascular Anesthesia, 2003; 17(6): 699-702. https://doi.org/10.1053/j.jvca.2003.09.010 

2. Vos JJ and Scheeren TWL. Intraoperative hypotension and its prediction. Indian Journal of Anaesthesia, 2019; 63(11): 877-885.  

3. Wesselink EM, Kappen, TH, Torn HM, Slooter AJC, van Klei WA. Intraoperative hypotension and the risk of postoperative adverse outcomes: a systematic review. British Journal of Anaesthesia, 2018; 121(4): 706-721. https://doi.org/10.1016/j.bja.2018.04.036