Stroke in Surgical Patients: A Narrative Review

Phillip E. Vlisides, M.D.; Laurel E. Moore, M.D.

Disclosures

Anesthesiology. 2021;134(3):480-492. 

In This Article

Intraoperative Considerations

Blood Pressure

Intraoperative hypotension is often implicated as a possible contributor to perioperative stroke, but specific thresholds that portend increased risk remain unclear for the noncardiac surgery patient. For example, in a recent retrospective, case-control study, the duration and severity of hypotension below a mean arterial pressure (MAP) of 70 mmHg were not associated with perioperative stroke.[62] One limitation of the study was that the results were primarily restricted to very mild hypotension (i.e., MAP of less than 70 mmHg). The data nonetheless suggest that factors other than mild intraoperative hypotension probably contribute substantially to postoperative stroke, although this conclusion is restricted to the institution studied. In a similar retrospective, case-control study, the investigators tested associations between stroke risk and time spent below various systolic and MAP thresholds in a broad, noncardiac surgery population (n = 48,241).[63] Time spent with MAP more than 30% below baseline was associated with stroke (odds ratio = 1.013/min hypotension). It is important to note, however, that none of the other absolute or relative thresholds studied, including MAP more than 40% below baseline, were associated with stroke. Of note, because there is no uniform definition for baseline blood pressure, measuring relative blood pressure changes with respect to stroke risk is fundamentally challenging. In summary, there is no clearly defined intraoperative blood pressure threshold below which noncardiac surgery patients are at increased risk for perioperative stroke. This supports the notion that intraoperative blood pressure is one of many possible factors that contribute to the risk of perioperative stroke.

Anesthetic Technique. Anesthetic technique has also been studied in relation to stroke risk. General anesthesia has been reported as an independent predictor of perioperative stroke in a large-scale investigation (more than 380,000 subjects) of hip and knee arthroplasty patients.[64] These results stand in contrast to smaller-scale investigations involving vascular[65] and gynecologic surgery[66] patients that demonstrated no associations with anesthetic technique and stroke risk. One explanation is that the effect size of anesthetic technique on stroke risk is small, requiring a large-scale investigation for detection. Alternatively, findings may be specific to surgical subtypes. Regional techniques are associated with less blood loss[67] and thromboembolic phenomena[68] in orthopedic surgery patients. Large-scale investigations involving broad surgical subtypes may provide further insights.

Last, large-scale, multicenter trials have investigated outcomes in relation to specific maintenance techniques (e.g., propofol, nitrous oxide, volatile agents). The Mortality in Cardiac Surgery Randomized Controlled Trial of Volatile Anesthetics (MYRIAD) Trial randomized 5,400 cardiac surgery patients to a volatile-based technique or propofol anesthesia. Stroke risk was similar between the volatile anesthetic group (0.8%) and propofol group (0.6%) in the per-protocol analysis. The Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia (ENIGMA)-II trial randomized 7,112 noncardiac surgery patients with cardiovascular risk factors to nitrous oxide (70% N2O in 30% O2) or no nitrous oxide (70% N2 in 30% O2) during surgical anesthesia.[70] There was no association between nitrous oxide and stroke at the 30-day or 1-year follow-up periods. Thus, for general anesthesia, the choice of maintenance technique does not appear to impact stroke risk. Similarly, the decision to choose general anesthesia versus regional anesthesia does not appear to impact stroke risk with the possible exception of patients undergoing joint arthroplasty.

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