Background:
Previous studies report that intraoperative hypotension worsens outcomes after aneurysmal subarachnoid hemorrhage (aSAH). However, the hypotensive harm threshold for major adverse cardiovascular events remains unclear.
Methods:
We included aSAH patients who had general anaesthesia for aneurysmal clipping/coiling. Major adverse cardiovascular events (MACE) were defined by a composite of acute myocardial injury, acute myocardial infarction, and other cardiovascular complications identified by electrocardiogram and echocardiography. We initially used logistic regression and change-point analysis based on the second derivative to identify mean arterial pressure (MAP) of 75 mmHg as the best threshold. Thereafter, our major exposure was MAP below 75 mmHg characterized by area, duration, and time-weighted average. The area below 75 mmHg represents the severity and duration of exposure and was defined as the sum of all areas below a specified threshold using the trapezoid rule. Time-weighted average MAP was derived by dividing area below the threshold by the duration of anaesthesia. All analyses were adjusted for baseline risk factors including age >70 years, female sex, severity of intracerebral haemorrhage, history of cardiovascular disease, and preoperative elevated myocardial enzymes.
Results:
Among 1029 patients enrolled, 254 (25%) developed postoperative MACE. Patients who experienced MACE were slightly older (59±11 vs. 54±11 y), were slightly more often women (69% vs. 58%), and had a higher prevalence of cardiovascular history (65% vs. 47%). Adjusted cardiovascular risk increased nearly linearly over the entire range of observed MAP. However, there was a slight inflexion at MAP of 75 mmHg. MACE was significantly associated with area (adjusted odds ratios [aOR] 1.004 per 10 mmHg.min, 95% confidence interval [CI]: 1.001-1.007, P=0.002), duration (aOR 1.031 per 10 min, 95%CI: 1.009-1.054, P=0.006), and time-weighted average (aOR 3.516 per 10 mmHg, 95%CI: 1.818-6.804, P<0.001) of MAP <75 mmHg.
Conclusions:
Lower blood pressures were associated with cardiovascular complications over the entire observed range, but worsened when MAP was <75 mmHg. Pending trial data to establish causality, it may be prudent to keep MAP above 75 mmHg in patients having surgical aSAH repairs to reduce the risk of major adverse cardiovascular events.
