Oxygen Saturation and Postoperative Mortality in Patients With Acute Ischemic Stroke Treated by Endovascular Thrombectomy

BACKGROUND: Monitored anesthesia care (MAC) and general anesthesia (GA) with endotracheal intubation are the 2 most used techniques for patients with acute ischemic stroke (AIS) undergoing endovascular thrombectomy. We aimed to test the hypothesis that increased arterial oxygen concentration during reperfusion period is a mechanism underlying the association between use of GA (versus MAC) and increased risk of in-hospital mortality. METHODS: In this retrospective cohort study, data were collected at the Cleveland Clinic between 2013 and 2018. To assess the potential mediation effect of time-weighted average oxygen saturation (Sp o 2 ) in first postoperative 48 hours between the association between GA versus MAC and in-hospital mortality, we assessed the association between anesthesia type and post-operative Sp o 2 tertiles (exposure–mediator relationship) through a cumulative logistic regression model and assessed the association between Sp o 2 and in-hospital mortality (mediator–outcome relationship) using logistic regression models. Confounding factors were adjusted for using propensity score methods. Both significant exposure–mediator and significant mediator–outcome relationships are needed to suggest potential mediation effect. RESULTS: Among 358 patients included in the study, 104 (29%) patients received GA and 254 (71%) received MAC, with respective hospital mortality rate of 19% and 5% (unadjusted P value <.001). GA patients were 1.6 (1.2, 2.1) ( P < .001) times more likely to have a higher Sp o 2 tertile as compared to MAC patients. Patients with higher Sp o 2 tertile had 3.8 (2.1, 6.9) times higher odds of mortality than patients with middle Sp o 2 tertile, while patients in the lower Sp o 2 tertile did not have significant higher odds compared to the middle tertile odds ratio (OR) (1.8 [0.9, 3.4]; overall P < .001). The significant exposure–mediator and mediator–outcome relationships suggest that Sp o 2 may be a mediator of the relationship between anesthetic method and mortality. However, the estimated direct effect of GA versus MAC on mortality (ie, after adjusting for Sp o 2 ; OR [95% confidence interval {CI}] of 2.1 [0.9–4.9]) was close to the estimated association ignoring Sp o 2 (OR [95% CI] of 2.2 [1.0–5.1]), neither statistically significant, suggesting that Sp o 2 had at most a modest mediator role. CONCLUSIONS: GA was associated with a higher Sp o 2 compared to MAC among those treated by endovascular thrombectomy for AIS. Sp o 2 values that were higher than the middle tertile were associated with higher odds of mortality. However, GA was not significantly associated with higher odds of death. Sp o 2 at most constituted a modest mediator role in explaining the relationship between GA versus MAC and mortality.