The relationship between cerebral oxygen saturation (SctO2) and blood pressure during hypotensive epidural anesthesia (HEA) is controversial. Hypotension may be associated with an increased risk of kidney injury, myocardial injury, and mortality in patients with mean arterial pressure (MAP) <55mmHg for prolonged periods , but a large population study found no association between MAP <70mmHg and stroke . Post-operative cognitive dysfunction (POCD) occurred in 19.6% of patients after total hip arthroplasty (THA) performed under general anesthesia; a decrease of SctO2 >11% was identified as a risk factor . Given the paucity of data regarding SctO2 for orthopedic patients, we investigated the association between SctO2 and HEA in patients presenting for THA.
One-hundred unilateral THA patients at the Hospital for Special Surgery were enrolled in this IRB-approved, prospective cohort study. Patients received a combined spinal epidural with local anesthetic dosed to induce hypotension. Epinephrine infusions were used to maintain MAP within 55-65mmHg. SctO2 (recorded using a near-infrared spectroscopy (NIRS) device), hemodynamic data (including non-invasive cardiac output (CO)), and vital signs were monitored continuously. Investigators were blinded to SctO2 and CO data. The primary outcome was the incidence of intraoperative CDEs, defined as a >20% reduction from baseline and/or SctO2<50%. Secondary outcomes included post-operative delirium evaluated via Confusion Assessment Method (CAM) and POCD evaluated via the Mini-Cog test with assessment at baseline and on post-operative days (POD) 1-2. Relationships between SctO2 and hemodynamic measurements were examined via Spearman’s correlation.
Baseline data are presented in Tables 1 and 2a. Four patients experienced a CDE as defined by a >20% decrease from baseline (incidence [95% CI]: 4.0% [1.6, 9.9]), but only one CDE exceeded 15-seconds (Figure 1). No patients experienced SctO2<50%. Average MAP was maintained intraoperatively within the 55-65mmHg goal (Table 2b). A weak negative correlation was seen between SctO2 and MAP; a very weak positive correlation was seen between SctO2 and CO (Table 2b). Seven patients scored positive for cognitive impairment (Table 3). Of the 4 patients who experienced a CDE, 1 scored positive for cognitive impairment on POD1 but negative on POD2. There were no incidences of post-operative delirium per CAM. No strokes were diagnosed.
There were only 4 CDEs in 100 patients; only 1 CDE lasted greater than 15-seconds. MAP during HEA for THA was not associated with CDE. Preservation of CO with epinephrine infusion, thereby maintaining cerebral oxygen delivery in spite of hypotension could explain these results. These findings are consistent with earlier HEA studies that demonstrated preserved cerebral blood flow velocity and low incidence of POCD and delirium [4,5]. Study limitations include exclusion of patients at high-risk for ischemic events and the small sample size. Future study is needed to identify limits of cerebral auto-regulation for individual patients allowing for tailored perioperative care that would balance the benefits of relative hypotension while maintaining oxygen delivery.
 Walsh M, Devereaux PJ, Garg AX, et al. Relationship between intraoperative mean arterial pressure and clinical outcomes after noncardiac surgery: toward an empirical definition of hypotension. 2013;119(3):507-515.
 Hsieh JK, Dalton JE, Yang D, et al. The association between mild intraoperative hypotension and stroke in general surgery patients. 2016;123(4):933-939.
 Lin R, Zhang F, Xue Q, et al. Accuracy of regional cerebral oxygen saturation in predicting postoperative cognitive dysfunction after total hip arthroplasty: regional cerebral oxygen saturation predicts POCD. 2013;28(3):494-497.
 Bombardieri AM, Sharrock NE, Ma Y, et al. An observational study of cerebral blood flow velocity during hypotensive epidural anesthesia. 2016;122(1):226-233.
 Sharrock NE, Fischer G, Goss S, et al. The early recovery of cognitive function after total-hip replacement under hypotensive epidural anesthesia. 2005;30(2):123-127.