Cerebral hemodynamics during sustained intraoperative hypotension

Abstract

Static cerebral autoregulation (CA) maintains cerebral blood flow (CBF) relatively constant above a mean arterial blood pressure (BP_mean) of 60-65 mmHg. Below this lower limit of CA (LLCA), CBF declines along with BP_mean. Data are lacking in describing how CA reacts to sustained hypotension since hypotension is usually avoided. In this study, we took advantage of a procedure requiring sustained hypotension. We assessed static CA for LLCA determination, and a more continuous CA, which counters short-term blood pressure variations. With these data, we analyzed CA during longstanding hypotension. Continuous arterial blood pressure and middle cerebral artery blood flow velocity (MCAV_mean) were monitored in 23 patients that required deep intraoperative hypotension. The LLCA was determined for every patient, and BP_mean below this LLCA was classified as the patient-specific hypotension. With the mean flow index (Mx_a), continuous CA (Mx_a-CA) was quantified. Mx_a was calculated and averaged after induction of general anesthesia (baseline), every 15 min during, and 15 min after 1 h of hypotension. Functioning CA was defined as Mx_a < 0.4. Data are expressed as median (25th-75th percentile). The LLCA was located at 56 (47-74) mmHg. At baseline, Mx_a was 0.21 (0.14-0.32) and 0.61 (0.48-0.78) during hypotension (P < 0.01), with no appreciable change over time, n = 12. After blood pressure restoration, Mx_a improved, 0.25 (0.06-0.35, n = 9). Mx_a-CA became and remained disturbed during the 1 h of hypotension, and improved after blood pressure restoration. This completely reversible situation suggests no ischemic hyperemia occurs and renders an adaptation mechanism during sustained hypotension unlikely.NEW & NOTEWORTHY Intraoperative hypotension is normally avoided by anesthesiologists. However, for the Personalized External Aortic Root Support (PEARS) procedure, deep-induced hypotension is an essential requirement for the surgeon to be able to manipulate the aortic root. In this procedure, blood pressure and middle cerebral artery blood flow velocity were monitored. In this study, we assessed cerebral autoregulation during sustained hypotension, to give an insight into its behavior during hypotension.

Keywords: cerebral autoregulation; cerebral autoregulation efficacy; cerebral blood flow velocity; cerebrovascular circulation; hypotension.