Dynamic cerebral autoregulation during step-wise increases in blood pressure during anaesthesia

Abstract

BACKGROUND Classically, cerebral autoregulation (CA) entails cerebral blood flow (CBF) remaining constant by cerebrovascular tone adapting to fluctuations in mean arterial pressure (MAP) between ∼60 and ∼150 mmHg. However, this is not an on–off mechanism; previous work has suggested that vasomotor tone is proportionally related to CA function. During propofol-based anaesthesia, there is cerebrovascular vasoconstriction, and static CA remains intact. Sevoflurane-based anaesthesia induces cerebral vasodilation and attenuates CA dose-dependently. It is unclear how this translates to dynamic CA across a range of blood pressures in the autoregulatory range. OBJECTIVE The aim of this study was to quantify the effect of step-wise increases in MAP between 60 and 100 mmHg, using phenylephrine, on dynamic CA during propofol- and sevoflurane-based anaesthesia. DESIGN A nonrandomised interventional trial. SETTING Single centre enrolment started on 11 January 2019 and ended on 23 September 2019. PATIENTS We studied American Society of Anesthesiologists (ASA) I/II patients undergoing noncardiothoracic, nonneurosurgical and nonlaparoscopic surgery under general anaesthesia. INTERVENTION In this study, cerebrovascular tone was manipulated in the autoregulatory range by increasing MAP step-wise using phenylephrine in patients receiving either propofol- or sevoflurane-based anaesthesia. MAP and mean middle cerebral artery blood velocity (MCA V mean ) were measured in ASA I and II patients, anaesthetised with either propofol ( n = 26) or sevoflurane ( n = 28), during 10 mmHg step-wise increments of MAP between 60 and 100 mmHg. Static CA was determined by plotting 2-min averaged MCA V mean versus MAP. Dynamic CA was determined using transfer function analysis and expressed as the phase lead (°) between MAP and MCA V mean oscillations, created with positive pressure ventilation with a frequency of 6 min −1 . MAIN OUTCOMES The primary outcome of this study was the response of dynamic CA during step-wise increases in MAP during propofol- and sevoflurane-based anaesthesia. RESULTS MAP levels achieved per step-wise increments were comparable between anaesthesia regiment (63 ± 3, 72 ± 2, 80 ± 2, 90 ± 2, 100 ± 3 mmHg, and 61 ± 4, 71 ± 2, 80 ± 2, 89 ± 2, 98 ± 4 mmHg for propofol and sevoflurane, respectively). MCA V mean increased more during step-wise MAP increments for sevoflurane compared to propofol ( P ≤0.001). Dynamic CA improved during propofol (0.73° mmHg −1 , 95% CI 0.51 to 0.95; P ≤ 0.001)) and...

Effects of phenylephrine on systemic and cerebral circulations in humans: a systematic review with mechanistic explanations

“…The systematic literature search yielded 2586 records. After removing 703 duplicates and two retracted papers, we screened 1881 records and finally identified 45 studies that met the eligibility criteria [3, 15–58]. Four additional studies were identified through PubMed and Google Scholar searches and screening relevant articles' reference lists [59–62].…”

“…Fifteen of the 49 eligible studies had been conducted in awake healthy subjects [15, 17, 18, 20, 30–32, 37, 39–41, 46, 47, 53, 58] and the remaining 34 studies in anaesthetised subjects [3, 16, 19, 21–29, 33–36, 38, 42–45, 48–52, 54–57, 59–62]. Among the latter, 31 involved patients undergoing various surgical procedures [3, 16, 19, 21–23, 25–29, 34–36, 38, 42–45, 48–52, 54, 55, 57, 59–62], two involved healthy volunteers [24, 33] and one involved patients with hyperdynamic sepsis or cardiac diseases [56].…”

“…Fifteen of the 49 eligible studies had been conducted in awake healthy subjects [15, 17, 18, 20, 30–32, 37, 39–41, 46, 47, 53, 58] and the remaining 34 studies in anaesthetised subjects [3, 16, 19, 21–29, 33–36, 38, 42–45, 48–52, 54–57, 59–62]. Among the latter, 31 involved patients undergoing various surgical procedures [3, 16, 19, 21–23, 25–29, 34–36, 38, 42–45, 48–52, 54, 55, 57, 59–62], two involved healthy volunteers [24, 33] and one involved patients with hyperdynamic sepsis or cardiac diseases [56]. Phenylephrine was administered as follows: bolus in 21 studies [3, 15, 17, 19, 22, 23, 26, 34–38, 42, 44, 49–54, 62]; infusion in 26 studies [18, 20, 24, 25, 27–33, 39–41, 43, 45–48, 55–61]; and bolus followed by an infusion in two studies [16, 21].…”

“…Among the latter, 31 involved patients undergoing various surgical procedures [3, 16, 19, 21–23, 25–29, 34–36, 38, 42–45, 48–52, 54, 55, 57, 59–62], two involved healthy volunteers [24, 33] and one involved patients with hyperdynamic sepsis or cardiac diseases [56]. Phenylephrine was administered as follows: bolus in 21 studies [3, 15, 17, 19, 22, 23, 26, 34–38, 42, 44, 49–54, 62]; infusion in 26 studies [18, 20, 24, 25, 27–33, 39–41, 43, 45–48, 55–61]; and bolus followed by an infusion in two studies [16, 21]. The study characteristics and findings are summarised in the online Supporting Information Table S1.…”

“…1b). In this analysis, we excluded cardiac output measurements using the following methods: FloTrac® (Edwards Lifesciences, Irvine, CA, USA) [23, 35, 49, 50, 52, 59]; Finometer® (Modelflow) (Finapres Medical Systems) [19, 38, 42]; ClearSight (Edwards Lifesciences, Irvine, CA, USA) [36]; Nexfin (Edwards Lifesciences) [43, 55]; and Pulsioflex (Getinge AB, Göteborg, Sweden) [26], as the accuracy of these technologies for cardiac output measurement was questioned [35, 49, 64–69]. We also excluded measurements obtained in patients with the following characteristics: low or high systemic vascular resistance (i.e.…”