Novel method for intraoperative assessment of cerebral autoregulation by paced breathing

Background. Cerebral autoregulation (CA) is the mechanism that maintains constancy of cerebral blood flow (CBF) despite variations in blood pressure (BP). Patients with attenuated CA have been shown to have an increased incidence of peri-operative stroke. Studies of CA in anaesthetized subjects are rare, because a simple and non-invasive method to quantify the integrity of CA is not available. In this study, we set out to improve non-invasive quantification of CA during surgery. For this purpose, we introduce a novel method to amplify spontaneous BP fluctuations during surgery by imposing mechanical positive pressure ventilation at three different frequencies and quantify CA from the resulting BP oscillations. Methods. Fourteen patients undergoing sevoflurane anaesthesia were included in the study. Continuous non-invasive BP and transcranial Doppler-derived CBF velocity (CBFV) were obtained before surgery during 3 min of paced breathing at 6, 10, and 15 bpm and during surgery from mechanical positive pressure ventilation at identical frequencies. Data were analysed using frequency domain analysis to obtain CBFV-to-BP phase lead as a continuous measure of CA efficacy. Group averages were calculated. Values are means (sd), and P <0.05 was used to indicate statistical significance. Results. Preoperative vs intraoperative CBFV-to-BP phase lead was 43 (9) vs 45 (8)A degrees, 25 (8) vs 24 (10)A degrees, and 4 (6) vs -2 (12)A degrees during 6, 10, and 15 bpm, respectively (all P=NS). Conclusions. During surgery, cerebral autoregulation indices were similar to values determined before surgery. This indicates that CA can be quantified reliably and non-invasively using this novel method and confirms earlier evidence that CA is unaffected by sevoflurane anaesthesia. Clinical trial registration. NCT03071432