Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: A prospective observational study.

BACKGROUND: Spinal anaesthesia-induced hypotension is frequently reported in patients undergoing caesarean section. Mechanistically, sympathetic blockade reduces the systemic vascular resistance and the left ventricular preload, causing hypotension, which is augmented by aortocaval compression. The corrected blood flow time (FTc) is affected by the preload and is inversely related to the afterload. OBJECTIVE: We hypothesised that the preanaesthetic carotid artery FTc could predict hypotension after induction in patients undergoing a caesarean section with spinal anaesthesia. DESIGN: A prospective observational study. SETTING: A tertiary referral centre in South Korea from September 2018 to November 2019. PARTICIPANTS: Thirty-eight parturients scheduled for elective caesarean section under spinal anaesthesia. INTERVENTIONS: Using carotid ultrasonography, FTc was measured twice prior to inducing spinal anaesthesia. FTc was calculated using both Bazett's (B) and Wodey's (W) formulae. Hypotension was defined as an SBP decrease to less than 80 mmHg, or less than 75% of baseline, or if symptoms consistent with hypotension occurred from the time of injection of the spinal anaesthetic until delivery. MAIN OUTCOME MEASURES: The primary endpoint was to determine the predictive value of preanaesthetic FTc for postspinal hypotension during caesarean delivery. RESULTS: Among the 35 patients who completed this study, hypotension occurred in 21 (60%). The areas under the receiver-operating characteristic curves for FTc (B) and FTc (W) were 0.905 [95% confidence interval (CI), 0.757 to 0.978, P < 0.001] and 0.922 (95% CI, 0.779 to 0.985, P < 0.001), respectively. The optimal cut-off values for predicting hypotension were 346.4 and 326.9 ms, respectively. The grey zone for FTc (B) and FTc (W) included 40 and 14% of the patients, respectively. CONCLUSION: Preanaesthetic carotid artery FTc was a reliable indicator of postspinal hypotension in parturients. Considering the grey zone, Wodey's formula is better than Bazett's formula. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03631329.