Association Between Hyperbaric Bupivacaine Dose and Maternal Hypotension: Retrospective Database Study of 8226 Women Undergoing Cesarean Delivery Under Spinal Anesthesia.

BACKGROUND: Low-dose (≤8 mg) hyperbaric bupivacaine for spinal anesthesia during cesarean delivery results in reduced efficacy, yet as a secondary outcome was associated with reduced frequency of spinal-induced hypotension. Our primary aim was to investigate the relationship between hyperbaric bupivacaine dose and the occurrence of spinal-induced hypotension for cesarean delivery.

METHODS: Retrospective study of cesarean delivery under spinal or combined spinal anesthesia with hyperbaric bupivacaine in 1 academic institution (2 centers-tertiary and district) from 2012 to 2018. Data were retrieved from the anesthesia information management systems (Metavision, iMDsoft, Tel Aviv, Israel) and the hospital information system, including potential confounding factors, maternal age and weight, hypertensive disease of pregnancy, single/multiple gestation, gestational age, vasopressor administration, planned/urgent surgery, position during anesthesia placement (sitting/lateral), and anesthesiologist seniority. Spinal-induced hypotension was defined as systolic blood pressure that either dropped >20% from baseline or <100 mm Hg. The primary outcome of interest was the incidence of spinal-induced hypotension according to hyperbaric bupivacaine dose. Logistic regression was used to characterize the association between the dose of hyberbaric bupivacaine and spinal-induced hypotension after adjusting for confounding factors.

RESULTS: A total of 8226 women were identified. The hyperbaric bupivacaine dose administered was <9 mg for 2395 (29.1%), 9-9.5 mg for 1031 (12.5%), 10 mg for 4155 (50.5%), and >10 mg for 645 (7.8%). We used a cutoff (<10 vs ≥10 mg) to assess for the primary outcome, using multivariable logistic regression. The incidence of at least 1 spinal-induced hypotension episode was higher in patients who received ≥10 mg hyperbaric bupivacaine, 75.8% vs 62.9% for doses below 10 mg, P < .0001; however, even women with lower doses had hypotension. Hyperbaric bupivacaine dose <10 mg was associated with a lower incidence of spinal hypotension, adjusted odds ratio (OR) of 0.774, 95% confidence interval (CI), 0.669-0.897, and P = .0006, adjusted for confounding factors.Umbilical cord pH was available for 2684 (32.6%) cases. There were significantly more neonates with pH < 7.2, among women who received hyperbaric bupivacaine ≥10 mg (10.1%) versus women who received <10 mg (6.8%), P = .0032; however, in the adjusted model, hyperbaric bupivacaine dose ≥10 mg was not associated with pH < 7.2 and an OR of 0.955 (95% CI, 0.631-1.446, P = .829).

CONCLUSIONS: Our major finding was that hypotension occurred at all doses of hyperbaric bupivacaine, yet occurrence of spinal hypotension was significantly associated with doses ≥10 mg after adjustment for potential confounders.