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Association between dose of hyperbaric bupivacaine, maternal hypotension, and neonatal outcome: Retrospective database study of 7111 women undergoing cesarean delivery under spinal anesthesia
Abstract Number: T2B-335
Abstract Type: Original Research
Background: A previous meta-analysis reported inadequate clinical analgesia using ≤8mg hyperbaric bupivacaine (HB) for spinal anesthesia for cesarean delivery (CD) (1). However, these low doses were associated with less maternal hypotension. Our primary aim was to investigate the relationship between HB dose and the occurrence of spinal hypotension. We also investigated the relationship between HB dose and vasopressor use and umbilical vein pH.
Methods: Retrospective study of CD in 1 institution (2 centers: district and tertiary), 2012-18. Data on all CD with spinal anesthesia and recorded HB dose were retrieved from the anesthesia information management system and hospital information system: patient age, vasopressor boluses (phenylephrine/ephedrine), emergency CD and umbilical cord pH (where available). Hypotension was defined as any systolic blood pressure either <80% baseline or <100mmHg from anesthesia start until delivery.
Results: 7,111 CD were included. HB dose administered was ≤8mg for 29%, 9-9.5mg for 12%, 10mg for 51% and >10mg for 8%. Incidence of ≥1 one spinal hypotension episode was higher in women who received ≥10mg HB, Figure; however even women with lower HB doses had hypotension. Phenylephrine was administered to 38% and ephedrine to 28% of the women. The Spearman Rank Correlation for dose of HB and phenylephrine was 0.4453, p<0.0001; and for dose of HB and ephedrine was 0.0129, p=0.28. A logistic regression model found higher likelihood of spinal hypotension with HB dose ≥10mg, OR 2.20, 95%CI 1.93 to 2.52; and with increased maternal age (continuous variable) OR 1.03 95%CI 1.02 to 10.4; but lower likelihood in emergency surgery OR 0.81, 95%CI 0.71 to 0.93. Umbilical cord pH was retrieved for 2392 CD (96.7% were electives); 0.5% had pH<7.0 and 9.5% had pH<7.2. 10.8% of the women receiving HB≥10mg had pH<7.2 versus 7.6% receiving HB<10mg, 0.0079.
Conclusion: Our major finding was a higher threshold value for increased risk of hypotension with ≥10mg HB. HB dose showed a moderate correlation with phenylephrine bolus doses. Since hypotension was observed regardless of HB dose, even the lower HB doses may require prophylactic vasopressors. We confirmed prior studies reporting that spinal hypotension is less frequent in emergency CD. Moreover, we observed a significantly higher frequency of neonatal acidosis with the higher doses of bupivacaine, likely associated with hypotension.
1. Arzola BJA 2011; 107: 308–18