Inadequate spinal anesthesia for postpartum tubal ligation: a single-center retrospective analysis (2003-2025)

There is a high risk of inadequate block with spinal anesthesia for postpartum tubal ligation that could be related to inadequate intrathecal dosing. This study aimed to investigate the association between intrathecal bupivacaine dose and inadequate blocks and to assess factors associated with inadequate blocks.

Patients undergoing a postpartum tubal ligation between 2003 and 2025 with spinal anesthesia with hyperbaric bupivacaine were included in this retrospective cohort study. Cases were grouped according to bupivacaine dose as low (7.5-9.75 mg), middle (10.5-12 mg), and high (≥13.5 mg). The primary outcome was the occurrence of an inadequate block, defined as supplementation with intravenous analgesics, or failed block with repeat neuraxial anesthesia or conversion to general anesthesia. Data were analyzed using Kruskal-Wallis and Fisher's exact tests and multivariable logistic regression.

An inadequate block occurred in 132/594 (22.2%) patients: 3/14 (21.4%, low dose), 95/336 (28.3%, middle dose), and 34/244 (13.9%, high dose). Inadequate blocks were less likely with ≥13.5 mg bupivacaine vs. 10.5-12 mg [OR 0.48, 95% CI (0.26 to 0.86); P = 0.015], and with more recent years since start of the study [0.95 (0.9 to 1); P = 0.029]. Longer surgical duration [(1.03 (1.01 to 1.04); P < 0.001] and higher intrathecal fentanyl dose [1.03 (1 to 1.05); P = 0.043] were associated with increased odds of inadequate block.

Intrathecal hyperbaric bupivacaine at a dose ≥13.5 mg was associated with lower odds of inadequate anesthesia for postpartum tubal ligation compared with 10.5-12 mg in the context of an evolving institutional practice.