Factors Associated with Inadequate Spinal Anesthesia and Conversion to General Anesthesia During Elective Cesarean Delivery: A Retrospective Observational Study from Southwestern Iran

Abstract

Background: Spinal anesthesia is the predominant anesthetic technique for elective cesarean delivery; however, inadequate spinal anesthesia remains a significant challenge in obstetric anesthesia. It may cause maternal pain and discomfort, delay surgery, and necessitate conversion to general anesthesia. Identifying perioperative risk factors may improve clinical decision-making and enhance maternal and neonatal safety. Objectives: This study aimed to determine the incidence of inadequate spinal anesthesia and conversion to general anesthesia and to investigate the factors associated with these outcomes among women undergoing elective cesarean delivery. Methods: In this retrospective observational study, the medical records of 370 pregnant women who underwent elective cesarean delivery in 2025 at hospitals affiliated with Abadan University of Medical Sciences were consecutively reviewed. Spinal anesthesia was used as the primary anesthetic technique in all patients. Demographic, obstetric, clinical, and anesthesia-related data were extracted from medical records, anesthesia charts, and surgical reports. Patients were categorized according to whether spinal anesthesia was successful or inadequate. Factors associated with inadequate spinal anesthesia were assessed using multivariable logistic regression, and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. The cumulative effect of three factors—body mass index (BMI), spinal anatomical abnormalities, and anesthesia duration ≥ 45 minutes—on anesthetic outcomes was also evaluated. Results: Among the 370 patients, spinal anesthesia was successful in 310 (83.8%) and inadequate in 60 (16.2%). Spinal anatomical abnormalities were associated with higher odds of inadequate spinal anesthesia (adjusted OR = 3.1; 95% CI, 1.3 - 7.3; P = 0.010). Similarly, anesthesia duration ≥ 45 minutes was associated with higher odds of inadequate spinal anesthesia in the multivariable analysis (adjusted OR = 3.4; 95% CI, 1.8 - 6.4; P < 0.001). The use of an intrathecal adjuvant in combination with hyperbaric bupivacaine was associated with lower odds of inadequate spinal anesthesia (adjusted OR = 0.5; 95% CI, 0.3 - 0.9; P = 0.021). Among the 60 patients with inadequate spinal anesthesia, 21 (35.0%) were managed with intravenous supplemental medication, whereas 39 (65.0%) required conversion to general anesthesia. In the exploratory cumulative analysis, the rates of inadequate spinal anesthesia and conversion to general anesthesia increased with the number of prespecified factors, with conversion increasing from 2.8% among patients with no factors to 36.7% among those with ≥ 2 factors (P < 0.001). Conclusions: Spinal anesthesia was successful in most elective cesarean deliveries, although 16.2% of patients experienced inadequate anesthesia and 10.5% required conversion to general anesthesia. Spinal anatomical abnormalities and anesthesia duration ≥ 45 minutes were associated with inadequate anesthesia. Exploratory analysis showed higher observed rates of inadequate anesthesia and conversion with increasing numbers of prespecified factors. These findings support careful perioperative assessment and preparedness for rescue interventions.