Inadvertent neuraxial block placement at or above the L1-L2 interspace in the super-obese parturient: a retrospective study.

BACKGROUND: Increasing body mass index (BMI) increases the difficulty of neuraxial procedures. We hypothesized that it may put patients at risk for inappropriately high dural puncture. The accuracy of anesthesiologists' estimates of the interspinous level in super-obese parturients has not been studied. We evaluated the frequency of inadvertently high epidural and/or intrathecal catheter placement (at or above the L1/L2 interspace) in parturients of BMI ≥50 kg/m2. METHODS: Inclusion criteria for this retrospective study were women with a BMI ≥50 kg/m2 who delivered by cesarean with an epidural or intrathecal catheter. The primary outcome was the percentage of catheters placed at or above L1/L2, determined by reviewing the retained foreign object radiograph. Secondary outcomes were agreement between the estimated and actual catheter location and subgroup analysis of catheters placed under ultrasound guidance. RESULTS: After excluding 15 cases for which the catheter location could not be determined and 10 cases for which the estimated level of insertion was not recorded, 125 cases were included. Inadvertent high placement occurred in 26/125 (21%, 95% confidence interval (CI) 15% to 29%) patients. There was poor agreement between the estimated and actual catheter location (27% accurate, unweighted κ-statistic 0.02). Eleven of 39 catheters placed with ultrasound (28%, 95% CI 17% to 44%) were at or above L1/L2 compared with 15/86 catheters placed without ultrasound (17%, 95% CI 11% to 27%, P=0.17). There were no neurological complications. CONCLUSIONS: A high rate of inadvertently high epidural or intrathecal catheter placement occurs in super-obese parturients. Ultrasound did not prevent this.