Correlation Between the Body Mass Index and the Distance From the Skin to the Lumbar Epidural Space in Term Parturients

Introduction Placement of lumbar epidural catheters is the gold standard practice for providing labor analgesia in parturients. The optimal insertion of the epidural catheter is determined by several patient-related factors, including body mass index (BMI), gestational age, race, ethnic background, and the anatomy of the spine. To date, several studies have been conducted to evaluate the lumbar epidural space depth in varied populations across the globe. However, limited data are available regarding the BMI and its correlation with the skin-to-lumbar epidural distance (SLED) in Indian parturients. Hence, this observational study was undertaken to investigate the correlation between the BMI and the SLED under ultrasound guidance in parturients with 37 to 42 weeks of gestational age visiting the labor room of a tertiary care institute in central India. Methods This observational study was conducted from January 2023 to December 2023 at the All India Institute of Medical Sciences (AIIMS), Raipur. Informed and written consent was acquired from all the participants before enrolling them in the study. Parturients with 37 to 42 weeks of gestational age, aged 20-40 years, belonging to the American Society of Anesthesiologists physical status 2, were included. Patients who refused to give consent, with a diagnosed mental disorder, intellectual disabilities, pre-eclamptic/eclamptic patients, or those with spine deformity were excluded. Baseline patient parameters, including age, height, weight, and gestational age, were recorded, and BMI was calculated. Patients were categorized into different BMI classes, as classified by the World Health Organization. Ultrasound imaging of the L3-L4 interspace was done. An in-built caliper of the ultrasound machine was used to measure the SLED. The mean SLED in each BMI category was noted. The primary outcome of the study was to determine the correlation between BMI and SLED. A P-value of less than 0.05 was regarded as statistically significant. Results Two hundred patients were included in the final analysis. The BMI (kilogram/meter²) of the patients ranged from 19.67 to 40.00, with the mean ± standard deviation (SD) of 28.40 ± 4.35 and the median interquartile range (IQR) of 27.60 (25.20-31.24). The SLED of the participants in centimeters (cm) ranged from 3.12 to 5.17, with the mean ± SD of 4.01 ± 0.42 and median (IQR) of 4.03 (3.82-4.18). The SLED in five groups of BMI was not normally distributed; therefore, the Kruskal-Wallis test was used to make group comparisons, and a significant difference was noted (χ2 = 159.650, P < 0.001). The data regarding BMI and SLED among the patients were normally distributed. Pearson's correlation was used to explore the correlation between the two variables, and a strong positive correlation was noted with a correlation coefficient (r) = 0.94 and P < 0.001. Conclusion The ultrasound may be incorporated as a useful tool in routine clinical practice in the care of parturients to determine the SLED before the actual insertion of the epidural needle. This approach may reduce the number of attempts at lumbar epidural catheter placement. It may be particularly helpful in obese parturients, in whom it is difficult to identify the anatomical landmarks of the spine by palpation.