Dear Editor, We would like to draw your attention to a clinical finding that often goes unnoticed: the relationship between epidural depth and body fat distribution in obese patients. Although an elevated body mass index (BMI) is generally linked with a deeper skin to epidural space distance (SESD), we observed the opposite in two morbidly obese women (BMI ≈ 40 kg/m²) whose SESD was unexpectedly shallow at 3.4 cm and 3.6 cm, determined using the loss of resistance (LOR) to saline technique by stabilizing the needle with a finger placed at the point of skin entry and the distance from needle tip to skin was measured using the markings on the needle and confirming it with a ruler. Both patients were scheduled for lower limb arthroplasty under combined spinal epidural anesthesia. The epidural space was identified at the L3–L4 interspace by midline approach using the LOR to saline technique. Based on existing BMI correlations, predicted depth was around 5.7 cm1; however, the ligamentum flavum was encountered sooner. Catheter placement was smooth, and both intra- and postoperative analgesia were satisfactory. Postoperative assessment revealed a gynoid pattern of fat deposition, marked gluteofemoral adiposity with minimal truncal/lumbar fat. Their waist-to-hip ratios were 0.76 and 0.77, and abdominal girths measured 102 and 105 cm. These measurements suggest that the distribution of adipose tissue, not BMI alone, may strongly influence epidural depth. In adults, SESD generally ranges from 4 to 6 cm and tends to increase with BMI. Yet BMI cannot distinguish where fat is stored. Regression models such as that proposed by Ravi et al.1 (depth mm =17.8 + 0.97 × BMI) works well in average weight populations but loses precision in obesity, where fat patterns vary. Our data clearly diverge from the values such models predict. We propose that gynoid (gluteofemoral) obesity yields a shallower SESD compared with android (central) obesity of equal BMI. In the gynoid type, adipose tissue accumulates around the hips and thighs, sparing the lumbar area; in the android type, it concentrates over the trunk and lower back, deepening the epidural space.2 Cantürk and colleagues found that abdominal circumference, a marker of android fat, closely correlates with SESD.3 Our observations reinforce that concept. Despite multiple studies on BMI and epidural depth, none have stratified results by obesity phenotype—a notable gap in current evidence. Unawareness of such anatomic variation may lead to excessive needle advancement and accidental dural puncture. Slow, incremental advancement with continuous tactile feedback remains essential.4 Pre-procedural ultrasound scanning can also estimate SESD and visualize tissue layers, improving first pass success and overall safety in obese patients.5 These two cases demonstrate that a higher BMI does not always indicate a deeper epidural space. The pattern of fat distribution, especially a gynoid habitus, can independently affect epidural depth. Including measurements such as waist-to-hip ratio, abdominal girth, and visible lumbar fat in the pre-anesthetic evaluation may help clinicians plan safer needle trajectories. Further prospective studies are needed to integrate body fat phenotype into epidural depth prediction models and refine regional anesthesia techniques for the growing obese population. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Sharma et al. (Mon,) studied this question.