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Prospective Observational Study of the Relationship Between Body Habitus Features and Neuraxial Block Depth and Assessed Difficulty
Abstract Number: T-04
Abstract Type: Original Research
Background: Body mass index (BMI) is a recognized predictor of neuraxial block (NB) difficulty, (1) and greater epidural depth, (2) however the importance of fat distribution has not been previously reported. We investigated the relationship between fat distribution, BMI, and body shape with NB difficulty and epidural depth.
Methods: A prospective IRB approved observational study of term pregnant women enrolled in a tertiary center, prior to NB request. We evaluated self-reported and actual BMI, height, weight, mid-arm and subscapular fatpads (digital caliper, mm), cervical-sacral spine distance (cm), epidural depth (ultrasound, cm) and NB difficulty (operator report and/or ≥2 needle passes). 4 experts assessed photographs (Likert scale 1-5) taken in lateral and sitting positions for NB difficulty and body-shapes (apple-A, pear-P, banana-B, hourglass-H).
Results: We recruited 133 women with self-reported mean±SD BMI of 29±5 kg/m2. Bland Altman analysis showed a mean difference between self-reported and actual BMI of -0.8 kg/m2 (95% CI -3.8 to 2.2). There was a significant correlation between actual BMI, mid-arm and subscapular fatpads, and the epidural depth (R-square=0.755, 0.674, and 0.661, respectively; all p<0.0001). There was agreement between expert assessments of NB difficulty (Cronbach’s Alpha=0.76 in lateral, and 0.71 sitting), but less agreement with expert assessments of body-shapes (Cronbach’s Alpha=0.54). Relationship between body-shapes and fat distribution, with assessments of epidural depth and of NB difficulty are shown in Table 1. Actual NB placement was difficult in 29 (22%) of the women. Expert assessments of NB difficulty in lateral and in sitting position, and longer cervical-sacral spine were associated with greater likelihood of actual difficult NB placement (OR 1.81, 95% CI 1.04-3.15; OR 1.96, 95% CI 1.09-3.45; and OR 1.10 95% CI 1.01-1.20 respectively), but BMI was not significantly associated.
Conclusions: Study findings suggest that fat distribution and body shape assessments do not predict epidural depth better than BMI measurement. However actual BMI should be measured as women underestimate when reporting their BMI. Visual expert assessment of NB difficulty appears to predict actual difficult NB placement. Predicting difficult NB is important as alternative strategies such as close supervision and ultrasound-guided insertion may be required.
1. Bamgbade et al. IJOA 2009;18:221
2. Narang et al. BJA 1988;60:402