Influence of Anthropometric Variables on the Spread of Epidural Anesthesia

Abstract

To the Editor: Previous studies performed during general surgery or cesarean section reported [1,2] or refuted [3,4] the influence of anthropometric variables such as height, weight, and age on the spread of epidurally administered anesthetics. In term pregnant patients, a reduction of volume injected is usually recommended [1], and considerable volume ranges have been reported to block a fixed dermatomal level. To improve the safety of epidural anesthesia used for cesarean section, we investigated the influence of other anthropometric variables on the spread of epidural anesthesia. Footprints have been used by paleontologists for retrospective anthropometric analysis of the human skeleton [5], and skeletal measurement has been used by De Nguyen et al. [6] to determine ideal body weight. Sixty ASA grade I consenting near-term pregnant patients, after approval from the hospital ethical committee, were included in this study. Height, weight before pregnancy, weight before anesthesia, the length of the foot from the tip of the first toe to the back of the heel, and wrist perimeter were recorded. Body mass index (BMI) was calculated (BMI = weight in kg/height in m2). Epidural puncture was performed with the patient in the sitting position via the midline approach at the L2-3 interspace. After negative aspiration and negative results from a 3-mL test dose (2% lidocaine with epinephrine 1/80,000), 15 mL of lidocaine 1.6%, with epinephrine 1/200,000, and fentanyl 100 micro gram were injected through a catheter inserted 3 cm into the epidural space. The upper level of anesthesia was determined by absence of pain in response to pinprick and was correlated to anthropometric variables using a Spearman test. Twenty percent of patients were obese according to BMI (>30 using the weight at term). Despite the same volume injected, the upper level of anesthesia ranged from T10 to T1 Figure 1. The mean number of blocked spinal segments at maximum extent of anesthesia was 17 +/- 1.6 SD. The only anthropometric measurement to correlate with the level of block was age (r = 0.39; P < 0.003). The block was adequate for cesarean section in 58 of 60 patients.Figure 1: Number of parturients (n) for each upper level of anesthesia (T = thoracic) obtained after injection of 15 mL lidocaine 1.6% in the epidural space.In conclusion, only age was found to correlate with the spread of anesthesia, but its coefficient of determination, r2 = 0.16, indicates that this variable is not more useful than those previously published. In this group, we failed to demonstrate any benefit of using new variables such as wrist perimeter or foot length on the spread of epidural anesthesia. Despite the use of a standardized technique, there was a large variation in the spread of anesthesia, and several uncontrollable factors affect the spread of local anesthetic within the epidural space. D. Chassard, MD J. Krichen, MD K. R. Berrada, MD M. Guiraud, MD B. Bryssine, MD P. Bouletreau, MD Anesthesia Department, Hotel Dieu, 69002 Lyon, France