Depth of the thoracic epidural space in paramedian approach.

Study Objective: To define the depth of the thoracic epidural space in the paramedian axis.

Design: Retrospective study.

Setting: Operating room of a tertiary care medical center.

Patients: Nine hundred ninety-eight consecutive adults scheduled for elective major cardiothoracic/abdominal surgery and postoperative thoracic epidural pain control.

Interventions: The thoracic epidural pain control was accomplished via paramedian approach at indicated levels in 977 of 998 patients with uniform and well-standardized technique routinely performed in this institute.

Measurements: The depth of the epidural space, defined as the distance from the needle tip just penetrating the epidural layer to the overlying skin, was measured by directly checking the length markers displayed on the needle. Association between demographic variables and epidural depths at different thoracic levels was analyzed.

Main Results: The mean thoracic epidural depth was (mean+/-SD) 5.11+/-0.94 cm, which was positively correlated with the body weight (regression coefficient=0.039, P<.001) and body mass index but was unrelated to sex, age, or body height. On stepwise linear multivariate regression analysis, each 10 kg of increase in body weight would result in a 0.39-cm increase in the depth. Besides, this paramedian depth was 0.34 cm longer at upper thoracic levels (T9 and upper) than that at lower levels (T10 and lower, P<.001).

Conclusions: Body weight, body mass index, and anatomical levels determine the paramedian thoracic epidural depth. The greater the patient's weight and the higher the puncture level, the deeper the thoracic epidural space from the body surface.