A new combined spinal–epidural apparatus: measurement of the distance to the epidural and subarachnoid spaces

A new combined spinal–epidural anaesthesia apparatus with a 27G lockable spinal needle was used in 151 patients. Two groups could be created, based on whether dural perforation was felt or not (group 1: with dural click; group 2: no dural click). Measurements of the epidural space depth and of the protrusion of the spinal needle from the epidural needle (tip-to-tip distance) were made. The mean depth of the epidural space was 5.59 cm. Correlations were found with body weight, weight-to-height ratio and body mass index (p < 0.001). The mean tip-to-tip distance measured was 7.0 mm in the patients of group 1, whereas in group 2 a distance of 8.9 mm was found. This difference was statistically significant. Correlations were found between the epidural space width and the patient's height, weight-to-height ratio and body mass index. Four patients felt paraesthesia during placement of the spinal needle and, in another four patients, aspiration was necessary to detect cerebrospinal fluid. Two patients needed epidural top-ups due to insufficient level of anaesthesia. The lockable spinal needle provides safe and stable conditions during injection and a high rate of success in reaching the subarachnoid space.