Straight versus flex back: Does it matter in spinal anaesthesia?

It is sometimes difficult for our patients to acquire recommended flexion of their back to perform subarachnoid block upon them. The aim of this study was to find out the degree of procedural success and patient preference when subarachnoid blocks were performed on patients with suboptimal flexion of the back.

Subarachnoid blocks were performed on 160 adult patients from both sexes without any spinal deformity. Procedures were performed with patients in the lateral or seated position with the back either straight or flexed. This approach divided the study population into 4 equal groups: Lateral with back straight (LS) or flexed (LF) and seated with back straight (SS) or flexed (SF). The primary endpoint was correct needle placement. Numbers of attempts, needle redirections and patients' preferred posture were determined to compare the outcome in different groups.

For both positions, the overall success rates were 95% and 100% in patients who had straight or flexed back, respectively (P=0.81). In the lateral position, significantly more patients of the LF group (40) than those of the LS group (32) had successful placement of spinal needle at first attempt (P=0.03). Altogether, 34 and 21 patients in the SS and SF groups, respectively, required cephalad redirections of the needle (P=0.003). Most patients preferred the straight back position (69.7-88%).

With a higher preference by patients for the straight back posture, the overall success rate of correct spinal needle placement was comparable among the groups who had their back placed in a straight or in a flexed posture for subarachnoid block.