Posture-related distribution of hyperbaric bupivacaine in cerebro-spinal fluid is influenced by spinal needle characteristics

Background: No studies have evaluated the relationship between duration of time sitting and spinal needle type on the maximal spread of local anaesthe tics. The few trials available have studied the influence of time spent sit ting on the spread of anaesthesia without standardising spinal needle types , and have not found any effect. Methods: In this randomised, blinded study, 60 patients scheduled for elect ive orthopaedic surgery of the lower limbs were divided into 4 groups. With the patient sitting erect, 15 mg hyperbaric bupivacaine were injected in a standard manner through a 24G Sprotte or a 27G Whitacre needle and patient s were placed supine after 1 min (24G/1 group and 27G/1 group) or 4 min (24 G/4 group and 27G/4 group). Results: Time to achieve maximum block height after injection was similar i n all groups. Block height levels were significantly lower at all time poin ts for the 24G/4 group. Maximum block heights were Th4 in the 24G/1, 27G/1 and 27G/4 groups, and Th6 in the 24G/4 group (P <0.0001). Conclusion: in a standard spinal anaesthesia procedure, when different leng ths of time spent sitting art! compared, spinal needle characteristics infl uence the maximum spread of hyperbaric bupivacaine. However, within the lim its of our study, a two-segment difference in block height is too small to consider using spinal needles as valuable tools to control block height dur ing spinal anaesthesia in our daily practice.