Determination of the minimum initial intrathecal dose of isobaric 0.5% bupivacaine for the surgical repair of a proximal femoral fracture: A prospective, observational trial

BACKGROUND Femoral neck fractures usually require operative fixation. Spinal anaesthesia is the preferred technique for many anaesthetists, although single-shot spinal anaesthesia may have severe haemodynamic sideeffects. OBJECTIVE To determine the initial minimum intrathecal dose of 0.5% isobaric bupivacaine required in order to achieve surgical anaesthesia within 15 min. DESIGN Prospective controlled trial using the Dixon and Massey up-and-down method. SETTING Patients awaiting surgery for proximal femoral fractures at Cork University Hospital were recruited between September 2012 and December 2012. PATIENTS With institutional ethics approval and having obtained written informed consent from each, American Society of Anesthesiologists physical status I to III patients aged more than 60 years were recruited. Twenty-three patients were recruited to the study, of which 22 were managed as per protocol. One patient was excluded because of the inability to insert an intrathecal catheter. INTERVENTION A 22-guage spinal catheter was inserted between the L3 and L5 vertebral levels. An initial dose of 1 ml 0.5% isobaric bupivacaine was arbitrarily chosen as a starting point. The dose in subsequent patients was determined by the outcome of the preceding spinal block and adjusted by 0.1 ml until data on six independent pairs of patients with successful block/failed block were acquired. MAIN OUTCOME MEASURES The minimum effective local anaesthetic dose of intrathecal 0.5% isobaric bupivacaine to achieve surgical anaesthesia was defined as the primary outcome. RESULTS The minimum effective local anaesthetic dose of 0.5% bupivacaine was 0.24 ml (95% confidence interval 0.18 to 0.68). CONCLUSION Our findings may influence clinicians initial dose selection for spinal anaesthesia when a spinal catheter is used. The dose may be less than previously thought. TRIAL REGISTRATION Clinicaltrials.gov identifier: NCT01680120.