Determination of the initial minimum effective dose of 0.5% bupivacaine with 20 µg of fentanyl for an operative fixation of fractured neck of femur: a prospective, observational trial.

ABSTRACT

BACKGROUND: Fractured neck of femur (FNF) is a common cause of morbidity and mortality in elderly. Spinal catheter allows fractionation of local anesthetic dose which combined with intrathecal opioid leads to a dose reduction and better hemodynamic stability. The primary objective of this paper was to investigate the initial minimum local anesthetic dose (iMLAD) of 0.5% isobaric bupivacaine with 20 µg of fentanyl administered via spinal catheter in order to commence the operative fixation of FNF. METHODS: A prospective, single-blinded, adaptive clinical trial with patients undergoing dynamic hip screw implantation (DHS) or hemiarthroplasty (HEMI) due to FNF. The Dixon and Massey's up and down method was used to determine the ED50 of intrathecal bupivacaine. This figure was confirmed with Probit analysis, in addition to the ED95. RESULTS: Using the Dixon and Massey's approach, the iMLADED50 for DHS was 0.29 mL (1.45 mg) and the iMLADED50 for HEMI was 0.33 mL (1.65 mg) of 0.5% isobaric bupivacaine. The Probit analyses demonstrated that the iMLADED95 for DHS and HEMI were 0.32 mL (1.6 mg) and 0.34 mL (1.7 mg) respectively. The mean cumulative dose of 0.5% bupivacaine for the whole surgery was 0.67 mL (3.35 mg) and 0.87 mL (4.35 mg) in the DHS and HEMI groups, respectively. CONCLUSIONS: This study demonstrates that the placement of a spinal catheter allows for careful titration of local anesthetic, enabling a reduction of the initial intrathecal dose of 0.5% isobaric bupivacaine below 0.4 mL (2 mg) and leading to a significant reduction of a dose required for the whole surgery when combined with an intrathecal opioid.