Determination of the minimum initial intrathecal dose of isobaric 0.5% bupivacaine for the surgical repair of a proximal femoral fracture

Fractional spinal anesthesia and systemic hemodynamics in frail elderly hip fracture patients

Background: Systemic haemodynamic effects of intrathecal anaesthesia in an aging and frail population has not been well investigated. We examined the systemic haemodynamics of fractional spinal anaesthesia following intermittent microdosing of a local anaesthetic and an opioid. Methods: We included 15 patients aged over 65 with significant comorbidities, planned for hip fracture repair. Patients received a spinal catheter and cardiac output monitoring using the LiDCOplus system. All measurements were performed prior to start of surgery. Invasive mean arterial pressure (MAP), cardiac index (CI), systemic vascular resistance index (SVRI), heart rate and stroke volume index (SVI) were registered. Two doses of bupivacaine 2.25 mg and fentanyl 15 µg were administered with 25-minute intervals. Hypotension was defined as a fall in MAP by >30% or a MAP <65 mmHg. Results: The incidence of hypotension was 30%. Hypotensive patients (n=5) were treated with low doses of norepinephrine (0.01-0.12 µg/kg/min). MAP showed a maximum reduction of 17% at 10 minutes following the first dose. CI, systemic vascular resistance index and stroke volume index decreased by 10%, 6%, and 7%, respectively, while heart rate was unchanged over time. After the second dose, none of the systemic haemodynamic variables were affected. Conclusions: Fractional spinal anaesthesia administered prior to surgery induced a minor to moderate fall in MAP, mainly caused by a reduction in cardiac output, induced by systemic venodilation, causing a fall in venous return. Our results are contrary to the widely held belief that hypotension is mainly the result of a reduction of systemic vascular resistance.

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

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.