Duration of low-dose spinal anaesthesia for hip fracture surgery.

Abstract

Godai correctly identifies the commonest concern held by anaesthetists about using low-dose spinal anaesthesia for hip fracture surgery, namely that the spinal will wear off intra-operatively or early postoperatively, subjecting the patient to potentially avoidable pain during prolonged surgery, and its consequences (including delirium). This concern is addressed under ‘Standard 3’ at www.hipfractureanaesthesia.com. Godai criticises Tighe for not presenting data to support his use of low-dose spinal anaesthesia. The Brighton Hip Fracture Database 1 contains data that supports Tighe's assertion that low-dose spinal anaesthesia is perfectly safe to use, even for longer procedures. Over the last 4 years, 1597/1909 (83.7%) patients with complete records have received spinal anaesthesia for fractured neck of femur surgery. Spinal anaesthesia ‘failed’ on 61 (3.8%) occasions, but only twice during surgery; review of the notes suggested both cases were more problems of sedation rather than of sensation; in the remaining 59 cases, ‘failure’ resulted from failure to insert the intended spinal anaesthesia. Of the successful 1536 spinal anaesthetics, 769 (50.1%) involved the administration of ≤ 1.5 ml 0.5% bupivacaine intrathecally; the median (IQR [range]) duration of surgery (entry into theatre to end of surgery) for the 571 of these cases for which theatre times were recorded was 83 (68–101 [30–315]) min. Only 46 (8.1%) operations lasted longer than 120 min; only two of these patients had neither supplemental nerve block nor intrathecal opioids. Further evidence for the duration of spinal anaesthesia is provided by data from 23 studies (1062 patients) used recently to calculate the dose (D50) of spinal bupivacaine providing half the maximum theoretical time to recovery of motor function (Emax) in ambulatory surgery 2. Extrapolating from these data, 7.5 mg (1.5 ml 0.5% bupivacaine) provides approximately 4 h of motor block [95% CI (3–6 h)] and so (presumably) sensory block of at least a similar duration. Prolonged, complex hip fracture surgery, for example involving multifragment peritrochanteric fixation, is therefore unusual, and is usually predictable pre-operatively. For all other operations, surgery performed by an appropriate surgeon should not exceed around two hours’ duration, and anaesthetists should challenge surgeons who routinely take longer than this because it exposes frail patients to the additional hypotensive risks of using higher volumes of spinal bupivacaine. What if a lower dose spinal anaesthetic begins to wear off intra-operatively? Sensory recovery occurs cephalad to caudally, and so operative pain is most likely to be felt as the cephalad end of the surgical incision is being manipulated/closed. Such pain is very unlikely to occur if either a supplemental fascia iliaca or lumbosacral plexus block has been co-administered before spinal anaesthesia (although these blocks have a ~5% failure rate). Alternatively, closure can be completed by supplementation with local anaesthetic infiltration. Finally, very occasionally, conversion to general anaesthesia may be required – this should not be viewed as a failure of an anaesthetic plan so much as a necessary evolution in the careful management of a trauma patient. The use of low-dose spinal anaesthesia for hip fracture surgery requires a more nuanced calculation than that proposed by Godai, balancing the extremely unlikely occurrence of failed analgesia, contributing to delirium, against the much more likely occurrence of hypotension with larger doses of spinal bupivacaine 3, 4, contributing to delirium. What is needed, of course, are properly conducted studies in this area, comparing, for example, efficacy and outcome between low dose (7.5 mg 0.5% bupivacaine) and normal dose (12.5 mg 0.5% bupivacaine) spinal anaesthesia + fascia iliaca block in hip fracture patients. The James Lind Alliance (JLA) is currently starting a research priority setting exercise into the management of patients with lower limb fragility fractures, and the appropriate dose of spinal anaesthesia would seem to be a research priority that I would encourage colleagues to promote to the JLA.