Low dose spinal anaesthesia should be used:
- <=1.8mls (9mg) 0.5% hyperbaric (heavy) bupivacaine for total hip replacement
- <=1.5mls (7.5mg) 0.5% hyperbaric (heavy) bupivacaine for all other procedures
The most common dose of 0.5% heavy bupivacaine administered to hip fracture patients nationally is 2.5mls . This dose is enough to block a young, fit, pregnant woman to the level of T4 bilaterally for Caesarean section.
However, spinal anaesthesia for hip fracture:
- involves (usually) an older, sicker, frailer patient
- aims for a unilateral block to T10
- aims to avoid significant hypotension
The volume of 0.5% heavy bupivacaine correlates with % fall in systolic blood pressure from pre-spinal values to the lowest recorded value, in hip fracture patients [1, 2].
A 20% fall in systolic blood pressure – the ‘least bad’ definition of hypotension currently in use – correlates with an injectate volume of ~ 1.5mls 0.5% bupivacaine [1, 2].
Only heavy bupivacaine and plain levobupivacaine are licensed for intrathecal use . Plain bupivacaine has similar hypotensive effects to heavy bupivacaine , but is not licensed for intrathecal use. Intrathecal levobupivacaine causes less hypotension than bupivacaine , but wears off more quickly .
Anecdotally, to be reliably effective low dose spinal anaesthesia needs to be administered at L23 (or L34), as osteoarthritic joint space narrowing is more pronounced in hip fracture patients below this level, increasing the likelihood of failed insertion .
Lower doses of 0.5% heavy bupivacaine wear off sooner than larger doses. 1.5mls 0.5% heavy bupivacaine provides reliable surgical anaesthesia for about 2.5 hours , BUT:
- surgical time should only exceed 2 hours for exceptionally difficult fractures, which are usually predictable pre-operatively
- if the spinal is wearing off, pain is experienced during skin closure of the upper wound margin and is avoided by pre-spinal nerve block (see Standard 2)
- very rarely, (only) additional lignocaine infiltration is required for skin closure.
Theoretically, there may be a higher risk of nerve damage at L23, BUT:
- this is very small (approximately 0.00001% cases) compared to the benefits of being able to use low dose spinal anaesthesia to mitigate hypotension (as occurs in approximately 90% cases)
- using a pre-spinal nerve block reduces the need for sedation during spinal administration, allowing the patient to report symptoms of nerve irritation.
1. White SM, Moppett IK, Griffiths R et al. Outcomes after anaesthesia for hip fracture surgery. Secondary analysis of prospective observational data from 11 085 patients included in the UK Anaesthesia Sprint Audit of Practice (ASAP 2). Anaesthesia 2016; 71: 506-14.
2. Wood RJ, White SM. Anaesthesia for 1131 patients undergoing proximal femoral fracture repair: a retrospective, observational study of effects on blood pressure, fluid administration and perioperative anaemia. Anaesthesia 2011; 66: 1017-22.
3. Whiteside JB, Wildsmith JA. Spinal anaesthesia: an update. Continuing Education in Anaesthesia, Critical Care and Pain 2005; 5: 37-40.
4. Herrera R, De Andrés J, Estañ L, Olivas FJ, Martínez-Mir I, Steinfeldt T. Hemodynamic impact of isobaric levobupivacaine versus hyperbaric bupivacaine for subarachnoid anesthesia in patients aged 65 and older undergoing hip surgery. BMC Anesthesiology 2014; 14: 97.
5. Fettes PD, Jansson JR, Wildsmith JA. Failed spinal anaesthesia: mechanisms, management, and prevention. British Journal of Anaesthesia 2009; 102: 739-48.
6. Erdil F, Bulut S, Demirbilek S, Gedik E, Gulhas N, Ersoy MO.The effects of intrathecal levobupivacaine and bupivacaine in the elderly. Anaesthesia 2009; 64: 942-6.