Which local anaesthetic?
- I would hazard the majority of readers use 0.5% heavy bupivacaine for their spinals, myself included
- One could equally use 0.5% isobaric bupivacaine, if you can tolerate the extra minute or so it takes to reach a T4 sensory block
- Use of other viable intrathecal local anaesthetics is described e.g. promising results with hyperbaric prilocaine
How much local anaesthetic?
- I imagine most give in the region of 2ml - 2.5ml (10-12.5mg)
- A systematic review and meta-analysis found low dose spinal (≤8mg i.e. ≤1.6ml of 0.5%) was associated with greater need for intra-operative analgesic supplementation, but less hypotension (BJA, 2011)
- Should you adjust the dose based on patient characteristics?
- The literature on this topic is replete with poor-quality, externally invalid studies
- Use of an adjusted dosing regimen based on patient height/weight led to a slower onset block with greater need for intra-operative analgesic supplementation, but also significantly less hypotension and vomiting
- There are multiple non-patient characteristics which can affect block height, speed of onset and risk of side-effects too, such as:
- Patient positioning
- Site (level) of injection
- Speed of injection ± use of barbitage
- In short: probably yes to a small degree, though many will choose to use similar doses for all-comers
(Opioid) Adjuncts
- Some long-acting opioid forms part of guidelines for provision of post-caesarean anaglesia
- Diamorphine 300-400μg was the go-to for many years, but is now largely unavailable
- In diamorphhine's absence one should use 100μg morphine and 15μg fentanyl (BJA, 2021)
- Similar efficacy and side-effect profile as diamorphine
- Rate of respiratory depression in morphine 1 in 10,000