St Michael, patron of caesarean anaesthesia.

Stephen Kinsella in Anaesthesia August 08, published a prospective audit on regional anaesthesia for caesarean section at St Michael’s Hospital, Bristol. The hospital delivers close to 5000 babies per annum, with about 1200 of those by caesarean. Their work seems very good: only 0.8% of RAs fail. And to conduct and publish an audit of this type suggests a dedicated and conscientious effort by this team of obstetric anaesthetists.

Prospective audits as a form of clinical evidence come with a well-described caveat: groups are not randomised nor blinded, and a patient’s type of treatment is strongly influenced by the type of that patient and this paper is no different. But one curiosity of this audit was the somewhat unimpressive performance of combined spinal epidural anaesthesia. Compared to the 6% incidence of intraoperative pain and 1% failure rate of spinal anaesthesia for non-emergent cesaerans, CSE anaesthesia had an18% intraoperative pain rate and a 3.27% GA conversion rate. A prospective audit in the USA (Bloom et al O&G 2005) also found that CSE was not significantly superior to spinal anaesthesia in avoiding GA conversion. Kinsella acknowledges that at St Michaels CSE was reserved for the “complex” cases, but it is contrary that a technique which is meant to fireproof the vulnerability of the single shot spinal to incomplete anaesthesia on audit performs inferiorly. One could speculate that these “complex cases” may have been less likely to have been offered GA when experiencing intraoperative pain because of a perceived risk of failed intubation.

Kinsella does not explore this relative failure of CSE. He does however consider the patient’s position when siting spinal anaesthesia. St Michaels anaesthetists tended to place spinal in the right lateral decubitus position. The sitting position was reserved for patients with obesity or anatomical difficulty and on univariate analysis 5.1% of sitters had failure (i.e. needing at least IV analgesia) versus 2.9% of those decubitus. This suggests that the caudad pooling of hyperbaric bupivacaine may result in inadequate block. CSE in the sitting position may be more likely to result in caudad pooling because of the time taken in placing and securing the epidural catheter. Kinsella does not indicate in what positions CSE was done, but if the cases were complex because of obesity, a sitting position is more likely to have been used.

So, what does it mean for CSE? Possibly it is falsely reassuring: it may result only in caudad anaesthetic which only weakly covers the thoracic dermatomes (only good enough to block cold!) followed by a sluggish onset of lumbar epidural anaesthesia when surgical dissection reveals the intrathecal dose’s inadequacy. I suggest that a “complex case” may be better served by a double space CSE technique with an initial epidural catheter placed nearer to the dermatome of the incision followed by the intrathecal dose in a lower space and the immediate repositioning of the parturient in the tilted supine position This PubMed page lists a few references in support of a double needle technique.