Some interesting research on common and not-so-common obstetric anaesthesia topics: both new trends and continuing trends, as well as a cautionary medicolegal reminder.

Supraglottic airways for GA Caesarean?

Metodiev & Mushambi's editorial looks at the attitude shift among obstetric anaesthesiologists to more favourably consider the LMA or SGA for Caesarean section under GA.

They review the evidence for aspiration risk, particularly noting what we learned from NAP4 (2011) but contrast this with many studies showing safety of SGAs for GA CS (over 8,000 patients in total, with Halaseah 2010 investigating 3,000 alone!). Interesting, but before we get too excited keep in mind that the populations studied are likely very different from parturients you may typically look after.

They conclude:

"...there is insufficient evidence to recommend universal or selective replacement of tracheal tubes with SGA devices during general anaesthesia for Caesarean delivery. Aspiration remains the main concern." – Metodiev & Mushambi (2020)

Cautionary reminders of neuraxial injury

McCombe & Bogod reviewed 21 years of obstetric anaesthetic medicolegal claims, noting common themes around consent, types of nerve injury, and recognition and management failures.

Not only is neurological injury the second most common reason for obstetric anaesthetic claims (behind inadequately managed pain during Caesarean section), it carries the highest average claim cost.

The review is full of many useful observations, but Reynold's 2000 advice regarding interspace level choice for spinal access is by far the most important: always access the intrathecal space at the lowest possible level, and "...the L2/3 interspace should not be an option."

McCombe & Bogod spend some time exploring the variability of cord termination level, individual variability of the intercristal line, and the inaccuracy of anaesthetist interspace level estimation. Well worth reading the whole review.

Which vasopressor for spinal hypotension?

Although most recent consensus guidelines have recommended phenylephrine infusion for managing hypotension during neuraxial anaesthesia for Caesarean section, Singh's 2020 meta-analysis suggests otherwise.

Performing a Bayesian network meta-analysis of 52 high-to-moderate quality RCTs with over 4,000 patients, they compared multiple vasopressors directly and indirectly to produce a probabilistic hierarchy of benefit for improving neonatal and maternal outcomes.

They found that norepinephrine (noradrenaline), metaraminol, and mephentermine showed the lowest likelihood of adverse neonatal acid-base effects, and ephedrine the greatest.

These top three vasopressors (notably not phenylephrine) vied similarly for secondary outcomes, with an 85% combined-probability that metaraminol & norepinephrine are the two best agents for avoiding maternal nausea and vomiting.

Fitzgerald et al. conducted a similar network meta-analysis earlier in the year, although using different methodology and a different mix of trials, also ranked metaraminol and norepinephrine ahead of phenylephrine.

Alternatives to intrathecal heavy bupivacaine

Finally, in this time of common drug shortages it's reassuring to have confidence in acceptable alternatives. Two recent meta-analyses have compared intrathecal heavy bupivacaine to both plain and ropivacaine.

Sng et al. conducted a Cochrane review of hyperbaric vs isobaric/plain bupivacaine for Caesarean section, including 10 studies and over 600 subjects. They found that intrathecal hyperbaric and isobaric bupivacaine were equally clinically effective, although hyperbaric showed slightly faster block onset (but only by 1 minute!).

Malhotra et al. compared intrathecal bupivacaine to intrathecal ropivacaine using a meta-analysis of 13 trials including over 700 patients. They found intrathecal ropivacaine results in faster recovery of motor block, but no difference in onset of motor or sensory effects. (It's generally accepted to use a dose-equivalence of at least 1.5:1 ropivacaine:bupivacaine, based on previous studies showing rough equivalence at this ratio.)

Neither study demonstrated any difference in the risk of conversion to general anaesthesia, need for intraoperative supplemental analgesia or vasopressor requirement – although patients receiving ropivacaine requested postoperative analgesia earlier.

Nonetheless, either is an acceptable alternative to intrathecal heavy bupivacaine.

The elephant in the room

The funny thing with obstetric anaesthesia is the more things appear to change, the more... well, actually things don't even seem to change all that much.

We just need regular reminding of the importance of the basics: vasopressors for spinal hypotension, intrathecal access at the lowest accessible interspace, one long-acting LA is similar to the next, and treat the obstetric airway with respect.

Relevant studies:

  1. Metodiev Y Mushambi M. Supraglottic airway devices for Caesarean delivery under general anaesthesia: for all, for none, or for some? Br J Anaesth. 2020 Mar 18.
  2. McCombe K Bogod DG. Learning from the law. A review of 21 years of litigation for nerve injury following central neuraxial blockade in obstetrics. Anaesthesia. 2020 Apr 1; 75 (4): 541-548.
  3. Singh PM, Singh NP, Reschke M et al. Vasopressor drugs for the prevention and treatment of hypotension during neuraxial anaesthesia for Caesarean delivery: a Bayesian network meta-analysis of fetal and maternal outcomes. Br J Anaesth. 2020 Mar 1; 124 (3): e95-e107.
  4. Fitzgerald JP, Fedoruk KA, Jadin SM et al. Prevention of hypotension after spinal anaesthesia for caesarean section: a systematic review and network meta-analysis of randomised controlled trials. Anaesthesia. 2020 Jan 1; 75 (1): 109-121.
  5. Sng BL, NLR Han, Leong WL et al. Hyperbaric vs. isobaric bupivacaine for spinal anaesthesia for elective caesarean section: a Cochrane systematic review. Anaesthesia. 2018 Apr 1; 73 (4): 499-511.
  6. Malhotra R, Johnstone C, Halpern S et al. Duration of motor block with intrathecal ropivacaine versus bupivacaine for caesarean section: a meta-analysis. Int J Obstet Anesth. 2016 Aug 1; 27: 9-16.