Remifentanil on the labour ward

Abstract

The case report of remifentanil-induced respiratory arrest on the labour ward makes grim reading [1]. Remifentanil is not licensed for obstetric use. Indeed, the Summary of Product Characteristics clearly advises ‘The safety profile of remifentanil during labour or delivery has not been demonstrated. There are insufficient data to recommend remifentanil for use during labour and Caesarean section.’ In the case described, the patient’s weight is not given, and we are left to guess the dosage rate. Assuming a weight in the range 60–80 kg, the remifentanil dosage over 20 minutes is calculable between 0.18 and 0.23 μg.kg−1.min−1. In a rigorously conducted regulatory study, the ED50 for sedation in surgical patients was 0.043 μg.kg−1.min−1, and this was associated with ‘significant incidences of nausea, pruritus, sweating, and respiratory depression’ [2]. Because of these safety concerns, the development of low-dose remifentanil infusions as an adjunct sedative was abandoned. In a separate study, infusion of remifentanil at 0.1 ± 0.025 μg.kg−1.min−1 was effective for acute postoperative analgesia, although this practice has never become widespread, probably because of safety concerns [3]. The dosage received in this case therefore seems hefty. Advocates of remifentanil obstetric analgesia should not take comfort in personal series of such use of remifentanil without obvious complications. In the world of iatrogenic harm, ‘absence of evidence is not evidence of absence’ [4] and series of a few tens or hundreds of cases without disaster does not prove that a technique is safe [5]. Even if we disregard the basics of opioid pharmacology, anything that involves dissolving a powder, diluting the solution, setting up a pump, avoiding accidental boluses or siphoning, and concluding with the safe flushing of the cannula is far from foolproof. Safe practice, briefing, safety consciousness and protocols will attenuate, but not abolish, these risks. Finally, a pulse oximeter is not a monitor of respiration – but a capnograph is. Capnography via nasal ‘specs’ is now available for sedation monitoring and might have averted disaster if used in this case. As we currently lack trial data showing clinical benefit from remifentanil obstetric analgesia, it is difficult to see how its use can be justified. Must we press on until a young mother dies? [6].