Analgesia in labour: inhalational and parenteral

Abstract 

Inhalational analgesia and parenteral opioids are the most widely used analgesics for labour pain because of their availability, simplicity of administration, and cost. However, their analgesic efficacy is limited compared with regional analgesia. Nitrous oxide in oxygen (Entonox) provides moderate pain relief and is safe for use in labour. Low-dose isoflurane (e.g. 0.25%) with Entonox gives superior pain relief compared with Entonox alone. The more recently introduced inhalational agent, sevoflurane, at a concentration of 0.8% also seems to provide superior pain relief compared with Entonox. Sedation scores tend to be increased with inhalational analgesia. Pethidine is the most widely used opioid for labour despite its side effects and lack of analgesia. Diamorphine is being increasingly used in the UK. There is no good evidence to distinguish analgesic efficacy amongst the standard parenteral opioids and opioid partial agonists and antagonists. Fentanyl patient-controlled analgesia (PCA), with a bolus dose of 20 μg and lockout of 5 minutes, seems to be efficacious but accumulates over time. Close maternal, fetal and neonatal monitoring is required. Parenteral remifentanil PCA, at a dose of 0.25–0.5μg/kg with a lockout time of 1–2 minutes, has a rapid onset and offset without accumulative effects, which makes it ideal for use in labour with improved analgesic efficacy. However, more sophisticated modes of drug delivery and careful titration and monitoring of the parturient are required when sevoflurane and remifentanil are used.

Keywords: diamorphine, Entonox, inhalational analgesia, parenteral analgesia, PCA, pethidine, remifentanil, sevoflurane