Effect of morphine on respiratory drive in trigger ventilated pre-term infants

The response to morphine (100 microgram (microg)/kg bolus, 10 microg/kg/h infusion) of 14 babies (median birth weight/gestation 1. 37 kg/30 weeks) trigger ventilated for hyaline membrane disease was compared to a group of 26 babies (median birth weight/gestation 1.1 kg/28 weeks) also trigger ventilated for hyaline membrane disease but not treated with morphine. The effect of morphine on triggered breath rate was very variable with no significant difference between the groups seen until 12 h after starting the infusion (mean [95% CI] difference=-17 [-33, -2] breaths/min). In those babies (n=11) who had plasma morphine levels measured there was no significant reduction in triggered rate over time despite significantly increasing plasma morphine levels. Babies who produced morphine-6-glucuronide at 12 h showed a significantly greater reduction in triggered breath rate than those who did not (median change -22 breaths/min compared to -4 breaths/min).