Morphine consumption and respiratory depression in children receiving postoperative analgesia from continuous morphine infusion or patient controlled analgesia

Thirty children, aged between five and 15 years, were randomly allocated to receive postoperative analgesia from continuous morphine infusion (CMI) or patient controlled analgesia (PCA), also using morphine. The children's morphine consumption, respiratory rates, oxygen saturations and observation points during which they were sleeping were recorded during two periods, one on the day of operation and one the following day. The median dose of morphine consumed by the children using PCA was significantly larger than that consumed by the children having continuous infusions. Children aged between nine and 15 years using PCA had significantly lower minimum respiratory rates and minimum oxygen saturations than similarly aged children receiving continuous infusions. There was no significant difference between the PCA and CMI groups in the number of observation times that the children were asleep or in the minimum respiratory rates and minimum oxygen saturations in the awake and sleeping children.     

THE EFFECT OF AGE ON THE SAFETY FACTOR IN NEUROMUSCULAR TRANSMISSION IN THE ISOLATED DIAPHRAGM OF THE RAT

An analysis of neuromuscular transmission has been made in phrenicnerve/diaphragm preparations from male rats aged 30 days or110 days. The amplitude of miniature end-plate potentials wasfound to decrease with age, being 0.969±SEM 0.058 mVat 30 days and 0.510±SEM 0.031 mV at 110 days. Over thesame period, the quantum content of the first end-plate potentialof a train of 40 at 10 Hz, increased from 144.5, SEM+11.1, –10.4to 346, SEM+41.4, –37.0. A corresponding change was observedalso in the average quantum contents of the last 30 end-platepotentials of each train; from 50.6, SEM+ 3.5, –3.2, to138.9, SEM+15.0, –13.6. The safety factor for neuromusculartransmission, calculated from these measured parameters, wasfound at 30 days to be only 70–80% of that at 110 days.It was estimated that the lower safety factor found in youngrats was approximately equivalent to the neuromuscular blockingaction of a dose of, at least, 0.0225 mg/kg of d-tubocurarine.Extrapolation of these results to man would support previousreports of increased sensitivity to d-tubocurarine inneonates.