Respiratory Effects of Intravenous Morphine Infusions in Neonates, Infants, and Children After Cardiac Surgery

Abstract

We evaluated the respiratory effects of intravenous morphine infusions in 30 patients (2 to 570 days old, mean 155 days) after cardiac surgery. Paco₂ during spontaneous breathing and CO₂ response curves during rebreathing were obtained on morphine infusions at drug steady state and during drug washout. Steady state morphine serum levels >20 ng/mL resulted in hypercarbia (Paco₂ > 55 mm Hg) and depressed CO₂ response curve slopes (−1·mm Hg ETco₂⁻¹·kg⁻¹) in 67% and 70% of patients, respectively (P < 0.05, compared to those with levels P = 0.025). No age-related differences in respiratory effect were seen in these studies at the same serum morphine level. Careful observation of any patient receiving morphine remains necessary, but neonates and young infants seem to have the same respiratory response to morphine infusions as older infants and children at the same blood level.