RESPIRATORY EFFECTS OF INTRAVENOUS MORPHINE INFUSIONS IN NEONATES, INFANTS, AND CHILDREN AFTER CARDIAC-SURGERY

We evaluated the respiratory effects of intravenous morphine infusions in 30 patients (2 to 570 days old, mean 155 days) after cardiac surge ry. Paco2 during spontaneous breathing and CO2 response curves during rebreathing were obtained on morphine infusions at drug steady state a nd during drug washout. Steady state morphine serum levels > 20 ng/mL resulted in hypercarbia (Paco2 > 55 mm Hg) and depressed CO2 response curve slopes (< 10 mL.min-1.mm Hg ETco2-1.kg-1) in 67% and 70% of pati ents, respectively (P < 0.05, compared to those with levels < 20 ng/mL ). During washout, morphine levels more than 15 ng/mL resulted in hype rcarbia in 46%, whereas levels less than 15 ng/mL were associated with hypercarbia in 13% (P = 0.025). No age-related differences in respira tory effect were seen in these studies at the same serum morphine leve l. Careful observation of any patient receiving morphine remains neces sary, but neonates and young infants seem to have the same respiratory response to morphine infusions as older infants and children at the s ame blood level.