EFFECTS OF MORPHINE AND PANCURONIUM ON LUNG-VOLUME AND OXYGENATION INPREMATURE-INFANTS WITH HYALINE-MEMBRANE DISEASE

To determine the effect of analgesia and paralysis on lung volume and oxygenation in premature infants supported by mechanical ventilation b ecause of hyaline membrane disease, functional residual capacity (FRC) , and arterial/alveolar oxygen tension ratio were measured in nine pre mature infants with hyaline membrane disease before and after the admi nistration of morphine sulfate and pancuronium bromide. Without a chan ge of positive end-expiratory pressure, ventilator rate and peak inspi ratory pressure were increased before the first set of measurements to minimize the contribution of the infants' own respiratory effort to t otal ventilation. These ventilator settings were then held constant (e xcept fraction of inspired oxygen) before and after the administration of the drugs. The FRC was measured with a multiple-breath N-2 washout technique by means of whole-body plethysmography to measure airway fl ow. The FRC and the ratio of arterial to alveolar oxygen tension decre ased in seven of nine patients after treatment with morphine and pancu ronium. The decrease in FRC for all patients was significant (2.4 +/- 2.9 ml/kg; p <0.05), and a significant correlation was demonstrated be tween the change in the arterial/alveolar oxygen tension ratio and the change in FRC (r = 0.82; p <0.01). Gestational age, birth weight, pos tnatal age, severity of lung disease, and time after the administratio n of morphine and pancuronium were not significantly correlated with t he change in FRC. We believe that a decrease in oxygenation caused by alveolar derecruitment occurred even though the ventilator settings ha d been increased before the first set of measurements. The decrease in FRC in these infants, who are thought to have alveolar instability be cause of surfactant deficiency, may have resulted from the loss of exp iratory braking mechanisms. We conclude that analgesia and paralysis s hould be used with caution under these circumstances.