Paralysis of ventilated newborn babies does not influence resistance of the total respiratory system

Paralysis with pancuronium bromide is used in newborn infants to facilitate ventilatory support during respiratory failure. Changes in lung mechanics have been attributed to paralysis. The aim of this study was to examine whe ther or not paralysis per se has an influence on the passive respiratory me chanics, resistance (Rrs) and compliance (Crs) of the respiratory system in newborn infants. In 30 infants with acute respiratory failure, Rrs was measured during paral ysis with pancuronium bromide and after stopping pancuronium bromide (group A). Rrs was also measured in an additional 10 ventilated infants in a reve rsed fashion (group B): Rrs was measured first in nonparalysed infants and then they were paralysed, mainly for diagnostic procedures, and the Rrs mea surement repeated. As Rrs is highly dependent on lung volume, several param eters, that depend directly on lung volume were recorded: inspiratory oxyge n fraction (FI,O-2), arterial oxygen tension/alveolar oxygen tension(a/A) r atio and volume above functional residual capacity (FRC). In group A, the Rrs was not different during (0.236+/-0.09 cmH(2)O.s.mL(-1) ) and after (0.237+/-0.07 cmH(2)O.s.mL(-1)) paralysis. Also, in group B, Rr s did not change (0.207+/-0.046 versus 0.221+/-0.046 cm.s.mL(-1) without ve rsus,vith pancuronium bromide). FI,O-2, a/A ratio and volume above FRC rema ined constant during paralysis. These data demonstrate that paralysis does not influence the resistance of the total respiratory system in ventilated term and preterm infants when me asured at comparable lung volumes.