Functional effects of a muscarinic receptor blockade during acute respiratory distress syndrome in double-muscled calves

Eighteen Belgian white and blue double-muscled calves suffering from the acute respiratory distress syndrome were studied. Fifteen of the calves inhaled ipratropium bromide (0.6 mg) four times a day for three to four days whereas the other three control calves inhaled sterile 0.9 per cent saline. All the animals were injected with ceftiofur sodium (1 mg/kg/day) for five days, the first injection being given one hour after the first inhalation of ipratropium bromide or saline. Arterial oxygen tension, alveolar arterial oxygen difference, carbon dioxide tension and arterial pH, respiratory and heart rates, oscillatory resistance and phase angle, measured by the mono-frequency forced oscillation technique, were recorded both before and one hour and 168 hours after the first inhalation. The measurement of oscillatory resistance and phase angle made it possible to resolve the impedance of the respiratory system into its real and imaginary components. The oscillatory compliance (Cosc) was determined from the imaginary component (Im). By one hour after the first inhalation of ipratropium bromide the oscillatory resistance was already significantly reduced and Im and Cosc had significantly increased, but the other parameters showed no significant improvement. However, between one hour and 168 hours after the first inhalation all the parameters reached physiological values. The control calves did not show any change. It was concluded that the pulmonary dysfunction associated with the acute respiratory distress syndrome in these calves was at least partly due to a severe bronchoconstriction.