Pulmonary mechanics during general anaesthesia. The influence of mechanical irritation on the airway

The changes in pulmonary resistance (RL) and compliance (CL), following airway irritation and surgical stimulation, were investigated in 19 anaesthetized, paralysed patients. Thirteen were normal, while six had objective evidence of chronic obstructive pulmonary disease (COPD). Broncho-carinal irritation with a suction catheter produced a 27% increase in RL (0.58+/-0.32kPa litre-1 s to 0.74+/-0.40, P less than 0.01) and a 10% decrease in CL (0.87+/-0.19 litre kPa-1 to 0.81+/-0.22, P less than 0.01). These changes were associated with a significant increase in systolic arterial pressure and heart rate during clinical stages of anaesthesia (end-tidal enflurane, 1.3+/-0.4%, PaCO2 5.20+/-0.53 kPa). These changes did not correlate with depth of anaesthesia, but all returned to the pre-irritation value within 5 min. There was no difference in subjects considered normal and those with COPD. Surgical stimulation did not produce significant changes in pulmonary mechanics; however, repeated broncho-carinal irritation during surgery was associated with a transient increase in RL (P less then 0.01).