Respiratory mechanical properties during fentanyl and alfentanil anaesthesia.

The purpose of this study was to assess the effects on respiratory mechanics of fentanyl and alfentanil in 20 subjects to be submitted to coronary artery bypass grafting. Using the end inflation occlusion method (EIOM) we obtained the elastance (E) and resistance (R) of the total respiratory system (rs), thoracic wall (w) and lungs (L). The total respiratory system was divided into thoracic wall and lungs by using an oesophageal catheter. The data were recorded before, immediately after, and two, five and ten minutes after fentanyl and alfentanil iv bolus, at doses of 30 and 120 micrograms.kg-1, respectively. The Ers increased at two, five and ten minutes and the EL at ten minutes after drug administration. The Rrs,min and RL,min increased at two, five and ten minutes and the RL,max at five and ten minutes. Both drugs provoked no change in Ew or Rw. It is concluded that the increased in Rrs,min and RL,min could be explained by opioid bronchoconstriction. No differences were found between the effects of fentanyl and alfentanil on respiratory mechanics.