Reduction in post-intubation respiratory resistance by isoflurane and albuterol

This study examined the bronchodilating effects of 0.6 MAC and 1.1 MAC isoflurane (ISF) on respiratory system resistance (Rrs) following tracheal intubation and determined whether albuterol supplements that effect.

Sixty-seven adult patients were anaesthetized with 2 micrograms.kg-1 fentanyl and 5 mg.kg-1 thiopentone and their tracheas intubated following administration of 1 mg.kg-1 succinylcholine. Respiratory system resistance was measured following intubation and the patients then randomized to receive either 1.1 MAC ISF in oxygen or 0.6 MAC ISF in 50% nitrous oxide and oxygen. Ten minutes later, Rrs was again measured. Patients were then further randomized to receive albuterol or a placebo using incremental doses of 2, 5, and 10 puffs (albuterol puff = 90 micrograms) delivered via a metered dose inhaler at ten minute intervals.

Isoflurane at 1.1 MAC decreased post-intubation Rrs by 23 +/- 5% (mean +/- sem) whereas the decrease was only 7 +/- 5% for 0.6 MAC ISF (P < 0.01). Two puffs of albuterol resulted in a further decrease of 12 +/- 3% (mean +/- sem) in Rrs compared with a 2 +/- 4% decrease in the placebo groups (P < 0.05). Additional puffs of albuterol resulted in no further changes in Rrs.

We conclude that following tracheal intubation the reduction in Rrs produced by ISF is highly concentration dependent. Albuterol results in a small further reduction in Rrs.