Acute effects of fentanyl on breathing pattern in anaesthetized subjects.
BACKGROUND
The predominant effect of opioids on respiratory pattern during anaesthesia is an increase in the duration of expiration (an effect on 'timing'), but there may also be changes in tidal volume (an effect on 'drive'). Timing and drive are controlled by separate neuronal systems, but are infrequently considered individually. The effects of opioids on breathing are not well characterized clinically because changes in carbon dioxide and anaesthetic levels usually occur at the same time, and can obscure the effects of the opioid.


METHODS
To study these effects in isolation, we established stable mild hypercapnia in female patients breathing spontaneously during sevoflurane anaesthesia, and then gave fentanyl 0.5 microg kg(-1) i.v. End-tidal carbon dioxide and sevoflurane concentrations were maintained constant, and the changes in timing of inspiration, expiration and tidal volume were measured.


RESULTS
The duration of inspiration increased by 30%, and the duration of expiration increased by 95%. Tidal volume increased in proportion to inspiratory duration, and the pattern of flow during the breath was recognizably changed, with a reduction in the rate of increase of flow at the onset of inspiration.


CONCLUSIONS
Small doses of opioid given when anaesthesia and carbon dioxide are stable affect respiratory timing predominantly, but in addition changes in the pattern of motor output can be detected.
Ferguson
L M
LM
University Department of Anaesthesia, Critical Care and Pain Medicine Edinburgh University, Scotland, UK.
Drummond
G B
GB
D000328:Adult; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation; D002245:Carbon Dioxide / Q000502:physiology; D045853:Exhalation / Q000187:drug effects; D005260:Female; D005283:Fentanyl / Q000494:pharmacology*; D006801:Humans; D001239:Inhalation / Q000187:drug effects; D008738:Methyl Ethers; D008875:Middle Aged; D015656:Respiratory Mechanics / Q000187:drug effects*; D000077149:Sevoflurane; D013990:Tidal Volume / Q000187:drug effects
D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D002245:Carbon Dioxide; D000077149:Sevoflurane; D005283:Fentanyl