Differential effects of isoflurane and propofol on upper airway dilator muscle activity and breathing.

Abstract

BACKGROUND:

Anesthesia impairs upper airway integrity, but recent data suggest that low doses of some anesthetics increase upper airway dilator muscle activity, an apparent paradox. The authors sought to understand which anesthetics increase or decrease upper airway dilator muscle activity and to study the mechanisms mediating the effect.

METHODS:

The authors recorded genioglossus electromyogram, breathing, arterial blood pressure, and expiratory carbon dioxide in 58 spontaneously breathing rats at an estimated ED50 (median effective dose) of isoflurane or propofol. The authors further evaluated the dose-response relations of isoflurane under different study conditions: (1) normalization of mean arterial pressure, or end-expiratory carbon dioxide; (2) bilateral lesion of the Kölliker-Fuse nucleus; and (3) vagotomy. To evaluate whether the markedly lower inspiratory genioglossus activity during propofol could be recovered by increasing flow rate, a measure of respiratory drive, the authors performed an additional set of experiments during hypoxia or hypercapnia.

RESULTS:

In vagally intact rats, tonic and phasic genioglossus activity were markedly higher with isoflurane compared with propofol. Both anesthetics abolished the genioglossus negative pressure reflex. Inspiratory flow rate and anesthetic agent predicted independently phasic genioglossus activity. Isoflurane dose-dependently decreased tonic and increased phasic genioglossus activity, and increased flow rate, and its increasing effects were abolished after vagotomy. Impairment of phasic genioglossus activity during propofol anesthesia was reversed during evoked increase in respiratory drive.

CONCLUSION:

Isoflurane compared with propofol anesthesia yields higher tonic and phasic genioglossus muscle activity. The level of respiratory depression rather than the level of effective anesthesia correlates closely with the airway dilator muscle function during anesthesia.

• Authors: Matthias Eikermann, Atul Malhotra, Philipp Fassbender, Sebastian Zaremba, Amy S Jordan, Shiva Gautam, David P White, Nancy L Chamberlin
• Journal: Anesthesiology (Anesthesiology) Vol. 108 Issue 5 Pg. 897-906 (May 2008) ISSN: 1528-1175 [Electronic] United States
• PMID: 18431126 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Isoflurane
• Propofol

Topics

• Animals
• Blood Pressure (drug effects)
• Dose-Response Relationship, Drug
• Electromyography
• Isoflurane (pharmacology)
• Male
• Models, Animal
• Motor Activity (drug effects)
• Muscle, Skeletal (drug effects, physiology)
• Propofol (pharmacology)
• Rats
• Rats, Sprague-Dawley
• Respiratory Muscles (drug effects, physiology)
• Respiratory Physiological Phenomena (drug effects)