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Correspondence  |   March 1995
Reply: Measurements of Occlusion Pressure during Anesthesia with Volatile Anesthetics in Humans
Author Notes
  • Jaume Canet, M.D., Staff Anesthesiologists, Department of Anesthesiology, Hospital Universitari Germans Trias i Pujol Badalona, 08916 Barcelona, Spain.
  • Joaquin Sanchis, M.D., Professor of Respiratory Medicine Hospital de Sant Paul, Universitat Autonoma de Barcelona Barcelona, Spain.
Article Information
Correspondence
Correspondence   |   March 1995
Reply: Measurements of Occlusion Pressure during Anesthesia with Volatile Anesthetics in Humans
Anesthesiology 3 1995, Vol.82, 799. doi:
Anesthesiology 3 1995, Vol.82, 799. doi:
In Reply:—When we stated that only a single previous work had studied occlusion pressure at increasing concentrations of haloge-nated agents, in this case enflurane, [1 ] we failed to mention the work by Drummond measuring occlusion pressure also with enflurane at 2% and 3% in six subjects. [2 ]
We think that our study does not contradict Drummond's finding that the ventilatory depression observed at increasing concentrations of enflurane could be attributable entirely to a reduction in central drive. We studied two different halogenated anesthetics, i.e., halothane and isoflurane, and observed significant differences between them in the mechanisms of ventilatory depression. The inspired concentrations of enflurane that Drummond's patients received were at the higher range of concentrations we used with isoflurane, which showed clear central ventilatory depression. During halothane anesthesia at 1.2 MAC, inspiratory occlusion pressure was greater than in the awake state making unlikely the possibility of central respiratory depression. The observed increase in end-tidal carbon dioxide therefore may be attributable to a significant peripheral ventilatory depression. A mathematical analysis of the occlusion pressure waveform also showed differences between the two anesthetics and at different concentrations, suggesting different effects on the mechanisms of transformation of central respiratory drive into occlusion pressure. Investigation of the effects of other drugs such opioids or atropine could elucidate the different ways of inducing ventilatory depression.
At any rate, analysis of waveform occlusion pressure curves, in agreement with Drummond's suggestion, certainly should be helpful for investigating the neural mechanisms of respiratory depression.
Jaume Canet, M.D., Staff Anesthesiologists, Department of Anesthesiology, Hospital Universitari Germans Trias i Pujol Badalona, 08916 Barcelona, Spain.
Joaquin Sanchis, M.D., Professor of Respiratory Medicine Hospital de Sant Pau, Universitat Autonoma de Barcelona Barcelona, Spain.
(Accepted for publication December 9, 1994.)
REFERENCES
Wahba WM: Analysis of ventilatory depression by enflurane during clinical anesthesia Anesth Analg 59:103-109, 1980.
Drummond GB: Comparison of decreases in ventilation caused by enflurane and fentanyl during anaesthesia Br J Anaesth 55:825-835, 1983.