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Anesthetic depth defined using multiple noxious stimuli during isoflurane/oxygen anesthesia. I. Motor reactions
A M Zbinden1, M Maggiorini, S Petersen-Felix
1Institute for Anesthesiology and Intensive Care, University Hospital, Bern, Switzerland.
Anesthesiology
|February 1, 1994
Summary
Different stimuli require varying inhaled anesthetic concentrations for patient response suppression. Reproducible, noninvasive methods like tetanic stimulation and trapezius squeeze can replace skin incision for assessing anesthetic potency.
Area of Science:
- Anesthesiology
- Pharmacology
Background:
- Minimal alveolar concentration (MAC) traditionally measures inhaled anesthetic potency using skin incision, a single event.
- This method limits repeated measurements and predicting responses to other stimuli.
Purpose of the Study:
- To investigate the potency of isoflurane against various noxious stimuli.
- To compare these findings with the traditional MAC for skin incision.
Main Methods:
- Determined end-tidal and arterial isoflurane concentrations in 26 patients to suppress responses to verbal command, trapezius squeeze, tetanic stimulation, laryngoscopy, skin incision, and intubation.
- Measured concentrations for 50% suppression of motor response.
Main Results:
- Isoflurane concentrations required for suppression increased in the order: vocal command < trapezius squeeze < laryngoscopy ≈ tetanic stimulation < skin incision < intubation.
- End-tidal concentrations ranged from 0.37 vol% for vocal command to 1.76 vol% for intubation.
Conclusions:
- Different stimuli necessitate distinct isoflurane concentrations to abolish motor responses.
- Tetanic stimulation and trapezius squeeze offer reproducible, noninvasive alternatives to skin incision for evaluating anesthetic potency.