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Volatile anesthetics depress spinal motor neurons
1Department of Anesthesia, University of California, San Francisco 94143-0648, USA. ira rampil@vaxine ucsf.edu or http://ira-mac.ucsf.edu
Anesthesiology
|July 1, 1996
Summary
Inhaled anesthetics like desflurane and sevoflurane reduce spinal motor neuron excitability, contributing to surgical immobility. This effect was observed across multiple anesthetic agents at equipotent concentrations.
Area of Science:
- Anesthesiology
- Neurophysiology
Background:
- Spinal alpha-motor neuron depression is linked to isoflurane-induced surgical immobility.
- Investigated if other inhaled anesthetics share this motor neuron depressant effect.
Purpose of the Study:
- To test if inhaled anesthetics, besides isoflurane, reduce spinal motor neuron excitability.
- To quantify the effect of different anesthetics on motor neuron function using F-wave analysis.
Main Methods:
- F-wave amplitude was measured in rats under desflurane, enflurane, halothane, or sevoflurane.
- Anesthetics were administered at various equipotent concentrations (0.6-1.6 minimum alveolar concentration [MAC]), including with nitrous oxide.
- F waves were recorded via electromyography after tibial nerve stimulation.
Main Results:
- All tested inhaled anesthetics dose-dependently decreased F-wave amplitude and increased M-F latency.
- M-wave amplitude remained unaffected, indicating preserved nerve conduction.
- Anesthetics reduced the F/M ratio, suggesting depressed motor neuron excitability.
Conclusions:
- Inhaled anesthetics tested appear to depress spinal motor neuron excitability.
- This depression may contribute to surgical immobility and is comparable at equipotent concentrations.
- The mechanism is hypothesized to involve hyperpolarization, but pre- vs. postsynaptic effects require further study.