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Isoflurane alters shivering patterns and reduces maximum shivering intensity
T Ikeda1, J S Kim, D I Sessler
1Department of Anesthesia, University of California, San Francisco, 94143-0648, USA.
Anesthesiology
|May 14, 1998
Summary
Isoflurane anesthesia alters shivering patterns, lowering the threshold and increasing initial gain due to clonic activity. However, it also reduces the maximum shivering intensity during hypothermia.
Area of Science:
- Anesthesiology
- Physiology
- Thermoregulation
Background:
- Shivering is characterized by threshold, gain, and maximum intensity.
- Isoflurane can induce clonic muscular activity, potentially altering shivering gain.
- Volatile anesthetics may limit maximum shivering intensity by inhibiting muscle strength.
Purpose of the Study:
- To evaluate the effect of isoflurane on shivering patterns.
- To determine isoflurane's impact on shivering gain and maximum intensity.
Main Methods:
- Ten volunteers underwent control and isoflurane (0.7% end-tidal) protocols.
- Skin temperature was maintained at 31°C, and core temperature was reduced to induce hypothermia.
- Shivering threshold, gain (oxygen consumption slope), and electromyography for clonic activity were assessed.
Main Results:
- Isoflurane decreased the shivering threshold (36.4°C to 34.2°C) and increased shivering gain (-684 to -1483 ml·min⁻¹·°C⁻¹).
- Shivering presented as bursts with quiescent periods under isoflurane, unlike linear increases in controls.
- Maximum shivering intensity was reduced by isoflurane (706 to 489 ml/min), with increased electromyographic activity at clonic frequencies.
Conclusions:
- Isoflurane anesthesia changes shivering patterns to a 'saw-tooth' pattern during hypothermia.
- Clonic activity combined with shivering increases initial gain, while peripheral inhibition limits maximum shivering intensity.
- Anesthetic effects on shivering gain and intensity have implications for thermoregulation during anesthesia.