The vasoconstriction threshold is increased in obese patients during general anaesthesia.
BACKGROUND
In anaesthetized patients, body temperature decreases often, but overweight patients become less hypothermic. Obesity in itself protects body heat, and thermoregulatory reflexes may maintain normothermia in obese patients. We tested the hypothesis that even slight obesity increases the vasoconstriction threshold.


METHODS
Twenty male patients aged 30-65 years scheduled for open abdominal surgery were allocated to two groups: body fat >/=25% (obese group, n = 10), or <25% (normal weight group, n = 10). Anaesthesia was maintained with 0.4% isoflurane and opioid. The thermoregulatory vasoconstriction threshold was defined by the tympanic membrane temperature at which the skin temperature gradient equalled 0 degrees C. Plasma adrenaline, noradrenaline and leptin were measured.


RESULTS
Age, height, heart rate and blood pressure did not differ between the two groups of patients. In the obese group the vasoconstriction threshold was higher than that in the normal weight group: 36.0 +/- 0.1 vs. 35.5 +/- 0.2 degrees C. Consequently, after 4 h of anaesthesia, the core temperature was highest in the obese patients: 36.4 +/- 0.1 vs. 35.5 +/- 0.2 degrees C.


CONCLUSIONS
These results suggest that core temperature is maintained in obese patients because their vasoconstriction threshold to a low environmental temperature is high.
Kasai
T
T
Department of Anaesthesiology, Kyoto Prefectural University of Medicine, Kyoto, Japan. kasai@koto.kpu-m.ac.jp
Hirose
M
M
Matsukawa
T
T
Takamata
A
A
Tanaka
Y
Y
D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D001833:Body Temperature Regulation / Q000502:physiology; D003080:Cold Temperature; D004837:Epinephrine / Q000097:blood; D005385:Fingers / Q000098:blood supply; D006801:Humans; D020738:Leptin / Q000097:blood; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D009765:Obesity / Q000503:physiopathology*; D012039:Regional Blood Flow / Q000502:physiology; D012881:Skin Temperature; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D020738:Leptin; D009638:Norepinephrine; D004837:Epinephrine