Nitrous oxide decreases shivering threshold in rabbits less than isoflurane.
BACKGROUND
Comparable minimum alveolar concentration (MAC) fractions of volatile anaesthetics produce similar thermoregulatory impairment. Nitrous oxide, however, decreases the vasoconstriction threshold less than sevoflurane or isoflurane. We tested the hypothesis that nitrous oxide also decreases shivering threshold less than isoflurane alone or in combination.


METHODS
Twenty-four rabbits were assigned randomly to one of three 0.3 MAC anaesthetic regimens: (i) nitrous oxide 69%; (ii) nitrous oxide 35% and isoflurane 0.3%; or (iii) isoflurane 0.6%. Body temperature was lowered by perfusing 10 degrees C water through a U-shaped thermode positioned in the colon. Shivering was evaluated by inspection.


RESULTS
The rabbits anaesthetized with nitrous oxide alone shivered at 37.0 (0.5) degrees C (P<0.01 vs other groups). In those given the nitrous oxide and isoflurane combination, the shivering threshold was 36.4 (0.5) degrees C and that in the isoflurane group was 35.9 (0.4) degrees C.


CONCLUSIONS
This study indicates that nitrous oxide reduces the shivering threshold less than isoflurane.
Imamura
M
M
Yamanashi Medical University, Yamanishi, Japan.
Matsukawa
T
T
Ozaki
M
M
Sessler
D I
DI
Nishiyama
T
T
Okuyama
K
K
Kumazawa
T
T
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D009609:Nitrous Oxide / Q000494:pharmacology*; D011817:Rabbits; D012768:Shivering / Q000187:drug effects* / Q000502:physiology
D018685:Anesthetics, Inhalation; D007530:Isoflurane; D009609:Nitrous Oxide