Influence of hypovolemia on the electroencephalographic effect of isoflurane in a swine model.
BACKGROUND
Hypovolemia alters the effect of several intravenous anesthetics by influencing pharmacokinetics and end-organ sensitivity. The authors investigated the influence of hypovolemia on the effect of an inhalation anesthetic, isoflurane, in a swine hemorrhage model.


METHODS
Eleven swine were studied. After animal preparation with inhalation of 2% isoflurane anesthesia, the inhalation concentration was decreased to 0.5% and maintained at this level for 25 min before being returned to 2% (control). After 25 min, hypovolemia was induced by removing 14 ml/kg of the initial blood volume via an arterial catheter. After a 25-min stabilization period, the inhalation concentration was decreased to 0.5%, maintained at this level for 25 min, and then returned to 2% (20% bleeding). After another 25 min, a further 7 ml/kg blood was collected, and the inhalation concentration was altered as before (30% bleeding). End-tidal isoflurane concentrations and an electroencephalogram were recorded throughout the study. Spectral edge frequency was used as a measure of the isoflurane effect, and pharmacodynamics were characterized using a sigmoidal inhibitory maximal effect model for the spectral edge frequency versus end-tidal concentration.


RESULTS
There was no significant difference in the effect of isoflurane among the conditions used. Hypovolemia did not shift the concentration-effect relation (the effect site concentration that produced 50% of the maximal effect was 1.2 +/- 0.2% under control conditions, 1.2 +/- 0.2% with 20% bleeding, and 1.1 +/- 0.2% with 30% bleeding).


CONCLUSIONS
Hypovolemia does not alter the electroencephalographic effect of isoflurane, in contrast to several intravenous anesthetics.
Kurita
Tadayoshi
T
Department of Anesthesiology and Intensive Care, Hamamatsu University School of Medicine, Japan. tadkur@hama-med.ac.jp
Morita
Koji
K
Fukuda
Kazushige
K
Uraoka
Masahiro
M
Takata
Kotaro
K
Sanjo
Yoshimitsu
Y
Sato
Shigehito
S
D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D006400:Hematocrit; D006439:Hemodynamics / Q000187:drug effects; D006470:Hemorrhage / Q000503:physiopathology; D020896:Hypovolemia / Q000503:physiopathology*; D007530:Isoflurane / Q000493:pharmacokinetics / Q000494:pharmacology*; D019344:Lactic Acid / Q000097:blood; D013552:Swine
D018685:Anesthetics, Inhalation; D019344:Lactic Acid; D007530:Isoflurane