Influence of hemorrhagic shock and subsequent fluid resuscitation on the electroencephalographic effect of isoflurane in a swine model.
BACKGROUND
The authors have previously reported that hemorrhage does not alter the electroencephalographic effect of isoflurane under conditions of compensated hemorrhagic shock. Here, they have investigated the influence of decompensated hemorrhagic shock and subsequent fluid resuscitation on the electroencephalographic effect of isoflurane.


METHODS
Twelve swine were anesthetized through inhalation of 2% isoflurane. The inhalational concentration was then decreased to 0.5% and maintained for 25 min, before being returned to 2% and maintained for 25 min (control period). Hemorrhagic shock was then induced by removing 28 ml/kg blood over 30 min. After a 30-min stabilization period, the inhalational concentration was varied as in the control period. Finally, fluid infusion was performed over 30 min using a volume of hydroxyethyl starch equivalent to the blood withdrawn. After a 30-min stabilization period, the inhalational concentration was again varied as in the control period. End-tidal isoflurane concentrations and spectral edge frequency were recorded throughout the study. The pharmacodynamics were characterized using a sigmoidal inhibitory maximal effect model for spectral edge frequency versus effect site concentration.


RESULTS
Decompensated hemorrhagic shock slightly but significantly shifted the concentration-effect relation to the left, demonstrating a 1.12-fold decrease in the effect site concentration required to achieve 50% of the maximal effect in the spectral edge frequency. Fluid resuscitation reversed the onset of isoflurane, which was delayed by hemorrhage, but did not reverse the increase in end-organ sensitivity.


CONCLUSIONS
Although decompensated hemorrhagic shock altered the electroencephalographic effect of isoflurane regardless of fluid resuscitation, the change seemed to be minimal, in contrast to several intravenous anesthetics.
Kurita
Tadayoshi
T
Department of Anesthesiology and Intensive Care, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu 431-3192, 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; D004569:Electroencephalography / Q000187:drug effects*; D005440:Fluid Therapy; D006439:Hemodynamics / Q000187:drug effects; D006895:Hydroxyethyl Starch Derivatives / Q000627:therapeutic use; D007530:Isoflurane / Q000493:pharmacokinetics / Q000494:pharmacology*; D010952:Plasma Substitutes / Q000627:therapeutic use; D012151:Resuscitation; D012771:Shock, Hemorrhagic / Q000188:drug therapy / Q000503:physiopathology*; D013552:Swine
D018685:Anesthetics, Inhalation; D006895:Hydroxyethyl Starch Derivatives; D010952:Plasma Substitutes; D007530:Isoflurane