Isoflurane but not mechanical ventilation promotes extravascular fluid accumulation during crystalloid volume loading.
BACKGROUND
The combination of isoflurane anesthesia and mechanical ventilation reduces urinary output and promotes redistribution of a crystalloid bolus into the extravascular space. The authors hypothesized that mechanical ventilation rather than isoflurane causes this alteration.


METHODS
The fate of a 25-ml/kg, 20-min, 0.9% saline fluid bolus was studied in four different experiments per sheep: while conscious and spontaneously ventilating (CSV), while conscious and mechanically ventilated (CMV), while anesthetized with isoflurane and mechanical ventilated (ISOMV), and while anesthetized with isoflurane and spontaneously ventilating (ISOSV).


RESULTS
By calculations based on the indicator dilution and mass balance principles, plasma expansion was similar between protocols. Isoflurane but not mechanical ventilation reduced urinary output and increased interstitial fluid volume (P < 0.001): At 180 min, mean total urinary outputs were 15.6 +/- 2.1 and 15.9 +/- 2.9 ml/kg in the CSV and CMV protocols and 2.7 +/- 0.6 and 3.1 +/- 1.1 ml/kg in the ISOSV and ISOMV protocols, respectively. The net changes in extravascular volume, assumed to be interstitial fluid volume, were 8.6 +/- 3.3 and 8.1 +/- 3.1 ml/kg, and 22.5 +/- 1.5 and 22.1 +/- 1.6 ml/kg in the corresponding protocols. Volume kinetic analysis demonstrated extravascular fluid accumulation associated with isoflurane anesthesia similar to the calculated interstitial accumulation of 20.2 +/- 0.5 and 26.5 +/- 0.3 ml/kg in the ISOSV and ISOMV protocols, respectively.


CONCLUSIONS
Isoflurane, but not mechanical ventilation, decreased urinary excretion and increased interstitial fluid volume. Volume kinetic analysis indicated "third-space" losses due to isoflurane. Perioperative fluid retention may be associated not only with surgical tissue manipulation, but with anesthesia per se.
Connolly
Cara M
CM
Resuscitation Research Laboratory, University of Texas Medical Branch, Galveston, Texas 77555-0801, USA.
Kramer
George C
GC
Hahn
Robert G
RG
Chaisson
Neil F
NF
Svensén
Christer H
CH
Kirschner
Robert A
RA
Hastings
Dennis A
DA
Chinkes
David L
DL
Prough
Donald S
DS
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000077324:Crystalloid Solutions; D005110:Extracellular Space / Q000378:metabolism*; D005260:Female; D005440:Fluid Therapy; D006439:Hemodynamics / Q000187:drug effects; D007530:Isoflurane / Q000494:pharmacology*; D007552:Isotonic Solutions; D010952:Plasma Substitutes / Q000008:administration & dosage*; D010953:Plasma Volume / Q000187:drug effects; D012121:Respiration, Artificial; D012756:Sheep; D014554:Urination / Q000187:drug effects
D018685:Anesthetics, Inhalation; D000077324:Crystalloid Solutions; D007552:Isotonic Solutions; D010952:Plasma Substitutes; D007530:Isoflurane