title: Effect of low isoflurane concentrations on the ventilation-perfusion distribution in injured canine lungs.
abstract: BACKGROUND
  Rapid recovery and weaning from ventilatory support and cardiovascular stability are suggested advantages of isoflurane inhalation, in concentrations ranging from 0.1 to 0.6 vol%, for long-term sedation in mechanical ventilated patients. This study was designed to determine whether isoflurane in low concentrations impairs pulmonary gas exchange by increasing ventilation and perfusion (V(A)/Q) mismatch during lung injury.
  
  
  METHODS
  Fourteen anesthetized dogs received in random order 0, 0.25, or 0.5 vol% end-tidal isoflurane before and after induction of lung injury with oleic acid. Gas exchange was assessed by blood gas analysis and by estimating the V(A)/Q distributions using the multiple inert gas elimination technique.
  
  
  RESULTS
  Administration of oleic acid produced a lung injury with severe V(A)/Q mismatch and 38 +/- 4% intrapulmonary shunting of blood. During lung injury, isoflurane accounted for a dose-related increase in blood flow to shunt units from 38 +/- 4 to 42 +/- 3 (0.25 vol%) and 48 +/- 4% (0.5 vol%) (P < 0.05), dispersion pulmonary blood flow distribution from 0.94 +/- 0.07 to 1.01 +/- 0.09 (0.25 vol%) and 1.11 +/- 0.11% (0.5 vol%) (P < 0.05), and a decrease in perfusion of normal V(A)/Q units from 58 +/- 5 to 55 +/- 4 (0.25 vol%) and 50 +/- 4% (0.5 vol%) (P < 0.05) (mean +/- SE). Isoflurane decreased arterial oxygen partial pressure from 72 +/- 4 to 62 +/- 4 mmHg (0.25 vol%) and 56 +/- 4 mmHg (0.5 vol%) (P < 0.05) and oxygen delivery from 573 +/- 21 to 529 +/- 19 ml. kg. min (0.25 vol%) and 505 +/- 22 ml. kg. min (0.5 vol%) (P < 0.05). Gas exchange, perfusion of shunt and normal V(A)/Q units, and pulmonary blood flow distribution was similar in absence of lung injury with and without isoflurane. Isoflurane 0.5 vol% lowered cardiac output during all conditions (P < 0.05). CONCLUSIONS Inhalation of low concentrations of isoflurane contributed to increased V(A)/Q mismatch and decreased systemic blood flow and oxygen delivery in mechanically ventilated animals with injured lungs.
authors.affiliation: Department of Anesthesiology, University of South Florida College of Medicine, Tampa, USA. putensen@uni-bonn.de
authors.forename: Christian
authors.initials: C
authors.lastname: Putensen
authors.forename: Jukka
authors.initials: J
authors.lastname: Räsänen
authors.forename: Gabriele
authors.initials: G
authors.lastname: Putensen-Himmer
authors.forename: John B
authors.initials: JB
authors.lastname: Downs
mesh_terms: D000465:Algorithms; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis; D004285:Dogs; D006439:Hemodynamics / Q000187:drug effects; D007530:Isoflurane / Q000494:pharmacology*; D008168:Lung / Q000187:drug effects*; D008171:Lung Diseases / Q000139:chemically induced* / Q000503:physiopathology*; D005741:Noble Gases / Q000032:analysis; D019301:Oleic Acid; D010101:Oxygen Consumption / Q000187:drug effects; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000187:drug effects; D014692:Ventilation-Perfusion Ratio / Q000187:drug effects*
chemical_list: D018685:Anesthetics, Inhalation; D005741:Noble Gases; D019301:Oleic Acid; D007530:Isoflurane