Ventilation-perfusion relationships during halothane anaesthesia and mechanical ventilation. Effects of varying inspired oxygen concentration.
Ventilation-perfusion relationships (VA/Q), assessed by a multiple inert-gas elimination technique, were studied during halothane anaesthesia and mechanical ventilation at different inspiratory oxygen fractions (FIO2). All nine patients (mean age 65 years, five smokers) displayed unaltered VA/Q distributions with increasing FIO2 from a mean of 29% to 53%. A further increase in FIO2 to a mean of 85% caused an increase in true shunt (VA/Q = 0) from 7 to 10% of cardiac output (P less than 0.01), but no increase in "low" VA/Q (VA/Q less than 0.1). On the return to FIO2 of 29%, true shunt was reduced to the initial level. The findings may fit in with release of hypoxic vasoconstriction when FIO2 is increased to 85%, or the opening up of a certain population of shunt vessels.
D000368:Aged; D000769:Anesthesia, Inhalation; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000502:physiology; D005260:Female; D006221:Halothane / Q000494:pharmacology*; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000502:physiology*; D012121:Respiration, Artificial; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects; D014692:Ventilation-Perfusion Ratio / Q000187:drug effects*
D002245:Carbon Dioxide; D010100:Oxygen; D006221:Halothane