Insufflated halothane increases venous admixture less than nitroprusside in canine atelectasis.
Although it generally is agreed that halothane is a pulmonary vasodilator, its effect on venous admixture and hypoxic pulmonary vasoconstriction are more controversial. The effects of 2.4% halothane on pulmonary vascular resistance and venous admixture were investigated in an isolated canine lobe made atelectatic. Halothane was administered by three different methods: insufflation, addition to the pulmonary artery blood through a bubble deoxygenator, or a combination of both techniques. Pulmonary vascular resistance was divided into arterial, venous, and middle segmental resistance by a vascular occlusion technique. Middle resistance increased with 3% O2 ventilation (0.0238 +/- 0.0092 cmH2O.ml-1.min-1) or after production of atelectasis (0.0225 +/- 0.0074 cmH2O.ml-1.min-1), compared to control ventilation in the nonatelectatic lung 0.01 +/- 0.0067 cmH2O.ml-1.min-1). Halothane by any delivery method variably decreased middle resistance, with increasing potency from addition of halothane through the bubble deoxygenator (0.0118 +/- 0.0047 cmH2O.ml-1.min-1) to halothane insufflation (0.0072 +/- 0.0058 cmH2O.ml-1.min-1), and finally to a combination of both techniques (0.0026 +/- 0.0041 cmH2O.ml-1.min-1). In contrast to vascular resistance, venous admixture in the atelectatic (8 +/- 5%) and nonatelectatic lobes (7 +/- 4%) was increased with halothane insufflation (11 +/- 4%), addition of halothane through the bubble deoxygenator (26 +/- 16%), and a combination of both techniques (22 +/- 13%). Compared to intravenous nitroprusside (26 +/- 12%), halothane insufflation was less potent in increasing venous admixture when total pulmonary vascular resistances were of similar magnitude (0.0526 +/- 0.0112 and 0.0484 +/- 0.0088 cmH2O.ml-1.min-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Johnson
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Department of Anaesthesia, Royal University Hospital, University of Saskatchewan, Saskatoon, Canada.
Hurst
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Mayers
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D000818:Animals; D004285:Dogs; D006221:Halothane / Q000008:administration & dosage / Q000494:pharmacology*; D066298:In Vitro Techniques; D007327:Insufflation; D008168:Lung / Q000098:blood supply; D009599:Nitroprusside / Q000494:pharmacology*; D011650:Pulmonary Alveoli; D001261:Pulmonary Atelectasis / Q000503:physiopathology*; D011652:Pulmonary Circulation / Q000187:drug effects* / Q000502:physiology; D012119:Respiration / Q000187:drug effects* / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology
D009599:Nitroprusside; D006221:Halothane