Abstract
Objective—To compare the effect of 2 concentrations of oxygen in inspired gas (fraction of inspired oxygen [FIO2] 1.0 or 0.4) on pulmonary aeration and gas exchange in dogs during inhalation anesthesia.
Animals—20 healthy dogs.
Procedures—Following administration of acepromazine and morphine, anesthesia was induced in each dog with thiopental and maintained with isoflurane in 100% oxygen (100% group; n = 10) or a mixture of 40% oxygen and air (40% group; 10). Dogs were placed in dorsal recumbency and were mechanically ventilated. After surgery, spiral computed tomography (CT) of the thorax was performed and PaO2, PaCO2, and the alveolar-arterial oxygen tension difference (P[A–a]O2) were assessed. The lung CT images were analyzed, and the extent of hyperinflated (−1,000 to −901 Hounsfield units [HUs]), normally aerated (−900 to −501 HUs), poorly aerated (−500 to −101 HUs), or nonaerated (−100 to +100 HUs) areas was determined.
Results—Compared with the 100% oxygen group, the normally aerated lung area was significantly greater and the poorly aerated and nonaerated areas were significantly smaller in the 40% oxygen group. The time to CT (duration of surgery) was similar in both groups. Although PaCO2 was similar in both groups, PaO2 and P(A–a)O2 were significantly higher in the 100% oxygen group. In both groups, pulmonary atelectasis developed preferentially in caudal lung fields.
Conclusion and Clinical Relevance—In isoflurane-anesthetized dogs, mechanical ventilation with 40% oxygen appeared to maintain significantly better lung aeration and gas exchange than ventilation with 100% oxygen.
