Halothane and Isoflurane Do Not Decrease Pao2 during One-Lung Ventilation in Intravenously Anesthetized Patients

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Abstract
We examined the effect of the inhalational anesthetics hal-othane (H) and isoflurane (IF) on arterial oxugenation during one-lung ventilation. Twenty consenting patients who required thoracotomy and one-lung ventilation were initially anesthetized only with the intravenous agents, di-azepam, Kentanyl, pancuronium, metocurine, and infusions of either ketatnine or methohexital. A double lumen endotracheal tube was inserted, and each patient's lungs were mechanically ventilated (two-lung ventilation, step 1) with 100% O2 while the patient was in the lateral decubitus position. After the pleura was opened, the nondependent lung was collapsed while the dependent lung continued to be ventilated with 100% O2. After serial PaO2 measurements indicated achievement of stable one-lung ventilation conditions (step 2), intravenous anesthetic agents were discontinued, and either H (n = 10) or IF (n=10) was administered (step 3) so that PETH = 7.70 ± 0.61 mm Hg and PETIF = 9.89 ± 1.08 mm Hg for more than 15 mm; at the end of step 3, PaH,/PETH = 0.82 (n = 5), PaIF/PETIF = 0.75 (n=5), PH / PETH = 0.64 (n=3), and PIF / PETIF = 0.68 (n = 3). The inhalational anesthetics were then discontinued, and intravenous agents were rein-stituted, allowing PETH and PETIF to decrease below 0.50 mm Hg (step 4). Two-lung ventilation was resumed at the end of the surgical procedure (step 5). PaO2 decreased from 442 ± 64 to 252 ± 70 mm Hg when one-lung ventilation was achieved (steps 1–2), and PaO2 increased from 258 ± 72 to 395 ± 65 mm Hg when two-lung ventilation was resumed (steps 4–5). There was no significant change in PaO2 during one-lung ventilation either before, during, or after the administration of H or IF (steps 2–3 and 3–4). The administration of both inhalational anesthetics did not cause a significant decrease in cardiac index (n = 20), 𝑄̇s/𝑄̇t, Po2 or pulmonary artery pressure (n = 10) or dependent lung compliance (n = 20). Our primary conclusion is that H and IF do not further impair arterial oxygenation during one-lung ventilation in intravenously anesthetized patients undergoing thoracotomy. Our respiratory, hernodynamic, and anesthetic depth measurements led us to our second conclusion, by the method of excluding other possible explanatory mechanisms, that these drugs probably did not inhibit hypoxic pulmonary vasoconstriction during one-lung ventilation.