The effects of different inspired oxygen fractions on gas exchange and Tei-index of myocardial performance in propofol-anesthetized dogs

Abstract

Objective To evaluate the influence of different inspired oxygen fractions (FiO(2)) on pulmonary oxygen exchange and Tei-index of myocardial performance in propofol-anesthetized dogs.Study design Prospective crossover, randomized, experimental trial.Animals Eight adult dogs weighing 8.6 +/- 1.8 kg.Methods The animals were anesthetized on five occasions, receiving either an FiO(2) = 1.0 (F100), 0.8 (F80), 0.6 (F60), 0.4 (F40) or 0.21 (F21). Propofol was used for induction (6.45 +/- 0.69 mgkg(-1) IV) followed by a continuous rate infusion (CRI, 0.7 mgkg(-1) minute(-1)). The dogs breathed spontaneously. The initial measurements of arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2), arterial hemoglobin saturation (SaO(2)), heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), stroke index (SI), preejection period (PEP) and left ventricular ejection time (LVET) were performed 30 minutes after beginning the CRI (T0) and then, at 15-minute intervals (T15-T60). From these measurements the following were calculated; alveolar oxygen partial pressure (PAO(2)), alveolar-arterial oxygen gradient (AaDO(2)), arterial oxygen partial pressure/inspired oxygen fraction ratio (PaO2/FiO(2)), arterial-to-alveolar oxygen tension ratio (PaO2/PAO(2)), respiratory index (RI), oxygen delivery ((D) over dotO(2)), PEP/LVET ratio, isovolumic relaxation time (IVRT) and Tei-index.Results At T30, PaCO2 in F100 was higher than in F21. The AaDO(2) mean in F100 was greater than in other treatments. PaO2/FiO(2) in F21 was lower than F100 and F80 at T0 and than in F80 and F60 at T15. At T15, PaO2/PAO(2) and RI in F100 were higher than in F80, F60 and F21. At T30, PaO2/PAO(2) in F21 was lower than in F100 and F60. At T30, PEP/LVET in F100 was higher than F80, F40 and F21, which was lower than F80 and F40.Conclusion The Tei-index and cardiovascular parameters are not affected by different FiO(2).