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

Veterinary anaesthesia and analgesia

PubMedID: 23910627

Ferro Lopes PC, Nunes N, Sousa MG, Nishimori CT, Carareto R, Dos Santos PS, Camacho AA. The effects of different inspired oxygen fractions on gas exchange and Tei-index of myocardial performance in propofol-anesthetized dogs. Vet Anaesth Analg. 2013;.
OBJECTIVE
To evaluate the influence of different inspired oxygen fractions (FiO2 ) 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 FiO2  = 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 (SaO2 ), heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), stroke index (SI), pre-ejection 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 (PAO2 ), alveolar-arterial oxygen gradient (AaDO2 ), arterial oxygen partial pressure/inspired oxygen fraction ratio (PaO2 /FiO2 ), arterial-to-alveolar oxygen tension ratio (PaO2 /PAO2 ), respiratory index (RI), oxygen delivery (D·O2 ), PEP/LVET ratio, isovolumic relaxation time (IVRT) and Tei-index.

RESULTS
At T30, PaCO2 in F100 was higher than in F21. The AaDO2 mean in F100 was greater than in other treatments. PaO2 /FiO2 in F21 was lower than F100 and F80 at T0 and than in F80 and F60 at T15. At T15, PaO2 /PAO2 and RI in F100 were higher than in F80, F60 and F21. At T30, PaO2 /PAO2 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 FiO2 .

CLINICAL RELEVANCE
An FiO2 of 1.0 and 0.21 impaired respiratory efficiency.