%0 Journal Article
%T Effect of 50% and maximal inspired oxygen concentrations on respiratory variables in isoflurane-anesthetized horses
%A John AE Hubbell
%A Turi K Aarnes
%A Richard M Bednarski
%A Phillip Lerche
%A William W Muir
%J BMC Veterinary Research
%D 2011
%I BioMed Central
%R 10.1186/1746-6148-7-23
%X Arterial partial pressures of O2 were significantly higher than preanesthetic levels at all times during anesthesia in the >0.95 FiO2 group. Arterial partial pressures of O2 did not change from preanesthetic levels in the 0.5 FiO2 group but were significantly lower than in the >0.95 FiO2 group from 15 to 90 min of anesthesia. Alveolar to arterial O2 tension difference was increased significantly in both groups during anesthesia compared to preanesthetic values. The alveolar to arterial O2 tension difference was significantly higher at all times in the >0.95 FiO2 group compared to the 0.5 FiO2 group. Oxygen delivery did not change from preanesthetic values in either group during anesthesia but was significantly lower than preanesthetic values 10 min after anesthesia in the 0.5 FiO2 group. Shunt fraction increased in both groups during anesthesia attaining statistical significance at varying times. Shunt fraction was significantly increased in both groups 10 min after anesthesia but was not different between groups. Alveolar dead space ventilation increased after 3 hr of anesthesia in both groups.Reducing FiO2 did not change alveolar dead space ventilation or shunt fraction in dorsally recumbent, mechanically ventilated horses during 3 hr of isoflurane anesthesia. Reducing FiO2 in dorsally recumbent isoflurane anesthetized horses does not improve oxygenation or oxygen delivery.Maximal FiO2 values (>95%) have been administered to horses to maintain or improve the arterial partial pressure of oxygen (PaO2) and tissue oxygenation since the advent of inhalant anesthesia [1]. Maximal FiO2 concentrations are used in the belief that their use optimizes arterial O2 content (CaO2) and O2 delivery (DO2) to tissues providing cardiac output (Q) is maintained [2]. Lower than expected (subnormal) PaO2 values are frequently encountered during equine inhalant anesthesia despite the use of maximal FiO2 [3-6]. Subnormal PaO2 values usually develop during the first 30 to 90 min of anest
%U http://www.biomedcentral.com/1746-6148/7/23