Evaluation of the effect of the inspired oxygen fraction on blood oxygenation during inhalant anaesthesia in horses: A systematic review with meta-analysis

Abstract

In anaesthetized horses, pronounced ventilation/perfusion mismatching often occurs. Several authors have investigated the effect of lower inspired oxygen fractions (FIO2 ) to reduce formation of absorption atelectasis. This systematic review compared the effects of low (<0.6) and high (>0.8) FIO2 on the arterial oxygen tension (PaO2 ), the alveolar-to-arterial oxygen tension difference (P(A-a)O2 ), and the PaO2/FIO2 ratio in horses during inhalation anaesthesia. Using the Systematic Review Protocol for Animal Intervention Studies, four experimental and one clinical investigations were deemed suitable for inclusion. A meta-analysis was performed on the four experimental studies. The PaO2 was significantly lower (p = 0.0007, mean difference −23.54 kPa, 95% CI −37.18, −9.90) with a lower FIO2 . However, the P(A-a)O2 was also significantly lower (p < 0.00001, mean difference −20.80 kPa, 95% CI −26.28, −15.32) when using a low FIO2 . For the PaO2/FIO2 ratio, only one study fitted the inclusion criteria, so no meta-analysis was performed. It is concluded that, while only a limited number of studies are available, the use of a higher FIO2 in horses during inhalation anaesthesia will result in higher levels of PaO2, but also a larger P(A-a)O2 difference. Further studies are needed to increase the level of evidence on this subject.