Evaluation of the Effect of the Inspired Oxygen Fraction on Blood Oxygenation during Inhalant Anaesthesia in Horses: A Systematic Review with Meta-Analysis.

Ioannis Savvas,Christina Braun,Yves Moens,Francesco Staffieri,Kiriaki Pavlidou,Stijn Schauvliege

doi:10.3390/ani11082245

Abstract

Simple SummaryIn anaesthetized horses, blood oxygenation impairment often occurs. This systematic review compared the effects of low and high inspired oxygen fractions on the arterial oxygen tension and other pulmonary gas exchange parameters in horses during inhalation anaesthesia. Five studies, four experimental and one clinical, were deemed suitable for inclusion. A meta-analysis was performed on the four experimental studies. The oxygen partial pressure was significantly lower with a lower inspired oxygen fraction. However, indices of pulmonary gas exchange were significantly worsened. It is concluded that, while only a limited number of studies are available, the use of a higher inspired oxygen fraction in horses during inhalation anaesthesia will result in higher levels of oxygen in the blood; it will also worsen the lung gas exchange status. Further studies are needed to increase the level of evidence on this subject.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.

Highlights

Since almost sixty years ago, studies in humans have shown that during halothane anaesthesia with spontaneous breathing, ventilation/perfusion relationship (V/Q) abnormalities and intrapulmonary shunt may develop, resulting in a reduction in the arterial partial pressure of oxygen (PaO2 )
One of the main causes of impaired oxygenation of the blood seems to be the development of atelectasis during anaesthesia, which reduces lung compliance and PaO2
This was confirmed in computed tomography (CT) studies in humans, which revealed atelectasis of the most dependent parts of the lungs in 90% of the anaesthetised patients [2,3]

Summary

Introduction

Since almost sixty years ago, studies in humans have shown that during halothane anaesthesia with spontaneous breathing, ventilation/perfusion relationship (V/Q) abnormalities and intrapulmonary shunt may develop, resulting in a reduction in the arterial partial pressure of oxygen (PaO2 ). One of the main causes of impaired oxygenation of the blood seems to be the development of atelectasis during anaesthesia, which reduces lung compliance and PaO2. There is supporting evidence that this condition may develop in humans, horses, and other animal species [1]. This was confirmed in computed tomography (CT) studies in humans, which revealed atelectasis of the most dependent parts of the lungs in 90% of the anaesthetised patients [2,3]. Gas absorption, and surfactant impairment are the major causative factors for atelectasis development [2]

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