Oxygen supplementation before induction of general anaesthesia in horses

Abstract

Summary Reasons for performing study Hypoventilation or apnoea, caused by the induction of general anaesthesia, may cause hypoxaemia. Preoxygenation may lengthen the period before this happens. No scientific studies are published on preoxygenation in equine anaesthesia. Objectives To determine whether supplementation of oxygen at a flow rate of 15 l/min for 3 min via a nasal cannula before induction of general anaesthesia is effective in elevating the arterial partial pressure of oxygen (PaO2) directly after induction. Study design Randomised, prospective clinical trial. Methods A total of 18 American Society of Anesthesiologists physical status 1 or 2 adult horses undergoing elective anaesthesia were randomly allocated to one of 2 groups. The first group (control) received no oxygen supplementation before induction of general anaesthesia, whereas the second group (oxygen) did. All horses were anaesthetised with intravenous detomidine, butorphanol, ketamine, midazolam and isoflurane. Directly after induction (T = 0) and 30 min later (T = 30) an arterial blood sample was taken for blood gas analysis. At T = 30 an estimate of intrapulmonary shunt fraction (Qs/Qt) was calculated. Results At T = 0 arterial partial pressure of oxygen (PaO2) was significantly higher in the oxygen group compared with the control group (11.0 ± 2.6 kPa vs. 7.4 ± 1.6 kPa; mean ± s.d., P = 0.005) and at T = 30 differences were not statistically significant. Partial pressure of carbon dioxide (PaCO2) and Qs/Qt did not differ between groups. Conclusions Supplementing oxygen by a nasal cannula before induction of general anaesthesia in horses is feasible and does effectively elevate the PaO2 immediately after induction. Future research is needed to determine whether supplementation of oxygen before induction of general anaesthesia in horses will affect outcomes.

Clinical insights: Equine anaesthesia and analgesia

“…Similarly, pre-induction oxygenation has been used in some critically ill horses with the expectation of improving tissue oxygenation. Pre-induction oxygen supplementation (15 L/min for 3 min) using a nasal canula with the tip placed at the level of the medial canthus of the eye effectively increased PaO 2 immediately following anaesthesia induction; however, there was no difference between preoxygenated and control (non-preoxygenated) horses at 30 min post induction [4]. Preoxygenation using the regimen described did not increase intrapulmonary shunt fraction or cause any detrimental effect on anaesthetic induction/recovery, oxygenation or ventilation during general anaesthesia.…”

Highlights of recent clinically relevant papers

“…In this study, UK‐based H. van Oostrom and colleagues in the Netherlands evaluated oxygen supplementation before induction of general anaesthesia in horses .…”

Development and Utilization of a Retarding Analyzer for Field Emission Investigation of LaB6/W Emitter

“…The configuration of the device, which is generally similar to that used by Van Oostrom in 1966 and by Latham and Mousa in 1986 [5,13] (mentioned hereafter as the retarding field analyzer), is depicted in Figure 1. The main feature of the retarding field method is that the resolving power of the analyzer is independent of its size as long as its geometry is conserved.…”

“…It is therefore aimed to provide an integrated description of a characterization tool with which a field emission investigation is possible with high accuracy and relatively low cost. A simple configuration similar to the retarding field analyzer used by Van Oostrom has been optimized, fabricated, and utilized for combined Fowler-Nordheim (FN) and quantitative total energy distribution (TED) measurements [5]. While the TEDs are highly sensitive to the measurement parameters, a description of the instrumental set-up and the device performance are presented.…”

“…where s(y) is another slowly varying function. Details of the FN equation and the related parameters are available elsewhere [5]. The TED has been calculated by Young and in an early work reviewed by Gadzuk and Plummer [10,11].…”