Influence on horse's pulmonary function using a modified 'Open-Lung-Concept'-Ventilation with different oxygen-concentration during general anaesthesia. [German]Original Title Einfluss einer 'modifizierten Open-Lung-Concept' Beatmung mit unterschiedlichen Sauerstoffkonzentrationen auf die intra- und postoperative Lungenfunktion des Pferdes wahrend der Allgemeinanasthesie.

摘要

The aim of this study was the evaluation of the influence of three different concentrations of inspired oxygen on the pulmonary function of horses in dorsal recumbency during general anaesthesia, and the recovery period. Thirty-six warmblood horses weighing at least 400 kg were included in the study. All horses were presented to the clinic for colic symptoms and underwent an emergency surgical procedure in dorsal recumbency. The horses were randomly allocated to one of three groups. Group A_35% was ventilated with an inspired oxygen fraction (FiO₂) of 35%, group B_55% with 55% and group C_90% with 90% using the open-lung-concept. Premedication (0.04-0.08 mg/kg romifidine i.v.), induction (0.05 mg/kg diazepam i.v. and 2.2 mg/kg ketamine i.v.), maintenance (inhalation: isoflurane) and hemodynamic pharmacological support (dobutamine and intravenous fluids) were identical in all horses. Arterial partial oxygen pressure (PaO₂), arterial partial carbon dioxide pressure (PaCO₂), arterial pH, PaO₂/FiO₂ ratio, heart rate, arterial blood pressure, respiratory rate, end-expiratory rate of carbon dioxide (EtCO₂), alveolar dead space, as well as inspiratory and end-expiratory concentration of isoflurane were analysed. Intra- and postoperatively arterial blood gases and acid-base status were measured. The quality and duration of the anaesthetic recovery period was scored. Included were the number of attempts to rise, time to first movement, time to sternal recumbency, time to standing position and the quality of recovery. The PaO₂ arterial oxygenation was significantly higher in horses of group C_90% than in horses of group A_35% or B_55%. However, there was no significant difference between the oxygenation of horses in group A_35% or B_55%. In the intra- and post-operative period, the PaO₂/FiO₂ ratio of group C_90% was higher than those of group A_35% and B_55%, with group B_55% having even lower values than group A_35%. At least one measurement during the anaesthetic period revealed arterial hypoxemia (PaO₂ <60 mmHg) in 33% of the horses in group A_35%, 50% of horses in group B_55% and only in 8% of horses in group C_90%. Arterial hypoxemia was observed particularly at the beginning of anaesthesia and mainly in horses with large intestinal distension. In the postanaesthetic period the PaO₂ was highest in horses of group C_90%, followed by those of group A_35%. Stats There was no significant difference in timing of events during the recovery period, except for an earlier regain of the swallowing reflex of horses in group B_55% compared to horses in group A_35%o. The number of attempts to rise, the over-all manner as well as the balance and coordination during the recovery period was equal in all groups. In conclusion, using lower concentrations of oxygen for modified open-lung-concept-ventilation during anaesthesia is possible, even in the critically ill equine patient. There was no improvement of the ventilation-perfusion mismatch when using lower oxygen concentrations. In horses with large intestinal distension, decreased concentrations of FiO₂ are accompanied with a high risk of hypoxemia. The oxygen concentration did not influence the duration or quality of the recovery period.