Epsilon Open Archive

Abstract

Complications related to the musculo-skeletal system (fractures and post-anaesthetic myopathy; PAM) after anaesthesia are more common in the horse than in other species. PAM has been shown to be related to hypotension during anaesthesia, which results in hypoperfusion of the muscle and probably hypoxia or ischaemia. In the present study peripheral perfusion in relation to central circulation was investigated during anaesthesia and in response to pharmacological provocations and during different modes of ventilation. The muscle metabolic response to anaesthesia was also evaluated. The effect of severe illness (colic) on metabolic parameters was studied before, during and after anaesthesia. Peripheral perfusion was assessed using laser Doppler flowmetry (LDF), and central circulation by conventional techniques. Muscle metabolism was studied with microdialysis, analysis of muscle biopsy specimens and biochemical markers in venous blood samples. Peripheral perfusion was more closely related to cardiac output than to arterial blood pressure. Compared to spontaneous breathing, intermittent positive-pressure ventilation negatively affected both central and peripheral perfusion. Central circulation was better preserved but respiration was more depressed during propofol-ketamine anaesthesia than during isoflurane anaesthesia. In clinically healthy horses both inhalation anaesthesia and propofol-ketamine anaesthesia were associated with an anaerobic metabolic response characterised by increased lactate in plasma, muscle and dialysate and in some cases by decreased muscle phosphagen stores. No muscle metabolic differences were detected between the dependent and non-dependent muscles (muscle biopsy and microdialysis) during lateral recumbency. Many colic horses entered anaesthesia with profoundly affected metabolism and activation of both the carbohydrate and lipid metabolic pathways due to increased sympathetic output resulting from pain and insufficient circulation. The content of ATP in these horses was low at start of anaesthesia but anaesthesia did not further deteriorate the metabolic stress. Horses that died or were euthanised at an early stage had the highest concentrations of lactate in plasma, muscle and dialysate before and during anaesthesia. During the first week after anaesthesia the metabolism and electrolyte balance were affected in both healthy and colic horses, but to a greater extent in colic horses.