ABSTRACT:The first case of post anaesthetic myelopathy in a horse is described. A two year old 530 kg Shire stallion underwent surgical removal of a granuloma in the ventral sternal region under general inhalation anaesthesia in dorsal recumbency. Total duration of the operation was 85 min. The anaesthesia was uneventful except for profuse sweating and arterial hypertension observed during the whole period. During recovery the horse was not able to stand, and flaccid paralysis of hind limbs, absence of reaction to an induced pain stimulus on the hind limbs and no patellar or anal reflex was recorded; in addition, tail tonus was weak. Panniculus reflex was absent distally from the 17 th intercostal space. Head, neck and front limb movement was not affected. The horse did not respond to treatment by intravenous administration of dexamethasone, hypertonic or isotonic saline. The status deteriorated and the horse was euthanised 4 h after the end of anaesthesia. The main pathological findings were haemorrhage, oedema and malacia of L5-L6 spinal cord segments and cauda equina. Histological examination of the spinal cord revealed haemorrhage and areas of necrosis predominantly in the grey matter of L5 and L6 segments. Impairment of spinal cord perfusion due to haemodynamic changes associated with dorsal recumbency and general anaesthesia is presumed. Predisposition factors could include young age, dorsal recumbency and high weight.
ABSTRACT:This research aimed to determine the effect of aerosolized salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance in healthy horses during general anaesthesia. Six healthy Thoroughbreds (body weight range 471-587 kg) underwent two general anaesthesias in dorsal recumbency with and without aerosolized salbutamol administration in randomized order with a one month washout period. The anaesthesia was induced by 1.1 mg/kg of xylazine, 0.02 mg/kg of diazepam and 2.2 mg/kg of ketamine, maintained with isoflurane in oxygen and air and horses were mechanically ventilated. Measurement of arterial and pulmonary arterial blood pressures, cardiac output and arterial and mixed venous blood gas analysis was carried out. Spirometry was performed using a Horse-lite. After achieving a steady state, baseline (T 0 ) values of cardiac output, systemic and pulmonary arterial blood pressures, heart rate, dynamic compliance, airway resistance and arterial and mixed venous blood gas values and pH were recorded in both groups. In the S-group (salbutamol), 2 µg/kg of aerosolized salbutamol were administered synchronously with inspirium into the tracheal tube. In both groups data were recorded at 15, 30, 45 and 60 min (T 15 , T 30 , T 45 , T 60 ) after the baseline. PaO 2 /FiO 2 ratio, oxygen consumption (VO 2 ), oxygen delivery (DO 2 ), pulmonary shunt values were calculated. Data were tested for normality and compared within each group: T 0 value with T 15 , T 30 , T 45 , T 60 values using Wilcoxon's test with Bonferoni correction (significance level 0.0125). For each time point, comparisons were made between the S-and C-groups (control) using Wilcoxon's test. In the S-group, there was a significant increase in values (mean ± SD) of cardiac output (l/min), T 0 (38 ± 7), a peak at T 15 (64 ± 25.5), significantly higher values persisted throughout the period of anaesthesia; heart rate (beats/min), T 0 (32 ± 2), T 15 (40 ± 6), T 30 (38 ± 5); DO 2 (l/min), T 0 (5.8 ± 0.8), a peak at T 15 (9.6 ± 3.2), significantly higher values persisted until the end of anaesthesia and VO 2 (l/min), T 0 (1.1 ± 0.5), T 30 (1.6 ± 0.7) and T 45 (1.8 ± 0.5). In the C-group, there was a significant decrease in values of PaO 2 /FiO 2 ratio from T 0 (176 ± 67) to a minimum at T 60 (114 ± 36) and in DO 2 from T 0 (6 ± 2.3) to a minimum at T 60 (4.3 ± 1.2). A comparison of the S-and C-groups did not reveal any difference in the baseline data. Subsequently, significantly higher values of cardiac output, heart rate, DO 2 , and the PaO 2 /FiO 2 ratio were found in the S-group compared to the C-group. Pulmonary arterial blood pressure was significantly lower in the S-group. Aerosolized salbutamol administration in healthy horses during general anaesthesia caused hemodynamic changes which resulted in an elevation of oxygen delivery. It can have a positive effect on arterial oxygenation, but the effect varies between individuals.
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