Vetnuus | November 2023 36 « BACK TO CONTENTS • Measure PCV, TPP and blood glucose as minimal pre-anaesthetic testing • If painful procedures are anticipated, pre-emptive analgesia (see above) should be given 20-60 minutes before the procedure commences Induction • Psittacines and other small birds o Wrap the patient loosely in a towel to prevent wing flapping and excessively struggling o Mask induction with 5% isoflurane – induction usually takes approximately 20 – 30 seconds • Waterfowl and other large birds o Place intravenous catheter in an accessible vein e.g. medial tarsal vein in waterfowl, basilic vein in ratites o Induce with intravenous drug (s) as described above Maintenance • For short procedures e.g. radiography, maintenance of anaesthesia via a face mask may be all that is required. The mouth and nares should be encased in the mask, which should be sealed around the head to prevent the escape of anaesthetic gas and to assist in ventilation if required. For small patients this can be achieved by stretching a rubber glove over the mask and making a small hole for the patient’s head. • For procedures longer than 5 minutes; or for compromised patients; or for rare or valuable birds, intubation is advisable. Remember that the avian trachea is composed of complete cartilage rings and the lumen diameter decreases caudal to the glottis. Therefore endotracheal tubes should be: o Non-cuffed or, if cuffed, never inflated o Relatively shorter than those used in mammals o Smaller diameter than the width of the glottis would suggest • Once intubated, avoid ventro-flexion of the neck. This can bring the tip of the endotracheal tube into contact with the tracheal mucosa, causing pressure necrosis. • If the patient’s condition precludes intubation (e.g. tracheal obstructions) an air sac catheter should be placed. • Once a stable plane of anaesthesia has been reached, the isoflurane concentration can be reduced, usually to 1.5 - 3%. Oxygen flow rates are typically high, usually 1-3 L/min even for small patients. • The patient should, wherever possible, be maintained in lateral or ventral recumbency. When placed in dorsal recumbency the weight of the viscera can compromise the ability of the air sacs to function correctly. Sternal lift, necessary to expand the air sacs, also becomes more difficult for the patient in dorsal recumbency. If dorsal recumbency is required for a procedure, assisted ventilation my well be required. • The patient’s head should be elevated above the level of the crop to prevent reflux of crop and other intestinal contents and potential aspiration. This is easily achieved by placing a pad under the head to lift it above the level of the crop. • It must be noted that if a surgical procedure is been performed that opens an air sac to room air, spontaneous ventilation through the open air sac will result in a lightening of the anaesthetic depth. Support • Body temperature. Birds have a high surface to body volume ratio and will lose body heat quickly when not active or when their metabolic rate slows. The rate and amount of heat loss is directly proportional to the size of the patient (the smaller the bird, the faster and greater the heat loss). Numerous techniques have been devised to prevent hypothermia in anaesthetised patients and are listed below. It must be noted, though, that irregardless of the thermal support provided, the patient’s body temperature will start to decline after approximately 20 minutes of anaesthesia. One of the most important means of minimising this heat loss is to have a plan and preparations in place before inducing anaesthesia to minimise the anaesthetic time. Other techniques that have been advocated include: o Warmed intravenous fluids throughout the procedure o Warmed and humidified anaesthetic gases o Radiant heat from overhead heat lamps o Heated air units (e.g. the Bair Hugger®) o Heat pads do not appear to be overly effective in providing heat support to avian patients o Circulatory support. Anaesthesia, especially when associated with surgical blood loss and/or pre-existing dehydration, can lead to decreased vascular perfusion. Warmed fluids given sub-cutaneously, intravenously or intra-osseously will provide both circulatory and thermal support. Balanced electrolyte solutions such as Lactated Ringer’s Solution, given at a rate of 10mls/kg/hour and even up to 30-60 ml/kg/hour, appear to be safe and effective in most birds. o Respiratory support. With prolonged anaesthesia (especially in patients that develop hypothermia, Technical I Article This article is sponsored by V-Tech
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