November 2023 37 hypoglycaemia, or hypovolaemia), the patient’s respiratory rate may slow and even stop. Cardiac arrest usually follows soon after. Adequate respiratory support, in the form of supplemental ventilation, is therefore essential for most avian anaesthetics. Intermittent Positive Pressure Ventilation (IPPV), performed either manually or by a ventilator, should be instituted early in the anaesthetic process, rather than waiting for problems to develop. Birds that are breathing by themselves while under anaesthesia will benefit from IPPV at a rate of 4-6 respirations per minute with sufficient pressure to create normal inspiratory depth. (Excessive pressure should be avoided.) If the bird is apnoeic, IPPV should be given at a rate of 10-12 respirations per minute. Monitoring • Monitoring of anaesthesia is vital in avian surgery. For this reason all anaesthetic procedures should be monitored by a staff member assigned to this task only. Safe and effective anaesthetic monitoring is a multimodal procedure, relying on visual assessment as well as monitoring equipment. • Manual assessment of the depth of anaesthesia requires monitoring of: o Respiratory rate and character. The anaesthetised bird should breathe at least once every 2 to 7 seconds. At a light plane of anaesthesia the respiratory rate and character can be rapid and deep. As the anaesthetic plane deepens the respiration slows and becomes shallower. Capnography is a useful tool for not only monitoring the patient’s respiratory rate, but also the effectiveness of its respiration. • Heart rate and rhythm. Decreases or changes in heart rate and rhythm are often mirrored and preceded by changes in respiration. If a Doppler is not been used, auscultation should be performed frequently, if not continuously. • The palpebral reflex (eyelid closure induced by stimulation of the ocular medial canthus or cere) disappears quickly as the anaesthetic plane deepens • The pedal (toe withdrawal) reflex and the corneal reflex (third eyelid movement in response to corneal manipulation) slow, but can remain present even at surgical planes of anaesthesia. • At deep anaesthetic planes, breathing becomes slow and shallow and all reflexes disappear. o Blood pressure monitoring is becoming increasingly more recognised as a valuable tool in anaesthetic monitoring. Although direct arterial pressure measurement is ideal, it is usually not practical in private practice. Indirect blood pressure measurement techniques, based on the detection of blood flow beneath an inflated cuff, are therefore recommended. Systolic blood pressure determination via ultrasonic Doppler flow detection has been found to correlate well with direct blood pressure. The blood pressure of various avian species under gaseous anaesthesia lies between 90-140 mmHg systolic. o Pulse oximetry is generally considered to be unsuitable in birds because of the lack of calibration for avian blood. It may, however, provide some information on trends in blood oxygenation in avian patients. o Electrocardiography has been employed in several avian practices, and has been reported to be a useful tool in monitoring the heart rate and rhythm, especially when auscultation is difficult to performing without interfering with the surgery. Recovery Depending on the type and duration of the anaesthetic, recovery to standing and perching usually takes 5 – 10 minutes. Full recovery usually takes 30 – 60 minutes. • Following anaesthesia, birds should be: o lightly wrapped in a towel to prevent injury from wingflapping or excessive movement during recovery; o placed in a darkened, quiet, heated cage and monitored closely till able to perch; extubated only when voluntary head movements are noted; o offered food and water as soon as the patient is fully recovered; o monitored for bleeding, regurgitation, dyspnoea, etc. v Technical I Article
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