When used for anaesthetic maintenance in donkeys , isoflurane is started at a higher rate initially , then adjusted according to the donkey ' s depth of anaesthesia . An initial higher O 2 flow rate is used to deliver the isoflurane to the patient ' s lungs quickly by increasing the total amount of gas passing through the system . This achieves a faster onset of anaesthesia , as the gas swiftly reaches the alveoli and is absorbed into the bloodstream , taking the isoflurane to the brain and central nervous system . The faster delivery means the donkey will reach the desired depth of anaesthesia rapidly . The O 2 flow can then be reduced to a lower rate , once the donkey is at a consistently adequate depth of anaesthesia . Reducing the O 2 flow rate for the maintenance of anaesthesia can avoid unnecessary costs and minimise environmental contamination .
A pulse oximeter ( placed on the donkey ' s tongue ) provided a reading of 99 %, which was considered appropriate . A Doppler sensor probe was placed and taped over the coccygeal artery at the base of the tail , with cuff size 5 proximal to the sensor probe to obtain arterial SAP . LRS was administered intravenously at 10 ml / kg / hour . In addition , the heart rate , respiratory rate and temperature were monitored every 5 min .
The initial assessment of the depth of anaesthesia revealed a weak anal tone and a diminished palpebral reflex . There was no evidence of nystagmus or lacrimation , indicating that the donkey was in stage 3 , plane 2 of anaesthesia , which is considered an adequate depth for surgery [ 12 ] . To ensure the donkey remained at the appropriate anaesthetic depth , its reflexes were monitored regularly throughout the procedure . It is important to note that a donkey ' s eyeballs do not exhibit the same rotational patterns as those of other species , which limits the effectiveness of certain depth indicators .
Lidocaine was administered as an intratesticular block of 2 mg / kg lidocaine per testicle before the surgeon commenced surgery .
During anaesthesia , the donkey ' s heart rate varied between 32 bpm and 40 bpm and the respiratory rate ranged from 9 to 15 breaths / min . Rectal temperature dropped to 35.2 ° C , so an active warming device was placed over the donkey , with blankets used to maintain and increase temperature . Observed EtCO 2 was in the range of 48 – 56 mmHg ( whereas the normal range would be 35 – 45 mmHg ).
Complications
Hypotension
The donkey ' s SAP dropped from 98 mmHg to 80 mmHg within 30 min of anaesthesia commencing . The patient ' s depth was assessed : the palpebral and anal tone had diminished , indicating a deep level of anaesthesia . The isoflurane vaporiser setting was reduced to 1.4 %. A bolus of 10 ml / kg LRS was administered to improve blood pressure , but it continued to drop to 74 mmHg over a 10-min period . Without the addition of other anaesthetic agents , further reduction of isoflurane posed a risk of the donkey becoming responsive to surgical stimuli , so a second dose of butorphanol ( 0.05 mg / kg ) was administered intravenously . This allowed the isoflurane concentration to be safely reduced to 1.2 %, due to the MAC-sparing effects of the opioid .
Initially , SAP increased to 80 mmHg , but , as the hypotension was not resolving quickly , further medication was required . Dobutamine was administered as a constant-rate infusion at 1 µ g / kg / min to increase cardiac contractility . These interventions resulted in an SAP of above 100 mmHg for the remainder of the procedure .
Hypoventilation
Another common concern in anaesthetised patients is hypoventilation , which is seen when the patient ' s
EtCO 2 level is above 45 mmHg . In this patient , the EtCO 2 levels recorded during this procedure were 48 – 56 mmHg , which is higher than the expected range of 35 – 45 mmHg . No IPPV was performed , as it is not recommended when EtCO 2 is below 60 mmHg [ 6 ] .
Hypothermia
The donkey ' s rectal temperature dropped to 35.2 ° C , so a HotDog ( Augustine Surgical , Inc ., USA ) warming device was placed over the patient , with blankets used to maintain and increase temperature . This successfully reduced the heat loss and the patient ' s body temperature gradually increased .
Warmed fluids can be used to mitigate a drop in body temperature . However , usually , these are not in themselves sufficient to avoid hypothermia , so direct warming methods should also be used .
Evaluation of arterial blood gases
A sample for blood gas analysis was taken from the auricular artery within 30 min of anaesthesia induction , with a second sample taken 40 min later . The observed blood gas values are illustrated in Table 3 ( page 21 ).
This analysis showed that the patient had a low
PaO 2 value . On recovery , a patient should be able to effectively oxygenate once extubated , and breathe room air at 21 % O 2
. A PaO 2 of 289 mmHg on 100 %
O 2 would drop once the patient was extubated to approximately 61 mmHg ( calculated as 21 % of 289 ).
20 Veterinary Nursing Journal