The data presented here supports that anesthesia for spay/castration clinics can be accomplished in remote locations where anesthesia machines and/or oxygen is not available. Furthermore, this study has evaluated anesthetic protocols that produced rapid unconsciousness, but allowed for reversal and rapid recovery of patients. This is important in many remote locations, as there are often few if any recovery cages/ holding areas, some of the patients are feral, and the longer the patient remain in the clinic’s care, the less patients that can be seen per day. Total patient time in the clinic was approximately 1 hr, with cat castrations requiring the shortest stay and dog OVH requiring the longest.
Surgery time ranged from 1 min to 1hr. This made estimation of IM drugs needed difficult. Not surprisingly, 1% of cats being castrated needed rescue anesthetics while 57% of dogs undergoing an OVH required additional anesthetics. In cats that were insufficiently anesthetized during surgery, alfaxalone IM provided a rapid deepening of anesthesia. Intramuscular alfaxalone has been evaluated in cats for physiologic stability and PK/PD profiles (10, 11). When administered to cats at 5mg/kg IM, cats showed good physiologic stability, but recovery was considered behaviorally poor (10). In a different study, intramuscular alfaxalone at the same dosage was shown to reach peak concentration (Tmax) in ~22 min (11) The cats in this study did not demonstrate any unpleasant recovery characteristics, likely due to the smaller dosage used in this study (1.0 mg/kg IM). Additionally, intramuscular alfaxalone worked rapidly enough to be considered a good choice for rescue anesthesia during a surgical procedure in a cat. Based on the Tmax of ~22 min, it was unexpected, but repeatable that the dose and route was sufficient. The success of the dose and route of alfaxalone in cats was likely due to the robust dosages of the induction agents used. For dogs that were inadequately anesthetized for surgery, alfaxalone IV provided suitable conditions for canine OVH and castration anesthetic maintenance. This agrees with data showing that following premedications, a constant rate infusion of alfaxalone produced suitable anesthesia conditions for dogs undergoing OVH (12). However, in both the Suarez study as in this study, many of the dogs required assisted ventilation to remain normoxemic (12).
Due to the lack of boarding space, and the potential for patients to be unsupervised outside, any animal that was not able to walk was administered atipamezole. While the loss of analgesia was considered, there is evidence in cats that administration of atipamezole did not negatively affect post-operative analgesia in cats that also received an opioid and ketamine as was used in this study(13). Additionally, all the animals received an NSAID to supplement analgesia. The vast majority of patients required the antagonism of dexmedetomidine with atipamezole (89-100% of groups). In the first three dogs that were castrated, the dogs became agitated/dysphoric after atipamezole administration. Ketamine at anesthetic dosages are associated with a high incidence of agitation in the recovery period in humans and veterinary patients (14, 15). Anesthesiologists often combine administration of ketamine with other CNS depressants such as benzodiazepines and alpha-2 adrenergic agonists to balance the risk of an agitated recovery from anesthesia (15). Thus, the most likely reason for the agitation following administration of atipamezole in those dogs was loss of CNS depression from dexmedetomidine, which was balancing the behavioral effects of ketamine in the relatively short castration surgery. Immediately following the three dysphoric dog neuter recoveries, the anesthesiologist decreased the dosage of ketamine from 7 mg/kg to 5 mg/kg and none of the subsequent neuters had dysphoric recoveries. The majority of patients only required one dose of atipamezole with four patients requiring second doses (feline neuter (n=1), canine OVH (n=1), canine neuter (n=2). Following OVH, three dogs demonstrated dysphoric recoveries. All three dogs were treated with acepromazine which successfully calmed them. In retrospect, it might have been possible to decrease the ketamine dose in OVH dogs too, and use then more alfaxalone for intraoperative maintenance. However, of the 28 canine OVH performed, only three had dysphoric recoveries (11%).
Body temperature during recovery ranged from 95.7 - 106 F (35.4 - 41.1 C). Inspection of Table 4 showed that the majority of patients remained normothermic. This was likely due to the combination of a warm surgery /recovery environment, the lack of cold, dry, anesthetic gases, and the rapid time of surgery/ anesthesia. One cat did become significantly hyperthermic (106F, 41.1C). Hydromorphone has been implicated in post anesthesia hyperthermia in cats (16), but it is unclear in this cat if the agitation was the cause or the result of the hyperthermia.
Two dogs being castrated had seizure-like activity during IM induction of anesthesia. Both dogs showed convulsive type behavior with loss of responsiveness, but neither dog became incontinent during the episode. Ketamine administration does enhance seizure like electroencephalogram waveforms (17), and it is has been implicated in causing seizures in a variety of veterinary species (15). Therefore it is possible that both dogs did have seizures following high dose ketamine administration. However, it is also possible that unbalanced absorption of ketamine and dexmedetomidine following IM administration might have resulted in an exaggerated Stage 2 plane of anesthesia (involuntary excitement) which appeared seizure-like and the loss of consciousness was due to anesthesia induction. Both of those dogs muscle fasciculation/ contraction stopped after IV alfaxalone administration and both dogs recovered uneventfully.
None of the cats were intubated during anesthesia. While endotracheal intubation of anesthetized cats is routinely performed, The Association of Shelter Veterinarians’ 2016 Veterinary Medical Care Guidelines for Spay-Neuter Programs indicated it is acceptable not to intubate cats for short duration surgeries (e.g OVH and castrations) as long as equipment for intubation is available in emergency situations (1). Based on pulse oximetry, cats remained normoxemic. Conversely, many dogs required assisted ventilation via an Ambu bag and endotracheal tube to maintain normoxemia. Placing and securing an endotracheal tube did not appreciably increase total patient time and proved important in patients that required ventilatory support, particularly when supplemental oxygen was not available.
A major limitation of this study is that it was not prospectively designed as a research project and thus many pieces of data are absent. However, it does provide valuable information regarding the use of total injectable anesthesia in dogs and cats, without rescue inhalants or oxygen. Physiologic assessment of dogs and cats anesthetized and sterilized with these protocols needs to be done. Additional limitations include: variability within each group in patient age and size, variability with four different surgeons, and varying health of patients. However, since this type of variability is expected in a remote-clinic setting, the overall success of the anesthetic plans with the variability is promising.