In today’s VETgirl online veterinary continuing education blog, we review the use of propofol during euthanasia in veterinary medicine. Perhaps one of the most important aspects of our veterinary oath is to relieve animal suffering. I know when I first entered practice after graduation I was surprised by the frequency in which I was performing euthanasia on companion animals. I soon realized how important this service is for the pets and for the pet parent and the impact my skills and my medicine can have on this last shared experience between pet parent and pet. We all tend to develop our own routine way of performing euthanasia be it a designated room with dim lighting, perhaps quiet music, maybe some fluffy pillows and beds – anything that might promote peace and relaxation. As for the medical side of euthanasia, we understand that the overdose of pentobarbital derivative used during euthanasia provides a peaceful transition for the pet. But outwardly, it may not always look so peaceful to the pet parent. During euthanasia, I’ll admit that I’m always holding my breath that during the euthanasia the pet will simply close their eyes (which we know doesn’t typically happen), fall asleep, and take his last breath peacefully. But sometimes we encounter rather unfortunate – albeit rare – side effects of the medication or of the body’s response to illness and the medication. For starters we know that the eyes of animals will typically remain open to some degree. And, just as in humans, animals can have involuntary or voluntary release of bladder and bowel function, some may vocalize from dysphoria or disease, and some may exhibit muscle fasciculations. As an attempt to minimize these adverse events, we can reach for adjunctive medications to mitigate these unwanted responses. Propofol is a popular adjunctive anesthetic used in euthanasia, but to date, no veterinary studies have been conducted to evaluate whether this added anesthesia agent has significant benefits when used in euthanasia.

So, Bullock et al wanted to evaluate this in a study entitled Comparison of pentobarbital-phenytoin alone vs propofol prior to pentobarbital-phenytoin for euthanasia in 436 client-owned dogs. In this study, the authors evaluated the adverse events observed during the euthanasia of client-owned dogs that received either pentobarbital/phenytoin (PP) alone or in combination with propofol. Clinicians participating in the study were asked to exclusively select either PP alone or PP and propofol to use on all their euthanasia, and to record patient observations throughout the process. The anesthetic(s) were given intravenously – no other route of administration such as intracardiac or intraperitoneal were accepted for inclusion into this study. A total of 236 dogs received PP alone and 200 dogs received both PP and propofol. Neither age nor sex were significantly different between the two groups. Although doses were not regulated in this study, the PP dose did not differ significantly between the two groups. The mean dose of propofol administered was 4.5 mg/kg, and in the PP and propofol group, the volume of propofol selected was often based on the same volume of PP used. No additional “top off” doses of propofol or PP were administered in any patient in either group.

The most commonly seen adverse events included things we would expect from our own experiences with euthanasia: muscle fasciculations, agonal breaths, and urination. The risk of developing muscle activity was decreased by the addition of propofol. Out of the following complications: muscle fasciculation, agonal breaths, passive urination/defecation, vocalization, dysphoria, and catheter complications, only the incidence of muscle fasciculations was significantly decreased by the addition of propofol. Adverse events occurred in about 1/3 of the of the dogs within the PP group, and addition of propofol did not significantly reduce the likelihood of an adverse event. In this study, Bullock et al propose 3 theories for why the administration of propofol produced a reduced risk of developing muscle fasciculations during euthanasia. The first theory is that propofol has a direct suppressive effect on muscle tone. The second theory is that propofol may exhibit a synergistic effect with the PP. The third theory is that the addition of a second medication resulted in prolonged time of medication delivery.

Limitations to this study include that participants were not blinded or randomized, there was no uniformity in doses of either propofol or PP used, and the delivery rate of medication was variable. Creation of such a controlled study would prove difficult due to the transparency required to the client during such an emotionally charged event. This study will hopefully open the doors to more studies surrounding the medical aspect of euthanasia. Dosing guidelines for medications delivered would be particularly helpful in order to avoid waste of controlled substances, yet above all else, ensure that the pet is provided enough medication for a peaceful transition. At this time, I will continue to utilize propofol prior to PP administration due to my personal experience with this medication, although this article may argue the benefit versus cost of adding propofol to the protocol due to lack of significant benefit other than a reduced risk of muscle fasciculations. In reality, I’m using refrigerated propofol that has recently expired on these patients. VETgirl continues to recommend that clinicians advise their clients of the possible side effects they may witness – especially the unsettling sight of agonal breaths! After all, it’s empathy and client communication that play such a pivot role in all aspects of veterinary medicine. This may help to lessen client anxiety about what they may witness, and minimize the client’s perception of these events if witnessed. More importantly, we often have a thankless job, but this is one area where pet owners are so grateful for our compassion. To all your veterinarians, veterinary technicians, front desk staff, practice managers, veterinary assistants… thank you for all that you do to save lives and end animal suffering.

Abbreviations:
PP- pentobarbital/phenytoin

References:
1. Bullock JM, Lanaux TM, Shmalberg JW. Comparison of pentobarbital-phenytoin alone vs propofol prior to pentobarbital-phenytoin for euthanasia in 436 client-owned dogs. J Vet Emerg Crit Care 2019;29(2):161-165.