Introduction

Euthanasia is a common but sometimes problematic procedure in cats. Obtaining venous access in very old or debilitated individuals can be technically difficult and stressful for the patient, client, and professional staff involved.¹ Intracardiac injection of euthanasia solution can be difficult due to the surrounding ribs, and intrahepatic injections can be challenging due to the presence of abdominal fat or fluid and the inability of many to palpate the liver. Owners often view the procedure as unacceptably slow when performed by intraperitoneal injection or as unpleasant when performed by intracardiac injection. Other methods of euthanasia exist but are less commonly used for client-owned animals. The depth of emotional attachment between animals and their owners or caretakers requires an additional layer of professional respect and care beyond the ethical obligation to provide a good death for the animal. An effective and humane alternative method of euthanasia that reduces stress during this emotionally charged time would be welcome. The 2020 edition of the AVMA Guidelines for the Euthanasia of Animals² lists the technique of intrarenal injection of a barbiturate, with a recommended amount of 3 mL of barbiturate (eg, sodium pentobarbital) per 4.5 kg body weight, as an acceptable method for euthanasia of an unconscious or anesthetized animal. The recommended dose of 3 mL of barbiturate/4.5 kg body weight is anecdotal and experiential, meaning less volume may be enough to achieve death consistently in cats; however, more research is needed before the recommendation is updated. A 2021 Veterinary Information Network³ Quick Poll of 2,159 veterinarians found that some veterinarians administered smaller doses; however, it was unknown if doing so was intentional or advantageous.⁴

The prerequisite to render the patient unconscious prior to intrarenal injection for euthanasia adds additional welfare protection by reducing the risk of pain and anxiety during the procedure. Physical restraint is stressful for many animals, regardless of the technique, so beginning with an anesthetic induction agent to allow the patient to become unconscious first helps ensure a more peaceful euthanasia process.^5,6 Although IV administration of euthanasia solution is standard in many situations, it does not always include prior sedation or anesthesia, the lack of which could negatively impact animal welfare and the euthanasia experience for the animal. It can also negatively impact the witnessing owner if something goes wrong or there are unexpected complications during the euthanasia technique. Performing intrarenal injections has been described,^1,7 and the technique is not difficult once an animal's kidney is isolated.

The purposes of the study reported here were to determine whether intrarenal injection of sodium pentobarbital is a viable method of euthanasia in anesthetized client-owned cats and to assess potential factors associated with time to cardiopulmonary arrest (TCPA) for such treated cats. We hypothesized that the outcome of intrarenal injection of sodium pentobarbital in anesthetized cats would have similar effects, in terms of TCPA and animal reactions, to those observed with IV injection of barbiturates. Although this study has been referenced previously,^8,9 the present report is the first publication of the results.

Materials and Methods

Results

The cats scheduled to be euthanized between March 1, 2009, and January 15, 2010, had a variety of conditions including neoplasia, organ failure, and reduced quality of life associated with advanced age; however, after evaluation, only 131 cats were included in the study. The most common reason for exclusion was an inability to definitively palpate and isolate either the left or right kidney due to obesity, abdominal fluid accumulation, or renal agenesis. No owners of these 131 cats declined intrarenal injections for their cats, and none expressed displeasure with the technique after their pet had died.

Of the 131 cats in the study, 56 were male and 75 were female. Median age and body weight were 16 years (range, 1 to 23 years) and 3.18 kg (range, 1.4 to 9 kg). The most common physical or behavioral conditions for these 131 cats were chronic kidney disease (n = 28 [21%]), age-related changes (25 [19%]), multiple conditions (19 [15%]), and neoplasia (16 [12%]; Table 1). The median TCPA did not differ for cats grouped by body weight, dehydration level, kidney size, or kidney injected (Table 2).

Most (124/131 [95%]) cats had no observable reaction to the intrarenal injection of sodium pentobarbital other than cardiopulmonary arrest. The remaining 7 (5%) cats had agonal respirations and movements, such as body stretching and muscle fasciculations, commonly witnessed with IV injections of barbiturates. Six of these 7 cats died during or immediately after the injection was complete, whereas the remaining cat had a TCPA of 2 minutes.

Attending veterinarians categorized death to be immediate when respirations ceased within seconds of the injection being completed and the heart was determined to be either in fibrillation or asystole when the chest was auscultated. More exact timing was not possible, as owners were present during most euthanasias and maintaining a respectful protocol and demeanor was of utmost importance.

The median TCPA did not differ between cats that did or did not exhibit these reactions (Table 2). Although it was unknown why these 7 cats demonstrated more active signs of dying, it is always advisable to ensure proper depth of unconsciousness.^5,6

The median TCPA for all cats was 0 minutes after completion of intrarenal injection of 6 mL of sodium pentobarbital, with most (74/131 [57%]) cats having had cardiopulmonary arrest before the injection was complete (TCPA, 0 minutes). The remaining cats had cardiopulmonary arrest either within 1 minute after the injection (29/131 [22%]) or between 1.5 and 8 minutes after the injection (28/131 [21%]). Of these latter 28 cats with a longer TCPA, 10 (36%) received a second injection of sodium pentobarbital. The median TCPA was 0 minutes for 121 (93%) of 131 cats that received 1 injection and 2.5 minutes for the 10 (8%) cats that received 2 injections.

A palpable kidney swelling was detected on injection for 106 cats, of which 86 (81%) had a TCPA ≤ 1 minute. Similarly, of the 25 cats in which clinicians failed to detect kidney swelling, 17 (68%) had a TCPA ≤ 1 minute. The median TCPA was longer (P = 0.02) for cats without palpable kidney swelling (1 minute) versus those with palpable kidney swelling (0 minutes).

Discussion

Results indicated that intrarenal injection of sodium pentobarbital was a viable method of euthanasia in the client-owned cats of the present study. Most cats (57% [74/131]) experienced cardiopulmonary arrest immediately upon injection, with an additional 22% (29/131) of cats having had a TCPA of ≤ 1 minute.

Patient variables (eg, body weight, estimated dehydration level, kidney size, and disease) appeared to have little effect on TCPA. The only variable in the present study that impacted TCPA was the presence or absence of palpable kidney swelling upon injection. The median TCPA increased from 0 minutes to 1 minute for cats in which there was no swelling of the kidney palpable after injection. This was to be expected, given that kidney swelling is a reliable indicator that an injection was given into renal tissue. A lack of renal swelling can be explained if some of the injection was given outside of the kidney (eg, into the abdominal space or the renal pelvis). Because the rationale behind the use of intrarenal injections is based on the organ's large blood supply, a prolonged TCPA is not unexpected when confirmation of injection into the vascular portion of the kidney is absent. On the other hand, kidney swelling with intrarenal injection did not guarantee an immediate death, perhaps because of renal tissue compromise due to underlying pathology affecting venous blood flow (eg, renal necrosis or blood clots) or simply the perception by the veterinarian of swelling when there was none.

In most cases, performing intrarenal injections in anesthetized cats is not technically challenging, but as is the case with any medical procedure, particularly those performed without visual confirmation, 100% accuracy is impossible. To increase competency with the intrarenal injection technique, practitioners are encouraged to learn and practice the method by using written resources, participating in hands-on cadaver technique laboratories, or both.^1,5,7,10,11 Like other clinical skills, performing intrarenal injection competently and confidently requires practice. Challenges with the procedure can involve difficulty finding a kidney, not being able to hold the kidney in position for the entirety of the injection, or mistaking another abdominal structure for the kidney (eg, a fecal ball, loop of intestine, or fat). One benefit of intrarenal injections, however, is that if needle placement is incorrect, the euthanasia solution will most likely be given into the intraperitoneal space, and although it will take longer for TCPA, this is also an acceptable method of euthanasia in cats.² The attending veterinarian prepared owners for this possibility by informing them that although death is likely to occur within a minute or so, in some cases more time may be needed for the euthanasia solution to be absorbed and infrequently a second injection is necessary. Known preexisting renal disease was not a deterrent to the technique's selection, and results of the present study indicated disease had little to no bearing on effectiveness.

Most cats in the present study had no observable reaction to the intrarenal sodium pentobarbital injection other than cardiopulmonary arrest. The remaining 5% demonstrated only agonal respirations and movements that occasionally also occur with other routes of barbiturate administration for euthanasia. To our knowledge, the frequency or severity of agonal reactions has not been reported; however, reactions observed after the intrarenal injections in the present study were not deemed out of the ordinary. Agonal reactions were not associated with an increased TCPA in the present study and are not considered common in anesthetized patients.¹²

Because most of the euthanasias included in the present study were performed in the presence of clients, owner acceptance of intrarenal injections was essential. Attending veterinarians informed those present that, under the circumstances, they felt an intrarenal injection (often referred to as medicine delivered in this [renal] area, rather than into a vein) would provide the most peaceful experience for all involved and that their cat would pass either immediately or within a few minutes. Owners were encouraged to ask questions, and if they expressed reservations about the procedure, catheter placement for IV administration of sodium pentobarbital was offered as an alternative. No owners declined intrarenal injections for their cats, and none expressed displeasure with the technique after their pet had died.

The results of the present study indicated that the effects of intrarenal injection of sodium pentobarbital were similar to those observed with IV injections of euthanasia solution. Intrarenal injections are not difficult to perform⁵ and have high owner acceptance when the procedure is explained with sensitivity. The method has several advantages, including speed of TCPA similar to IV methods with no need to access veins. It is appropriate for any species in which the kidney can be located, and it removes active signs of death.^7,12 Yet intrarenal injection is still not commonly used,¹³ likely due to the comfort of performing euthanasia as taught in veterinary school and because the AVMA has historically regarded IV administration as the preferred method.⁵ In conclusion, results of the present study suggested that intrarenal injection of barbiturate for euthanasia in cats can be ideal in cases where obtaining IV access would be stressful for the owner or patient and is an attractive option for euthanasia in the home environment or when owners elect to be present in the clinic setting.