Comparison of Intrarenal and Intravenous Injections of Sodium Pentobarbital for Euthanasia in New Zealand White Rabbits (Oryctolagus cuniculus)
Peripheral venous access in rabbits can be difficult to obtain. When failure occurs, there is a dire need for alternative vascular access routes to be available. The AVMA categorizes intrarenal injection of pentobarbital as acceptable with conditions for euthanasia. Animals must be in an unconscious state, and only minimal studies using intrarenal administration have been reported. A total of 53 rabbits were used to conduct 3 separate analyses to assess and measure the efficacy, efficiency, and validity of the intrarenal route for euthanasia in New Zealand White rabbits by assessing the time to cardiopulmonary arrest (TCPA). Animals were sedated with 40 mg/kg ketamine and 50 μg/kg dexmedetomidine intramuscularly into the lumbar muscles, and timing started at the beginning of the injection and ended when cardiac and respiratory arrest were observed. Cardiac and respiratory arrest following intravenous injection of pentobarbital was significantly quicker (cardiac, 6 to 24 s, median 9 s; respiratory, 6 to 19 s, median 9 s; P < 0.001) than for the intrarenal route (cardiac, 40 to 900 s, median 411 s; respiratory, 23 to 900 s, median 120 s; P < 0.001), with no negative animal reactions observed during euthanasia injection performance. Four animals did not achieve TCPA within 15 min after administration. Although TCPA was longer with intrarenal compared with intravenous euthanasia (P < 0.001), this study demonstrates that the intrarenal approach under anesthesia is a feasible alternative to the intravenous approach, as it can be reliably performed without observed animal distress or alterations in organ pathology. The overall information from this study can help guide both laboratory and practicing clinicians considering this technique. Still, factors such as variable times to cardiopulmonary arrest and technical skill should be considered.
Experimental design summary. All animals were randomly assigned to intravenous or intrarenal administration groups and prescreened for study enrollment with biochemical analysis and parenchyma ultrasound of both kidneys. Animals were then sedated intramuscularly with 40 mg/kg ketamine and 50 μg/kg dexmedetomidine. All animals were confirmed to be in the correct anesthetic plane with lack of response to noxious stimuli, and a peripheral ear vein catheter was placed. Animals were then euthanized according to their assigned group and timed from the moment of injection and ending at cardiac and respiratory arrest with each value recorded separately.
Intrarenal injection procedure in an anesthetized rabbit. Starting at the xyphoid process of the sternum and using a walking technique, the kidney can be isolated by manual traction in a dorsocaudal position. (A) Isolation of the left kidney (red X) in dorsocaudal position (between thumb and forefinger) caudal to the rib cage with injection demonstration. (B) Dorsal view of left kidney isolation (red X) located between thumb (dorsal) and forefinger (ventral).
Injection confirmation into the renal cortex/medulla on gross and cut surface during necropsy of New Zealand White rabbits following intrarenal injections of pentobarbital. First and second analyses confirmed correct intrarenal placement into the renal cortex/medulla. Correct placement (C and D) confirmed that use of 2% EBD resulted in dark blue pyramid shapes within the renal cortex/medulla (black arrows). Those without the use of EBD (A and B) were confirmed successful placement with areas of hemorrhage (red arrows).
Clinical assessment for timepoints for cardiac and respiratory arrest comparing the intravenous and intrarenal routes of pentobarbital in rabbits. Animals that were noted to exceed the 15-min allotted timeframe were recorded at 15 min (900 s) and a second dose of euthanasia solution was administered. The black lines indicate the median with range. The intrarenal route demonstrates statistically significant differences, elevated times, and variability to arrest. *, P ≤ 0.001.
Gross and histologic necropsy findings of the left kidney after intrarenal injection with pentobarbital in rabbits. Varying amounts of hemorrhage within the retroperitoneal space and fat pads (black arrows) are present (A, B, C). Histology represents the image of a grade 0 (D), 1 (E), and 2 (F) hemorrhages, all taken at 40× original magnification.
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