Comments on this case are welcomed, especially if you can share your experiences with Acepromazine, Diazepam, Torbutrol and isoflourane titration in snakes.
A large Egyptian cobra (Naja annulifera) bit and envenomated itself dorsal and anterior to its vent, initially causing a large sterile abscess which was opened to reveal inflamed but basically healthy looking tissue. View the initial page of photos here. Over a period of several weeks, the abscess grew slowly larger and a plug of necrotic tissue formed. On further surgical exploration and aggressive debriedment on November 18, 2002, we found severe cellulitis and some interesting-looking bacterial chains on microscopic examination of the removed tissue.
This large, powerful and aggressive venomous snake was head-tubed quite successfully with the aid of the indispensable Midwest Pro Bagger tool (http://www.tongs.com). A latex glove was wrapped around the body of the snake and the end of the tube, and a mask was applied to the open end of the tube using 5% isoflourane. In a short time the snake was drowsy enough to back out of the tube with a secure grip behind the head and intubate directly with the help of a long avian speculum. A cuffed endotracheal tube was used, but inflated slowly and minimally to avoid damage to the non-flexible airway. The area of the abscess was thoroughly infiltrated with Lidocaine. In our experience using local anesthetic permits us to remain at a lighter plane of general anesthesia while keeping the patient comfortable and stable.
We located the heart by palpation (which is very high in this animal, about 15% of the total body length down from the head) and placed a pulse oximeter while continuing to manually monitor the heart rate and respiration. Since we have had to spend more than an hour in the past reviving elapid snakes in the past after using 5% isoflourane, we decided to titrate the flow more carefully for this procedure. The iso was dialled down to 3% during the initial debriedment, then down to 2 1/2% as maintenance. Towards the end of the procedure it was dialled down to 1 1/2%. We constantly monitored heart rate, muscle tone and respiration and dialled the flow up or down a half percent as it seemed appropriate. This titration kept heart rate and voluntary respiration up to very acceptable levels in this animal and it did not need to receive more than a few assisted respirations. All in all I am pleased with this protocol as it seems to put the patient at much less risk, but I welcome comments from others who have had more experience titrating iso flow during reptile surgeries. Photographs of the debriedment procedure can be viewed here.
Some hours postoperatively the snake was given Diazepam .8mg/kg and Torbutrol .4 mg/kg SQ as we interpreted its extremely aggressive behavior as a sign of discomfort - not that this snake is anything but aggressive normally. It seemed a bit more upset than usual, so I suggested a pain scrip. The onset was quite rapid, about 3-5 minutes, as the animal lost some of its muscle tone and ceased to be violent and aggressive. However its heart and breathing rate did not appear to be affected, and the animal remained able to move and respond to stimulus albeit in a slow and relaxed manner.
The effects of this drug continued for about eight hours while the snake was kept around 88-90F, and I monitored its heart rate, respiration and changes in behavioral response every hour during this period. The snake's responsiveness definitely changed over this period, but its vitals did not as far as I could tell. I stopped palpating for a heartbeat after the snake became too feisty to easily slip a tube over its head without a struggle, about four hours in, but a cobra's heart is large enough to be visualized on the dorsal aspect if the snake is in the proper position. Its respiration rate increased somewhat during this latter period in response to my approaching the cage, but remained consistent when it did not know it was being observed. At approximately eight hours this snake had returned to its normal aggressive reactions and fast movements in response to a handler's approach.
The follow-up to this surgery was the removal of a drainage tube 72 hours later. We premedicated about three hours before surgery with Acepromazine .25mg/kg IM. Testing the snake's reactions by waving a hand outside the cage demonstrated no real behavioral effect; it still responded quickly with a threat display. But for some reason I had foolish hopes that this animal might be a bit slower than usual when the time came to transport him to the clinic. 2.5 hours after the drug was administered, I attempted to toss him directly in the lockbox by hooking and tailing instead of using the Pro Bagger as per normal protocol. This animal does not struggle or show signs of stress when placed free in the lockbox, and has been known to bloody its mouth when confined in a bag, so I picked the procedure which seemed safest for the patient.
Attempting to confine this completely awake, aware, strong and angry venomous snake which is thicker than my arm and longer than I am tall was an experience that I cannot properly describe without resorting to language unfit for a professional forum.
After it had charged both of us open-mouthed and chewed and sprayed venom all over the lockbox, I asked my assistant to grab the Pro Bagger which neatly concluded that situation. With minor difficulties involving venom all over the bag and the floor, the snappish snake was tubed out of the Pro Bagger after transport to the clinic and again given Diazepam and Torbutrol at 75% of the initial dose. Aside from concerns for human safety, this patient has a track record of biting itself and other inappropriate targets that could cause mouth injury, so we decided that sedation was probably the best protocol. We examined the oral cavity for injury (fortunately there was none), delivered Ceftazidime IC and pulled the drainage catheter. The site appeared to be healing nicely. Again the drug worked like a charm, quickly relaxing the animal and offering analgesia while not significantly affecting its heart rate and respiration.
While one patient is not a significant statistical sample, I feel fairly safe in concluding that Acepromazine at .25mg/kg is not a good protocol for premedicating large nasty cobras, and Diazepam/Torbutrol seems like a very promising one.
A few months after this surgery, it was apparent that granulation tissue was continuing to form at the surgical site. A third surgery was performed on January 13, 2003 to remove this tissue. Necrotic and nonviable tissues were debrieded and the wound closed with staples and nonabsorbable suture. The animal was placed on prophylactic antibiotics (Ceftaz 20mg/kg q72) and Buprenex 0.3 mg/kg q36 to q48 for pain management. A good correlation was observed between the animal's behavior and the cycle of Buprenex administration, with the periods of least aggression corresponding to the times when the drug would be expected to be at peak effectiveness and the most extreme aggression when the drug was not at best effect.
This animal clearly demonstrated a learned aversion response to the repeated handling and manipulation for medication, making safe restraint even more of a challenge. The presentation of tools that had been formerly effective in capture caused a violently aggressive response that put the animal at high risk for mouth injury or an additional self-envenomation. Most snakes willingly enter a Pro Bagger, but this animal now responded by biting at the bagstick instead of entering the bag. When forced into the bag, it bit at the cloth and refused to enter the lower sock to be directed into the tube. When finally tubed, it snapped and chewed at the smooth sides of the tube so violently that it managed to bloody its own mouth despite having nothing to bite.
While brute-force methods (pinning) are effective in restraining a venomous snake for the handler's safety, preventing the animal from doing injury to itself is much more problematic. This patient has a history of violent self-injury via self envenomation and mouth injury from biting capture tools. One of the most experienced handlers in the field today (George Van Horn) was unable to prevent this animal from injuring itself during restraint, and consequently removed it from the venom line. We decided to use a chemical restraint protocol in the patient's best interest.
A pole syringe was purchased from Campbell Pet Company; this product has interchangeable 1cc and 3cc heads and the drug is delivered by placing the needle and pushing. We felt that the hub of the needle would not provide sufficient leverage and might be injurious to the animal's skin, so we placed a 1/2" needle through a sterile red rubber lab tube stopper and tested this on a grapefruit until we were satisfied with our technique.
A dose of .8mg/kg Diazepam had previously caused very significant muscle relaxation in this animal for many hours, so we cut this dose in half (.33 mg/kg). A short section of the animal was very briefly immobilized with a pair of short Gentle Giant tongs (Midwest) and its head occupied with a hook. Delivery of this small volume of drug IM (.015cc's in this 2.3 kilo snake) was fast enough that we could withdraw before the animal had time to struggle or cause itself injury by biting the capture instruments.
Onset of sedation was less than 10 minutes, with symptoms becoming even more pronounced at 20 minutes. The animal was alert and able to lift its head and move freely around the cage, but did not attempt to strike and its movements to evade capture were slow. It was safely head-tubed without fuss or struggle and the additional injections (Ceftaz and Buprenex) were administered. The surgery site was scrubbed with chlorhexadine. Its heart rate and respiration were rapid during these procedures (plenty of loud hissing vocalizations!) but slowed to what appeared to be a normal rate on later observation after release. We observed marked tail twitching and tail lashing behavior during the procedures which is not usual in a snake. The animal moved voluntarily across the cage and drank from its waterbowl a few minutes after release, demonstrating good muscle coordination.
We will continue to titrate the dose down until we have achieved the minimum sedation level that is safe for the patient. This report will be continued as treatment progresses.