A SAFE METHOD OF SIGHTHOUND ANESTHESIA, by Rodger I. Barr, DVM
Whether it be man or beast, the greatest risk in elective or non-essential surgery is the anesthetic. In Veterinary Medicine, this risk is a minimal one when in the hands of a graduate DVM. That is unless yours, perhaps, is a sighthound. The greatest medical injustices perpetrated against these breeds is the lack of istruction in veterinary medical colleges concerning the differences between these breeds and all other dogs of the world.
The most commonly used anesthetic regimine in veterinary medicine incorporates a short-acting thiobarbiturate such as surital fallowed by gas anesthesia utilizing either Metophane or Halothane. For most breeds this type of regimine is more than satisfacory; for the sighthounds it has the potential of being very dangerous, even fatal. Little research has been directed at the actual reasons for these breed differences, so although cold, hard facts are not available, educated guesses are.
Three factors are responsible for the short-term effects of the thiocarbiturates. They are highly lipid-soluable, meaning they are absorbed into fat almost immediately after intravenous injection. They are then metabolized by the liver over a variable period of time, and subsequently excreted in the urine. With most breeds, the routine injection of a thiobarbiturate with no other anesthetic agent employed, will result in approximately 10 to 15 minutes of anesthesia before recovery occurs. The sighthound will remain under for usually 30 to 35 minutes, in some cases longer, some never recover. The reasons for this are obvious, when one considers the method of action of the above-mentioned anesthetic.
Redistribution into the fat is the greatest reason for fast recovery from thiobarbiturate; if the patient in question happens to have very little fat, this anesthetic agent which normally obliges the anesthetist by retiring to insignificant tissue such as fat, remains in the bloodstream continuing to depress the central nervous system as well as the cardiovascular system. An unaware anesthetist will then begin gas anesthesia at the point at which the thiobarbiturate normally wears off, that in this case is merely doubling up the anesthesia load, thus depressing the patient even more. At the very least, the patient will recover in three hours or so and not be fully recovered up to 24 hours. In addtion to the absence of body fat in many of the sighthound breeds, it seems their livers are unable to deal effectively as some breeds with many drugs which rely on this important organ for metabolism... supporting even more the need to find an alternative method for anesthetic control of the sighthound surgical patient.
To critisize an existing method without offering a viable alternative would render this article unnecessary. To avoid this fate, I would now like to present my candidate for the safest, most effective method of sighthound anesthetic induction. The fallowing method has been used on over 200 sighthounds by the author as well as many other animals who, for one reason or another, require a SAFER method. I have, to date, never lost a sighthound from this method. Someday a problem is bound to occur, but at this point in time, I haven't even had any close calls or unexpected responses. The drug for which I speak is a human drug know generically as Oxymorphone. It is a synthetic narcotic produced by the Endo Drug Company under the commercial name of Numorphan. It is supplied in 1.5 mg/ml in 10 cc vials and is handled as a narcotic. It is almost fully reversable. In other words, upon completion of the procedure, one can almost immediately raise the patients level of consciousness dramatically, through the use of a narcotic reversing agent such as nalline or levallophan. All sighthounds receive intravenous fluids during general anesthesia. All dogs recieve atropine sulfate prior to to anesthetic. At this time 0.05 mg/lb of oxymorphone is combined in a single syringe with 0.1 ml/10 lbs of acepromazin. ( 1.5 mg oxymorphone and 0.3 cc acepromazin for a 30 lb dog.) This combination is injected intravenously over a 15 to 20 second period; faster than this can result in a brief excitement phase. Apprehensive dogs can recieve as much as 0.075 mg/lb of oxymorphone. Within five minutes, the dogs can be intubated with very little manual restraint. Many animals will respond excessively to sharp noises at this stage. Depending on the procedure as well as the level of depression the patient has achieved one may or may not incorporate the use of Metophane, a gas anesthetic. Upon completion of the surgery, Nalline is injected I.V. at a dosage equivalent to the induction dosage of Oxymorphone. This method has been used for several years at Colorado State University on thousands of dogs, many of which where track greyhounds. During my post-graduate training at this institution, three sighthounds were mistakenly anesthetized using thiobarbiturate. One died of malignant hyperthermia during surgery ( high body temperature). A Scottish Deerhound suffered cardiac arrythmias and had to be defibrillated. The third, a greyhound, took a page out of Rip Van Winkle and slept for three days. These numbers are statistically far too few to draw any accurate conclusions, but who among you would want to volunteer your hounds to complete the study?
For all practitioners, the safest drugs are those agents in which we have confidence and are most familiar. So those who use the thiobarbiturate or some other anesthetic regimen, there's obviously no reason to change. This article is directed at that person who has tried a method and is looking for something better.
Hopefully, in the future, through improved education we can avoid some of the unnecessary problems and errors we've committed in the past. When that day comes, we all benefit.
Dr. Rodger I. Barr, DVM
Foley Boulevard Animal Hospital
11247 Foley Boulevard
Coon Rapids, MN 554
"...fordi vi fortjener det!" - Azaar, Bahij og Djilál