Saving Sighthounds from Anesthetic Drug Death!
Due to Sighthound’s peculiar quirks, they have a potentially life-threatening, slow recovery reaction to and from anesthetic drugs.
Over the decades there have been a great many sighthounds who have died on the surgical table, especially Greyhounds, Scottish Deerhounds and Irish Wolfhounds, and or who have had significant difficulty awakening from anesthetics. Note, Great Danes appear to have the same heightened sensitivities, and great caution must be taken with them as well. Originally, most of these deaths were due to the administration of barbiturate anesthesia (pentobarbital) that was both slowly metabolized, and then combined with inaccurately high doses administered according to the sighthound's weight, resulted in respiratory arrest.
Today, the replacement drug in the U.S. is propofol, but even with this new, safer drug, recovery in Sighthounds can be double what is normal, taking 40 minutes instead of 20 minutes. It is a fact that each time my Wolfhounds are recovering from a surgical procedure it takes a minimum of 40 minutes for them to be able to stand. Why is this?
According to the Purina Corporation website article “Saving Sighthounds from Anesthetic Drug Death!” anesthetic drugs are highly fat-soluble, and Greyhounds (along with other lean-bodied sighthounds) sensitivity to these drugs was originally thought to result from a reduced ability of their tissues to “soak up” the drug, keeping it away from the brain. However, more recent work has implicated a reduced ability of the dog’s liver to break down and remove the drug from the body. Specifically, there appears to be a deficiency of an important drug metabolism enzyme, called cytochrome P450 (CYP) in these Sighthounds.
Identifying gene mutations responsible for breaking down, or metabolizing, commonly used drugs in Greyhounds and other sighthound breeds is the focus of research underway at Washington State University. Lead investigator Michael Court, BVSc, PhD, professor and the William R. Jones Endowed Chair, says the goal is to develop a drug sensitivity test from saliva, urine or blood that will identify dogs with a slow drug metabolism of certain drugs.
Most interestingly, these mutations are found primarily in Greyhounds and some sighthound breeds but rarely in non-sighthound breeds.
Until the development of a new drug that can ascertain a dog’s speed of metabolism and drug sensitivity tests are available proceed with great caution with your Irish Wolfhound under anesthesia! The outcome of which is decidedly dependent on the attending veterinarian's qualifications and their ethical Standard of Care.
Review and ask questions of your veterinarian before any surgical procedure! I urge Sighthound owners to find a Veterinarian who is experienced in Sighthound care. Discuss with your veterinarian the high-risks of anesthesia as Isoflurane must be administered with oxygen, and a veterinarian must be skilled and have very well-trained veterinary technicians. Oxygen and cardiovascular monitoring must be used in conjunction with the anesthesia. In rare cases, hypoxemia has occurred where the hound is deprived of sufficient oxygen while under anesthesia, causing irreversible damage and death. Most importantly, Irish Wolfhounds cannot be dosed according to their weight. A typical female Wolfhound weighing 150 pounds undergoing isoflurane anesthesia should be administered a dose for only a large dog weighing approximately 75 pounds. Appropriate dosing with propofol is imperative.
On this all-important subject is the proficiency of the attending veterinarian intubating the patient. I require that ONLY my veterinarian intubate my hounds and that NO veterinary technician is permitted to do so. I do so because there have been at least two incidents where dog's esophagus' have been mistakenly intubated and severely damaged. These dogs went on to die afterward from the related implications.
The National Greyhound Adoption Program (NGAP) publishes the following protocol they use on over 1000 Greyhounds annually
“We will anesthetize at least 1,000 greyhounds per year and have developed certain dosing protocols that are extremely safe for induction. Proper use of anesthesia during the procedure is certainly critical. Technicians must be skilled at regulating the isoflurane vaporizer and know how and when to regulate it based on the greyhound's breathing and reaction during the surgical procedure. If the appropriate protocol is followed using our anesthesia induction drugs, dogs will wake up calmly without thrashing around and come back to the full use of their limbs gradually and without injury. For the most part, even though we are using dexdomitor to induce sleep, we do not administer antesedan to wake them immediately. We simply let them awaken gradually. If you are going to use Antesedan after a procedure, we generally use 0.4 to 0.5 ml intravenously or intramuscularly. During all of our surgical procedures after intubation, dogs are monitored with vital signs monitors, including CO2, Doppler (indicating heartbeat), and temperature checks every 15 minutes.”
Dr. Aime Berman, DRVC Medical Director
“For almost every greyhound, the following is what we give intravenously. Total volume in the syringe should be 2mls. A few minutes after giving this IV injection, most greyhounds can be intubated and placed on oxygen and isoflurane. This cocktail typically works for all-sized greyhounds. However, if the dog is over 80 or 90 pounds, an additional 0.1 ml of each drug can be given.
0.5 ml Dexdomitor (0.5mg/ml)
0.5 ml Hydromorphone (2mg/ml)
0.5 ml Ketamine (100mg/ml)
0.5 ml Midazolam (5mg/ml)
For older greyhounds, or those with compromised kidneys or livers and/or heart disease, we use Butorphanol, Diazepam, and Propofol.
Place an IV catheter and give:
0.4 mg/kg Butorphanol (10mg/ml) IV, wait a few minutes
0.4 mg/kg Diazepam (5mg/ml)
6.0 mg/kg (or just to effect) Propofol (10mg/ml)
You should be able to intubate and place on oxygen and isoflurane after administering this protocol. If the dog is not staying asleep, 0.1 ml or 0.2 ml of Dexdomitor can be given IV in addition to the above Butorphanol/Diazepam/Propofol combination.”
Finally, here is an excellent article about Scottish Deerhound anesthesia that is certainly applicable to the Irish Wolfhound. Titled "Deerhound Anesthesia" by Dr. Betty Stephenson DVM, and reprinted from the March/April 2014 Claymore on the Scottish Deerhound Club of America "Health & Genetics" website. Read through it -- print it off -- and provide a copy to your Veterinarian(s) for future reference. Also, in an emergency, the attending doctor may not be your regular medical caregiver. So, I strongly urge you to have an electronic version of this article on your smartphone or iPad for quick and handy reference in the event of an emergency while traveling with your hound or in the middle of the night at 3 AM while you are at an Emergency Clinic.