Veterinary anesthesia: Understanding risk management, adverse outcomes

Denver — Considering the latest advances in veterinary anesthesiology, how should veterinarians prepare for cases that require anesthesia? What's new and what has changed?

Dr. Kurt Grimm

Kurt Grimm, DVM, MS, PhD, Dipl. ACVA, Dipl. ACVCP, is a veterinary anesthesiologist, owner of Veterinary Specialist Services in Conifer, Colo., and works with the surgeons at the Veterinary Referral Center of Colorado in Denver. He has edited several texts on anesthesia and pain management.

Grimm spoke with DVM Newsmagazine recently about his field and the challenges of anesthetizing complex patients.

DVM:How has the field of anesthesiology changed in recent years? Do you think the advances have kept pace with growth in other areas of veterinary medicine?

Grimm: The profession has changed so much in the last 15 years. When I graduated in 1995 there wasn't a great emphasis on the care of geriatric pets because a lot of sick animals, especially older ones, were euthanized. Today, for a lot people, that's a last resort. So we are dealing with a lot of complex cases, coexisting diseases and cases that we may not have been trained very well to handle but are now forced to manage.

For example, I see many cats with stable chronic kidney disease and horrible dental disease. That's one of the biggest reasons I get called out to private practices — to give anesthesia for generally routine procedures like dentistries but on older patients that have chronic kidney disease.

Additionally, there wasn't a perceived need or a market in private practice for anesthesiologists. Historically, there were so few board-certified anesthesiologists in private practice people didn't think about using our services to manage anesthetic-related risks. In the last decade that started to change. As surgeons have advanced in the level of surgery that they're performing, having an anesthesiologist there can bring the level of anesthesia and monitoring to a higher level.

However, not all cases have to be referred nor should they be. If practitioners are appropriately prepared they can probably do just as good of a job as most of us. But the types of patients that they don't routinely anesthetize or that are very complex — an anesthesiologist is better prepared to deal with the risks and potential complications that may arise during anesthesia.

DVM:What do you recommend for preoperative care, and how might you modify your approach for the more complex patient?

Grimm: You gather history, do diagnostics and identify the things that are impacting the patient. Then you develop an anesthetic plan that tries to mitigate the risks. When you run into cases that have a long list of coexisting problems, the risks increase. Every time you add another element to the equation, it makes things more complex; you must plan to manage all the risks simultaneously. Occasionally we find something we didn't expect to find, and it postpones the surgery or even changes the owner's decision about going forward with surgery.

If a patient has a pre-existing condition that you either know about or suspect based on physical examination, then it's hard to justify not doing pre-anesthetic diagnostic testing to assess the patient's current status.

I think you'll find plenty of people who say packed cell volume and total solids are adequate for preoperative blood work, but a number of us believe that both a complete blood count and serum chemistry are good practices. If something unexpected is found, then you can consider other diagnostic tests — ultrasounds, X-rays, ECGs — to figure out whether it's a serious problem. The odds of finding something significant with young, healthy animals is relatively low, but occasionally one of them will have, for example, elevated BUN and/or creatinine values. It's worth taking time to figure out if it's either a serious problem or simply dehydration, which can be easily corrected with preinduction fluid administration.

The more information you have, then the more informed decisions you can make about what anesthetics to use or, more importantly, not to use, and what you can rule out as a cause of any intraoperative complication.

Sometimes the sicker patients are easier to plan for. Usually they've been well worked up so you have a lot of information and a complete history.

DVM:How should practitioners prepare when faced with administering anesthesia to patients with more complex medical issues?

Grimm: It's all about management of risk, and monitoring is the key to risk management in anesthesia. Occasionally there will be two diseases present in the same patient, which normally would be managed completely opposite to each other if either presented by itself. For instance, consider heart disease and kidney disease. One of the things that puts stress on the kidneys is hypovolemia. But if the animal has bad heart disease, and you give too much fluid to prevent hypovolemia, then congestive heart failure may develop.

When you get caught in those situations, you have to come up with a plan that gives you several options. If you start to have problems with blood pressure, then you have to re-evaluate whether you want to give more fluid or add inotropic medications to help support myocardial contractility.

If the patient is doing well, then you might want to stop or slow fluid administration. Close monitoring, like ECG, constant use of pulse oximetry; intermittent arterial blood pressure; arterial blood gases to monitor oxygenation, ventilation and lactate production; and auscultation of the lungs to make sure that you aren't developing pulmonary edema, are essential.

Older patients generally do well as long as you adjust drug dosages, account for any concurrent diseases and monitor appropriately. One consideration with older patients is that, over time, they can use up their reserve organ function. For example, as patients age they may lose the extra nephron function they had when they were young. Liver function probably is decreasing with age, too. You have less margin for error, but if you monitor them carefully problems can be caught quickly, and you can intervene to reduce further cellular injury and loss of organ function.

Obese patients are commonly anesthetized for routine procedures, and they usually do quite well if managed appropriately. Where they really become tough to deal with is during the recovery process while weaning them off oxygen and putting them back on room air. They're still under the depressive effects of the anesthetic drugs and the opioids we often use for pre-anesthetics, so close monitoring of ventilation and oxygenation is important.

Again, it all boils down to good monitoring and early intervention if you detect a problem.

While they're anesthetized, patients with upper-airway diseases such as tracheal collapse, laryngeal paralysis and brachycephalic airway syndrome usually do well because they are getting oxygen, and you have a protected airway.

There may be some challenge at induction if you have a hard time with intubation. And most of the time they extubate well but, sometimes, after you pull the tube out, you can't get them to oxygenate. Then you have to put an airway back in and figure out another plan. Of course at that point you may be talking tracheostomy or other surgical intervention, but often a slow, carefully monitored recovery will allow extubation without emergency surgery.

DVM:What advice can you give practitioners, especially when it comes to avoiding adverse outcomes?

Grimm: Be prepared before you start. The hardest thing about anesthesia is that you don't have the luxury of time. If you're caught off-guard, then you're trying to play catch-up. Veterinarians who are prepared or technicians who are well-trained are at an advantage because they don't have to spend precious time trying to figure out what's going on and learning how to solve the problem. They've developed the skills they need to deal with those emergencies.

Additionally, selecting cases to anesthetize that don't exceed the skill level of the people in your practice can minimize catastrophic complications and poor anesthetic outcomes.

Our profession is very diverse, and care providers have a range of skill levels, environments they work in and constraints they work under. One standard anesthetic or monitoring protocol doesn't fit all, and I think everybody has to remember that.

The adverse outcome that everybody worries about is death, which is an extreme and permanent catastrophic outcome. Most published studies indicate that about 1 in 2,000 dogs and cats die during the anesthetic period. If you look only at sick patients, it tends to increase to about 1 in 500. Interestingly, for healthy human patients it's unusual to have an anesthetic death.

There are many reasons dogs and cats are so much more prone to anesthetic mortality, but to improve mortality rates in the veterinary profession we may want to approach an accidental death or complication in a manner similar to when a plane crashes. In that case the NTSB (National Transportation Safety Board) tries to dissect the situation the best it can, recreate it, figure out what went wrong and what can be done to prevent future incidents.

I think that's a good approach to take in our practices. Sometimes it makes a difference, sometimes it doesn't. But an honest evaluation of what happened is usually beneficial.

Wetzel is a freelance writer in Cleveland, Ohio.