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How to Make Anesthesia Safer, Part 1

By Phil Zeltzman, DVM, Dipl. ACVS

Posted: May 2, 2012, 3:45 p.m. EDT

Achieving low mortality and low morbidity is not good enough in 2012. Our goals should also include excellent analgesia, patient comfort and minimal stress.

The American Animal Hospital Association recently published another great white paper, this time on the art of anesthesia. The “guidelines are not meant to establish a universal anesthetic plan or legal standard of care,” explain the authors (R. Bednarski et al., “AAHA Anesthesia Guidelines for Dogs and Cats,” JAAHA 2011, Vol. 47, p. 377–385). But they are an excellent review of common practices.

Full disclosure: What follows is not a summary of the article, but the first of a two-part review of a few great points made by the authors.

1. Breed-specific Concerns
Despite common concerns expressed by owners of certain breeds, “Few are documented,” the authors remind us. Two exceptions:
Brachycephalic dogs and cats clearly have a higher risk of upper airway obstruction.

Sight hounds may have a slower recovery when propofol or thiopental are used. Since thiopental is not available in the U.S., this is a good reminder to be cautious with propofol in those breeds.

veterinary anesthesia guidelines
Many things should be taken into consideration when anesthetizing an animal, including breed, age, temperament and health concerns.
We asked Richard Bednarski, a board-certified anesthesiologist at The Ohio State University and first author of the article, to clarify this important point about greyhounds.

“Studies indicate that the effects of propofol last twice as long as in other breeds. If you consider that it takes half an hour for other breeds to recover from a single propofol bolus, then a greyhound may take an hour.

“Therefore this may not be a significant clinical issue. Studies have identified a deficient cytochrome metabolic pathway in greyhounds. It may be the same one involved with delayed recovery from barbiturates.”

2. No Universal Recipes
The patient’s temperament should be taken into consideration. An aggressive or fearful patient may require higher drug dosages, whereas lower dosages may suffice for a quiet or depressed patient.

3. Caution with Sedation
Patients under general anesthesia, “Sedated patients require appropriate monitoring and supportive care.” These patients may require intubation and/or oxygen supplementation.

4. How Recent is Recent?
“There is no evidence to indicate the minimum time frame before anesthesia within which laboratory analysis should be performed.” So that time frame is up to the clinician. It should be reasonable in order to pick up changes that increase the anesthetic risk. Any pre-existing disease, the patient’s particulars and recent changes in the patient’s health are reasons to consider recent blood work.

American Society of Anesthesiologists Status Chart
1. Normal healthy patient
2. Patient with mild systemic disease
3. Patient with severe systemic disease
4. Patient with severe systemic disease that is a constant threat to life
5. Moribund patient who is not expected to survive without the operation.
5. Consider the ASA
Considering your patient’s American Society of Anesthesiologists score is a good way to prepare your team for potential risks. Studies show that, logically, patients with a higher ASA score have a higher risk of anesthetic complications.

6. Communicate
“There are routine surgeries, but there is no routine anesthesia,” as the saying goes. Risks should be verbally explained to pet owners, and should be summarized in the consent form, which the owners sign before anesthesia. “The proposed anesthetic plan and any available medical or surgical alternatives” should be discussed with the client.

7. Fasting Times
Pediatric patients (6 weeks to 4 months) should be allowed to eat up to four hours before surgery. Beyond 4 months, food should be withheld overnight. One exception exists: emergency situations. In such cases, pay extra attention to airway protection in case of vomiting or regurgitation and subsequent aspiration.

8. Premedication
Benefits of premedication include “lowered patient and staff stress, ease of handling, and reduction of induction and inhalant anesthetic doses.”

However, it is important to anticipate the side effects of “premeds.” They include “dysphoria related to benzodiazepines, bradycardia related to alpha-2 agonists and opioids, and hypotension related to acepromazine.” Appropriate dosing (adapted to each patient and each situation) and balanced anesthesia can circumvent these side-effects.

9. Analgesia
We are very fortunate to have a variety of analgesic drugs and techniques at our disposal, which often work synergistically. They include opioids, NSAIDs, local blocks (SQ lidocaine), nerve blocks, CRIs (Constant Rate Infusions) and NMDA receptor antagonists (e.g. ketamine).

endotracheal tube
The endotracheal tube should be left in place until a brachycephalic patient is alert. Photos Courtesy of Dr. Phil Zeltzman

10. Renal Disease
The authors are very clear: “No one anesthetic drug or drug combination is better for renal disease; most important is to maintain blood pressure and adequate renal perfusion.”

To achieve this important goal, azotemic patients could be perfused with crystalloids at 1.5–2 times maintenance to hopefully lower their azotemia before anesthesia is planned.

During anesthesia, crystalloid fluid rates as high as 20–30 mL/kg/hr have been recommended in kidney patients. Fluid therapy is then continued during the post-anesthetic phase.

Alternatively, low-dose mannitol can induce diuresis by increased renal perfusion pre-operatively.

11. Cardiac Disease (Part 1)
One important risk with cardiac disease is fluid overload, which can lead to congestive heart failure. The IV fluid rate should therefore be tailored to each patient, taking into consideration blood pressure, central venous pressure, oxygenation and lung sounds.

In spite of the required preop fasting period, “Cardiac medications should be administered normally the day of surgery.” It is important to understand potential side-effects of the patient’s drug regimen. For example, ACE inhibitors and beta-blockers may lead to hypotension, so inotropes may be required intraop.

12.  Cardiac Disease (Part 2)
Proof that universal recipes are not ideal for all patients: Some medications may be less than ideal in cardiac patients. For example, ketamine may be contraindicated in patients with hypertrophic cardiomyopathy, because it increases heart rate at higher doses. Alpha-2 agonists are not ideal in patients with mitral valve disease. Balanced anesthesia should help mitigate such side-effects.

Read PART 2 of this series here.

For more practical tips, visit AAHA's website. To watch a video of AAHA's anesthesia guidelines in action at Newport Harbor Animal Hospital, click here.

Dr. Phil Zeltzman is a mobile, board-certified surgeon near Allentown, Pa. He is the co-author of “Walk a Hound, Lose a Pound: How You and Your Dog Can Lose Weight, Stay Fit, and Have Fun Together.



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How to Make Anesthesia Safer, Part 1

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Reader Comments
I would like to see the demise of the terms "routine surgery" and "routine anesthesia". At least before the procedures and recovery have been completed. No anesthetic or surgical procedure is routine in advance. We shouldn't record it this way in our medical records and we shouldn't think of them this way. Indeed, this thinking might actually even contribute to some degree to lack of adequate vigilance for these procedures!
Len, santa cruz, CA
Posted: 11/8/2012 7:28:23 PM
Lost my first greyhound (3 yrs old) while under. The vet was careless. Had him under for 2 hours (quick cleaning??? and mole removal ???) Also the BIGGEST problem was that they did NOT monitor him as promised. They stopped recording vitals after 20 minutes.... Needless to say we sought legal advise. I KNOW that it is never safe in GH's. BUT - monitoring the dog would have helped to identify problems as they were happening. I honestly think the dog died earlier than the 2 hours - but no one noticed. This was VCA clinic - not a fly by night back country vet. We'll never know what happened. After a huge battle - they refunded all fee's and made a donation to the rescue group. I did not care about the money - I wanted them to find out what why monitoring stopped and why he was under 2 hours... and ensure it did not occur again to anyone else. My fear is they just didn't care. Needless to say - we changed vets and I make sure I tell EVERYONE I can about what this experience so that they know the importance of finding an Experienced Sight Hound Vet. Thank you for trying to continue the education process for all breeds that have higher risk.
GreytAunt, Rye, NH
Posted: 5/3/2012 12:02:35 PM
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