Anesthetics: What Are They and How Do They Help Your Pet

By T. J. Dunn, DVM on Mar. 10, 2011

By T. J. Dunn, Jr., DVM

The perfect anesthetic eliminates all awareness of pain or discomfort and is 100 percent safe. The patient is unaware of its administration and it has effects other than blocking pain perception so it allows the patient to be fully conscious and communicative. It can be given as often as needed since it is not eliminated by nor stresses internal organs.

Unfortunately, the perfect anesthetic doesn’t exist. We can be thankful, though, that a variety of highly effective and safe anesthetics have been developed and are in common use today.

The veterinarian’s goal when administering injectable and inhaled anesthetic agents is to eliminate the dog’s awareness of pain or discomfort so that needed procedures can be accurately accomplished with minimal stress to the patient. The need to have an immobile patient during a surgical procedure is obvious.

In addition, some diagnostic procedures such as radiography and CT scans or those requiring physical manipulation or restraint rely on anesthesia for proper accuracy and data gathering. Without a fully relaxed, pain-free and immobile patient many vital diagnostic and surgical procedures would never be done.

Although the perfect anesthetic described above is a fantasy, those that are currently available to veterinarians are truly revolutionary compared to what was used in "standard anesthetic protocol" just a few decades ago.

For example, intravenous anesthetics based upon phenobarbital used to be commonly employed to render an animal unconscious during surgical or diagnostic procedures. The amount needed to induce a surgical level of anesthesia would persist for over an hour before the patient would even begin to recover even if the procedure only lasted five minutes!

And for longer procedures, repeated administrations of intravenous anesthetic would result in many patients still showing effects of the anesthetic many hours and even days after the event. Cardiac suppression, low blood pressure, tissue levels of oxygen and carbon dioxide often bordered on dangerous levels, and liver function was adversely impacted. The early days of inhalant gas anesthesia using ether and other agents had potentially harmful effects on the human veterinary staff if they inadvertently inhaled escaped gasses in the surgery room air.

With modern injectable and gas anesthetic agents and with advanced anesthetic delivery machines and methods, veterinary anesthesia closely parallels the safety level that is expected and achieved in human medicine.

Modern Anethesia Safety Issues

Veterinarian Will Novak has advanced training and certification in veterinary anesthesiology and is a board certified specialist with the American Board of Veterinary Practitioners. He shared with us his insight into modern anesthesia safety issues.

"The most significant change in the last ten years is doctors providing pre-operative blood tests so that they can determine the pet’s health status prior to general anesthesia," he explained. "The second biggest change is the monitoring of the patient with such instruments as a pulse oximeter which checks the patient’s heart rate and blood oxygen levels. The use of ECG's to check heart parameters also adds a level of monitoring security."

The successful outcome of any anesthetic-requiring procedure is only in part tied to the actual anesthetic. Careful patient evaluation, as Novak states, prior to the procedure is imperative! A conscientious physical examination, thorough medical record review, blood and urine testing, and clear communication and agreement between the doctor and client regarding the pros and cons of performing the procedure are absolutely necessary for consistent success. The doctor must “know the patient”; the dog owner must know the risk-versus-benefit parameters of the procedure. The doctor-client-patient relationship should be based upon objective testing before the procedure is done; only then can realistic subjective assessment of the expected benefits be performed.


Dog owners should set aside the idea that age alone dictates whether or not an anesthetic-required procedure should be considered. An excellent example is a recent patient of mine named Digger, a 16-year-old West Highland White Terrier. He was suffering from long-standing oral infections, advanced gingivitis, loose teeth, foul mouth odor and he had difficulty eating due to the pain in his mouth. Too much emphasis on chronological age interfered with judgments made years prior regarding the health benefits of a thorough dental procedure under anesthesia. Now the owner was desperate to help little Digger.

The clinic staff assured the owner that Digger’s chronological age was of secondary relevance; of primary importance were Digger’s total health status (irrespective of age) and the objective measurement of his health parameters. Usual hospital protocols were followed and his blood and urine test results were quite good. Appropriate pre-anesthetic medications were given, monitoring devices provided us with real time patient data, an intravenous catheter delivered fluids and IV induction anesthesia, and modern gas anesthesia was administered through an endotracheal breathing tube during the dental procedure.

Within five minutes after the final polishing of Digger’s remaining teeth and a thorough rinsing of his oral cavity he was awake and wondering how he got in the recovery cage! The prospects for a newly energized, comfortable, healthier, and huggable Digger were excellent.

Many other successful cases underscore that fact that chronological age does not, by itself, disqualify the use of general anesthesia.

Advancements in Anesthetics

What improvements might we see in the future regarding anesthesia in animals? Novak predicts, "In the near term most of the anesthesia improvements will be in gas anesthetics. These are great products because they are so easy to control in the patient. We currently use one called sevoflurane, which is the same one often used in human pediatric cases. We are continually looking for safer and better ways to provide pain free procedures. Most of the safety in the future of both human and pet anesthesia is based on improvement in the protocols and patient monitoring."

Note that Novak emphasizes patient monitoring. New patient monitoring instruments and techniques are available to veterinarians today that are vastly improved over what was considered practical just a few years ago.

The American College of Veterinary Anesthesiologists recommends specific patient monitoring guidelines that many animal hospitals follow. These include close observation and recording of circulatory status (heart rate and blood pressure), ventilation assessment (depth and frequency of respirations and blood gas concentrations), and fine tuning the concentration of anesthetic delivered to the patient. Placement of an intravenous catheter allows for quick administration of supportive medications if they are needed. In addition, there should be a trained staff member who is responsible for direct observation of the patient throughout the anesthetic period.

Be aware that problems arising in a patient under anesthesia may not be related to the anesthetic at all! Surgically induced blood loss, hypothermia, low blood pressure, vomiting with subsequent inhalation of gastric contents, and undiagnosed pathology such as an infection that triggers septic shock and circulatory collapse all could contribute to an adverse outcome for the patient. Treating every patient as a unique entity is precisely why close patient monitoring is the norm during anesthetic events.

The next time your veterinarian brings up the topic of anesthesia be encouraged that modern veterinary medical protocols and anesthetic agents, both injectable and gas, are widely available to all practitioners. Ask questions, do the pre-operative tests, obtain input on what procedures the veterinarian considers appropriate for your dog.

If the "pros" for doing the procedure far outweigh the "cons," your dog’s health status and quality of life stand to improve thanks to modern anesthetic administration and standardized protocols that greatly improve the prospects for a successful outcome for every patient.

Image: Honou / via Flickr


T. J. Dunn, DVM


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