A disturbing e-mail arrived the other day: Hello, Dr. Bellows: I have a 5-year-old yellow Labrador Retriever that I have routinely cleaned her teeth (with enzyme toothpaste and a brush, recently using Sonicare). Despite all best efforts, she is building up tartar and I think may have a dark spot (cavity on a rear molar).
I appreciate your time and hope you can provide some insight. Our Labrador has had general anesthesia several times, but I'm a bit skeptical to put her under anesthesia unless it is absolutely necessary.
I have seen some advertisements for non-general dental cleaning and was wondering if you are familiar with other anesthesia options? Can cleanings be done with IV sedation or simple acepromazine? Or do you intubate to protect the airway from debris?
Client anxiety about anesthesia is similar to dread of flying — fear of the unknown. To allay this trepidation, we take time to explain what happens and what we do to make the experience as safe as possible.
Case for anesthesia
To evaluate and clean teeth properly, general anesthesia is mandatory. Some veterinarians and non-veterinarians advertise anesthesia-free dentistry. This is a disservice to the patient, client and our profession.
The American Veterinary Dental College (AVDC) developed a position statement for veterinarians and the public. The AVDC prefers to use the more accurate term non-professional dental scaling (NPDS) to describe anesthesia-free dentistry.
Naturally, owners of pets are concerned when anesthesia is required. However, performing NPDS on an unanesthetized pet is inappropriate for the following reasons:
Professional dental scaling includes scaling the surfaces of the teeth above and below the gingival margin (gum line), followed by dental polishing. The most critical part of a dental scaling procedure is scaling the tooth surfaces that are within the gingival pocket (the subgingival space between the gum and the root), where periodontal disease is active. Because the patient cooperates, dental scaling of human teeth performed by a professional trained in the procedures can be completed successfully without anesthesia. However, access to the subgingival area of every tooth is impossible in an unanesthetized canine or feline patient. Removal of dental tartar on the visible surfaces of the teeth has little effect on a pet's health, and it provides a false sense of accomplishment. The result is purely cosmetic.
What can you do?
Choose the correct patient
When a client asks whether his or her dog or cat is too old for anesthesia, remember age is not a disease. However, older patients often are discriminated against that need urgent dental care to decrease pain and improve quality of life. No amount of antibiotics is going to help a companion animal suffering with mobile teeth secondary to Stage 4 periodontal disease. My point: Letting the periodontal syndrome rage on is far more dangerous than professional oral hygiene care performed under general anesthesia.
When the physical exam is normal in our office, age-appropriate and condition blood tests and electrocardiograph evaluations are performed. Thanks to the advent of easy-to-operate, economical blood analyzers, which deliver almost instantaneous valuable results, and handheld electro-cardiographic devices, all anesthetic procedures are preceded with patient blood analysis and ECG (Photo 2). Much like a pilot performing a pre-flight checklist, run through a list of critical systems beforehand. I also want to know as much as possible about the patient. Argument can be made that preanesthetic testing lacks evidence-based medical rational (preanesthesia lab testing and ECG equals or does not equal a successful anesthetic event), if you compare preoperative testing to a pilot's preflight checklist, both the veterinarian and pilot want to know as much as practically possible before an event. It just adds to our comfort knowing as much about our patient as practical before performing a procedure that will drastically alter its current status. Additionally, the testing makes the client feel more secure. Before dental anesthesia, my own clinically normal 4-year-old Lowland Sheepdog's blood work revealed a 3.9 creatinine, albumin 1.9, urine specific gravity 1.014 with 3+ protein and a urine-protein-creatinine ratio of 6.2!
For procedures expected to last less than two hours, our protocol is:
If all the preoperative tests are normal before the patient is anesthetized in our office, the doctor signs off on the case. Much like our pilot example, the procedure helps confirm that the tests were performed and evaluated.
The correct anesthesia protocol
Anesthesia protocols vary by patient age, condition, co-morbidity factors, length of and type of procedure. Local anesthetics are used on all operative dental procedures where tissue is incised. There are many anesthesia protocols; the best one is the one that you are most comfortable with. Here is the one that has met with success in our office:
For healthy dogs, our first choice is hydro-morphone 0.1 to 0.2 mg/kg or morphine 0.5 to 1.0 mg/kg combined with acepromazine 0.010 to 0.040 mg/kg. No anticholinergic unless patient demonstrates need, are pediatric or brachycephalic.
As they become more debilitated or aged, we shift toward hydromorphone 0.1 to 0.2 mg/kg alone or with midazolam 0.2 to 0.4 mg/kg. Still no anticholinergic unless specific need.
For healthy cats, our first choice is hydro-morphone 0.2 mg/kg or butorphanol 0.2 mg/kg combined with medetomidine 0.010 to 0.015 mg/kg, plus atropine.
As cats become more debilitated or aged, we use butorphanol 0.2 mg/kg or hydromorphone 0.2 mg/kg with 0.2 to 0.4 mg/kg midazolam. Ketamine is added 1 to 5 mg/kg as needed if fractious and not HCM cats. [HCM cats get a touch of medetomidine (0.005 mg/kg) as the next step.]
Induction agents (ket/val, propofol, etomidiate) are given intravenous after catheter placement.
Anesthesia is generally maintained with isoflurane or sevoflurane and oxygen. Little isoflurane or sevoflurane is metabolized, the insolubility of the inhalants allows for a speedier induction and recovery. Patient temperature is controlled in many ways including blankets, warm intravenous bottles placed next to the patient under the blankets, and a warm air Bair Hugger.
Intraoperative local anesthesia blocks are used to decrease pain, and the need for excessive anesthesia when painful procedures and contemplated.
The third leg of the anesthetic safety trilogy is evaluating the patient while anesthetized and after. Anesthesia monitoring varies from observing respiration and noting mucous membrane color refill, to arterial blood gas evaluation. American Animal Hospital Association (AAHA) anesthesia guidelines require that one or more of the following monitors must be used on the anesthetized patient:
As with any complicated endeavor, it is far better to know more. Some manufacturers incorporate multiple monitors into a master unit.
ECG evaluations before and during anesthesia give the veterinarian information regarding heart rate, rhythm and abnormal complexes. Lead 2 is primarily used to monitor rate and rhythm in patients under anesthesia. Handheld units used as part of the pre-operative patient evaluation can also perform single-lead continuous readings during the dental procedure.
Electrocardiograms can also be generated using esophageal probes. While anesthetized, the probe is inserted into the esophagus until the distal electrode reaches the area dorsal to the heart base. If the ECG tracing appears small, the probe may not be inserted far enough. If inserted too deep, the tracing can appear inverted.
The electrocardiogram gives minimal information on cardiac contractility and tissue perfusion. Presence of normal-appearing complexes does not indicate the patient's tissues are adequately perfused. The ECG should be used with another form of monitoring (end tidal CO2 and/or blood pressure) for patient evaluation during anesthesia.
Respiratory depression from anesthetic premedication, induction agents and inhalant anesthetics occur. The effects of these medications are dose-dependent and, when multiple agents are used, may become synergistic.
Apnea monitors alert the clinician when the patient's respiratory rate is depressed or stops. Most respiratory monitors detect exhaled airflow. The sensor is attached between the endotracheal tube and anesthesia machine's delivery tubes. Every time the animal exhales, the monitor emits an audible sound. When choosing an apnea monitor, it is important that the signal is loud enough to easily hear over the ambient noise and that an alarm sounds when breathing stops.
Hemoglobin travels through the blood in two forms: oxyhemoglobin and reduced hemoglobin. Most oxygen transported to the tissues is carried on the hemoglobin molecule. The pulse oximeter estimates the patient's oxygenation via light absorption measurement of arterial hemoglobin oxygen saturation. One of the most effective placements of the oximeter probe is on the tongue. Dental procedures by their nature involve movement and instruments in the mouth, which often dislodge the tongue oximeter probe. Other areas for probe placement include the pinna, toe, prepuce, vulva, metacarpus (tarsus), digits, tail and rectum.
Oxygen saturation should be maintained between 95 percent and 100 percent, particularly if the animal is breathing 100-percent oxygen. Saturation readings of 90 percent or less indicate marked desaturation, hypovolemia, shock or anemia.
The oximeter measures only the level of oxygen saturation and heart rate, which may be elevated when the patient hyperventilates in response to discomfort. Unfortunately, a hyperventilating patient also can inhale excessive anesthetic progressing to hypovolemia. Pulse oximeters do not measure how forcefully the heart is beating.
Blood pressure measurement
In human medicine, blood pressure measurement is part of most examinations and constantly evaluated under general anesthesia. In small animal practice, blood pressure measurement is equally important. The mean arterial pressure (MAP) should be greater than 60 mm Hg under anesthesia. If blood pressure drops below this level, the anesthetic concentration should be lowered.
Noninvasive blood pressure measurement uses a cuff placed around the patient's limb or tail at the level of the heart. In cats, the tail base may have to be clipped. The cuff diameter should be 40 percent of the circumference of the limb or tail base (3 cm in cats, 4 cm for small dogs, and 5 cm and up for larger dogs). Normal readings for anesthetized dogs and cats are systolic 90-105 mm Hg, diastolic 40-60 mm Hg, mean 60-70 mm Hg.
Commonly used types of noninvasive blood pressure monitors include:
Pressure-plethysmography provides systolic, diastolic and mean pressure using an inflatable cuff to occlude blood flow, and a sensor is placed distal to the cuff to detect arterial pulsation. The cuff is wrapped above the carpus, tail or below the hock, and the sensor placed on the same limb just below the cuff. Accurate placement over an artery is not essential. The cuff automatically inflates to a pressure, which occludes the underlying arteries and then deflates gradually. When the cuff pressure is equal to systolic arterial pressure, flow proceeds and arterial pulsation returns. After systolic and diastolic arterial pressures have been determined, the computer calculates the mean pressure.
Carbon dioxide measurement
Carbon dioxide is produced by all cells, transported by the circulatory system and eliminated through the lungs. Alveoli are sites of gas exchange. The highest concentration of carbon dioxide should occur at the end of expiration when the diluted gases from the trachea and primary bronchi are no longer being sampled. Changes in carbon dioxide levels reflect changes in metabolism, circulation and respiration. Measuring expired carbon dioxide allows an estimation of arterial CO2, which lets the veterinarian know whether the anesthetized patient is ventilating adequately.
Blood-gas acid/base monitoring
Blood-gas acid/base measurement can provide useful information in the anesthetized patient. While capnography and pulse oximetry give an indirect indication of respiratory function, direct measurement of pO2 and pCO2 can be made using arterial blood-gas measurements (obtained from the femoral or lingual artery). Typically, these measurements are done serially as rapid changes can occur with changes in the patient's respiratory function. As such, these parameters are sensitive indicators of what is at times a challenge in the compromised patient under anesthesia.
While venous blood gas is not as sensitive for measuring respiratory function, it can give valuable information about a patient's acid/base status. Acid/base condition is affected by both respiratory and cardiovascular function and as such is a valuable indicator in the anesthetized patient. Look for acidosis when CO2 accumulates due to compromised respiratory function, or when cardiovascular compromise leads to poor tissue perfusion. Analyzing the values also will indicate the degree the patient has compensated for the abnormality.
When the PCO is increasing (pH decreasing) and PO2 is dropping, the patient needs to be ventilated and the endo-tracheal tube evaluated for patency as well as the soda lime checked for expiration. If PCO2 is too low (and PH increasing), then the patient is over ventilating.
Temperature control and monitoring is important for dental patients. Dental procedures often last hours, during which the animal may be exposed to air conditioning and water irrigation. As the patient temperature decreases, so does the blood pressure and heart rate. Temperature monitors can be as straightforward as a technician inserting a rectal thermometer every 15 minutes and recording results, to a real-time constant digital evaluation.
Putting it all together....
Molly, a 16-year-old Poodle was presented to our office for dental care. Her owners, two general surgeons, could not tolerate her breath; even guests in their homes complained. As soon as I entered the exam room, I knew this dog was in dental trouble; the odor was intolerable.
Why did these highly educated, loving pet owners let poor Molly suffer so long? For the first 10 years of her life, they were afraid of anesthesia, and for the last six, three veterinarians said she was too old to safely perform dental care.
This story has a good ending. After age- and condition-appropriate blood and urine tests, radiographs and electrocardiogram, she was placed under three hours of general anesthesia for extraction of 26 teeth. Two weeks post procedure, her owners were ecstatic to have a "new dog".
How can we as veterinarians allay our client's fear of anesthesia for dental procedures? The answer is threefold: choose the correct patient, the correct anesthesia protocol, and proper monitoring during and after the procedure, so everyone wins.
Dr. Bellows owns Hometown Animal Hospital and Dental Clinic in Weston, Florida. He is a diplomate of the American Veterinary Dental College and the American Board of Veterinary Practitioners. He can be reached at (954) 349-5800; e-mail, [email protected]