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Understanding anesthesia in canine dentistry

They also represent a source of fear and concern for pet owners—witness the burgeoning anesthesia-free dental cleaning services that have become popular.

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Premedication prior to dental surgery allows for a calm patient at induction and permits pre-oxygenation with a face mask.
Premedication prior to dental surgery allows for a calm patient at induction and permits pre-oxygenation with a face mask.

They also represent a source of fear and concern for pet owners—witness the burgeoning anesthesia-free dental cleaning services that have become popular.

Given this situation, it is worth investing time and energy to establish comprehensive dental anesthesia standard operating procedures (SOPs) to minimize the incidence of unexpected adverse events. Part of the power of SOPs is they provide structure to the sequence of steps that ultimately become routine, ensuring certain aspects of patient care are not accidentally omitted. Think of every patient leaving your hospital after a successful (i.e. uneventful) dental surgery as a walking endorsement and promotion for your practice’s reliability and its worthiness of clients’ trust.

A robust dental anesthesia SOP needs to effectively address the unique challenges dental surgery presents, such as:

  • prolonged duration of anesthesia, sometimes unexpectedly;
  • aged patients with concurrent diseases; and
  • oral pain.

According to the North American Veterinary Anesthesia Society (NAVAS), all patients undergoing dental procedures should be anesthetized with an endotracheal tube (ETT) secured in place to ensure a patent airway and to prevent aspiration of foreign material.

The following addresses the special anesthesia and analgesia challenges associated with canine and feline dental procedures in relatively healthy patients.

Pre-anesthesia evaluation

Monitoring throughout the dental procedure with appropriate equipment and a trained anesthetist is critical to ensuring a successful outcome.
Monitoring throughout the dental procedure with appropriate equipment and a trained anesthetist is critical to ensuring a successful outcome.

Whenever possible, evaluate the extent of oral pathology to anticipate the degree of postoperative pain and the duration of anesthesia. You’ll need to be flexible though, as the full extent of oral pathology is often not determined until the patient is under anesthesia and dental radiographs have been performed.

Be very cautious about scheduling anesthesia and dentistry for a dog that is anorexic or losing weight. Both conditions are rarely caused by dental disease. Therefore, it is wise to look for another explanation for such symptoms before proceeding. A full investigation of the patient’s underlying health is highly recommended to avoid postoperative complications and poor recovery.

Anticipated problems

The following are associated with all anesthesia delivery:

  • hypotension;
  • hypoventilation;
  • hypothermia; and
  • hypoxemia.

These issues are part and parcel of anesthesia delivery. Depending on the patient’s health status, duration of the procedure, support, and the anesthesia drug protocol selected, they may be mild, moderate, or severe. In addition, the following events are particular to dental/oral surgery and need to be considered and planned for:

  • tracheal and pharyngeal trauma due to repeated endotracheal tube motion;
  • post-extubation airway spasm and obstruction as a result of pharyngeal trauma and fluid accumulation;
  • tracheal aspiration of fluid and solid material;
  • postoperative oral pain;
  • excess bleeding during maxillary tumor resection; and
  • venous air embolism during use of dental drills.

Premedication

Perform dental blocks as soon as possible and prior to cleaning to allow adequate time for onset of effective block.
Perform dental blocks as soon as possible and prior to cleaning to allow adequate time for onset of effective block.

Patients undergoing dental surgery are rarely in acute pain prior to the procedure, unless they have suffered a head injury or have a mandibular or maxillary tumor. Beyond pain management in these situations, the purpose of premedication for all patients is to calm the animal and facilitate handling, as well as to help reduce dose requirements for induction drugs and inhalants. Pain control for most dental procedures comes afterward, once the patient is under anesthesia and can undergo dental nerve blocks. Opioids that are excellent analgesics are unfortunately poor solo premedication choices when the goal is to calm a patient. All patients undergoing general anesthesia benefit from premedication.

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Choose from among the following to facilitate IV catheter placement and handling:

  • Acepromazine 0.05 mg/kg + butorphanol 0.2 mg/kg IM
  • Acepromazine 0.05 mg/kg + meperidine 4.0 mg/kg IM
  • Acepromazine 0.05 mg/kg + methadone 0.25 mg/kg IM
  • Acepromazine 0.05 mg/kg + hydromorphone 0.05 mg/kg IM (Note: high risk of vomiting)

(Dex)medetomidine 2-5 ug/kg IM can be substituted for acepromazine to achieve more profound relaxation. For any of these premedication combinations, you may consider lowering the dose in elderly or less anxious patients as long as the goal of a calm patient who does not resist handling can be achieved at the lower doses.

If an IV catheter can easily be placed without chemical restraint, consider IV premedication with butorphanol 0.1 mg/kg + midazolam 0.1 mg/kg. You may opt to add atropine 0.02 mg/kg or glycopyrrolate 0.01 mg/kg IM to the above protocols except when (dex)medetomidine sedation is chosen.

Induction

Choose from the following titrated to effect in 1/4 doses IV:

  • IV alfaxalone 2 mg/kg
  • IV propofol 3 mg/kg +/- ketamine 2 mg/kg (mixed in one syringe or administered as ketamine followed by propofol)
  • IV ketamine 5 mg/kg + diazepam (or midazolam) 0.2 mg/kg

The use of mask or chamber induction is discouraged as it:

1) presents no safety advantage compared to IV anesthetic induction and can be less safe due to high doses of potent inhalants;

2) is resented by most patients, especially those with facial or oral discomfort; and

3) exposes the anesthetist to unacceptable levels of waste anesthetic gas.

Maintenance

Deliver sevoflurane or isoflurane by cuffed endotracheal tube. For maxillary resection, and any time you are unhappy with the level of analgesia provided by dental nerve blocks, supplement inhalant anesthesia with your choice of opioid (e.g. fentanyl, hydromorphone, morphine) or ketamine constant rate infusion or a combination of the two.

Monitoring

In addition to a trained and attentive anesthetist overseeing a procedure, the following are NAVAS’s standard monitoring procedures:

  • Blood pressure with either an oscillometric or Doppler-based monitor
  • Temperature, whether nasal, rectal, or esophageal. You might be surprised at just how quickly and profoundly your patients become hypothermic
  • Heart rate and rhythm via some form of continuous audio signal (ECG, pulse oximeter, Doppler sound) so you don’t miss an episode of sudden bradycardia associated with vagal stimulation during dental manipulations. Place an esophageal stethoscope before the other monitors are operational and as a backup in case the audio signal disappears unexpectedly
  • Respiratory rate and rhythm—this requires keen powers of observation and a thorough knowledge of what is normal and abnormal when it comes to breathing patterns
  • Verifying an intact ETT cuff seal by intermittently delivering a breath and listening for gas escaping around the mouth
  • Blood loss assessment—keep a close eye on the amount of blood loss during maxillary surgery
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Support

Sometimes a patient needs to remain under anesthesia for longer than anticipated as a result of extensive dental pathology or difficulties with extractions. It is never a “bad” decision to complete the dental surgery in two separate visits. However, if a healthy patient is properly supported so that monitoring trends demonstrate a pattern of stable vital signs, the animal can remain under anesthesia for many hours.

What kind of support is required to provide these working conditions for the dentist?

1) Heat supplementation to prevent hypothermia: ensure the heat source has a thermostat and does not come in direct contact with the patient. Thermostats can fail though, so it is important to run your hands between the heat source and the patient to ensure the proper amount of heat is being delivered. Accidental patient burning is painful and avoidable. It also is deleterious to a practice’s reputation Accidental burns involve some or all of the following circumstances:

  • failure or absence of a thermostat;
  • direct contact between the patient and the heat source;
  • prolonged contact with the heat source; and
  • wet fur.

2) IV fluid therapy should continue throughout the entire period of anesthesia, though at a tapering rate to avoid iatrogenic fluid overload in the event of a prolonged surgical period. American Animal Hospital Association (AAHA) has recently published its fluid therapy recommendations. The guidelines are well thought out and discourage a one-size-fits-all for fluid therapy during anesthesia. The hourly crystalloid fluid rate for dogs under anesthesia is 5 mL/kg/hour and for cats, it is 3 mL/kg/hour to be reduced during longer periods of anesthesia.

Post-dentistry analgesia

Here are a few recommendations to maximize your success with dental nerve blocks:

  • Perform dental blocks with bupivacaine prior to all extractions
  • Time the dental nerve block placement so at least five and preferably 10 minutes elapse before surgical manipulation starts
  • Placing a nerve block and then performing non-painful manipulations such as dental radiographs, charting, or cleaning is a way to use up some of the time required for bupivacaine’s onset of effect
  • Do not dilute bupivacaine with lidocaine or saline, as this will delay the onset and shorten the duration of the postsurgical analgesia
  • 0.2-0.5 mL/site is a recommended volume of bupivacaine to instill, and a total dose of 2 mg/kg
    (0.4 mL/kg of 0.5% bupivacaine) is an acceptable total dose for both canine and feline patients. At this dose, there is no need to dilute the bupivacaine and there is probably enough volume to permit a repeat of a block if it appears to be patchy or ineffective
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Follow the nerve blocks with postoperative injectable carprofen, meloxicam, or robenacoxib. These can be dispensed as home analgesia for three or more days post-dentistry. Although one peri-operative dose of NSAID is unlikely to cause your patient difficulties, be sure to document effective urine concentrating ability by way of a urinalysis before prescribing NSAID medication to go home with the patient.

Systemic opioid use in combination with dental nerve blocks may predispose the patient to post-anesthesia agitation or dysphoria after dental extraction surgery, but is appropriate after maxillary surgery.

Keep in mind the above approach to analgesia for oral surgery works well for all procedures except maxillary surgery, which is usually associated with underlying painful cancer and the surgical site cannot be rendered completely numb with local nerve blocks. As such, systemic analgesia is required peri-operatively and extending out a week or more after surgery. There are several options for analgesia following maxillary surgery and often a multimodal approach employing a combination of an opioid (e.g. fentanyl patch or oral trans-mucosal buprenorphine) with a NSAID will be more effective. l

Originally from Montreal, Que., in Canada, Nancy Brock, DVM, DACVAA, graduated from the University of Guelph in 1982. She completed residency training in anesthesia and critical care at the University of California, Davis in 1988, becoming a diplomate of the American College of Veterinary Anesthesia and Analgesia (ACVAA) in 1995. Dr. Brock helps veterinarians deliver safe, effective anesthesia/surgical pain control to their patients via telephone consultations and live video telemedicine support. She is the current secretary of the North American Veterinary Anesthesia Society (NAVAS) and can be reached at info@mynavas.org.

Kris Kruse-Elliott, DVM, PhD, DACVAA, received her DVM from Oregon State University in 1984 and became board certified as a diplomate of the ACVAA in 1989. Currently, she is the anesthesiologist in charge of anesthesia services for Sage Veterinary Centers, a large San Francisco Bay area-based group of specialty veterinary practices. Dr. Kruse-Elliott is the current president of NAVAS.

For resources and more information about anesthesia safety, visit the North American Veterinary Anesthesia Society’s website at mynavas.org.

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