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BREED CONSIDERATIONS FOR GENERAL ANESTHESIA

BREED CONSIDERATIONS FOR GENERAL ANESTHESIA

Scientific evidence supports only one breed-specific sensitivity to particular anesthetic drugs: greyhounds. But although other breeds may not have a true anesthetic sensitivity, they may still require specific considerations because of their anatomic, physiologic and metabolic characteristics. Some breeds also have a predisposition to diseases that can affect the course of anesthesia.

Considering breed differences and with proper preoperative workup, one can design a safe anesthetic plan with the lowest chances of complications.

  • Greyhounds (and other sighthounds) metabolize some drugs more slowly than the average dog. They lack the cytochrome P450 enzyme, needed for the metabolism of barbiturates, which can prolong recovery following anesthesia with thiopental up to four times. For induction, a ketamine/benzodiazepine combination, alfaxalone or propofol are safer choices. Compared to mixed-breed dogs, greyhounds also metabolize propofol more slowly, which may result in delayed recovery (slowly administer only to effect).

In addition to this, dogs with low body fat are more prone to hypothermia during anesthetic procedures and tend to have higher concentrations of lipophilic drugs (most anesthetic drugs) in the circulation. Recovery occurs through redistribution of the drug from the brain to the bloodstream and then to fat, but the lower volume of distribution maintains the concentration of drug in the brains, which can lead to prolonged recovery times.

  • About 73% of Dobermanns have a deficiency of von Willebrand factor protein, which impairs normal clotting. Because dogs with von Willebrand’s disease may require additional treatment to limit bleeding, this breed should be screened before elective surgery. If a Dobermann with unknown status is presented for emergency anesthesia, a buccal mucosal bleeding time (BMBT) should be performed.
    Dobermanns also have predilection for developing dilated cardiomyopathy.
  • Miniature Schnauzer (especially female) are at risk of developing sick sinus syndrome. The occult disease may be unmasked by anesthesia and can be fatal without an available pacemaker. Therefore, it is recommended to evaluate an ECG before giving a Miniature Schnauzer any anesthetic drug.
  • Certain familial lines (European) of Boxers seem to have an exaggerated response to the sedative and hypotensive effects of acepromazine. American lines do not appear to have this sensitivity. Although there is currently no published clinical evidence to support Boxer sensitivity to acepromazine, the use of anticholinergic is recommended in conjunction with acepromazine to prevent bradycardia (unless heart disease is present), the use of reduced doses (0,01-0,025 mg/kg) or avoiding acepromazine altogether in European-breed Boxers.
  • Brachycephalic breeds should be monitored closely after premedication, with oxygen source and endotracheal tube (they generally require smaller size) ready, because excessive sedation and muscle relaxation could result in occlusion of the upper airway. Avoiding heavy sedation is recommended. Short-acting induction agent (propofol) should be administered slowly to effect to reduce the likelihood of apnea, because of potentially difficult intubation. Pre-oxygenation can provide a longer window of time to intubate before the patient becomes hypoxic. At recovery, brachycephalic dogs should be extubated when they are bright, alert and will no longer tolerate the endotracheal tube, and they should continuously be monitored for hypoventilation, hypoxia and/or upper airway occlusion, which can result from residual sedation and muscle relaxation.

Because brachycephalic syndrome has been associated with gastrointestinal disease, and Bulldogs and Shar Peis are at greater risk for congenital hiatal hernias, some veterinary anesthetists routinely administer proton pump inhibitors to these dogs.

  • Herding dogs (e.g. collies, Australian Shepherds, Shetland sheepdog) may have a genetic mutation in the ABCB1 gene (formerly MDR1) that affects their ability to transport certain substances across cell membranes, which can lead to toxic accumulation of some drugs in the central nervous system. Of anesthetic agents, acepromazine and butorphanol have currently been found to produce exaggerated sedation and respiratory depression in dogs with this mutation. They should be used with caution at a reduced dose (by 25%) in dogs that are heterozygous and avoided in homozygous dogs.
  • The size of toy and small breeds poses a special anesthetic challenge. They are more susceptible to hypothermia due to greater surface area relative to body weight, so precautions should be taken to reduce heat losses. The small size of patients can also affect the accuracy of oscillometric monitoring – Doppler blood pressure measurement is more accurate for patients under 10 kg. Obtaining an accurate weight and using the appropriate dose of drugs is very important. It is also recommended to dilute relatively high concentrated drugs to ensure more accurate dosing.
  • Giant breeds generally require lower drug dosages than smaller dogs to achieve the same desired effect. Drug metabolism is more closely correlated to body surface area than to body weight, so calculating the dose based on lean body mass or body surface area would be more appropriate than on actual body weight.

LITERATURE

Duke-Novakovski T., de Vries M., Seymour C.: BSAVA Manual of Canine and Feline Anaesthesia and Analgesia, 3rd Ed. BSAVA, 2016

Kennedy M. J., Smith L. J.: Canine Breed-Specific Considerations for Anesthesia. Veterinary Practice News, August 2014

Krein S., Wetmore L. A.: Breed-Specific Anesthesia. Clinician’s Brief, March 2012