Anesthesia and Sedatives in Cavalier King Charles Spaniels

In general, dogs affected with mitral valve disease and/or brachycephalic (short-muzzled) dogs may have an increased risk to anesthesia (anaesthesia) and sedatives. Pre-anesthetic evaluation, premedication, induction, maintenance of anesthesia (anaesthesia), and monitoring of anesthetized dogs and possible complications need to be taken into account.

In a March 2017 review of 1,269,582 dogs experiencing anesthetic episodes, including 982 dogs having anesthetic-related deaths, the researchers found that increasing age was associated with increased odds of death, as was undergoing non-elective procedures. The odds of death were significantly greater when pre-anesthetic physical examination results were not recorded  or when pre-anesthetic hematocrit (Hct) levels (the ratio of the volume of red cells to the volume of whole blood) was outside the reference range. Underweight dogs had almost 15 times the odds of death as nonunderweight dogs. The only hematologic or physiologic variable identified as significant was Hct outside the reference range in dogs, which was associated with a 5.5-fold increase in the odds of death, compared with results for dogs that had values within the reference range.

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MVD-affected Cavaliers

Anesthesia tends to reduce blood pressure, which in turn may slightly reduce the volume of mitral valve CKCS under anesthesiaregurgitation. Particularly in older dogs, anesthesia may have an adverse effect upon the blood pressure and kidney function, rather than on any cardiac function. Nevertheless, dogs with severe left atrial enlargement cannot excrete a sodium load efficently, and therefore during an anesthetic procedure, administration of a saline or lactated Ringer's solution (which contains sodium) is not recommended. Instead, an intravenous sugar solution of 5% dextrose in water (D5W) is advised.

Specialists recommend that an anticholinergic (Atropine or Glycopyrrolate) should be administered as needed during the procedure. The dog's heart rate and rhythm should be monitored durng the anesthetic procedure.

An excellent review of all aspects of anesthetizing dogs with MVD is discussed in this 2012 article by Austrian veterinarians Drs. Roswitha Steinbacher and René Dörfelt. See below this table from that article, listing "Cardiovascular effects of some important drugs used for anaesthesia". See also this very thorough outline of the process for cardiac patients, by the Veterinary Anesthesia & Analgesia Support Group..

Cardiovascular effects of some important drugs used for anaesthesia

In the August 2016 issue of Clinician's Brief, Colorado State University veterinarians Khursheed Mama and Marisa Ames thoroughly summarize the current views on the use of anesthesia on dogs in varying stages of mitral valve disease, as well as with common concurrent disorders. They state:

"Proper anesthetic management of patients with cardiac disease depends on the nature and severity of the disease. In a broad sense, the anesthetic approach to the cardiac patient is different for compensated vs decompensated heart disease. In addition, concurrent disease and requisite supportive therapies can cause decompensation of previously compensated heart disease. Understanding the underlying structural abnormalities and resultant physiologic consequences can influence the anesthesia protocol, periprocedural monitoring, and plans for emergency interventions."
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Brachycephalic Cavaliers

Care also should be taken when anesthesia may have to be administered to cavaliers with short muzzles or other brachycephalic features. In a March 2012 report by a team of Tufts University veterinary anesthesiologists, cavaliers are among brachycephalic breeds which require special attention when being sedated and anesthetized. Their advice includes:

"Avoid excessive sedation. Avoid α2-agonists. Administer acepromazine at half dose. Preoxygenate. Use short-acting induction agent. Use appropriately sized endotracheal tubes. Extubate after patient is sitting up, vigorously chewing, bright, alert."
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Dexmedetomidine

Dexmedetomidine often is used to sedate dogs before heart x-rays and echocardiographs. In a January 2016 report, researchers examined the effects of dexmedetomidine on six heart-healthy dogs undergoing chest x-rays and echocardiograms to determine if the sedative caused any changes in the resulting measurements. They found that the x-rays and echos performed after dosing dexmedetomidine resulted in significantly higher measurements of the vertebral heart score and cardiac size, and that moderate to severe mitral regurgitation and mild pulmonary regurgitation occurred in all six dogs. They concluded:

"Moderate-to-severe mitral regurgitation and mild pulmonic regurgitation occurred in all dogs after dexmedetomidine administration. Findings indicated that dexmedetomidine could cause false-positive diagnoses of valvular regurgitation and cardiomegaly in dogs undergoing thoracic radiography and echocardiography."
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Other Consequences

In a July 2010 article, Dr. George Strain reported permanent hearing loss to  62 dogs and cats -- none being cavaliers -- following anesthesia for dental and ear cleaning procedures. Forty-three of the reported cases occurred after dental procedures, and 16 cases after ear cleanings. See also Dr. Strain's October 2012 article.

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Research News

September 2016: CSU vets aptly summarize using anesthesia on MVD-affected dogs. In the August 2016 issue of Clinician's Brief, Colorado State University veterinarians Khursheed Mama and Marisa Ames thoroughly summarize the current views on the use of anesthesia on dogs in varying  stages of mitral valve disease, as well as with common concurrent disorders. They state:

"Proper anesthetic management of patients with cardiac disease depends on the nature and severity of the disease. In a broad sense, the anesthetic approach to the cardiac patient is different for compensated vs decompensated heart disease. In addition, concurrent disease and requisite supportive therapies can cause decompensation of previously compensated heart disease. Understanding the underlying structural abnormalities and resultant physiologic consequences can influence the anesthesia protocol, periprocedural monitoring, and plans for emergency interventions."

March 2016: Study shows that the heart x-ray and echo sedative dexmedetomidine can cause false diagnoses of MVD and heart enlargement. Dexmedetomidine often is used to sedate dogs before heart x-rays and echocardiographs. In a January 2016 report, a team of Taiwan researchers examined the effects of dexmedetomidine on six heart-healthy dogs undergoing chest x-rays and echocardiograms to determine if the sedative caused any changes in the resulting measurements. They found that the x-rays and echos performed after dosing dexmedetomidine resulted in significantly higher measurements of the vertebral heart score and cardiac size, and that moderate to severe mitral regurgitation and mild pulmonary regurgitation occurred in all six dogs. They concluded:

"Findings indicated that dexmedetomidine could cause false-positive diagnoses of valvular regurgitation and cardiomegaly in dogs undergoing thoracic radiography and echocardiography."

March 2012: Cavaliers are listed among brachycephalic breeds requiring extra care when being anesthetized.  In a March 2012 report by a team of Tufts University veterinary anesthesiologists, cavaliers are among brachycephalic breeds which require special attention when being sedated and anesthetized. Their advice includes:

"Avoid excessive sedation. Avoid α2-agonists. Administer acepromazine at half dose. Preoxygenate. Use short-acting induction agent. Use appropriately sized endotracheal tubes. Extubate after patient is sitting up, vigorously chewing, bright, alert."
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Related Links

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What You Can Do

If and when your cavalier is going to have an anesthetic procedure, make sure your veterinarian knows in advance about the possible hazards to your dog, and offer the veterinarian a copy of  this 2012 article by Austrian veterinarians Drs. Roswitha Steinbacher and René Dörfelt, and a copy of this 2016 article by Colorado State University veterinarians Khursheed Mama and Marisa Ames.

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QuiggsDedication

This article is dedicated to a ten year old male cavalier King Charles spaniel named Quiggs (right), who died in July 2015 of a cardiac reaction to anesthesia and sedation during a routine dental cleaning procedure.



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Veterinary Resources

Post-anesthesia deafness in dogs and cats following dental and ear cleaning procedures. Cathryn K. Stevens-Sparks, George M. Strain. Vet. Anaesthesia & Analgesia. July 2010;37(4):347-351. Quote: Objective: The present study was performed to document hearing loss in dogs and cats following procedures performed under anesthesia. Most cases of reported hearing loss were subsequent to dental and ear cleaning procedures. Study design: Prospective and retrospective case survey. Animals: Subjects were dogs and cats with deafness, personally communicated to one author, cases discussed on a veterinary information web site, and cases communicated through a survey of general practice and dental specialist veterinarians. Methods: Reported deafness cases were characterized by species (dog, cat), breed, gender, age, and dog breed size. Results: Sixty-two cases of hearing loss following anesthesia were reported between the years 2002 and 2009. Five additional cases were reported by survey respondents. Forty-three cases occurred following dental procedures. Sixteen cases occurred following ear cleaning. No relationship was observed between deafness and dog or cat breed, gender, anesthetic drug used, or dog size. Geriatric animals appeared more susceptible to post-anesthetic, post-procedural hearing loss. Conclusions: Deafness may occur in dogs and cats following anesthesia for dental and ear cleaning procedures, but the prevalence is low. The hearing loss appears to be permanent.

Breed-Specific Anesthesia. Stephanie Krein, Lois A. Wetmore. NAVA Clinicians Brief; March 2012; 17-20. Quote: "Certain breed differences can lead to greater risks for airway obstruction, increased responsiveness to anesthetic drugs, and delayed recovery, all of which can result in increased anesthesia-related morbidity and mortality. ... If cardiac disease is suspected, a full cardiac workup with a veterinary cardiologist is recommended. ... Brachycephalic Breeds (e.g. bulldog, pug, Boston terrier, boxer, Cavalier King Charles spaniel, Pekingese). Problem: Brachycephalic airway syndrome; increased respiratory effort; potential for upper airway obstruction. Avoid excessive sedation. Avoid α2-agonists. Administer acepromazine at half dose. Preoxygenate. Use short-acting induction agent. Use appropriately sized endotracheal tubes. Extubate after patient is sitting up, vigorously chewing, bright, alert. ... Brachycephalic breeds have anatomic considerations that may affect anesthetic outcome.Most brachycephalic breeds suffer from brachycephalic airway syndrome (BAS), which is characterized by stenotic nares, elongated soft palate, everted laryngeal saccules, and hypoplastic trachea. Affected dogs have narrower upper airways than do dogs with normal anatomic features. Because in brachycephalic breeds additional airway contraction can occur with stress (ie, increased respiratory effort, turbulent flow), clinicians need to be prepared for possible upper airway obstruction. Furthermore, brachycephalic dogs must be monitored closely after premedication, throughout anesthesia and the postoperative period, and after extubation. An oxygen source and endotracheal tube should be readily available. Many brachycephalic dogs respond well to acepromazine in conjunction with an opioid; however, the sedative dose should be half of that used for nonbrachycephalic dogs. Full mu-opioid agonists can be used but because they may cause excessive respiratory depression, a reversal agent should be available. Dexmedetomidine should be avoided because of the presence of high vagal tone in these breeds. Anticholinergics, such as glycopyrrolate, may be used to decrease airway secretions and counteract high vagal tone. Preoxygenation is recommended before dogs with BAS are induced. Propofol or a similar short-acting drug should be used for induction and intubation should be completed as rapidly as possible.Mask inductions should be avoided, and smaller endotracheal tubes should be used. Because brachycephalic breeds tend toward obesity, controlled or mechanical ventilation is often necessary.Most problems associated with mechanical ventilation occur during induction and recovery, so monitoring is particularly important. Extubation should be postponed until the patient is bright, alert, swallowing—even chewing on the endotracheal tube. If extubation is attempted while the patient is sedated and groggy from anesthesia, there is increased risk for upper airway obstruction. If upper airway obstruction occurs, the patient should be reintubated."

Canine Deafness. George M. Strain. Vety.Clinics.Sm.Anim.Pract. Oct.2012. Quote: Conductive deafness, caused by outer or middle ear obstruction, may be corrected, whereas sensorineural deafness cannot. Most deafness in dogs is congenital sensorineural hereditary deafness, associated with the genes for white pigment: piebald or merle. The genetic cause has not yet been identified. Dogs with blue eyes have a greater likelihood of deafness than brown-eyed dogs. Other common forms of sensorineural deafness include presbycusis, ototoxicity, noise-induced hearing loss, otitis interna, and anesthesia. ... Definitive diagnosis of deafness requires brainstem auditory evoked response testing. ... Anesthesia-Associated Deafness: Although uncommon, some dogs or cats that undergo anesthesia, especially fordental cleaning procedures, recover from anesthesia with bilateral deafness that in most cases is permanent. In a study of 62 reported cases in dogs and cats, no association was observed between deafness and breed, gender, anesthetic drug used, or dog size. Forty-three of the reported cases occurred after dental procedures, and 16 cases after ear cleanings. Geriatric animals seemed more susceptible to the hearingloss, which might reflect a bias because of dental procedures being performed more often on older animals. In at least one case, deafness was the result of a persistent otitis media with effusion, suggesting possible eustachian tube dysfunction subsequent to vigorous jaw manipulation during a dental procedure (unpublished observation). For most cases the cause is unknown and ongoing studies are pursuing possible mechanisms.

Anaesthesia in dogs and cats with cardiac disease – An impossible endeavour or a challenge with manageable risk? R. Steinbacher, R. Dörfelt. Wiener Tierärztliche Monatsschrift – Veterinary Medicine Austria. 2012. Quote: "Anaesthesia in patients with mitral valve insufficiency: Heart rate and blood pressure should be assessed already during preanaesthetic examination, in order to obtain reference values for intraoperative monitoring of these parameters. During anaesthesia, an increase of regurgitation must be avoided. Therefore, no centrally effective α2-agonists or massive infusion therapy should be given to avoid any increase in afterload. In these patients, a significant decrease in heart rate also leads to increased regurgitation as the increased ventricular filling enhances contractility. Any drugs, which induce an increase in vascular tone and, consequently, in afterload, like dopamine (in vasoconstrictive doses) and ephedrine, should also be avoided. Reducing the systemic vascular resistance by administering very small doses of acepromazine as a premedication in order to reduce the afterload is beneficial, as it reduces regurgitation and increases cardiac output despite reduced contractility. Excessive vasodilation, however, causes a drop in blood pressure, which in most cases can hardly be compensated for by the patient. Opioids like methadone or butorphanol, in combination with acepromazine, produce adequate sedation and, in addition, analgesia. As opioids, above all µ-agonists (e.g. methadone), can reduce the heart rate if administered at higher doses, an anticholinergic drug (like atropine or glycopyrrolate) should always be at hand when µ-agonists are used, in order to be prepared in case a drop in heart rate should occur. Whenever possible, induction of anaesthesia should be performed under complete monitoring and good preoxygenation. In severe cases, etomidate is a good choice as it has minimum cardiovascular side effects. In stable patients, low doses of ketamine can be used as an alternative, together with benzodiazepines or low doses of propofol. Negative inotropic drugs like propofol at high doses and thiopental can increase the regurgitation fraction in patients with severe valvular disease due to reduced forward propulsion of the blood and should therefore be used with caution. To maintain anaesthesia, inhalation anaesthetics can be used at concentrations that should be as low as possible. Another possibility is a partial or total intravenous anaesthesia using propofol, fentanyl or ketamine combinations (subanaesthetic doses). In case hypotension and bradycardia should occur, these can be treated by administration of anticholinergics. In doing so, the target heart rate should lie within the preanaesthetic range or slightly above. Should hypotension not be accompanied by bradycardia and not return to normal levels after reducing the concentration of the inhalant, positive inotropic drugs like dobutamine should preferably be administered."

Effects of intravenous dexmedetomidine on cardiac characteristics measured using radiography and echocardiography in six healthy dogs. Hsien-Chi Wang, Cih-Ting Hung, Wei-Ming Lee, Kui-Ming Chang, Kuan-Sheng Chen. Vet. Radiology & Ultrasound. January 2016;57(1):8-15. Quote: "Dexmedetomidine is a highly specific and selective α2-adrenergic receptor agonist widely used in dogs for sedation or analgesia. We hypothesized that dexmedetomidine may cause significant changes in radiographic and echocardiographic measurements. The objective of this prospective cross-sectional study was to test this hypothesis in a sample of six healthy dogs. Staff-owned dogs were recruited and received a single dose of dexmedetomidine 250 μg/m2 intravenously. Thoracic radiography and echocardiography were performed 1 h before treatment, and repeated 10 and 30 min after treatment, respectively. One observer recorded cardiac measurements from radiographs and another observer recorded echocardiographic measurements. Vertebral heart score and cardiac size to thorax ratio on the ventrodorsal projection increased from 9.8 ± 0.6 v to 10.3 ± 0.7 v (P = 0.0007) and 0.61 ± 0.04 to 0.68 ± 0.03 (P = 0.0109), respectively. E point-to-septal separation and left ventricle internal diameter in diastole and systole increased from 2.4 ± 1.1 to 6.6 ± 1.9 mm, 32.3 ± 8.1 to 35.5 ± 8.8 mm, and 19.4 ± 6 to 27.0 ± 7.2 mm, respectively (P < 0.05). Fractional shortening and sphericity index decreased from 40.7 ± 5.8 to 24.4 ± 2.9%, and 1.81 ± 0.07 to 1.58 ± 0.04, respectively (P < 0.05). Moderate-to-severe mitral regurgitation and mild pulmonic regurgitation occurred in all dogs after dexmedetomidine administration. Findings indicated that dexmedetomidine could cause false-positive diagnoses of valvular regurgitation and cardiomegaly in dogs undergoing thoracic radiography and echocardiography."

Anesthesia for Dogs with Myxomatous Mitral Valve Disease. Khursheed Mama, Marisa Ames. Clinician's Brief. August 2016. Quote: Proper anesthetic management of patients with cardiac disease depends on the nature and severity of the disease. In a broad sense, the anesthetic approach to the cardiac patient is different for compensated vs decompensated heart disease. In addition, concurrent disease and requisite supportive therapies can cause decompensation of previously compensated heart disease. Understanding the underlying structural abnormalities and resultant physiologic consequences can influence the anesthesia protocol, periprocedural monitoring, and plans for emergency interventions. This discussion focuses on the anesthetic management of dogs with varying stages of myxomatous mitral valve disease and commonly observed comorbidities.

Factors associated with anesthetic-related death in dogs and cats in primary care veterinary hospitals. Nora S. Matthews, Thomas J. Mohn, Mingyin Yang, Nathaniel Spofford, Alison Marsh, Karen Faunt, Elizabeth M. Lund, Sandra L. Lefebvre. J. Amer. Vet. Med. Assn. March 2017;250(6):655-665. Quote: Objective: To identify risk factors for anesthetic-related death in pet dogs and cats. Design: Matched case-control study. Animals: 237 dogs and 181 cats. Procedures: Electronic medical records from 822 [Banfield] hospitals were examined to identify dogs and cats that underwent general anesthesia (including sedation) or sedation alone and had death attributable to the anesthetic episode ≤ 7 days later (case animals; 115 dogs and 89 cats) or survived > 7 days afterward (control animals [matched by species and hospital]; 122 dogs and 92 cats). Information on patient characteristics and data related to the anesthesia session were extracted. Conditional multivariable logistic regression was performed to identify factors associated with anesthetic-related death for each species. Results: The anesthetic-related death rate was higher for cats (11/10,000 anesthetic episodes [0.11%]) than for dogs (5/10,000 anesthetic episodes [0.05%]). Increasing age was associated with increased odds of death for both species, as was undergoing nonelective (vs elective) procedures. Odds of death for dogs were significantly greater when preanesthetic physical examination results were not recorded (vs recorded) or when preanesthetic Hct [Hematocrit (Hct) Levels: the ratio of the volume of red cells to the volume of whole blood] was outside (vs within) the reference range. ... Underweight dogs had almost 15 times the odds of death as nonunderweight dogs. ... The only hematologic or physiologic variable identified as significant through multivariable modeling was Hct outside the reference range in dogs, which was associated with a 5.5-fold increase in the odds of death, compared with results for dogs that had values within the reference range. ... Conclusions and Clinical Relevance: Several factors were associated with anesthetic-related death in cats and dogs. This information may be useful for development of strategies to reduce anesthetic-related risks when possible and for education of pet owners about anesthetic risks.

Anesthetic Protocols for Brachycephalic Dogs. Tasha McNerney. Vet. Team Brief. March 2017. Quote: Brachycephalic dogs are becoming more popular as pets, which means veterinary nurses are more likely to be asked to anesthetize these dogs in practice. Brachycephalic dogs have a relatively broad, short skull, usually with the breadth at least 80% of the length.2 They often have anatomic abnormalities (eg, stenotic nares, elongated soft palate, hypoplastic trachea, laryngeal collapse, everted laryngeal saccules), known as brachycephalic syndrome, which can cause upper airway obstruction and mandate the use of special protocols when administering anesthesia.

Postanaesthetic pulmonary oedema in a dog following intravenous naloxone administration after upper airway surgery. Natalie Bruniges, Clara Rigotti. Vet. Rec. Casereports. June 2017;5(2). Quote: A cavalier King Charles spaniel was anaesthetised for upper airway surgery. A constant rate infusion of fentanyl at 6 μg/kg/hour and top-up boluses (5 μg/kg in total) were used for intraoperative analgesia. Intermittent positive pressure ventilation (IPPV) was instituted due to tachypnoea and inability to maintain normocapnia. Apnoea and severe hypercapnia developed after cessation of IPPV. IPPV was recommenced for 10 min to reduce hypercapnia, after which spontaneous ventilation returned. The patient had not awakened 45 minutes after isoflurane was turned off and 0.01 mg/kg naloxone was administered intravenously due to suspected fentanyl-induced narcosis. Following immediate arousal, the patient vomited and suddenly developed symptoms and radiographic changes consistent with pulmonary oedema. General anaesthesia was reinduced and 1 mg/kg furosemide was administered intravenously. IPPV was started with application of positive end expiratory pressure in an air/oxygen mixture for 60 minutes. Recovery was uneventful. This is the first report of a dog developing pulmonary oedema following intravenous naloxone.

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