Anesthesia for high-risk dogs and cats

Doses on this pageEvery dose below is quoted from the cited source. Verify against the current label/formulary and the patient's full clinical picture.

Grading risk with ASA status

The ASA scale runs from class 1 to class 5. The AAFP guidelines list examples for each class:

• Class 1 is a normal patient, for example one presented for elective neutering.
• Class 3 is "severe systemic disease limiting activity but not incapacitating," such as well-controlled diabetes.
• Class 5 is a moribund patient not expected to live 24 hours without surgery [2].

Portier and Ida's 2018 systematic review pooled observational studies. The abstract reports 15 studies covering 258,298 dogs, cats, rabbits and pigs. The review found that ASA III or higher dogs had 3.26 times the risk of anesthesia-related death within 24 hours, and cats had 4.83 times the risk within 72 hours [1]. Combined data from dogs and cats also showed 2.34 times the risk of severe hypothermia during anesthesia in the higher-grade group [1].

The authors flagged several limitations:

• In dogs, results diverged sharply across studies once follow-up extended past 24 hours.
• Definitions of "anesthesia-related" death differed between studies.
• Collapsing five grades into two may have lost information.
• The scale itself is subjective [1].

They concluded that the classification "still needs to be refined to decrease inter and intra-raters variability" [1].

The AAFP guidelines cite one feline study that found ASA status a better predictor of perianesthetic complications than age. The guidelines also cite the CEPSAF enquiry, which identified age over 12 years as a risk factor independent of ASA status [2]. Separately, the AAFP panel notes that occult disease in cats makes accurate ASA assignment difficult [2].

Mortality figures across ASA classes and breeds

The authors of a 2026 review on canine mitral valve disease cite Redondo and colleagues (2024). According to that work, peri-anesthetic mortality rose from 0.08 percent in ASA 1 dogs to 15.73 percent in ASA 5 dogs [3].

A 2025 secondary analysis drew on a prospective, multicentre cohort of 55,019 canine procedures from 405 centres in 21 countries. After euthanasias and non-anesthetic deaths were excluded, 54,542 procedures remained. Over an observation window running from premedication to 48 hours after extubation, anesthesia-related mortality was 0.69 percent [4].

Brachycephalic dogs had higher crude mortality, 0.82 versus 0.65 percent. That difference weakened after ASA adjustment (adjusted RR 1.19, 95% CI 0.96 to 1.47) [4]. ASA-adjusted risk was elevated for the Chihuahua (RR 1.80) and the Spanish Water Dog (RR 2.72) [4].

The study's authors listed several limitations:

• Breed was recorded by clinicians.
• Data on urgency and procedure type were missing.
• Centre clustering was not modelled.
• Many comparisons were run without correction for multiple testing [4].

They described their findings as support for "breed-aware, ASA-centred risk communication" [4].

Source: Redondo et al. 2025 [4].

Preanesthetic workup in cats

The AAFP guidelines call for a physical examination before every anesthetic, with results compared against previous visits if available [2]. The guidelines recommend chemistry, CBC and urinalysis for mature and senior cats. Other tests, such as blood pressure, thoracic radiography and retroviral testing, are listed by life stage, and specific tests are indicated based on physical examination findings and signalment. NT-proBNP screening is described as a test to consider in at-risk breeds, because cardiomyopathy is often clinically silent [2].

A retrospective study cited in the guidelines looked at cats with a mean age of 11.6 years. Roughly 16 percent had concerning bloodwork results, and protocols were changed or procedures postponed in 9 percent of cases [2]. When a cat becomes distressed before an elective procedure, the panel describes rescheduling as a reasonable option. The panel notes that an incomplete examination raises the chance of missed comorbidities [2].

Feline comorbidities

The AAFP guidelines address several conditions [2]:

• Hypertrophic cardiomyopathy. The panel calls alpha-2 agonist use in these cats "controversial." It weighs concern about increased afterload against the possible benefits of lower stress and reduced inhalant requirements at low doses.
• Hyperthyroidism. A euthyroid state is described as desirable before elective anesthesia. The panel suggests starting antithyroid medication 2 to 3 weeks beforehand and rechecking thyroxine. For thyrotoxic cats needing emergency anesthesia, beta blockers are mentioned.
• Renal disease. The guidelines recommend IRIS staging to guide therapy. Some clinicians suggest preanesthetic intravenous fluids for cats with IRIS stage 3 or higher. Stopping enalapril 24 to 48 hours before anesthesia "may reduce the risk of intraoperative hypotension."
• Diabetes mellitus. The panel describes insulin decisions based on preprocedure glucose: no insulin below 8 mmol/l, half the regular dose at 8 to 15 mmol/l, and the full dose above 15 mmol/l. It recommends scheduling diabetic cats as the first case of the day and monitoring glucose every 30 minutes.
• Asthma. Asthma medications continue through the morning of anesthesia. Preoxygenation is advised if the cat tolerates it. Terbutaline is described as reducing complications during bronchoscopy.
• Obesity. Doses are based on ideal body weight. Mortality data cited in the guidelines show cats over 6 kg were three times more likely to die perioperatively than cats of 2 to 6 kg.
• Urinary obstruction. If hyperkalemia causes ECG changes or potassium exceeds 7 mEq/l, the panel advises lowering potassium and protecting the heart before sedation or anesthesia.

For critical emergencies, the guidelines advise stabilizing the patient before surgery whenever possible. They also recommend a hospital standard operating procedure for receiving emergencies, with simulated training for all team members [2].

Dogs with myxomatous mitral valve disease

Levinzon and colleagues' 2026 narrative review argues that a single ASA score "may not accurately reflect" anesthetic risk in dogs with preclinical mitral valve disease [3]. Its authors propose staging dogs with physical examination, radiographic vertebral heart size (VHS) and vertebral left atrial size (VLAS), NT-proBNP and point-of-care ultrasound. They state that echocardiography "remains the gold standard" [3].

The review sets out the following stages [3]:

• Stage B1. These dogs have soft murmurs, VHS below 10.5 and VLAS below 2.3. In the authors' view, they can receive standard protocols with minor modifications.
• Grey zone. These dogs have VHS of 10.5 to 11.5 or VLAS of 2.3 to 3.0. When further diagnostics are not feasible, the authors advise erring "on the side of caution" and managing them like Stage B2 dogs. Purely elective procedures may be deferred.
• Stage B2. The authors describe tailored protocols, enhanced monitoring and readiness for hemodynamic support. They consider alpha-2 agonists contraindicated at this stage because of increased afterload and bradycardia. They suggest small repeated fluid boluses (2 to 5 mL/kg) rather than large volumes.
• Stages C and D. The authors state these dogs should not undergo elective procedures until stabilized, and they recommend cardiology consultation and referral.

The review's authors advise continuing cardiac medications through anesthesia and giving oral pimobendan on the day of the procedure. They add that some anesthesiologists withhold enalapril until after recovery [3].

They also cite a retrospective study at a referral centre. In that study, dogs with heart disease, including those with Stage B2 or higher disease, had no more complications or deaths during routine dental procedures than healthy dogs [3]. The review describes this as one retrospective study at a referral centre.

Monitoring, staffing and recovery

The AAFP guidelines cite evidence that "having a dedicated anesthetist decreases mortality." They describe pulse and pulse oximetry monitoring as associated with lower mortality [2]. The mitral valve disease review calls for a dedicated clinician or well-trained technician to reassess depth, pulse, capillary refill and temperature [3]. The AAFP panel recommends checklists, emergency drug sheets calculated for each patient, and anesthesia records updated at least every 15 minutes [2].

For the purposes of its guidelines, the AAFP panel suggests SAP below 90 mmHg and MAP below 60 mmHg as the thresholds for hypotension [2]. The canine review notes that ASA 3 and higher patients generally have lower blood pressure under anesthesia [3].

Both sources treat recovery as a high-risk period. The canine review states that 47 to 81 percent of anesthetic deaths occur postoperatively [3]. The feline guidelines put 60 percent of cat deaths in recovery [2].

Before using any dose aboveVerify against the current label/formulary and the patient's full clinical picture.