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Hypotension

Hypotension is a common complication during anesthesia and is defined as BP values of systolic <80–90 mm Hg, mean <60–70 mm Hg, and diastolic <40 mm Hg.44 Evaluation of other physiologic parameters (capillary refill time, peripheral pulse palpation) can be used to aid in the diagnosis of inadequate blood flow. Balanced anesthetic techniques such as additional opioid or a local block may permit a further decrease in inhalant dose, thus improving BP. Complete avoidance of the inhalant anestheticmediated dose-dependent vasodilatation can be achieved by application of partial or total intravenous anesthesia techniques (Figures 7 and 8). An IV crystalloid (5–20 mL/kg, depending on patient needs) and/or colloid (1–5 mL/kg) bolus can be administered IV. If the patient is also bradycardic, administer an anticholinergic (atropine, glycopyrrolate) or sympathomimetic (e.g., ephedrine). If decreased cardiac contractility or excessive vasodilation are causing hypotension, administer a positive inotrope or vasoconstrictor, respectively (see table below). If hypotension continues, ensure that the patient is not hypoglycemic, hypothermic, or anemic/hypoproteinemic and that there is no electrolyte imbalance. Initiate BP support and corrective therapy if these abnormalities are present.

Drugs to support blood pressure in the anesthetized patient.

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IMPORTANT: The authors, reviewers, and editors of the material in the 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats have made extensive efforts to ensure that treatments, drugs, and dosage regimens are accurate and conform to the standards accepted at the time of publication. However, constant changes in information resulting from continuing research and clinical experience, reasonable differences in opinions among experts, unique aspects of individual clinical situations, and the possibility of human error in preparing such an extensive text require that the veterinarian exercise individual judgment when making a clinical decision and, if necessary, consult and compare information from other sources. In particular, the veterinarian is advised to check the drug’s product insert before prescribing or administering it, especially if the drug is unfamiliar or is used infrequently. 

These guidelines are supported by generous educational grants from IDEXX Laboratories, Inc., Midmark, and Zoetis Petcare.