Anesthesia-related complications: From the guidelines

To be a safe anesthetist, it’s paramount to minimize anesthesia-related complications and risks by first assessing and addressing a multitude of patient- and procedure-specific parameters, including how the veterinary team, anesthetic equipment and drugs, and clients will influence them. Checklists, structured anesthetic plans, proactive team training protocols, and client education and communication—adjusted for each patient—can help make anesthesia care as safe, effective, and practical as possible.

Minimizing anesthetic risk also involves preparing for veterinary patients’ problematic physiologic responses to anesthesia. Learn to identify such responses as early as possible and scrutinize their cause. These highlights from the 2020 AAHA Anesthesia Guidelines for Dogs and Cats feature four anesthesia-related complications and their corrective measures. Refer to the complete guidelines for further information, including specific drugs and dosages.

Hypotension

Prolonged capillary refill time and weak peripheral pulses signal inadequate blood flow, and hypotension is defined as systolic ≤ 90 mm Hg, mean ≤ 70 mm Hg, and diastolic ≤ 40 mm Hg blood pressures.¹ Management may include:

• Avoiding inhalant anesthetic-mediated dose-dependent vasodilatation by using partial or total intravenous (IV) anesthesia.
• Administering an additional opioid or local block and decreasing the inhalant dose.
• Giving a bolus IV crystalloid or colloid, or both.
• Administering an anticholinergic or sympathomimetic to hypotensive patients who also have bradycardia.
• Giving a positive inotrope to patients whose diminished cardiac contractility is causing hypotension.
• Administering a vasoconstrictor to patients whose excessive vasodilation is causing hypotension.
• Initiating blood pressure support and corrective therapies for hypoglycemia, hypothermia, anemia, hypoproteinemia, and electrolyte imbalance when applicable, because these disturbances can contribute to hypotension.

Anesthesia-related complications: Hypoventilation

Observation allows subjective estimates of a patient’s respiratory rate and depth, but capnometry provides objective quantification. In awake patients, end-tidal carbon dioxide (ETCO₂) is ~ 35-45 mm Hg. In patients in a proper surgical plane of anesthesia, ETCO₂ is ~40-55 mm Hg.

Hypoventilation can cause hypercarbia, respiratory acidosis, and hypoxemia. If ETCO₂ is climbing, rule out excessive anesthetic depth by evaluating the vaporizer setting and assessing indicators of the patient’s surgical anesthetic plane. Start positive-pressure ventilation (PPV) if ETCO₂ is >60 mm Hg.

If possible, ensure that the patient is hemodynamically stable before starting PPV, because PPV can compromise venous return and adversely affect cardiac output. Deliver breaths manually by closing the adjustable pressure-limiting valve and squeezing the reservoir bag. (A mechanical ventilator can be used if the anesthetist is skilled in its use.) Close the valve only when delivering a breath. A safety pop-off relief valve protects against the consequences of forgetting to reopen the valve.

Recheck the patient’s blood pressure, and if it decreases after starting PPV, reduce the peak airway pressure and consider giving an IV crystalloid fluid bolus if the patient may be hypovolemic.

If hypercapnia persists, check for excessive dead space, exhausted CO₂ absorbent, dysfunction of one-way valves in a rebreathing circuit, or insufficient oxygen flow in a nonrebreathing circuit. If the machine is malfunctioning, quickly replace it with a different machine.

Anesthesia-related complications: Hypothermia

Ensure patients’ warmth throughout their perianesthetic period. Preventing hypothermia (core body temperature <98°F) helps avert many other anesthesia-related complications: impaired perfusion, cardiovascular dysfunction, respiratory compromise, delayed drug metabolism, cerebral depression, impaired wound healing, discomfort, and prolonged recovery.

Prevent severe thermal injury and use only supplemental heat sources designed specifically for anesthetized patients.  The most effective of these is a circulating warm water blanket or a warm air circulation system. Other methods that may slow heat loss include warm IV fluids, a fluid line warmer, and baby socks or bubble wrap to cover the patient’s feet.

Shivering increases oxygen consumption, so continue to give supplemental oxygen to shivering patients in recovery, especially those who have underlying respiratory or cardiovascular dysfunction.

Anesthesia-related complications: GER and regurgitation

When anesthetized patients exhibit gastroesophageal reflux (GER) and regurgitation, ensure endotracheal intubation and suction the esophagus, then lavage with saline or tap water. Instill diluted bicarbonate into the esophagus to increase pH.

It’s difficult to prevent GER and regurgitation, but preanesthetic administration of cisapride and omeprazole can minimize it. To help neutralize reflux pH in at-risk patients, also consider instructing clients to give omeprazole on the evening before and morning of anesthesia.

These measures help reduce the risks of esophagitis, aspiration pneumonia, and esophageal stricture.

Recovery

A large percentage of anesthetic-related deaths in dogs and cats occur within the first three hours postoperatively. Have trained veterinary personnel continue vigilant patient monitoring and supportive care, and administer applicable therapies until the patient is alert, normothermic, calm, comfortable, and ambulatory (unless the patient isn’t expected to be ambulatory postoperatively).

Photo credit: Kateryna Kukota via iStock / Getty Images Plus

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