Anesthetic recovery is one of the most important periods of the anesthetic process, yet veterinary patients often receive minimal attention during this time. Important considerations in the recovering animal include ensuring a smooth and rapid return of consciousness, support of normal physiologic functions, and assessment and management of pain.
Preanesthetic Patient Management
Promotion of a smooth anesthetic recovery begins in the preanesthetic period. A discussion of the details of preanesthetic patient preparation is beyond the scope of this article; however, basic considerations include ensuring normal physiologic activity and minimizing pain and stress. Animals that are stressed in the preanesthetic period are likely to have stressful recoveries.
Hospitalization increases stress levels in many pets, leading to increased levels of circulating catecholamines, such as epinephrine and norepinephrine. These sympathetic neurotransmitters cause tachycardia and hypertension and increase the likelihood of tachyarrhythmia. High sympathetic tone may also decrease gastrointestinal motility, increasing the risk for regurgitation during anesthesia and subsequent postanesthetic esophagitis. Some patients, especially geriatric animals, may be better anesthetic candidates if they are not hospitalized the night before a procedure. A detailed discussion of the benefits and risks of hospitalization with the client will determine whether hospitalization is better for an individual animal.
Historically, veterinarians have advocated withholding food and water from pets for 12 hours before anesthesia. While several hours of fasting from solid food is still recommended, access to water should be allowed until the time for anesthesia. Prolonged fasting may actually increase the likelihood of reflux of acidic gastric fluid.1
Including appropriate antianxiety and analgesic drugs and techniques in the preanesthetic plan can significantly enhance recovery quality. A low dose of acepromazine may benefit an anxious animal and smooth both induction and recovery. Popular preemptive analgesics include opioids, such as butorphanol, transdermal fentanyl, buprenorphine, hydromorphone, and morphine; the alpha-2 adrenergic agonists xylazine and medetomidine; and such nonsteroidal antiinflammatory drugs as carprofen and meloxicam. Preemptive use of local anesthetic agents and techniques also greatly minimizes postoperative pain and improves recovery quality. Popular regional techniques include epidural injections, brachial plexus blocks, and such infiltrative blocks as dental and intercostal nerve blocks. Bupivacaine is the longest-lasting local anesthetic; thus, it may provide the most significant pain relief from preanesthetic injection into the recovery period. Recent reviews provide detailed information regarding local anesthetic drugs and techniques in dogs and cats.2,3
Patient Management During Anesthesia
The effect of anesthetic induction drugs on recovery depends on the duration of anesthesia and the drug used for maintenance. If the procedure is brief, the choice of induction drug may significantly influence recovery quality; however, if the animal is maintained under anesthesia longer than 20 to 30 minutes, the drug used to maintain anesthesia becomes more important for recovery quality than the induction drug. For short procedures, propofol has become the injectable anesthetic induction agent of choice-it offers a smoother and faster recovery than other injectable induction drugs. However, propofol does not provide analgesia, so other drugs must be given for pain relief during painful procedures, even if the procedure will be short.
Other options for rapid induction are isoflurane and sevoflurane. Either of these insoluble anesthetic agents offers rapid induction of anesthesia via face mask delivery; however, mask delivery can be stressful (consider chamber if possible) and is not be recommended when it is necessary to gain control of the airway rapidly. Pulmonary disease slows inhalant inductions. Sevoflurane may be preferred over isoflurane because it is less pungent and may be more readily accepted by the animal than isoflurane.
Whether sevoflurane or isoflurane offers better anesthetic recovery quality is controversial. Sevoflurane is slightly less soluble in blood than is isoflurane; as a result, recovery is a few minutes faster after discontinuation of sevoflurane than after isoflurane, but the difference has not been shown to be statistically significant. Additionally, speed of recovery does not necessarily equate to smoothness of recovery quality, and isoflurane and sevoflurane seem to offer similar quality of recovery in small animal patients. The decision of which inhalant to use is primarily a matter of personal preference and availability.
Providing intraoperative analgesia during painful procedures can help smooth recovery. Constant-rate infusion of such drugs as lidocaine, ketamine, and/or morphine has become popular for canine patients. In isoflurane-anesthetized cats, lidocaine infusion has been associated with hemodynamic compromise and cannot be recommended.4 Further research to determine the appropriate pharmacokinetics of lidocaine infusion in cats may allow for its use in the future. For extremely painful procedures, such as total ear canal ablations and forelimb amputations, placement of diffusion catheters before recovery from anesthesia allows for repeated administration of local anesthetic solutions into the painful site.