True liver dysfunction also warrants special attention; however, increases in the liver enzymes of an otherwise healthy patient are not an absolute reason to avoid anesthesia. In patients with liver dysfunction, hypoglycemia can be a concern due to insufficient glycogen storage and impaired gluconeogenesis. Dextrose supplementation may be necessary. If hypoproteinemia is present, the administration of fresh frozen plasma may be warranted. In general, delayed anesthetic recovery can be expected with the use of any anesthetic agent metabolized by the liver. Therefore, inhalants and drugs with specific antagonists such as opioids and α-2 agonists can be useful.
Areas of Controversy
The authors recognize that opinions vary regarding the administration of certain perianesthetic drugs. Some of these are briefly outlined here.
There are misconceptions about the effects of acepromazine in patients with seizure history. There is no evidence to show that acepromazine increases the risk of seizures in epileptic patients or patients with other seizure disorders.17,18
Indiscriminate use of anticholinergic drugs such as atropine and glycopyrrolate as part of a pre-medication protocol is controversial. Some think they should not be used routinely because the action will be short, and they may cause tachycardia, which increases myocardial O2 consumption and the potential for myocardial hypoxemia.
In contrast, the preemptive use of anticholinergics may be indicated for procedures with an increased risk of vagal bradycardia (e.g., ocular surgery) as well as in conjunction with opioid administration, to offset the potential bradycardic effects of the opioid. Anticholinergics may also be indicated in dogs with brachycephalic syndrome, which is associated with airway obstruction and higher resting vagal tone, making these dogs more prone to developing bradycardia than are other breeds.19
The simultaneous use of anticholinergics with α-2 agonists has been debated. Some practitioners prefer to administer anticholinergics to reduce the magnitude of bradycardia and associated drop in cardiac output. However, the combination creates the potential for myocardial hypoxemia to develop as a result of increased myocardial work. Use of anticholinergics should be based on individual patient risk factors and monitored parameters such as heart rate and blood pressure.20,21