ACEPROMAZINE AND BUTORPHANOL

Acepromazine (10 mg/ml) was given at a dose of 0.05 mg/kg intramuscularly in the same syringe with butorphanol (10 mg/ml) at a dosage of 0.4 mg/kg intramuscularly. Acepromazine is a phenothiazine tranquilizer that acts by depressing the reticular activating system and suppressing the sympathetic nervous system.¹ It also has a marked antiemetic effect by inhibiting dopamine in the chemoreceptor trigger zone.¹ Butorphanol is an opioid that exhibits kappa agonist and mu antagonist effects, as it binds with opioid receptors in the CNS to produce analgesia and sedation.¹ Opioids are commonly used with tranquilizers to produce neuroleptanalgesia (a state of tranquility, altered awareness, and analgesia) and marked sedation.

Advantages

Disadvantages

The combination did not appear to affect the senses of touch, sight, or hearing at the observed dosages. Therefore, it did not provide enough sedation for phlebotomy and was not cost-effective (Table 2). Blood collection was attempted but was unsuccessful (< 50 ml blood collected).

SEVOFLURANE

Sevoflurane was given by mask at 4% to 5% for induction and 4% for maintenance with oxygen at a rate of 1 to 2 L/min. Sevoflurane is an inhalant anesthetic that has been approved in the United States for use in people since 1995.¹⁷ It has chemical properties similar to those of isoflurane but has a higher minimum alveolar concentration (MAC; the potency of an inhalation anesthetic, based on the concentration necessary to produce no response in 50% of patients exposed to a painful stimulus).¹ In practical terms, this means that sevoflurane is less soluble in blood and, therefore, allows more control over anesthetic depth and a more rapid recovery time.^17,18

When compared with other inhalants, such as halothane or isoflurane in people, sevoflurane has minimal cardiovascular effects such as arrhythmias, myocardial depression, and hypotension.¹⁷ It is also less irritating to the airways.¹⁷ Researchers have shown that arterial blood pressures in cats during sevoflurane-oxygen anesthesia were significantly higher than in those receiving either isoflurane- or halothane-oxygen anesthesia.¹⁹ However, other studies have shown that hypotension can occur with sevoflurane at twice the MAC, or a surgical plane of anesthesia, as well as with the other common inhalants.¹⁹ Like all inhalant anesthetics, excretion of sevoflurane occurs in the lungs and depends on pulmonary ventilation, blood flow, and drug solubility.¹

Advantages

Administration was painless and did not produce emesis or a prolonged excitatory phase. Induction was rapid, as an appropriate level of anesthesia was obtained in one to three minutes. Because cardiac output and peripheral perfusion are maintained, venipuncture and blood collection were smooth and efficient, with collection times ranging from five to 10 minutes. The cats were in a true state of anesthesia and were not responsive to environmental stimuli. This was safer for both the handler and the cat.

Recovery was rapid and was associated with minimal to no excitation. Cats were bright and alert within one hour. We also noted that cats were active and wanted to eat within an hour of recovering, and they did not vomit their food.

Disadvantages

Mask induction was stressful for a few of the more tense and aggressive cats. Preanesthetics were considered, but the benefits of rapid induction and recovery outweighed the disadvantage of occasional stress. In addition, gas inhalants are not reversible, and sevoflurane costs more than other gas inhalants (Table 2). Environmental exposure of the phlebotomist and handler was also a concern, even with an appropriate scavenging system. This protocol should not be used by pregnant women or women attempting to become pregnant. The sequelae of long-term exposure to low levels of sevoflurane are largely unknown. We were also concerned about inducing and maintaining anesthesia without securing an airway. An endotracheal tube was always available in case we needed intubation once we reached an appropriate depth of anesthesia with sevoflurane administered through the mask. However, intubation was never required.