What can I use for induction if propofol and thiopental are not available? (Proceedings)


What can I use for induction if propofol and thiopental are not available? (Proceedings)

Aug 01, 2011

The practice of veterinary anesthesia has been impacted by the short supply of propofol and discontinued production of thiopental. Thiopental is officially in the "Discontinued Drug" list of the FDA. The company that used to make thiopental decided to stop production because of its stand against the use of this drug for lethal injections. On the other hand, propofol shortage was first experienced by human and veterinary practitioners as a result of a recall due to the presence of particulate matter in the propofol vials in the fall of 2009. This was followed by another recall of propofol due to microbial contamination found in another manufacturer's supply. Ultimately, the latter company stopped their production of propofol. It appears that there is still a short supply of propofol for practitioners. As a result of these events, veterinary practitioners have to find alternatives to propofol and thiopental for inducing anesthesia in dogs and cats. There are still injectable drugs on the market that can be utilized for this purpose. Hopefully, another injectable agent, alfaxalone, will be introduced to the US in the near future that will lessen the impact of the shortage problem of injectable agents. The objective of this presentation is to discuss the available injectable drugs and their methods of administration including dosages, expected effects and side effects.

Ketamine combinations

Ketamine is a dissociative agent approved by the FDA for use in cats but not in dogs. It is not used alone in dogs because of the high incidence of seizure, muscle rigidity, and violent and excessive movement. Even though it is not approved in dogs, it is used as an induction agent in dogs and cats in combination with a sedative. The sedatives that have been used include diazepam, midazolam, acepromazine, xylazine, medetomidine, dexmedetomidine, and Telazol.

Ketamine can be given simultaneously with a benzodiazepine. With the other sedatives (acepromazine and alpha-2 agonists), profound sedation must be achieved in dogs before it is administered. Ketamine is recommended as an induction agent in dogs and cats that received an alpha-2 agonist as premedicant. In cats, it can be used as a sole induction agent but the quality of induction is not as smooth compared when it is used with a sedative.

Ketamine will increase heart rate, blood pressure, and cardiac output by indirectly stimulating the sympathetic system; however, it has a direct negative effect on myocardial contractility. The respiratory depressant effect of ketamine is less compared with propofol and thiopental. Apneustic breathing is common following ketamine induction. Airway reflexes are usually present with ketamine. Some animals will swallow during endotracheal intubation but they can be intubated.

Table 1 shows the different ketamine combinations
Ketamine should not be given to patients with brain disease, hypertension, severe liver disease, and cats in renal failure. Ketamine will also increase intraocular pressure (IOP). Profound sedation mitigates this increase in IOP.