The Efficient Use Of Ketamine In Administering Anesthesia

With a few caveats that most clinicians wouldn’t classify as non-trivial, ketamine has been described as the “perfect anesthetic.” The World Health Organization has even taken the step of classifying ketamine as an “essential medicine.” It has a unique method of action, and its potential for harmful cardiovascular effects or respiratory depression is low. It can be given through various routes of administration and even has the useful advantages of bronchodilation and anti-inflammatory properties.

Further, ketamine has several methods of action depending on the site of administration. After IM or IV doses, ketamine non-competitively binds to the phencyclidine site of the N-methyl-D-asparate (NMDA) receptor. When given topically, ketamine blocks the conductance of ion channels and thus can display local anesthetic properties. It can also be given orally, nasally, rectally, subcutaneously and epidurally, although these routes are less common, and the bioavailability is also low.

The two biggest downsides of ketamine use in modern practice are the massive amounts of secretions seen after use and the occasionally severe hallucinations in some patients. The secretions can be largely mitigated with the administration of an antisialogogue, such as glycopyrrolate, 15-30 minutes before the dose of ketamine. The hallucinations are another matter entirely and are described as “out of body” experiences. These occur more commonly in females, patients older than 16 years of age and with larger ketamine doses. This is to be believed, because ketamine is a dissociative anesthetic, and patients appear conscious but become disconnected from their surroundings, as well as their own body, or process sensory input.

The chances of severe side effects are lowered with co-administration of a benzodiazepine, such as midazolam or if the patient is given a hypnotic, such as propofol, immediately before the ketamine. Ketamine is not recommended for use in any patient with elevated CSF pressure, as it increases CBF and thus raises CSF.

In my practice, which does not include pediatrics, I do not vary the dose except for extremes in body size. For patients between 50-150 kg, after premedication, as mentioned above, I will give no more than 20 mg IV, which I supplement with another 10 mg every 45-60 minutes. I also typically run an infusion of propofol at a rate of 50-100 mcg per kg every minute. Once the procedure comes close to an end, I slow down the propofol infusion and do not give any more ketamine in the last 45 minutes. This method has served me very well in my anesthetic practice.

Although I have not been able to eliminate any narcotic administration, I have found that my use of narcotics has decreased by at least 50 percent. This has the added benefit of less post-op nausea, and most patients tolerate this approach very well, often wondering when the surgery is going to start.