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Anesthesia

Why anesthesia does not work for all

10/10/2007

Question:

I am wondering why a person with no previous drug abuse is almost impossible to put under for a procedure? This person is 6 ft and 250lbs but has had no success using pain killers like morphine when hospitalized. Most recently he was not able to be put under for a colonoscopy. They think it is a history of drug use but it is not. Will you tell me what the other posiblilties it could be for future of this persons care.

Answer:

Thanks for your question.

There are very interesting variations in how people respond to anesthetic and sedative drugs. Recently I had a patient to whom we gave roughly ten times the usual "premed" sedative IV dose of midazolam (Versed) without any apparent effect on her. This patient was a rather petite middle-aged woman without a history of drug use or abuse. We often see large variations in how people respond to opioid pain-killer medicine (morphine is an example) also. A person who is of large build, as you describe, would be expected to need more sedative and pain-killer medicine than a person of average build.

You describe the experience as "no success using pain-killers". However, almost always, there is a dose-response curve. In other words, more drug, more effect. The problem is that prescriptions for opioids like morphine are usually written with a maximum stated dose, because of concerns for the side-effects of morphine, which include the suppression of breathing. Nurses cannot administer more than the prescribed dose. Even with patient controlled analgesia (PCA) the machine has preset limits, again for safety reasons. In these circumstances, somebody has to over-ride the prescribed or preset limits, while supervising the administration to make sure that unpleasant or dangerous side-effects do not occur.

There are also genetic variations in the metabolism of and response to PARTICULAR drugs including opioids. Sometimes switching opioids - e.g. trying hydromorphone instead of morphine, will produce results. Other times, additional pain-killer medications from a different class - e.g. ketamine - can be added with good effect.

The lack of success with colonoscopy suggests that similar drugs to the ones I've described above were used. Anyone with really high requirements for these medications will not have a great experience in the common setting of colonoscopy with nurse-administered sedation. In this setting, there will again be reluctance to administer the very high doses that might be necessary. The drug called propofol, which is both a sedative and anesthetic agent can be given by a properly credentialed anesthesia provider to achieve the deep sedative state needed for this outpatient procedure, and still produce safe, calm operating conditions, a relatively pleasant experience for the patients, and quick recovery for home-going.

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Response by:

Gareth S Kantor, MD Gareth S Kantor, MD
Assistant Professor of Anesthesiology
School of Medicine
Case Western Reserve University