Preoperative pharmacology and anesthetic risk.

Chronic or preoperative drug therapy may contribute to the overall risk of anesthesia by modifying organ function directly, or by altering the response of the patient to anesthetic agents or adjuvants. Many drug-patient and drug-drug interactions can be predicted from analysis of their expected effects upon the neurohumoral control systems that normally maintain physiological homeostasis, especially those involving the release or termination of action of catecholamines or acetylcholine. Current concepts of biotransformation, especially as regards hepatic microsomal function, are so broad that estimates of the toxic potential of the metabolites of anesthetic drugs still require an empirical approach for each agent considered.