[Acute selective tolerance to remifentanil after prolonged infusion].

We describe the cases of 3 patients who received anesthesia with remifentanil continuously infused at rates of 0.8 to 1.25 micrograms.kg-1.min-1 for at least 3 hours. Upon emergence from anesthesia, after withdrawal of the anesthetic gas, satisfactory levels of consciousness, spontaneous breathing and absence of pain were achieved under maintenance doses of remifentanil greater than 0.8 microgram.kg-1.min-1; such doses are related to the development of ventilatory depression, apnea and significant sedation. Acute tolerance to remifentanil is under debate at present. Such tolerance involves decreased efficacy of an opiate or the need for higher doses to maintain an effect after exposure. The development of tolerance is related mainly to the pharmacokinetics of an opiate, a short half-life and infusion periods exceeding 3 hours, and in the case of remifentanil, to the use of high doses. The most likely explanation for de phenomena described would be the development of selective acute tolerance to ventilatory depression and to sedation, with no effect on the antinociceptive effects of remifentanil. Clinical trials should be carried out to assess the development of acute tolerance to remifentanil and its possible perioperative repercussions.