ED50 of Alfentanil for Induction of Anesthesia in Unpremedicated Young Adults

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Abstract
The ED50 and ED90 of alfentanil for unconsciousness and anesthesia were determined. A bolus of alfentanil was given to 28 healthy unpremedicated adults undergoing gynecologic or orthopedic procedures in 1 of 4 dosages: 100, 150, 200 or 250 .mu.g/kg. Three indicators of induction were assessed 90 s later: eyelid reflex, response to verbal commands to breathe and response to placement of a nasopharyngeal airway. Succinylcholine, given at 90 s, was followed by tracheal intubation 1 min later. From probit analysis, the ED50 and ED90 for loss of voice response were 92 and 111 .mu.g/kg, respectively, and for loss of nasopharyngeal airway response, 111 and 169 .mu.g/kg. A high incidence of chest wall rigidity (75%) and movements of the limbs (54%) or eyes (25%) was seen. There were statistically significant increases of the heart rate prior to stimulation and of both the heart rate (21% rise) and systolic blood pressure (10% rise) from control to the peak value following intubation. Differences between alfentanil doses were not significant. Naloxone was required in 36% of patients for end-tidal PCO2 [CO2 tension] greater than 48 mmHg at emergence from anesthesia; no patient required additional naloxone. Nausea or vomiting occurred in 39% of all subjects. Two patients recalled placement of the nasopharyngeal airway. Evidently alfentanil is an anesthetic, and its ED50 (analogous to MAC [minimum anesthetic concentration] of inhalational agents) is 111 .mu.g/kg. The blood pressure and heart rate responses to laryngoscopy and intubation were modest after doses that allowed for extubation as early as 51 min after induction.