Fentanyl-induced Ventilatory Depression

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Abstract
To determine whether infants are more sensitive than older patients to the ventilatory-depressant effects of fentanyl, patients were anesthetized with fentanyl and nitrous oxide (N2O) and ventilatory depression was assessed following elimination of N2O and in the immediate postoperative period. Three groups of patients were studied: infants (1-12 mo old, n = 14), children (1-5 yr old, n = 14), and adults (23-38 yr old, n = 13). Skin-surface PCO2 was measured to determine the peak PCO2 occurring at the end of anesthesia when end-tidal N2O concentration was < 6%. Naloxone was administered if PCO2 exceeded 70 mmHg. During recovery from anesthesia, ventilatory pattern was recorded using impedance pneumography to determine the longest breath-to-breath interval and the number of episodes of central apnea (defined as breath-to-breath intervals .gtoreq. 10 s in infants and children and .gtoreq. 20 s in adults). Elevation of PCO2 correlated with increasing plasma fentanyl concentrations but did not differ between groups. Four patients (two infants, one child, and one adult) required naloxone. The only subject who had a low plasma fentanyl concentration but required naloxone was a 6-wk-old infant; this was the only subject younger than 3 mo. For each range of fentanyl concentrations, the incidence of apnea increased with age, as did the number of episodes of apnea per subject. Fentanyl-induced ventilatory depression, as assessed by elevation of resting PCO2 during emergence from anesthesia and disruption of ventilatory pattern during recovery from anesthesia, is not greater in infants older than 3 mo than in children and adults. Whether infants and children differ from adults in the degree of ventilatory depression as assessed by other techniques, e.g., responses to inspired CO2, hypoxia, or inspiratory resistance, remains to be determined.