The authors compared the effects of administration of fentanyl 200 μg on the Ventilatory response to carbon dioxide in two groups of nine healthy unpremedicated subjects: one group received fentanyl as an intramuscular injection; in the other group, fentanyl was injected into the epidural space. In the intra muscular group, the slope of the venti-latory response to CO2 did not decrease significantly. In the epidural group, the slope of the Ventilatory response to CO2 decreased significantly from 2.48 ± 1.05 to 1.77 ± 0.7, 1.74 ± 0.7, and 2.07 ± 0.74 L·min-1·mm Hg−1 at 30, 60, and 120 min after injection (x ± SD, P ≤ 0.05), respectively. At each time of the study, plasma fentanyl levels were significantly lower in the epidural group than in the intramuscular group (P ≤ 0.05). These results suggest that epidural fentanyl induces a non systemic Ventilatory depression that may be due to the rostral spread of the drug.
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Nègre et al. (1987) studied this question.