Can parturients distinguish between intravenous and epidural fentanyl?

We tested the hypothesis that the sedative, euphoric, and analgesic effects of intravenous fentanyl would distinguish intravenous from epidural administration. One hundred ASA I and II labouring parturients received 100 micrograms fentanyl either iv or via an epidural catheter in a double-blind, randomized, cross-over fashion. Nineteen anaesthetists (8 staff and 11 residents) participated and correctly guessed the route of administration of the fentanyl in 61/66 intravenous doses and in 69/75 epidural doses yielding a sensitivity of 92.4%, a specificity of 92.0%, a positive predictive value of 91.0%, and a negative predictive value of 93.2%. Of the 41 patients that were crossed over, 38 (92.7%) were able to detect a difference between the routes of administration. Most patients experienced prompt, short-lived symptoms with iv fentanyl but no important differences in fetal heart rate pattern or in maternal desaturation were seen between the groups. This study suggests that subjective symptoms will accurately distinguish intravenous from epidural fentanyl administration in labouring parturients (P < 0.001), and should serve as a safe and reliable intravenous test dose for epidural anaesthesia in the obstetric population.