The ideal technique for identifying the epidural space remains unclear. Five-hundred-forty-seven women in labor who requested
epidural analgesia were randomly allocated to three groups according to the technique by which the epidural space was identified: 1) loss-of-resistance with air (air; n = 180), 2) loss-of-resistance with
lidocaine (
lidocaine; n = 185), and 3) loss-of-resistance with both air and
lidocaine (air-plus-
lidocaine; n = 182). We assessed ease of epidural
catheter insertion, characteristics of the blockade, quality of
analgesia, and complications. The inability to thread the epidural
catheter occurred in 16% of the air, 4% of the
lidocaine, and 3% of the air-plus-
lidocaine patients (P < 0.001). More patients from the air group had unblocked segments (6.6% versus 3.2% and 2.2%, respectively; P < 0.02). The incidence of accidental dural
puncture was greater in the air group (1.7% versus 0% in the other two groups; P < 0.02).
Pain scores, time to onset of
analgesia, upper sensory level, motor blockade, and the incidence of
hypotension, transient neurological deficits, postpartum
urinary retention, and
postdural puncture headache were comparable. Identification of the epidural space with air was more difficult and caused more dural
punctures than with
lidocaine or air plus
lidocaine. Additionally, sequential use of air and
lidocaine had no advantage over
lidocaine alone.