Duration of intrathecal labor analgesia: early versus advanced labor.

Early first-stage labor pain is primarily visceral in origin. Increasing pain intensity and transition to somatic nociceptive input characterizes late first- and second-stage labor pain. The effect of this change in nociceptive input on the duration of intrathecal labor analgesia has not been well studied. This prospective cohort observational study compares the duration of intrathecal labor analgesia after intrathecal injections made in early labor (3- to 5-cm cervical dilation) and those made in more advanced labor (7- to 10-cm cervical dilation). Forty-one parturients (18 in early labor and 23 in advanced labor) received intrathecal sufentanil (10 micrograms) and bupivacaine (2.5 mg) as part of a combined spinal-epidural technique. Patients rated their pain using a 0-10 verbal pain scale prior to intrathecal injection and every 20 min thereafter. Duration of analgesia was defined as the lesser of time until the pain score exceeded 5 or until a request for supplemental epidural analgesia was made. The duration of spinal analgesia was significantly less when intrathecal injection was made in advanced labor (120 +/- 26 min) compared with early labor (163 +/- 57 min, P < 0.01). We conclude that cervical dilation and stage of labor significantly impact the effective duration of intrathecal sufentanil/ bupivacaine labor analgesia.