Major Finding: Total bupivacaine consumption per hour of analgesia was significantly lower among patients who received 10 mL over 60 minutes (10.3 mg/hour), compared with 11.3 mg/hour for those receiving 2.5 mL/15 minutes and 11.1 mg/hour for 5 mL/30 minutes.
Data Source: Randomized, controlled, double-blinded trial of 180 laboring women.
Disclosures: Dr. Wong said she had no financial conflicts of interest.
SAN ANTONIO — Providing epidural anesthesia in programmed boluses of higher volume with a longer duration between doses decreased total anesthetic consumption and variability without decreasing patient satisfaction in a randomized, controlled, double-blinded study of 180 laboring women.
Increasing evidence suggests that delivery of epidural anesthesia via intermittent bolus provides more effective anesthesia than does continuous infusion, said Dr. Cynthia A. Wong of Northwestern University, Chicago.
In a previous study, Dr. Wong and her colleagues reported that the currently available pumps used for patient-controlled epidural anesthesia (PCEA) also can be programmed to automatically deliver boluses at regular intervals, and that this “programmed intermittent epidural bolus” (PIEB) resulted in similar analgesia but with a smaller bupivacaine dose and better patient satisfaction, compared with continuous epidural infusion (CEI) for maintenance of epidural labor analgesia (Anesth. Analg. 2006;102:904-9).
As a follow-up, the current study investigated the effect of specific combinations of bolus volumes and time intervals to determine which is optimal. The subjects were healthy nulliparas with cervical dilation 2-5 cm. All received combined spinal-epidural anesthesia comprising intrathecal bupivacaine 1.25 mg/fentanyl 15 mcg and a test dose of epidural lidocaine 45 mg/epinephrine 15 mcg. The epidural maintenance solution consisted of bupivacaine 0.0625% with fentanyl 2 mcg/mL. Breakthrough pain was treated with PCEA and if needed, a manual bolus dose by the anesthesiologist.
The maintenance epidural technique was initiated 15 minutes after the intrathecal injection. Patients were randomized to one of three groups: 66 received 2.5 mL by the pump every 15 minutes (2.5/15), 60 received 5 mL every 30 minutes (5/30), and 54 got 10 mL every 60 minutes (10/60). Thus, all patients received the same total volume of drug but it was distributed differently, Dr. Wong noted.
All of the women had successful analgesia, and there were no differences in maximum oxytocin dose or mode of delivery among the groups.
The primary outcome, total bupivacaine consumption per hour of analgesia, was significantly lower in the 10/60 group compared with the other two, with a mean of 10.3 mg/hr versus 11.3 mg/hr for the 2.5/15 patients and 11.1 mg/hr with 5/30. There was also less variability in dosing from hour to hour in the 10/60 group, she noted.
There were no significant differences in any secondary variable, including Visual Analog Pain score, motor block (Bromage greater than 0), number of PCEA requests, time to first request for manual bolus, number of subjects requiring manual bolus, patient satisfaction score, or extent of sensory blockade, as measured by both cold stimulus and von Frey hair threshold tests.
The mechanism isn't entirely clear. All studies of PIEB have shown that the technique provides equal or better analgesia than does CIE with a lower dose of drug. But, if as hypothesized, the reason is that boluses provides better spread in the epidural space, then it is “interesting” that this study found no difference in the extent of sensory blockade among the three groups. Indeed, data on the extent of sensory blockade in other studies of PIEB have been inconsistent, she said.
Other variables, such as differences in catheter design or patient demographics, might also contribute to the variability in extent of analgesia, she added.
In response to a question from the audience about whether these findings have changed her clinical practice, Dr. Wong noted that there is currently no commercially available pump that delivers both PCEA and PIEB.
However, her institution has “considerably backed off using continuous infusion rate” and now relies more on patient-controlled bolusing, resulting in a lower manual re-bolus rate. “There's very solid evidence that giving the drug as a bolus, by whatever means—by the patient, the machine, or the anesthesiologist—is a more efficient technique.
There is currently no commercially available pump that delivers both PCEA and PIEB.
Source DR. WONG