Patient-controlled epidural analgesia: the role of epidural fentanyl in peripartum urinary retention.

Background: Urinary bladder function is impaired during labor and delivery, predisposing to urinary retention. The effect of low-dose epidural opioid on bladder function remains unclear. We tested the hypothesis that adding low-dose fentanyl to epidural ropivacaine for patient-controlled labor analgesia does not promote urinary retention.
Methods: Laboring women who requested patient-controlled epidural analgesia were randomly assigned in a double blind study to 0.2% ropivacaine (R-group, n=100) or 0.2% ropivacaine with fentanyl 2 microg/mL (RF-group, n=98). Urinary bladder distension was assessed clinically every hour. The post-void residual urine volume was measured by ultrasonography. Urine volume exceeding 100 mL was drained by catheterization. Bladder volume of > or =300 mL, as determined by catheterization was considered as evidence of urinary retention.
Results: Thirty percent of the patients in each group developed urinary retention during labor. There was no statistically significant difference between the groups. There was an excellent correlation between bladder volume as estimated by ultrasonography and that by catheterization: catheterization volume=0.93 x ultrasound volume + 25; r(2)=0.83. The bias (mean error) was -1+/-99 mL and the precision (average absolute error) between the ultrasound estimate and actual bladder volume determined by catheterization was 58+/-79 mL.
Conclusion: Addition of fentanyl to patient-controlled epidural analgesia did not increase the risk of urinary retention. Ultrasound measurements were effective and reliable in assessing urinary bladder volumes during labor.