Figure 2: Pooled estimate for risk of unblocked segments during labor epidural analgesia after use of air or liquid in the loss-of-resistance (LOR) technique. Twentyfive of 262 patients in the air group and 12 of 270 patients in the liquid group had unblocked segments. The pooled estimate and 95% confidence interval (CI) are to the right of 1, suggesting that, compared to use of liquid, use of air for LOR is associated with a significantly higher risk of unblocked segments (p = 0.03); RR, relative risk.