Blocked dermatomes 15 min and 24 h after an injection of ropivacaine or saline in the paravertebral space in the paravertebral group and control group, respectively. Evaluations of blocked dermatomes were performed through cold ice tests; at 15 min, significantly more patients had at least one dermatome blocked in the paravertebral group than in the control group (84.8% [95% CI, 77.7 to 90.3] vs. 43.7% [95% CI, 35.4 to 52.2]; P < 0.001). At 24 h, the difference between the two groups concerning blocked dermatomes was still observed, although it was less marked (78.2% [95% CI, 69.9 to 85.1] vs. 64.9% [95% CI, 56.1 to 73.0]; P = 0.019).