Abstract: We included 33 trials with a total of 2293 participants from 0.9 to 12 (mean or median) years of age. Most trials were at low risk of selection, detection, attrition, and reporting bias, however the lack of blinding of participants and personnel caring for participants resulted in 25 trials being judged as at high or unclear risk of bias. We identified five ongoing trials. Ultrasound guidance probably reduces the risk of failed block (risk difference (RD) −0.16, 95% confidence interval (CI) −0.25 to −0.07; 22 trials; 1789 participants; moderate-quality evidence). When ultrasound guidance was used, there was a small to moderate reduction in pain one hour after surgery, equivalent to a reduction of 1.3 points on the revised Bieri FACES pain scale (scale; 0 = no pain, 10 = maximal pain) (standardized mean difference (SMD) −0.41, 95% CI −0.74 to −0.07 (medium effect size); 15 trials; 982 participants; moderate-quality evidence). Ultrasound guidance increases block duration by the equivalent of 42 minutes (SMD 1.24, 95% CI 0.72 to 1.75; 10 trials; 460 participants; high-quality evidence). There is probably little or no difference in the time taken to perform the block (SMD −0.46, 95% CI −1.06 to 0.13; 9 trials; 680 participants; moderate-quality evidence). It is uncertain whether the number of needle passes required is reduced with the use of ultrasound guidance (SMD −0.63, 95% CI −1.08 to −0.18; 3 trials; 256 participants; very low-quality evidence). There were no occurrences of major complications in either the intervention or control arms of the trials (cardiac arrest from local anaesthetic toxicity (22 trials; 1576 participants; moderate-quality evidence); lasting neurological injury (19 trials; 1250 participants; low-quality evidence)). There may be little of no difference in the risk of bloody puncture (RD −0.02, 95% CI −0.05 to 0.00; 13 trials; 896 participants; low-quality evidence) or transient neurological injury (RD −0.00, 95% CI −0.01 to 0.01; 18 trials; 1230 participants; low-quality evidence). There were no occurrences of seizure from local anaesthetic toxicity (22 trials; 1576 participants; moderate-quality evidence) or block infections without neurological injury (18 trials; 1238 participants; low-quality evidence). Ultrasound guidance for regional blockade in children probably decreases the risk of failed block. It increases the duration of the block and probably decreases pain scores at one hour after surgery. There may be little or no difference in the risks of some minor complications. The five ongoing studies may alter the conclusions of the review once published and assessed.

Plain-language summary: We included 33 well-designed studies with a total of 2293 children in which ultrasound guidance was compared with another method of nerve localization (traditional landmarks techniques or nerve stimulator) for regional blockade in children. Sources of funding included a government organization (two studies), a charitable organization (two studies), and an institutional department (13 studies). Two studies declared that they received industry help (equipment loan). The source of funding was unclear for 14 studies. Ultrasound guidance for regional blockade in children may decrease the occurrence of failed block. It may also increase duration of the block and reduce pain at one hour after surgery. Ultrasound guidance may decrease the number of needle passes required to perform the block. However, because the vast majority of blocks in children are performed with the child under deep sedation or general anaesthesia, the true value of this finding might be arguable. There were no major complications in the included trials. There may be little or no difference between study groups in risks of minor complications. Altogether, whether or not these findings justify the extra cost of ultrasound guidance should probably also take into account the anaesthesiologist's expertise and local resources. The five ongoing studies may alter the conclusions of the review once published and assessed. We assessed the quality of the evidence as moderate for decreased occurrence of a failed block and improved pain scores at one hour; high for prolonged block duration; and very low for decreased number of needle passes.