Abstract: We included in the review seven studies with a total of 852 participants. The methodological quality of the included studies was generally ranked as showing low risk of bias in most domains, with the exception of one study, which did not mask participants. We were able to include data from 838 participants in the meta-analysis. We found no statistically significant differences between participants receiving air and those given saline in any of the outcomes evaluated: inability to locate the epidural space (three trials, 619 participants) (risk ratio (RR) 0.88, 95% confidence interval (CI) 0.33 to 2.31, low-quality evidence); accidental intravascular catheter placement (two trials, 223 participants) (RR 0.90, 95% CI 0.33 to 2.45, low-quality evidence); accidental subarachnoid catheter placement (four trials, 682 participants) (RR 2.95, 95% CI 0.12 to 71.90, low-quality evidence); combined spinal epidural failure (two trials, 400 participants) (RR 0.98, 95% CI 0.44 to 2.18, low-quality evidence); unblocked segments (five studies, 423 participants) (RR 1.66, 95% CI 0.72 to 3.85); and pain measured by VAS (two studies, 395 participants) (mean difference (MD) -0.09, 95% CI -0.37 to 0.18). With regard to adverse effects, we found no statistically significant differences between participants receiving air and those given saline in the occurrence of paraesthesias (three trials, 572 participants) (RR 0.89, 95% CI 0.69 to 1.15); difficulty in advancing the catheter (two trials, 227 participants) (RR 0.91, 95% CI 0.32 to 2.56); catheter replacement (two trials, 501 participants) (RR 0.69, 95% CI 0.26 to 1.83); and postdural puncture headache (one trial, 110 participants) (RR 0.83, 95% CI 0.12 to 5.71). Low-quality evidence shows that results do not differ between air and saline in terms of the loss of resistance technique for identification of the epidural space and reduction of complications. Applicability might be compromised, as most of the results described in this review were obtained from parturient patients. This review underlines the need to conduct well-designed trials in this field.

Plain-language summary: Adults (18 years of age and older) undergoing surgical procedures, pregnant women in obstetrical labour and patients receiving postoperative pain relief. The evidence is current to September 2013. We found seven studies with a total of 852 participants. The maximum time that a participant was followed by the doctor was 24 hours after giving birth. The quality of the included studies was considered reasonable. The following results were examined: inability to locate the epidural space; accidental catheter placement (mis-insertion of the catheter); combined spinal epidural failure (cases of failed regional anaesthetic technique, which combines the benefits of spinal and epidural anaesthesia); unblocked segments (patchy block); and pain. We found no convincing evidence that results differed when air or saline was used. Because conducted studies were only reasonably well conducted (results very similar across studies; minor issues with study design; and not enough data), we ranked the overall quality of the evidence as low. The applicability of findings might be compromised, as most of the results described in this review were obtained from parturient patients. Low-quality evidence shows that results do not differ between air and saline in using loss of resistance technique for identification of the epidural space and in reducing complications.