Air versus saline in the loss of resistance technique for identification of the epidural space

Review question

Which technique, air or saline, is more efficacious and safe in reducing complications during the loss of resistance technique (sudden loss of pressure on the plunger of the syringe, making the plunger slide smoothly) for identification of the epidural space, and what guidance can be provided to clinicians in their clinical practice? (The epidural space surrounds the spinal cord and its covering layers, through which the spinal nerves pass as they connect to other nerves leading to and from all parts of the body.)

Background

A survey of anaesthesiologists showed that 53% of those who replied used loss of resistance technique (LOR) with saline, 37% used LOR with air and 6% LOR with both air and saline; 3% used a different technique with or without one of the above LOR approaches. The methods used for identification of the epidural space are important for good quality of anaesthesia and for avoidance of complications such as epidural haematoma (i.e. accumulation of blood between the skull and the dura mater) and occasional low back pain.

Study characteristics

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.

Key results

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.

Quality of the evidence

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.

Conclusion and future research

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.

Authors' conclusions: 

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. 

Read the full abstract...
Background: 

The success of epidural anaesthesia depends on correct identification of the epidural space. For several decades, the decision of whether to use air or physiological saline during the loss of resistance technique for identification of the epidural space has been governed by the personal experience of the anaesthesiologist. Epidural block remains one of the main regional anaesthesia techniques. It is used for surgical anaesthesia, obstetrical analgesia, postoperative analgesia and treatment of chronic pain and as a complement to general anaesthesia. The sensation felt by the anaesthesiologist from the syringe plunger with loss of resistance is different when air is compared with saline (fluid). Frequently fluid allows a rapid change from resistance to non-resistance and increased movement of the plunger. However, the ideal technique for identification of the epidural space remains unclear.

Objectives: 

• To evaluate the efficacy and safety of both air and saline in the loss of resistance technique for identification of the epidural space.

• To evaluate complications related to the air or saline injected.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2013, Issue 9), MEDLINE, EMBASE and the Latin American and Caribbean Health Science Information Database (LILACS) (from inception to September 2013). We applied no language restrictions. The date of the most recent search was 7 September 2013.

Selection criteria: 

We included randomized controlled trials (RCTs) and quasi-randomized controlled trials (quasi-RCTs) on air and saline in the loss of resistance technique for identification of the epidural space.

Data collection and analysis: 

Two review authors independently assessed trial quality and extracted data.

Main results: 

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).

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