An In Vitro Study to Evaluate the Utility of the “Air Test” to Infer Perineural Catheter Tip Location

Abstract

Injection of air under ultrasound guidance via a perineural catheter after insertion ("air test") has been described as a means to infer placement accuracy, yet this test has never been rigorously evaluated. We tested the hypothesis that the air test predicts accurate catheter location greater than chance and determined the test's sensitivity, specificity, and positive and negative predictive values using a porcine-bovine model and blinded expert in ultrasound-guided regional anesthesia. The air test improved the expert clinician's assessment of catheter tip position compared to chance, but there was no difference when compared to direct visualization of the catheter without air injection.

Continuous Adductor Canal Blocks Are Superior to Continuous Femoral Nerve Blocks in Promoting Early Ambulation After TKA

“…Catheter tip location was confirmed by injecting 0.5 mL of air via the catheter under ultrasound [20]. After catheter placement, onset of sensory anesthesia in the target nerve distribution was confirmed before the patients' transition to the operating room.…”

Comparative Echogenicity of an Epidural Catheter and 2 New Catheters Designed for Ultrasound‐Guided Continuous Peripheral Nerve Blocks

“…Despite the newer application of echogenic technology to catheters, to date there is no way to distinguish the shaft of the catheter from the tip, and precise placement of the tip in proximity to the target nerve or plexus is ultimately the goal of continuous peripheral nerve block–mediated pain relief . Therefore, other methods, such as the “air test” may continue to be used to infer the catheter tip position when performing ultrasound‐guided continuous peripheral nerve blocks . Ultimately choice of catheter for a continuous peripheral nerve block must account for multiple factors, including but not limited to physician preference, placement technique, and cost.…”

A Pilot In Vitro Evaluation of the “Air Test” for Perineural Catheter Tip Localization by a Novice Regional Anesthesiologist

“…Commercially available catheters used in regional anesthesia vary widely in terms of echogenicity, 1 and there is no consistent method to identify the tip of the catheter with 2‐dimensional ultrasound imaging. The “air test” has been described as a method for quickly assessing perineural catheter tip location immediately after insertion 2 , 3 ; a small volume of air injected via the catheter appears hyperechoic relative to the hypoechoic fluid injected via the placement needle in the vicinity of the target nerve. The utility of the air test has been previously evaluated in the hands of an expert practitioner 3 .…”

“…The “air test” has been described as a method for quickly assessing perineural catheter tip location immediately after insertion 2 , 3 ; a small volume of air injected via the catheter appears hyperechoic relative to the hypoechoic fluid injected via the placement needle in the vicinity of the target nerve. The utility of the air test has been previously evaluated in the hands of an expert practitioner 3 . Compared to chance, the expert's use of the air test results in a more reliable assessment of perineural catheter tip location; however, the expert is also able to reliably identify catheter tip location without the air test 3 .…”

“…The utility of the air test has been previously evaluated in the hands of an expert practitioner 3 . Compared to chance, the expert's use of the air test results in a more reliable assessment of perineural catheter tip location; however, the expert is also able to reliably identify catheter tip location without the air test 3 . In contrast, the utility, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for novices have not yet been studied, although we have previously speculated that this group may be the ideal target cohort for the air test.…”