RA aseptic technique



Alwin Chuan and Michael Fredrickson

Hospital acquired infections (HAI) are common and result in significant patient morbidity and mortality. The introduction of UGRA has raised the issue of US equipment as a potential vector for HAI, with probes and coupling gel already implicated in HAI outbreaks.1,2 Unfortunately, because of a lack of high quality evidence, recommendations for aseptic technique for regional anesthesia are often based on “what is probably a good idea” or “what is hard to criticise”. This is exemplified by common aseptic technique recommendations for peripheral perineural catheter placement, which are often extrapolated from the widely accepted standards for epidural and central venous catheterisation. Infection of the latter poses a completely different risk to patients. For example, while colonisation of peripheral plexus catheters is relatively common 8-10 with the exception of catheters used for trauma, in ICU and for prolonged periods,11 progression to clinically significant infection is exceedingly rare. 8-10,12-14 Furthermore, compared to intravenous cannulae, perineural catheter related bacteraemia is unlikely due to non-communication of catheter with the blood stream (exception potentially are psoas compartment catheters). 9

Current policies on infection control in relation to US equipment published by governmental bodies and national societies make recommendations according to the invasiveness of the medical procedure. The following is a "common-sense" approach based on current evidence, which is inevitably a balance between efficiency, potential antiseptic related neurotoxicity and effectiveness for preventing HAI.


Probe disinfection

For both invasive (e.g. intraoperative use inside a sterile field where there is a high risk of infection) and semi-invasive procedures (e.g. intracavity use where equipment is exposed to mucus membranes or non-intact skin), recommendations are for disinfection by immersion with high level chemical disinfectants (glutaraldehyde, ortho-phthalaldehyde, peracetic acid). This recommendation exists even if probes are sheathed due to the 2% risk of sheath cover tears, some of which may be invisible. 4 For non-invasive applications such as diagnostic scanning on intact skin, recommendations are for low-level disinfection without immersion (e.g. wiping with a paper cloth), with the exception of patients colonized with multiresistant organisms, in which intermediate level disinfectants are more appropriate (70% isopropyl alcohol, hypochlorite, or phenolic based compounds). 2,5,6

Whether UGRA is regarded as invasive, semi-invasive or non-invasive remains controversial. Routine high-level disinfection would impact considerably and negatively on costs, infrastructure requirements and patient turnover, while treating UGRA as non-invasive might contribute to HAI. Most practitioners regard UGRA as falling somewhere between semi- and non invasive

In a recent study 7, an intermediate level disinfectant (70% isopropyl alcohol) was used to disinfect linear array probes used for single shot UGRA, with or without sterile sheaths. A 3-step process involved bulk removal of material, wiping with cloth soaked in disinfectant and air-drying. Acceptable disinfection was consistently achieved in all cases.

In general, the probe should be cleaned with a disposable cloth to remove bulk contaminants. An intermediate level disinfectant (e.g. 70% isopropyl alcohol) 7 is then used to disinfect the probe and cable. The same approach can be used for the keyboard, control-buttons and probe holders. This process is quick and efficient (3-5 min to air dry). If there is concern about re-colonisation during storage, then the process can be repeated just before patient use.

Clear adhesive dressings (e.g. Opsite, Tegaderm) used as a probe sterile barrier remain controversial as there is the potential for residual adhesive, which then forms a biofilm with the potential for contamination. This biofilm can be difficult to remove.

Choice of antiseptic

Choice of antiseptic for regional anesthesia is a trade off between the goal of preventing needle puncture/catheter related infection, and the risk of antiseptic induced neurotoxicity secondary to needle or injectate contamination. Alcoholic solutions have better antiseptic properties than aqueous solutions and promote more rapid drying. Chlorhexidine is more effective than iodine which can themselves also discolour the probe. Chlorhexidine has the highest neurotoxicity potential, and for this reason the 0.5% preparation is preferred over the 2% solution: 0.5% chlorhexidine in 70% alcohol  is a suitable antiseptic for all block types.  All antiseptics should be allowed to air dry prior to needle insertion.  Single use alcohol wipes (e.g. alcowipe) are acceptable for low risk single injection techniques and have the advantage of a rapid drying time.

Additional precautions for all techniques

1. Personal hygiene and protection, including hand washing with alcohol based solutions. At a minimum, non-sterile gloves and a ‘no-touch’ technique of avoiding contamination of sterile needle and the skin insertion site. For immunocompromised patients, patients with multiresistant organisms, or for perineural catheter placement, use sterile gloves, mask, drape and probe sheath. A sheath should also be used where there is a risk of probe blood contamination (e.g. ankle block). Neuraxial blocks necessitate full barrier precautions including gown.

2. A single use gel (e.g. US gel sterile packet, or K-Y lubricating gel sachet) is preferred over multi-use gel bottles due to the potential risk of nosocomial infection with the latter. For immunocompromised patients, catheter placement, and neuraxial blocks, use sterile gel.

3. Be particularly careful not to contaminate/splash antiseptic onto open needles or catheters, and protect the equipment from contamination by covering if not immediately used. NEVER allow injectate (e.g. saline for loss-of-resistance) to be drawn up from an open container on the block tray. This significantly increases the risk of inadvertently drawing up antiseptic into a syringe for injection. If gloves become contaminated with antiseptic, they should be changed.




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2.            Ohara T, Itoh Y, Itoh K. Ultrasound instruments as possible vectors of staphylococcal infection. J Hosp Infect 1998; 40:73-77

3.            Rutala WA, Weber DJ et al. Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008. Centers for Disease Control 2008. From  http://www.cdc.gov/hicpac/Disinfection_Sterilization/acknowledg.html. Accessed Jan 08, 2013.

4.            Rooks VJ, Yancey MK, Elg SA, Brueske L. Comparison of probe sheaths for endovaginal sonography. Obstet Gynecol 1996; 87:27-29.

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6.            Frazee BW, Fahimi J, Lambert L et al. Emergency department ultrasonographic probe contamination and experimental model of probe disinfection. Ann Emerg Med 2011; 58:56-63.

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