How many times have you told a patient “The gel will be cold?” How many times have you watched a patient retract from the transducer because of the cold gel? How about a pediatric patient? Could warm gel improve your rate of clinically successful scans? It seems easy enough to install gel warmers alongside our ultrasound machines. But, should we do this?
Clinician Preference
In a recent Twitter poll, slightly more than half of respondents (53%) said they would use a gel warmer, if it was available. 6% noted they had them and liked them, and 0% indicated they had them and did not like them.
Gel warmers are commonly used for ultrasound examinations by our Pediatrics, Ob/Gyn, and Radiology colleagues to increase patient comfort.
The Concern
If bacteria grow better at higher temperatures, will gel warmers increase the incidence of skin infection?
What is the Evidence?
We wish to summarize the literature involving ultrasound gel at room temperature versus a warmed temperature, specifically involving:
- Bacterial infection rates
- Patient satisfaction scores
1. Bacterial Infection Risk
In the 1980s, multiple case reports described patient infections from warmed water-baths causing bacterial growth in other mediums, such as peritoneal dialysis fluids and neonatal ICU blood products.1,2 None of these cases involved ultrasound gel, but they lay the groundwork for infection concern.
More recently, observational trials show mixed results. Provenzano showed no increased risk of bacterial growth in warmed gel bottles,3 while Spratt4 and Westerway5 showed a moderate risk of growth. The organisms that grew are not known to be pathogenic to humans. However, ultrasound gel is a known carrier of organisms and has caused patient infections in the past.6 Table 1 summarizes these studies and reports.
Table 1: Relevant literature on the risk of bacterial growth in warmed ultrasound gel
| Study | Study Methodology | Findings |
|---|---|---|
| Ashline et al. (1980)2 | Case report | Patient diagnosed with bacterial peritonitis due to contaminated dialysate from contaminated warming water. Patient later died from pneumonia and found to have purulent ascites, peritonitis, and cul-de-sac abscess on autopsy. |
| Muyldermans et al. (1988)1 | Case series | A NICU blood product warmer was found to be contaminated with pseudomonas which infected several neonates. Organisms incubated at 37°C. |
| Provenzano et al. (2013)3 | Observational study | Of 212 samples, no warmed bottles grew bacteria from gel inside the bottle. Organisms incubated at 37°C. |
| Spratt et al. (2014)4 | Observational study | The tips of gel bottles stored in the 20°C–40°C range exhibited the highest rate of non-specific contamination, with 25 of 42 samples (59.5%) showing positive growth. For gel bottles stored at warmer temperatures of >40°C range, the incidence of contamination was lower. Specifically, 4 of 13 bottles tips sampled (30.7%) and 1 of 13 gel samples (7.7%) were non-specifically contaminated. |
| Westerway et al. (2017)5 | Observational study | 171 total samples, 7 of which were in warmers. Small sample size (7) but the warmer group (42°C) was the only group that grew any bacteria. |
Westerway and Spratt have published the highest quality evidence to date, although they were only small observational studies. The sample sizes were small, and the temperature ranges were too wide to be clinically implementable. The findings are moderately convincing at best and not very generalizable. Nonetheless, it seems these limited studies are what national guidelines are based on (Table 2).
Table 2: National guidelines on the use of ultrasound gel warmers
| Publication | Guideline | Recommendation |
|---|---|---|
| Ashcroft et al. (2014) [PDF] | Infection Prevention And Control of Canada Position Statement (IPAC) | “Warmed gel should only be used only when required. Bottles should be removed from the warmer as soon as soon as possible and dried immediately.” Gel warmers must be cleaned weekly with low level hospital-approved disinfectant, and immediately if the warmer becomes soiled. |
| Barry et al. (2017) [PDF] | Infection Prevention And Control of Canada Position Statement (IPAC) | “Do not warm gel due to the increased risk of bacterial multiplication.” – This recommendation was based on the findings of Spratt.4 |
| Nyhsen et al. (2017)7 | European Society of Radiology Ultrasound Working Group | “Gels should be stored at room temperature. The multiplication of pathogens in gel bottles increases considerably when kept warm for patient comfort, thus turning bottle warmers into incubators.” “Therefore, if gel warmers are used, only bottles for immediate use should be warmed.” – This recommendation was based on data from Westerway.5 |
2. Patient Satisfaction
The 2017 Heated Ultrasound Gel and patient Satisfaction (HUGS) trial was a prospective observational study which demonstrated that adult patients do not prefer warm over room temperature gel when blinded to both.
In this study, they analyzed 120 adult patients, with 59 patients scanned with room temperature (27.9°C) gel and 61 scanned with warmed (38.9°C) gel. A variety of scans were performed. Sonographers wore heat-resistant gloves and were not privy to the study hypothesis.
Overall, groups showed no statistical difference in Visual Analog Scale satisfaction scores of 83.9 mm (room temperature gel) versus 87.6 mm (warm ultrasound gel). The authors conclude that that there is no patient satisfaction benefit to warmed gel.8
To date, no studies have looked at the pediatric population regarding comfort or ability to successfully complete ultrasound examinations. Anecdotally, some pediatric ultrasound specialists have noted difficulty performing ultrasound examinations with cold gel and favor warm gel.
Summary
The existing evidence about warmed ultrasound gel and the bacterial infection risk is limited. There seems to be a guideline “creep” with IPAC’s recommendations moving from “when required” in 2004 to “do not warm gel” in 2017. Although warmed gel does not seem to impact patient satisfaction for adults, future studies are needed focusing on:
- Bacterial infection risk to the patient
- Quality of ultrasound imaging, especially with pediatric scans
The evidence-based verdict on warmed ultrasound gel seems still out.
References
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1.Muyldermans G, de S, Pierard D, et al. Neonatal infections with Pseudomonas aeruginosa associated with a water-bath used to thaw fresh frozen plasma. J Hosp Infect. 1998;39(4):309-314. https://www.ncbi.nlm.nih.gov/pubmed/9749402.
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2.Ashline V, Stevens A, Carter M. Nosocomial peritonitis related to contaminated dialysate warming water. Am J Infect Control. 1981;9(2):50-52. https://www.ncbi.nlm.nih.gov/pubmed/10283820.
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3.Provenzano D, Liebert M, Steen B, Lovetro D, Somers D. Investigation of current infection-control practices for ultrasound coupling gel: a survey, microbiological analysis, and examination of practice patterns. Reg Anesth Pain Med. 2013;38(5):415-424. https://www.ncbi.nlm.nih.gov/pubmed/23974866.
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4.Spratt H, Levine D, Tillman L. Physical therapy clinic therapeutic ultrasound equipment as a source for bacterial contamination. Physiother Theory Pract. 2014;30(7):507-511. https://www.ncbi.nlm.nih.gov/pubmed/24678757.
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5.Westerway S, Basseal J, Brockway A, Hyett J, Carter D. Potential Infection Control Risks Associated with Ultrasound Equipment – A Bacterial Perspective. Ultrasound Med Biol. 2017;43(2):421-426. https://www.ncbi.nlm.nih.gov/pubmed/28341192.
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6.Moshkanbaryans L, Meyers C, Ngu A, Burdach J. The importance of infection prevention and control in medical ultrasound. Australas J Ultrasound Med. 2015;18(3):96-99. https://www.ncbi.nlm.nih.gov/pubmed/28191249.
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7.Nyhsen C, Humphreys H, Koerner R, et al. Infection prevention and control in ultrasound – best practice recommendations from the European Society of Radiology Ultrasound Working Group. Insights Imaging. 2017;8(6):523-535. https://www.ncbi.nlm.nih.gov/pubmed/29181694.
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8.Krainin B, Thaut L, April M, et al. Heated Ultrasound Gel and Patient Satisfaction with Bedside Ultrasound Studies: The HUGS Trial. West J Emerg Med. 2017;18(6):1061-1067. https://www.ncbi.nlm.nih.gov/pubmed/29085538.
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