Post‐Procedure Perforation Rates in Ultrasound Transducer Covers Used for Ultrasound‐Guided Percutaneous Procedures in Emergency Medicine: A Comparison Between Polyurethane Covers and Polyethylene Covers

ABSTRACT

Introduction

The use of sterile transducer covers for ultrasound‐guided percutaneous procedures in Emergency Medicine is common. The guidance on how transducers should be disinfected post‐procedure is much debated and has considerable cost and logistical implications. The perforation rate of transducer covers when used for percutaneous procedures in the Emergency Department setting has not previously been explored and could impact disinfection recommendations.

Method

This pragmatic prospective observational cohort study quantifies and compares the perforation rates of two different transducer cover types in a single Emergency Department. Details on the patient, procedure, and operator were recorded, and transducer cover perforation was retrospectively assessed by pouring a litre of water into each cover and recording details of any leakage.

Results

Polyethylene transducer covers had a post‐procedure perforation rate of 15.1%, more than 6 times that of polyurethane transducer covers which had a perforation rate of 2.4%. The study also shows operators are largely unaware of this perforation.

Discussion

Given the post‐procedure perforation rates identified, relying solely on the transducer cover as the means of infection control appears unwise, particularly as the operator is largely unaware of perforation occurring. Differences in transducer cover construction affects perforation rate. However, the chronology and aetiology of the damage are not clarified in this study, neither was resultant transducer contamination evaluated.

Conclusion

This single centre observational study demonstrated significant variation in post‐procedure perforation rates of two different transducer covers from a single manufacturer. Further research is required to determine the optimal probe cover and disinfection regime for infection control.

Summary.

• Current Australasian guidelines suggest that an ultrasound transducer must undergo high‐level disinfection (HLD) after every single ultrasound‐guided percutaneous procedure, in addition to the use of a sterile transducer cover.

• This threatens restricting patient/physician timely access to ultrasound equipment, has significant financial and logistical implications, and has unclear incremental benefit over the use of a sterile transducer cover and low‐level disinfection (LLD).

• There exists an evidence gap regarding the integrity (post‐procedure perforation rate) of sterile transducer covers to inform this debate.

• In this large cohort study, we discovered leaks in 15.1% of cheaper polyethylene covers and 2.4% of polyurethane covers from 764 emergency ultrasound‐guided percutaneous procedures.

• Although this study was conducted in a single centre with use of covers that may not be used universally, these data emphasise the need for contemporaneous transducer cleaning and clinicians to prioritise appropriate inter‐procedure transducer disinfection.

• Further research is required to determine the optimal probe cover and disinfection regime for infection control.

1. Introduction

Ultrasound‐guided procedures in the emergency department where skin integrity is compromised with the insertion of a needle are commonplace. This poses several infection control considerations. Ultrasound transducers, given their proximity to the needle‐entry site, represent a source of contamination from both environmental organisms and from blood‐borne pathogens. A 2015 Australian study in ED and ICU showed that 57% of transducers tested were contaminated with blood, and 46% with other microbiological contaminants [1]. The Australasian Society for Ultrasound Medicine (ASUM) in conjunction with The Australasian College for Infection Prevention and Control (ACIPC) published a guideline in 2017 for reprocessing ultrasound transducers based on the AS/NZS4187 standards. These guidelines recommend the use of sterile transducer covers for every real‐time ultrasound‐guided procedure, followed by high level disinfection (HLD), unless the transducer is some distance away from the needle and contamination with blood or bodily fluids is not possible [2]. There is little evidence of transducer cover failure rates to date [3]. These guidelines have subsequently been a topic of debate as HLD imposes significant financial and logistical implications. An intersocietal statement published in the Journal of Ultrasound Medicine argues that Low Level Disinfection (LLD) is adequate when paired with a transducer cover [4]. They argue transducers should be treated in the same way as a clinician's own hands, which receive LLD disinfection, but are then covered for every procedure by sterile gloves. As a starting point to address this argument, it is important to establish the rates of perforation of different transducer covers after percutaneous procedures.

2. Objective

The primary objective of this study was to quantify the rate of post‐procedure perforation of commercially available, single‐use, sterile polyurethane transducer covers. Toward the end of the study, the polyurethane transducer covers were replaced by polyethylene transducer covers. This enabled a comparison between the two transducer covers to be performed.

3. Method

This prospective observational cohort study was undertaken at Sir Charles Gairdner Hospital, Perth, Western Australia, a single tertiary hospital Emergency Department, with an established ultrasound training programme, seeing 78,000 adult‐only patients per year. Staff were informed and educated prior to its implementation. The salient inclusion criterion was any use of a sterile transducer cover for procedural ultrasound with a patient aged over 16. Recruitment was via convenience sampling. No formal sample size calculation was undertaken; we elected a sample size that was considered feasible and highly likely to be adequate over a 6‐month study period.

Those performing ultrasound‐guided procedures where a needle penetrates the skin under ultrasound guidance (predominantly difficult vascular access) were asked to carry out the procedure independently using their normal technique. There was no standardisation or instruction for application or removal of the transducer covers. Post‐procedure, rather than discarding the used transducer cover, operators were asked to place the cover into a zip lock bag, complete the study data collection form, and place it with the transducer cover into a tamper proof box until collection by the study team.

The study team (FM and LC), wearing appropriate personal protective equipment, then visually inspected each cover for leaks. This pragmatic test entailed pouring 1 L of tap water into each cover and observing for macroscopic leakage.

Visible leaks were divided into six categories: very slow drip, slow drip, fast drip (a quantitative metric to measure the drip rate more precisely was not identified, therefore this measure was subjective), constant stream visible defect < 1 mm, constant stream visible defect 1 to 2 mm, constant stream visible defect > 2 mm. The location of the leak was not precisely recorded or measured but was in the distal portion of the cover where the cover was in contact with the ultrasound transducer.

Operators were asked to document the procedure type, indication, known risk factors for blood‐borne virus transmission (history of intravenous drug use, hepatitis B, C or HIV), risk factors for susceptibility to infection (chemotherapy, immunodeficiency, other immunosuppression), operator characteristics (clinician role (Consultant with Diploma of Diagnostic Ultrasound (DDU), Consultant, Registrar, Resident Medical Officer, Intern, Nurse, Medical Student, other) and estimated prior experience of ultrasound guided procedures (1–5, 6–10, 11–25, 26–100, 101–500, > 500)), and awareness of damage to the transducer cover. Due to low response frequencies in some groups, data was grouped. Experience by role was defined as High (DDU Consultant, Consultant), Medium (Registrar), and Low (All other groups). Experience by the number of previous procedures performed was categorised into Expert (> 500), Advanced (101–500), Intermediate (26–100) and Beginner (all other groups).

The polyurethane transducer covers were evaluated initially, which was the standard equipment in the department at the time of study commencement. Partway through the study, and entirely independently, for cost saving measures, the standard transducer cover was changed to polyethylene; this reflects opportunistic evolution of the original study, rather than a prespecified objective for the initial study. This gave the opportunity to apply the methodology with the polyethylene covers and to perform a comparison. Absolute perforation rates were described for each type of transducer cover. The chi‐square test was used to assess for significance when comparing the results between the two types of ultrasound transducer covers. Logistic regression was used when comparing results between operator experience groups.

3.1. Ethics Statement

The proposal was submitted as a quality improvement project (Activity 32,764). The proposal was reviewed by the organisation's Governance, Ethics, Knowledge, Outcomes (GEKO) committee and determined to be of negligible risk. As per the National Statement on Ethical Conduct in Human Research, the project was exempt from review by the hospital Human Research and Ethics Committee.

4. Results

The study findings are summarised in Table 1. The polyurethane cohort had 527 covers collected; of these, 506 met the inclusion criteria of being used for a procedure where a needle penetrated the skin. The polyethylene cohort had 269 covers collected, of which 258 met the inclusion criteria, with similar exclusion rates of 4.0% and 4.1% respectively. Patient groups were comparable, with similar numbers having risk factors for blood borne diseases, as well as for immunosuppression.

TABLE 1.

Summary of data between both cohorts.

Study factor	Polyurethane		Polyethylene
	n	%	n	%
Total number of covers	527	100.0	269	100.0
Number excluded	21	4.0	11	4.1
Number included	506	96.0	258	95.9
Number of leaks	12	2.4	39	15.1
Very slow drip	0	0.0	0	0.0
Slow drip	1	8.3	12	30.8
Fast drip	0	0.0	8	20.5
< 1 mm stream	8	66.7	7	17.9
1–2 mm stream	1	8.3	6	15.4
2 mm stream	2	16.7	6	15.4
Reported damage	5	1.0	13	5.0
Correctly identified leak	1	8.3	5	12.8
Risk factor for communicable disease	54	10.7	27	10.5
Risk factor for immunosuppression	53	10.5	35	13.6
Most common procedure (PIVC)	356	70.4	186	72.1
Second most common procedure (nerve block)	74	14.6	31	12.0
Third most common procedure (arterial line)	37	7.3	22	8.5

Note: A risk factor for blood borne virus transmission for the purposes of this study was retrospectively defined as previous or current intravenous drug use, HIV infection, hepatitis B or hepatitis C infection. Risk factors for susceptibility to infection was again retrospectively defined based on responses as the use of steroids, receiving immunotherapy, chemotherapy, or other immunosuppression (Assumed if history of transplant, mycophenolate mofetil, tacrolimus, methotrexate, hydroxychloroquine, disease‐modifying anti‐rheumatic drugs not specified, asplenia, haematological malignancy, AIDS). Those reported but excluded were anorexia, treated hepatitis C, diabetes, liver cirrhosis, liver failure. Patients were either considered at risk or not at risk, therefore if more than one risk factor was present the result remained the same.

4.1. Perforation Rate

The post‐procedure perforation rate for the polyurethane transducer covers was 2.4% (12/506). The perforation rate for the polyethylene transducer covers was 15.1% (39/258). This represents more than a 6‐times increase in the post‐procedure perforation rate when using polyethylene covers compared to the polyurethane covers (p‐value 2.47 × 10⁻¹¹).

4.2. Operator Experience

Data based on operator experience are summarised in Table 2. Registrars were the most frequent operators making up 50.6% and 43.4% of operators in the two cohorts. Staff with intermediate experience (26–100 prior procedures performed) were the most common operators; 36.2% in the polyurethane cohort and 33.7% in the polyethylene cohort. Operator experience and clinical role were similar between the two cohorts (Figures 1 and 2). The groups deemed to have the least experience (Low and Beginner) were used as the reference groups for an investigation into the effect of operator experience (defined by both role and the number of previous procedures performed) on the rate of perforation, summarised in Table 3. There was no statistically significant relationship between operator experience and the odds of perforation in either cohort. Analysis of both individual and pooled data revealed no statistically significant difference between any group. This reflects the distribution of data with low frequencies across several categories, resulting in low certainty estimates.

TABLE 2.

Summary of data based on operator experience.

Experience	Polyurethane				Polyethylene
	Procedures		Perforation rate		Procedures		Perforation rate
	n	%	n	%	n	%	n	%
Operator role
DDU consultant	67	13.2%	0	0.0%	50	19.4%	4	8.0%
Consultant	86	17.0%	3	3.5%	30	11.6%	7	23.3%
Registrar	256	50.6%	6	2.3%	112	43.4%	18	16.1%
RMO	83	16.4%	1	1.2%	54	20.9%	8	14.8%
Intern	4	0.8%	1	25.0%	2	0.8%	0	0.0%
Nurse	9	1.8%	1	11.1%	9	3.5%	2	22.2%
Not specified	0	0.0%	0	0.0%	1	0.4%	0	0.0%
Medical student	1	0.2%	0	0.0%	0	0.0%	0	0.0%
Procedures performed
1–5	15	3.0%	2	13.3%	14	5.4%	1	7.1%
6–10	8	1.6%	0	0.0%	14	5.4%	1	7.1%
11–25	56	11.1%	2	3.6%	23	8.9%	3	13.0%
26–100	183	36.2%	4	2.2%	87	33.7%	14	16.1%
101–500	152	30.0%	3	2.0%	73	28.3%	15	20.5%
> 500	92	18.2%	1	1.1%	47	18.2%	5	10.6%

Abbreviations: DDU, diploma of diagnostic ultrasound; RMO, resident medical officer.

FIGURE 1.

Number of ultrasound guided procedures previously completed by operators. In both cohorts the most common number of prior procedures completed by operators was between 26–100, followed by 101–500, then greater than 500. This shows both studies had a similar experience level between operators.

FIGURE 2.

Clinical role of operator. In both cohorts the most common role of the operator was a registrar. DDU (Diploma of Diagnostic Ultrasound) consultants, consultants and RMOs performed a similar proportion of procedures within each study and between studies. Other clinical roles performed very few if any procedures.

TABLE 3.

Summary of statistical comparison between operator experience groups.

Experience	Polyurethane			Polyethylene			Pooled data
	OR	95% CI	p	OR	95% CI	p	OR	95% CI	p
Role
Low	0.03	0.01–0.10	< 0.01	0.18	0.09–0.35	< 0.01	0.09	0.05–0.15	< 0.01
Medium	0.75	0.18–3.07	0.69	1.07	0.46–2.49	0.87	0.81	0.40–1.62	0.54
High	0.63	0.12–3.17	0.57	0.89	0.35–2.25	0.81	0.74	0.34–1.61	0.45
Procedures
Beginner	0.05	0.02–0.15	< 0.01	0.11	0.04–0.27	< 0.01	0.07	0.04–0.15	< 0.01
Intermediate	0.42	0.10–1.72	0.23	1.76	0.60–5.23	0.31	0.96	0.42–2.20	0.92
Advanced	0.38	0.08–1.73	0.21	2.38	0.81–7.03	0.12	1.17	0.51–2.68	0.71
Expert	0.21	0.02–1.88	0.16	1.1	0.30–4.05	0.89	0.61	0.21–1.75	0.36

Note: Low and beginner groups were used as reference.

Abbreviations: CI, confidence interval; OR, odds ratio; p, p‐value.

The procedure type being conducted was comparable between the two groups, with ultrasound‐guided peripherally inserted venous catheters (PIVC) by far the most common procedure (Figure 3).

FIGURE 3.

Procedure performed. In both cohorts, the most common procedure performed was peripheral intravenous vascular cannulation.

4.3. Leak Detection Rate

In the covers with a leak, the operator was aware they had damaged the cover in 8.3% of polyurethane cases and 12.8% of polyethylene cases. Across the 764 probe covers tested in both groups, 18 individuals reported knowingly damaging the probe cover; however, a perforation was only correctly identified in 6. The remainder of the 51 perforated covers occurred unknowingly. Registrars across both groups reported the most incidences of probe cover damage, 3 out of 5 in the polyurethane group and 11 out of 13 in the polyethylene group, as well as correctly identifying a leak equally or most frequently, 1 out of 2 and 4 out of 5, in the polyurethane and polyethylene groups respectively.

The leak rate of covers used in the two most common procedures, PIVC and nerve blocks, closely correlated to the overall mean in each cohort (Polyurethane cohort PIVC 2.2%, Nerve Block 1.4%; Polyethylene cohort PIVC 14.5%, Nerve Block 16.1%). The size of the leaks identified differed between the different transducer cover types (Figure 4). A constant stream with a visible defect of < 1 mm was most common with the polyurethane covers, representing 66.7% of leaks identified, whereas a slow drip was the most common leak with the polyethylene covers, representing 30.8% of those identified.

FIGURE 4.

Size of leaks identified in transducer covers. Most leaks identified in polyurethane covers were constant streams with visible defects < 1 mm, whereas polyethylene cover defects were more evenly spread.

5. Discussion

This study brings to attention several important points not previously demonstrated in the literature. These may help frame future guidance on infection control measures specifically for ultrasound transducers in the emergency department setting.

The post‐procedure perforation rate between two commonly used, commercially available, sterile single‐use transducer covers demonstrated that transducer covers vary significantly in their post‐procedure perforation rate. In this study, a 2.4% perforation rate for polyurethane covers is compared to a 15.1% perforation rate for polyethylene covers. We cannot conclude from this single study that all polyethylene transducer covers have a higher perforation rate than polyurethane covers, or that these findings apply to other materials/brands, so further research is required. Acknowledging the broad similarities between the two cohorts in the types of procedures performed, the predominant operator role (registrars or consultants) and prior experience (intermediate, advanced or expert), the authors hypothesise that the difference in perforation rates may stem from the distinct transducer cover material. Polyurethane and polyethylene transducer covers are likely to perform differently given the different plastic formulas, construction methods, and wall thickness in their design. The relationship between transducer cover perforation rates and the type of plastic material, brand, and thickness could be evaluated in future research. The polyethylene covers were also cheaper than the polyurethane covers. It is plausible that the polyethylene is less forgiving, therefore susceptible to manufacturing issues, damage when applying or removing the transducer cover, yielding a slow leak in testing, in contrast to the constant flow leaks seen in the polyurethane covers, which the authors would better associate with definite needle puncture. This appears to make relying solely on the transducer cover as the means of infection control unwise. In addition, it was shown that the operator is usually not aware that the cover has been damaged, and so only accessing higher levels of infection control based on awareness of a cover breach would also be ineffective. Correlation between operator experience and leak detection is significantly impaired by the low frequency of both reported damage and the presence of a proven perforation across experience categories. Future research could explore the relationship between operator experience and transducer cover perforation rate.

Another interesting element shown in this study was that the population that requires ultrasound to guide procedures often has risk factors for carriage of blood borne viruses (10.7 and 10.5% in the two groups), or risk factors for immunosuppression (10.5 and 13.6% in the two groups). This is not surprising as difficult intravenous vascular access patients often have poor veins because of prior intravenous drug use, administration of chemotherapy, and multiple prior intravenous cannula placements. This places further importance on the requirements for adequate infection control measures.

6. Limitations

There are several limitations to this study. This was a prospective observational cohort study that was opportunistically extended to be a comparative rather than descriptive study when a second transducer cover type was introduced to the study centre. This was a convenience sample with an unknown total number of transducer covers used during the study period, which could have led to selection and spectrum bias.

Whilst this study has established there are significant post‐procedural leak rates, and furthermore significant variation between probe cover types, we did not explore when the leak occurred in the process. We did not examine the covers pre‐procedure and were not able to determine whether the cover damage was present pre‐procedure, occurred on cover application, during the procedure, or during the removal of the transducer covers post‐procedure. The authors feel the timing of transducer cover damage is not of great importance, as in any one of these cases the underlying transducer could be contaminated. Future research could explore baseline transducer cover perforation rates, which could potentially be done through comparison between transducer covers used for percutaneous procedures and those used for diagnostic scanning.

This single centre study examined two commercially available transducer covers from a single manufacturer, and the results cannot be generalised to other transducer cover construction materials or brands, particularly with other potential confounders. The transducer cover brand name is not being reported due to the lack of prior research on this topic and to not prejudice the manufacturer; this will limit the reproducibility and generalisability of the findings. This study, however, clearly establishes a likely range in rates of transducer cover leak rates on which future research and guidelines can be based.

Transducer cover damage is being used as a surrogate marker for transducer contamination and possible subsequent iatrogenic infection. This study did not document how many actual transducers were contaminated with blood or other microorganisms post procedure. In addition, follow up to determine infection rates in these patients was not performed. Determining actual infection rates, which are very low, would require an enormous sample size and is impractical in a single centre study.

Using ultrasound to guide difficult vascular access is now accepted as the standard of care. The rates of hospital acquired infections specifically related to the use of ultrasound are difficult to quantify as infection is rare, transmission would have multiple steps, the difference in efficacy between low and high‐level disinfection is extremely small, and enormous sample sizes would be required. This study does not provide enough conclusive evidence at this stage to base recommendations. In framing future guidelines, authors will need to consider the efficacy of low and high‐level disinfection, the impact of sterile transducer covers, together with the health economic impact of their recommendations.

7. Conclusion

This single centre, observational study demonstrated that there was a marked variation in the post‐procedure perforation rate of two different types of single‐use sterile ultrasound transducer covers made of different materials from the same manufacturer; 2.4% and 15.1% for polyurethane and polyethylene covers respectively. This study did not determine actual transducer cover or transducer contamination post‐procedure. Although these findings need to be replicated in future research and to account for any confounders, the results of this study support the suggestion that reliance on transducer covers alone to provide comprehensive protection for the transducer may be inadequate.

Author Contributions

The study was conceived by J.R., F.M., C.M., J.M., J.S. and L.C. were responsible for study conduct and data collection. J.R., F.M. and L.C. were responsible for statistical analysis. J.R., F.M., C.M., L.C. and J.S. developed the manuscript. F.M. and L.C. created the final manuscript for which J.R. takes overall responsibility.

Conflicts of Interest

The authors declare no conflicts of interest.

Rippey J., Morris F., Moseley C., Sowerby J., Chiverton L., and Mason J., “Post‐Procedure Perforation Rates in Ultrasound Transducer Covers Used for Ultrasound‐Guided Percutaneous Procedures in Emergency Medicine: A Comparison Between Polyurethane Covers and Polyethylene Covers,” Australasian Journal of Ultrasound in Medicine 28, no. 4 (2025): e70025, 10.1002/ajum.70025.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.