The aim of this single-arm, open-label clinical study was to investigate the safe use and performance of the SC by HCPs under real-life conditions in an ICU for cardiovascular surgery patients. The objectives of the study were to assess (1.) the acoustic quality of auscultations with the SC (primary performance endpoint) and (2.) the overall usability of the SC (secondary performance endpoint) in the daily clinical routine by different HCPs (user groups) including physicians and nurses which were further characterized by their level of clinical experience. The study was approved by the local ethics committee (21-702-MP Mono-IVE17) and the federal authority (94.1-03-5,660-13,526).

Upon hospital admission on the day prior to their elective cardiovascular surgery adult patients (≥18 years) were asked for informed consent to participate in the study. Patients who provided informed consent were screened for inclusion and exclusion criteria (see definitions in Supplementary file). In included patients, the participating users performed auscultations as part of their standard postoperative care with the SC.

After each auscultation the users entered the following information and rating on a study-specific and access-restricted page embedded into the patients’ electronic medical record:

A total of 34 physicians and nurses with different levels of professional experience participated in this study and were assigned to one of the following groups:

User group 1: Fully trained physicians (e.g., senior physician, board-certified physician, medical specialist, physicians with at least 8 years of working experience) (n = 8).

User group 2: Physicians in specialty training (e.g., residents) (n = 7).

User group 3: Fully trained nurses with at least 10 years of working experience (n = 10).

User group 4: Fully trained nurses with less than 10 years of working experience (n = 9).

The SC (Stethoglove GmbH, Hamburg, Germany) is a hygienic stethoscope cover and a safe and effective solution to minimize the risk of patient-to-patient infections caused by contaminated stethoscopes in a health care environment (Figure 1, product images).

The non-sterile, single-use glove is pulled over the stethoscope’s bell and part of the tube(s), while held in the hand of the user (Figure 2, product handling images).

The SC is made of thermoplastic urethane (TPU) and is latex-and powder-free. The TPU material is impermeable for microorganisms such as bacteria, fungi and viruses. Such impermeability was demonstrated with decontaminated stethoscope bells wrapped in a the SC cover, which were exposed for 30 min to confluently grown bacterial (S. aureus, B. diminuta) and fungal (A. niger, C. albicans) cultures on agar plates. Swabbing of the unwrapped stethoscope diaphragm post exposure revealed no contaminations [internal report, unpublished data]. Viral impermeability was tested in accordance with Method C of ISO Norm 16,604 (2004) using the blood-borne pathogen Bacteriophage Phi-X1274. Cut-outs from four different areas of a the SC cover were exposed to the virus-containing suspension in a penetration cell and a sequence of pressures ranging from 0 to 20 kpa was applied each for 5 min. No virus penetration was detected [internal report, unpublished data].

Regarding acoustic quality the SC has demonstrated excellent transmission of auscultation sounds in both lab tests and a usability test with HCPs [unpublished data]. By combining this impermeability for microorganism with the preserved acoustic quality of auscultation sounds the SC ensures proper and safe patient-to-patient use of stethoscopes by HCPs in their day-to-day practice and thus improves patient protection from HAIs.

In this study the following performance and safety endpoints were defined:

In addition, the influence of gender, BMI and auscultated organ/body site on the primary and secondary performance endpoints were evaluated.

The continuous parameter “rating of the acoustic quality during auscultation measured on a 5-point Likert scale (poor, moderate, reasonable, good, very good)” was used as primary performance endpoint. No verification of a pre-defined hypotheses was planned. Instead, a total of 508 recorded auscultations with the SC was calculated to be required based on the following assumptions: a sampling error of 5% (precision), a prognostic accuracy of 95% (reliability), an expected mean of 4 (assessment of acoustic quality, “good”), and a variance of 2.3 points (homogeneity).

Both the primary and secondary performance endpoints were first evaluated descriptively and then stratified by the following influencing factors: patient gender, BMI and auscultated organ/body site. All analyses were performed within all users, and within each user group. Missing values were not replaced.

All measured differences between groups were investigated for numeric variables by means of a two-sided t-test for independent samples (comparison of 2 groups) and a one-factorial ANOVA (Welch-Test, comparison of more than 2 groups) with a type I error of 0.05. Since no formal hypothesis testing was done, all p-values were interpreted in a descriptive manner.

A total of 54 patients were enrolled in this study and 534 auscultations with the SC were performed with an average of 9.9 auscultations per patient. Patient characteristics are shown in Table 1.

More males (n = 39) than females (n = 15) participated in this investigation which represents the typical gender distribution in cardiovascular patients. The mean BMI in the patient cohort was 27.8 ± 5.2 kg/cm². The majority of patients (n = 35) were overweight, 13 patients suffered from class I and 3 patients from class III obesity.

The rate of auscultations per organ and body site, were evenly distributed between lung (36.1%), abdomen (33.2%), and heart (28.8%), while only 1.9% of the auscultations were performed at other body sites (e.g., carotid artery) (Table 2). No adverse device effects (ADEs) were reported during the study.

The overall acoustic quality of auscultations with the SC was “good” as rated by all users with a mean of 4.2 on a 5-point Likert scale (primary performance endpoint). To further explore this result, we evaluated only those auscultations, that were rated “good” (score of 4) or “very good” (score of 5), as these ratings were considered most meaningful in terms of acoustic quality.

A total of 86.1% of all auscultations was rated “good” or “very good” across all users, and this value is in good agreement with the values of each user group (Table 3).

These results are important for different reasons. First, they indicate a high level of satisfaction among all users with regard to the overall quality of auscultation sound transmission through the specific the SC material. Second, these findings indicate that the SC is capable of ensuring a high degree of auscultation accuracy in different body regions. This finding is of utmost clinical relevance as data on acoustic quality of commercially available stethoscope covers are scarce. Moreover, other technologies such as fully disposable single-use stethoscopes have been reported to come with substantial impairment of auscultation accuracy which may potentially lead to misdiagnoses and may therefore ultimately even impact patients’ safety (17, 18).

When stratified for BMI, the ratings “good” or “very good” were recorded for 91.9% of auscultations in normal weight patients. As expected, the rating of the acoustic quality decreased with increasing BMI (85.1% in overweight patients, 85.3% in class I obese patients, and 62.5% in class III obese patients). This observation is not surprising, as with increasing body fat mass in thoracic or abdominal body areas, heart, lung or gastrointestinal tones would appear muted during normal auscultations. This observation is thus not attributable to the medical device.

When stratified for gender, the percentage of all auscultations rated as “good” and “very good” was 81.6% in females and 87.7% in males. Both values are in good agreement with the overall rating by all users (Table 3). The slight difference between males and females might be rather due to their anatomical differences in the upper thoracic area, rather than device-related.

When stratified for auscultated body site the rating of the acoustic quality was stated as “good” and “very good” for 87.6, 89.2, and 84.2% of all auscultations of the heart, lung, and abdomen. These results are in good agreement with the overall rating by all users (Table 3). Very few auscultations (N = 10) were performed on “Other” body sites including carotid and femoral arteries and stomach. The percentage of auscultations rated as “good” or better was lower (40.0%) than for heart, lung, or abdomen. However, this finding is not unexpected and not considered to be attributable to the SC given the general challenge in auscultating these “Other” body sites and their generally low sound profile, especially if no pathological alterations have occurred.

In regard to the secondary performance endpoint, this study showed that the SC is easy to handle and may thus enable quick implementation into the clinical routine of HCPs. Handling of the product was rated for 96.4% of all auscultations to be” reasonable,” “good” or “very good” (score of 3, 4, or 5 on the 5-point Likert scale), highlighting the high degree of acceptance by the users and their general willingness to use the SC in their daily work.

The stratification analysis showed that despite some expected differences between males and females, body sites as well as among BMI classes, which do all apply to auscultations in general, the SC presented with an overall good performance profile throughout the study and for all patients independent from gender, BMI or auscultated body site. Even in highly obese patients, for which it is well known that auscultations can be truly challenging, the device performed in a satisfying manner based on the user ratings.

The high level of acceptance for the product observed in the present study is encouraging when considering the generally extremely low compliance of HCPs towards sufficient stethoscope hygiene or the general reluctance to adopt new technologies or procedures to improve it. Even though stethoscope cleanliness guidelines exist (14), and despite tremendous educational efforts, this problem remains a key challenge. In fact, most of the approaches taken to enhance stethoscope hygiene have been ineffective and ultimately failed (2, 12, 13). In a recent observational investigation, Boulee et al. evaluated physicians’ frequency and methods of stethoscope and hand hygiene practices. In only 18% of the 400 observed interactions, stethoscopes were cleaned at all, and when done, less than 4% complied with the CDC guidelines (14). The authors concluded that stethoscope hygiene is largely neglected in daily clinical routine and they strongly urged that the compliance towards stethoscope cleanliness needs to be rapidly addressed (12). To this end, Muniz and colleagues assessed the reasons for poor stethoscope hygiene compliance and anonymously surveyed nurses, nurse practitioners, and physicians at a large academic pediatric hospital. They found that perceived barriers for low stethoscope hygiene included lack of materials on hand, lack of time, and most importantly, lack of visual reminders (13).

Another interesting observation from this study was the rapid learning curve of the SC application which substantially differs from other stethoscope single-cover concepts that usually target the sole coverage of the stethoscope diaphragm. The SC, however, covers the stethoscope bell including the users auscultating hand. After its use, it is easily pulled off the hand (which is still holding the stethoscope) and discarded. In fact, the SC concept is based on the same principles as other single-use protective equipment that is used in clinical routine (e.g., medical gloves). Notably, this may represent a conceptual advantage when compared to other commercially available standard microbiological stethoscope barriers as these require manual placement of the clean cover on a potentially contaminated stethoscope. These maneuvers carry a considerable risk for iatrogenic contamination of either the clean disc, the user’s hand, or both. To the contrary, this risk could be minimized or even fully eliminated with the SC approach.

The high acceptance of the SC within the user groups in this study and rapid learning curve of the handling indicates that HCP may adapt this medical device in the daily clinical routine.