No Difference in Auscultation Through Clothing or Directly on Skin

Author: Michael Vlessides

Effective auscultation of heart sounds and murmurs is possible over clothing, given firm pressure on the stethoscope, according to a University of Florida research team. Their study demonstrated no difference between that technique and placing the stethoscope directly on the skin, a result that may have several benefits, including decreased exam time, less chance of stethoscope contamination and increased patient comfort.

“Physicians frequently auscultate over a patient’s clothing or hospital gown,” said Joseph E. Lagrew II, MD, an anesthesiology resident at the University of Florida, in Gainesville. “There are a number of reasons why this occurs, including ability to perform an exam in a more timely manner, less interpersonal awkwardness and less likely transmission of skin microbes.” Nevertheless, classic medical teaching suggests that optimal transmission of heart sounds to the stethoscope occurs when the bell or diaphragm is placed directly on the patient’s skin.

Previous research of heart sounds (Postgrad Med J 2015;91[1077]:379-383) found no difference in sound transmission through one layer of clothing. “However, we wanted to take this a step further,” Dr. Lagrew explained. “Because previous research was subjective, we wanted to look at this objectively and also wanted to include heart murmurs, because that’s why most of us listen to the patient in the first place.”

After the recordings were imported to a computer, the files were processed via an analyzing program for the peak amplitude of S1 and S2 heart sounds, as well as the average amplitudes of any murmurs. The composite waveforms were then analyzed to assess decibel-magnitude differences between the two approaches. The study was powered to detect noninferiority within a 3-decibel difference in amplitude between the skin and clothing for both normal and abnormal heart sounds.

Dr. Lagrew reported the findings at the 2018 annual meeting of the International Anesthesia Research Society (abstract PA124).

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The study cohort comprised 80% clinic patients who were evaluated while wearing their clothing from home and 20% inpatients who wore a hospital gown during the exam. The average patient age was 65 years; 63% were women, and the average body mass index was 30.4 kg/m².

“The physicians who auscultated were instructed to press firmly with the stethoscope while listening. Those were the only instructions they were given,” Dr. Lagrew explained.

The study found that there was no difference in sounds regardless of whether the auscultation was performed directly on the skin or over one layer of clothing/the hospital gown (P=0.58). This difference persisted for both normal heart sounds (S1 and S2; P=0.43), as well as for murmurs (P=0.74). Similarly, no differences were found based on either operator experience or area auscultated.

Although the researchers were comfortable with the study’s findings, they noted a potential limitation with the decibel level threshold chosen, as other studies found a range of lower minimal detectable differences. Nevertheless, powering a study to meet a lower threshold was not feasible, Dr. Lagrew said.

Differences in patient body habitus and comorbidity phenotype also may affect the efficacy of auscultation, he noted. “Ultimately, we hope to qualify certain situations where a single layer of clothing or skin may be the better technique for auscultation, though further analysis is ongoing.”

Susan Goobie, MD, an associate professor of anesthesia at Harvard Medical School, in Boston, found the study interesting, especially the results of listening for difficult-to-catch cardiac sounds. “My biggest worry as a clinician is not the normal heart sounds but detecting a grade 1, 2, 3 or 4 murmur,” she said. “Can we detect a grade 1 murmur through clothing? Because I find that hard to do with my ears and the stethoscope on the skin.”

“That’s an important consideration,” Dr. Lagrew said. “Of the murmurs that we had—and most were grade 2 or 3, but some were grade 1—there was no difference.”

For Mara Serbanescu, MD, a resident at the Johns Hopkins University School of Medicine, in Baltimore, auscultation through clothing comes with another possible confounder. “Did you notice there was a lot of background noise when working through clothing?” Dr. Sebanescu asked. “That’s my biggest problem when I listen through clothes: I hear other things, too.”

“From my perception, it didn’t seem like that there was that much difference in background noise, but that wasn’t specifically studied,” Dr. Lagrew replied.

In the end, the researchers noted that while these findings are contrary to classic teaching, they nonetheless demonstrate the potential applicability of a simple concept. “I think this is encouraging,” Dr. Lagrew concluded, “and shows that it’s important to think about the things we have been teaching in medical schools for years, not necessarily to take as dogmatic fact.”