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Pulmonary Auscultation in the Operating Room: A Prospective Randomized Blinded Trial Comparing Electronic and Conventional Stethoscopes

Hoffmann, Clement MD*; Falzone, Elisabeth MD*; Verret, Catherine PhD, MD; Pasquier, Pierre MD; Leclerc, Thomas MD§; Donat, Nicolas MD§; Jost, Daniel MD; Mérat, Stephane PhD, MD; Maurice, Guillaume de Saint PhD, MD; Lenoir, Bernard PhD, MD*; Auroy, Yves PhD, MD; Tourtier, Jean-Pierre PhD, MD

doi: 10.1213/ANE.0b013e31829ec0a5
Technology, Computing, and Simulation: Brief Report
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BACKGROUND: We compared the subjective quality of pulmonary auscultation between 2 acoustic stethoscopes (Holtex Ideal® and Littmann Cardiology III®) and an electronic stethoscope (Littmann 3200®) in the operating room.

METHODS: A prospective double-blind randomized study with an evaluation during mechanical ventilation was performed in 100 patients. After each examination, the listeners using a numeric scale (0–10) rated the quality of auscultation. Auscultation quality was compared in patients among stethoscopes with a multilevel mixed-effects linear regression with random intercept (operator effect), adjusted on significant factors in univariate analysis. A significant difference was defined as P < 0.05.

RESULTS: One hundred comparative evaluations of pulmonary auscultation were performed. The quality of auscultation was rated 8.2 ± 1.6 for the electronic stethoscope, 7.4 ± 1.8 for the Littmann Cardiology III, and 4.6 ± 1.8 for the Holtex Ideal. Compared with Holtex Ideal, auscultation quality was significantly higher with other stethoscopes (P < 0.0001). Compared with Littmann Cardiology III, auscultation quality was significantly higher with Littmann 3200 electronic stethoscope (β = 0.9 [95% confidence interval, 0.5–1.3]).

CONCLUSIONS: An electronic stethoscope can provide a better quality of pulmonary auscultation than acoustic stethoscopes in the operating room, yet with a magnitude of improvement marginally higher than that provided with a high performance acoustic stethoscope. Whether this can translate into a clinically relevant benefit requires further studies.

Published ahead of print July 18, 2013

From the *Department of Anesthesiology and Intensive Care Medicine, Percy Military Teaching Hospital, Clamart; French Military Institute of Biomedical Research Brétigny-sur-Orge; Department of Anesthesiology and Intensive Care Medicine, Begin Military Teaching Hospital, Saint Mandé §Burns Treatment Center, Percy Military Teaching Hospital, Clamart; Emergency Medical Service, Paris Fire Brigade, Paris; and Department of Anesthesiology and Intensive Care Medicine, Val-de-Grace Military Teaching Hospital, Paris, France.

Accepted for publication May 2, 2013.

Published ahead of print July 18, 2013

Funding: Not funded.

The authors declare no conflicts of interest.

This report was previously presented, in part, at the SFAR congress 2011.

Reprints will not be available from the authors.

Address correspondence to Clement Hoffmann, MD, Department of Anesthesiology and Intensive Care Medicine, Percy Military Teaching Hospital, HIA Percy, 101 Ave., Henri Barbusse, BP 406-92141 Clamart Cedex, France. Address e-mail to clement.hoffmann@yahoo.fr.

In the operating room, pulmonary auscultation helps to diagnose misplacement of an endotracheal tube (esophageal intubation, placement into the mainstem bronchus) and to evaluate other pulmonary abnormalities (e.g., pneumothorax, bronchospasm, pulmonary edema, etc.).1–4

The aim of this study was to compare, in the operating room, the quality of pulmonary auscultation between 2 acoustic stethoscopes (Littmann Cardiology III®, 3M™, St. Paul, MN; and the Holtex Ideal® simple flag, Holtex, Aix-en-Provence, Bouches du Rhône, France) and an electronic stethoscope (Littmann Electronic Model 3200®, 3M), which is designed to amplify sounds and reduce ambient noise.

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METHODS

A prospective double-blind randomized study was performed in 3 hospitals (military teaching hospitals Val-de-Grâce, Bégin, Percy; Paris). We compared the conventional stethoscope Holtex Ideal simple flag, with a high performance conventional stethoscope, the Littmann Cardiology III, and with a recently available electronic stethoscope, the Littmann Electronic Model 3200. We included consenting anesthesiologists. All of them had normal hearing as measured by routine audiometry within the prior year.

After approval from each Local Research Ethics Committee, which waived the requirement for oral informed consent from patients, all consecutive patients who had general anesthesia for various surgeries (visceral, orthopedic, vascular, and gynecological surgery) were enrolled. Auscultation was assessed during mechanical ventilation. While patients were lying down, their lungs were ventilated with a Zeus® Infinity® Empowered (Dräger Medical, Lübeck, Germany) or Primus® ventilator (Dräger Medical) with tidal volume set to 8 mL/kg (ideal body weight).

Participants were asked to evaluate 3 types of stethoscopes for each patient. All physicians were blinded with a mask, and they did not touch the stethoscopes during the evaluation. An independent practitioner determined the right placement of the stethoscope for each auscultation. He adjusted the headset on the participant’s ears and placed the chestpiece of the stethoscope in the proper position. The order of stethoscopes was randomized for each auscultation (a number was assigned to each stethoscope, and random permutations were applied for each evaluation). The sound amplification level was set at the middle of the scale (4/8) on the electronic stethoscope. At the end of each examination, the quality of auscultation was rated by the listeners using the numeric scale described in a previous study.5 This scale ranges from 0 to 10, with 0 corresponding to “I can hear nothing” and 10 corresponding to “I can hear perfectly.”

Results were expressed as mean ± SD (compatibility with normal distribution was controlled). Auscultation quality was compared in patients among stethoscopes with a multilevel mixed-effects linear regression with random intercept (operator effect), adjusted on significant factors in univariate analysis (xtmixed procedure with Stata 11, StataCorp LP, College Station, TX). A significant difference was defined as P < 0.05.

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RESULTS

Eight consenting anesthetists joined the study. The age of participants was 39 ± 15 years (female: 3; male: 5). One hundred surgical patients were included, aged 53 ± 19 years and with a body mass index of 29.7 ± 4.8 kg/m2. Pulmonary auscultation was performed in the operating room with the 3 stethoscopes on each patient. The delivered tidal volume was 542 ± 91 mL with 11.7 ± 2.9 respiratory cycles per minute and a positive end-expiratory pressure of 2.7 ± 2.1 cm H2O. The mean quality of auscultation was rated 8.2 ± 1.6 for the Littmann 3200 electronic stethoscope, 7.4 ± 1.8 for the Littmann Cardiology III acoustic stethoscope, and 4.6 ± 1.8 for the Holtex Ideal acoustic stethoscope.

Compared with the Holtex Ideal, auscultation quality was significantly higher with other stethoscopes (P < 0.0001): Littmann Cardiology III (β = 2.8 [95% confidence interval {CI}, 2.4–3.3]) and Littmann 3200 electronic stethoscope (β = 3.7 [95% CI, 3.3–4.1]) adjusted on tobacco consumption (P = 0.03), respiratory history (P = 0.03), and respiratory frequency (P = 0.02). Interoperator variance was significant (P = 0.003; intraclass correlation: 6.9%).

Considering the same model and compared with the Littmann Cardiology III, auscultation quality was significantly higher with the Littmann 3200 electronic stethoscope (β = 0.9 [95% CI, 0.5–1.3]).

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DISCUSSION

Our study suggests that, compared with acoustic stethoscopes, the electronic stethoscope is able to improve the quality of pulmonary auscultation in the operating room. Many studies have been published about the electronic stethoscope, but none showed an improvement for the auscultation. Iversen et al.6 found no difference in pulmonary auscultation, except for rhonchi (P = 0,03), but their study was not double blinded. In another study, nurses and doctors preferred the conventional stethoscope, but they only evaluated cardiac auscultation.7 Nevertheless, the electronic stethoscope amplifies environmental noise and that can preclude its use.8 Some studies also recommended ultrasound in confirming endotracheal tube placement.9,10 Our study also revealed a significant difference between 2 types of acoustic stethoscopes.

Our study has several limitations. First, the evaluation of stethoscopes was subjective. Second, we found a statistically significant difference in lung auscultation quality among stethoscopes, but the clinical relevance of this finding remains a question. Further studies should establish whether the detection rate of adverse events could be improved and whether subpopulations such as obese patients would benefit most from this modality. Third, neither the programmable setting of the sound amplification level of the Littmann 3200 nor the correct placement for each auscultation was adjusted by each practitioner, contrasting with real-life practice.

In conclusion, we suggest that an electronic stethoscope can provide a better quality of pulmonary auscultation than acoustic stethoscopes in the operating room, yet with a magnitude of improvement only marginally higher than that provided with a high performance acoustic stethoscope. Whether this can translate into a clinically relevant benefit requires further study.

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DISCLOSURES

Name: Clement Hoffmann, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Dr. Hoffmann has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Name: Elisabeth Falzone, MD.

Contribution: This author helped design and conduct the study.

Attestation: Dr. Falzone has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Catherine Verret, PhD, MD.

Contribution: This author helped design the study and analyze the data.

Attestation: Pr. Verret has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Pierre Pasquier, MD.

Contribution: This author helped conduct the study.

Attestation: Dr. Pasquier has seen the original study data and approved the final manuscript.

Name: Thomas Leclerc, MD.

Contribution: This author helped design and conduct the study and analyze the data.

Attestation: Dr. Leclerc has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Nicolas Donat, MD.

Contribution: This author helped conduct the study.

Attestation: Dr. Donat has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Daniel Jost, MD.

Contribution: This author helped write the manuscript.

Attestation: Dr. Jost has seen the original study data and approved the final manuscript.

Name: Stephane Mérat, PhD, MD.

Contribution: This author helped design and conduct the study.

Attestation: Pr. Mérat has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Guillaume de Saint Maurice, PhD, MD.

Contribution: This author helped design and conduct the study.

Attestation: Pr. de Saint Maurice has seen the original study data and approved the final manuscript.

Name: Bernard Lenoir, PhD, MD.

Contribution: This author helped design the study and analyze the data.

Attestation: Pr. Lenoir has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Yves Auroy, PhD, MD.

Contribution: This author helped design and conduct the study.

Attestation: Pr. Auroy has seen the original study data and approved the final manuscript.

Name: Jean-Pierre Tourtier, PhD, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Pr. Tourtier has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

This manuscript was handled by: Dwayne R. Westenskow, PhD.

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ACKNOWLEDGMENTS

The authors would like to especially acknowledge Julie Trichereau (Epidemiologic and Public Health Military Center, Marseille, France) for her valuable contribution and her statistical expertise.

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REFERENCES

1. Brunel W, Coleman DL, Schwartz DE, Peper E, Cohen NH. Assessment of routine chest roentgenograms and the physical examination to confirm endotracheal tube position. Chest. 1989;96:1043–5
2. Riley RH, Marcy JH. Unsuspected endobronchial intubation–detection by continuous mass spectrometry. Anesthesiology. 1985;63:203–4
3. Owen RL, Cheney FW. Endobronchial intubation: a preventable complication. Anesthesiology. 1987;67:255–7
4. Sitzwohl C, Langheinrich A, Schober A, Krafft P, Sessler DI, Herkner H, Gonano C, Weinstabl C, Kettner SC. Endobronchial intubation detected by insertion depth of endotracheal tube, bilateral auscultation, or observation of chest movements: randomised trial. BMJ. 2010;341:c5943
5. Tourtier JP, Fontaine E, Coste S, Ramsang S, Schiano P, Viaggi M, Libert N, Durand X, Chargari C, Borne M. In flight auscultation: comparison of electronic and conventional stethoscopes. Am J Emerg Med. 2011;29:932–5
6. Iversen K, Greibe R, Timm HB, Skovgaard LT, Dalsgaard M, Hendriksen KV, Hrobjartsson A. A randomized trial comparing electronic and conventional stethoscopes. Am J Med. 2005;118:1289
7. Grenier MC, Gagnon K, Genest J Jr, Durand J, Durand LG. Clinical comparison of acoustic and electronic stethoscopes and design of a new electronic stethoscope. Am J Cardiol. 1998;81:653–6
8. Houtsma AJ, Curry IP, Sewell JM, Bernard WN. Dual-mode auscultation in high noise level environments. Aviat Space Environ Med. 2006;77:294–5
9. Chun R, Kirkpatrick AW, Sirois M, Sargasyn AE, Melton S, Hamilton DR, Dulchavsky S. Where’s the tube? Evaluation of hand-held ultrasound in confirming endotracheal tube placement. Prehosp Disaster Med. 2004;19:366–9
10. Pfeiffer P, Rudolph SS, Børglum J, Isbye DL. Temporal comparison of ultrasound vs. auscultation and capnography in verification of endotracheal tube placement. Acta Anaesthesiol Scand. 2011;55:1190–5
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