Health care applications of simulation have focused on student and physician training.1 Current focus includes the use of patient simulation in the development, maintenance, and evaluation of clinical competencies and as a tool for interdisciplinary training. However, simulation remains useful to test pieces of equipment.2 Mimicking clinical events could permit the safe bench marking of medical equipment in austere environment.3 Aeromedical evacuation creates a unique environment that challenges even the most experienced clinician.4 The availability and use of diagnostic tools is essential to the delivery of continuous, supportive en route care. Air transports of patients with significant pulmonary or cardiac impairment are common and maintaining the appropriate monitoring is of key importance. Many air medical transport programs use pulse oximeters, end-tidal carbon dioxide detectors, and other devices as indirect measures of respiratory and cardiac status. Thus, these methods do not replace auscultation during flight, which may be needed to identify critical clinical change.5–7 Auscultation of the lungs can be essential when confirming the placement of endotracheal tubes or diagnosing conditions such as pneumothorax, pulmonary edema, and asthma. Cardiac auscultation is also helpful in assessing the integrity of heart. Hence, the availability and use of a stethoscope is essential to the delivery of continuous, supportive en route care. However, aeromedical evacuations occur in high ambient noise environments, and that can preclude the use of the conventional stethoscope.8–11 This inability seriously handicaps physical assessment by air medical transport teams.
The aim of this study was to compare the capabilities of a traditional and an amplified stethoscope (which is expected to reduce background and ambient noise and also to increase the signal strength) to assess breath and heart sounds during medical transport aboard a Boeing C135 plane (jet turbine), which is used for aeromedical evacuation by the French Air Forces. We compared a recently available electronic stethoscope, the Litmann Electronic Stethoscope Model 3000, with a widely used conventional stethoscope, the Litmann Cardiology III (3M, St. Paul, Minnesota), in a prospective study. We assessed the capability of clinicians at detecting in flight pathologic heart and lung sounds. Sounds were mimicked using a mannequin-based simulator SimMan 3G (Laerdal Medical, Stavanger, Norway).
MATERIALS AND METHODS
We included consenting medical personnel, all experienced in air medical transport and with a minimum of 3 years of experience, from the following clinical positions: intensivist and nurse anesthesiologists. The participants involved were asked to evaluate in flight the 2 types of stethoscopes (they used in everyday practice conventional stethoscopes).
We used the SimMan 3G to assess cardiac and lung sounds, with high reproductibility obtained by prerecorded sounds (volume setting, 3 of 5). The SimMan mannequin was installed in the plane and prepared as a real patient. The participants were allowed to familiarize themselves with the simulator heart and lung sounds before the flight (normal sounds and abnormal sounds: crackles, wheezing, one-sided lung silence, as well as systolic, diastolic, and Austin-Flint murmur), using conventional and electronic stethoscopes. The clinical situation that was mimicked was aeromedical aeroevacuation of patients aboard a C135 (medically configured), at standard flying altitude (10,000 m).
To perform the comparative clinical study, 2 units of each stethoscope model were used. A number was assigned to each stethoscope, and a procedure was developed to randomly select 1 stethoscope of both type at a time. Participants were not allowed to observe their fellow staff before their own performance. Measurements of ambient noise levels were practiced during cruising altitude.
Participants examined the mannequin’s breath and cardiac sounds, with a variety of activated abnormalities. Seven abnormal sounds (crackles, wheezing, right and left lung silence, as well as systolic, diastolic, and Austin-Flint murmur) were simulated in random order. Each of the abnormal sounds was assessed by each participant with each stethoscope. Abnormal sounds and stethoscopes were both randomly selected to limit an order effect. Bell and diaphragm filtering modes were used respectively for heart and lung auscultation. The correct placement for each auscultation was determined by each participant. A programmable setting of the sound amplification level of the Litmann 3000 was activated, providing amplification, adjusted by each practitioner. Hence, clinicians were not blinded during auscultation. They were instructed to restrict each examination to no more than 1 minute. At the end of each pathologic examination, a diagnosis was asked.
The comparison for diagnosis assessed (correct or wrong), between using the electronic and conventional stethoscopes, were performed as a McNemar test, both for heart and lung auscultations. A significant difference was defined by P < 0.05. No calculation of sample size was committed previously.
We included 5 consenting participants: 4 intensivists, 1 nurse anesthesiologist. They were invited from 3 French military hospitals (hospital Val-de-Grâce, Paris; hospital Percy, Clamart; and hospital Bégin, Saint Mandé). Mean (SD) age of clinicians was 36 (11) years. A total of 70 evaluations were performed (30 heart auscultations, 40 lung auscultations). The mean (SD) ambient noise level was 85 (1) dB. For simulated cardiac sounds, diagnosis was right in 0/15 and 4/15 auscultations, respectively, with conventional and electronic stethoscopes (McNemar test, P = 0.13). For simulated lung sounds, right diagnosis was found with conventional stethoscope in 10/20 auscultations versus 18/20 with electronic stethoscope (McNemar test, P = 0.013).
Aboard a C135, compared with the conventional Litmann Cardiology III stethoscope, the electronic model Litmann 3000 was considered by clinicians to be better for hearing lung sounds (mimicked by a mannequin-based simulator). No benefit was found for heart sounds. In flights on this type of plane, this prospective randomized study suggests that the main limitations of acoustic stethoscopes are partly solved by the electronic stethoscopes.
The truly unique and challenging aspect of en route care is that it must be provided in an environment that is entirely different from the intensive care unit in a hospital. Environmental conditions as noise, vibration, altitude, light, and duration of the mission must be considered. In aeromedical evacuations, an aircraft (helicopter or fixed wing) is used to evacuate critically ill patients. Several sources of noise exist in such vehicles, and their interaction with the interior space and fuselage is complex and varies in time owing to the wide range of conditions and maneuvers encountered during typical evacuation. For example, ambient noise levels in the range of 85 to 100 dB occurred in the cabin of a C135 aircraft. In contrast, normal heart and lung sounds in an healthy adult are roughly 22 to 30 dB. Conventional stethoscopes are highly prone of interference from such high ambient noise environments, owing to an inherently poor signal-to-noise ratio.
Few trials explored in-flight auscultation. The effect of noise on auscultation has been studied in helicopters. The physiologic study published by Poulton et al12 was disappointing. Two electronic amplifying stethoscopes (Labtron 3000, Happauge, NY; Starkey ST3, Chicago, IL) were investigated, aboard a jet helicopter Allison C-28. Based on frequency spectrum analysis, they found that jet helicopter turbine engine noise and human lung and cardiac sounds share a substantially overlapping frequency spectrum, with amplification of one amplifying the other. They concluded not only that the stethoscope is not an adequate tool for the assessment of breath sounds on rotary aircraft but also that strategies using acoustical or amplification of sound (even associated with filtration) in that environment must necessarily fail. Another simulation study was published by Hunt et al.13 The capabilities of a traditional and an amplified stethoscope (Medmax M×2; Medmax Inc., Denver, CO), used by flight nurses to hear breath sounds during air medical transport in a MBB BO-105 helicopter (internal noise ranged from 100 to 103 dB), were explored.10 A breath sound model was developed on mannequin, with audiotapes to closely mimic normal breath sounds. Experimental listening sessions were performed during real flight. No breath sounds were heard by any flight nurse using either a traditional or an amplified stethoscope. The authors concluded that the stethoscope was an inadequate tool for the high-noise environment in flight. A more optimistic study was performed by Stone et al.14 The use of an esophageal stethoscope had enabled flight crews to identify effectively breath sounds in a simulated BO-105 helicopter in-flight sound environment (98 dB).
We had previously the opportunity to investigate the capabilities of traditional and amplified stethoscopes to assess heart and breath sounds during real medical transport. Two prospective randomized studies were performed.15,16 In both studies, the quality of lung and cardiac auscultations was described using a visual rating scale (ranging from 0 to 100 mm, 0 corresponding to “I hear nothing,” 100 to “I hear perfectly”). Comparisons were accomplished using a t test for paired values. In a first study, aboard Falcon 50, 32 comparative evaluations were performed. For cardiac auscultation, the value of the rating scale was 5.8 (1.5) and 6.4 (1.9), respectively, for the traditional and amplified stethoscope (Littman Cardiology III vs. Littman 3100; P = 0.018), whereas there was no significant difference found concerning breath sound auscultation.15 These results cannot be extended to other vectors, such as C135, more contaminated by structurally transmitted noise. In a second study, aboard C135, a total of 36 comparative evaluations were performed, to compare the traditional stethoscope Littman Cardiology III and one model of electronic stethoscope (Littman Stethoscope Model 3000, the predecessor of the 3100 model).16 For lung sounds, the quality of auscultation was estimated at 27 (17) mm for traditional stethoscope and 68 (13) for electronic stethoscope (paired t test, P = 0.0003). As in the current data, it suggested that the main limitations of acoustic stethoscopes are partially solved by the electronic stethoscopes concerning lung auscultation. For cardiac auscultation, the value of the visual rating scale showed no significant difference between the 2 types of stethoscopes. This seems in contradiction with the current data. However, one could note that mainly normal lung sounds were subjectively assessed in real-life medical evacuations and that an older model of electronic stethoscope was used.
A number of limitations appear in this study too. We acknowledge that some potential for bias exists because it was impossible to blind the practitioners to the stethoscope being used, as far as amplification was adjusted by each practitioner (like in real-life practice). This could influence a tendency toward the high-tech electronic version. However, our focus on this study was to determine 7 abnormal sounds, and practitioners were blinded on that point. Cardiac auscultation was always performed using the bell of the stethoscope. Many clinicians use both the diaphragm and the bell (even for sounds that, in theory, should be better heard with the bell), and this would seem even more likely if there is trouble hearing the heart sounds with the bell. Participants could choose where to listen for sounds. In a patient, this may not make a huge difference, but in a mannequin with speakers, the sounds are not hearable at all spots, and it could have influenced results. Moreover, we studied the quality of auscultation with various reproducible stimuli, rather than for real patients. Although the realism of the SimMan is fair and allows unlimited exposure to the same sound, it is not perfect, and sample size was small. Real patient’s sounds in flight might not be exactly similar to SimMan 3G in that environment, and results must be interpreted cautiously. Moreover, mannequin skin is stiffer than human skin, and it may be harder to get a good coupling of the stethoscope surface to the plastic skin surface than it is to get a good coupling on real human skin. Another limitation is that we tested auscultation aboard a C135, with specific vibrations as confounding factors, and our results might not be extended to other vectors, especially for helicopters, more contaminated by structurally transmitted noise. Bearing these caveats in mind, the simulation technology (with specific cardiopulmonary simulators) has been used to improve cardiac auscultation.17–19 The simulation remains a safe and useful environment to test new pieces of equipment before bringing them in clinical situation.
Aboard a Boeing C135, compared with the conventional Litmann Cardiology III stethoscope, the electronic model Litmann 3000 was considered to be better for hearing simulated lung sounds. No benefit was found for heart sounds. We conclude that flight practitioners involved in aeromedical evacuation in a C135 plane are more able to practice lung auscultation with this amplified stethoscope than with a traditional one. Future developments in signal processing of sonic waves are undoubtedly necessary for better cardiac auscultation.
Long recognized and used in aviation training, simulation was initially adopted for medical training and crisis management in the field of anesthesia but since has been used in an increasingly diverse group or medical specialties, including emergency medicine and surgery. Mannequin-based simulators offer a unique evaluation tool in aeromedical evacuation setting. They enable evaluation of advanced skills and management of rare and life-threatening scenarios, without endangering patients. Simulation remains a safe and useful tool to test new pieces of equipment before bringing them in clinical situation.
1. Gaba DM. The future’s here, we are it. Simul Healthc 2006; 1: 1–2.
2. Savoldelli GL, Schiffer E, Abegg C, et al. Learning curves of the Glidescope, the McGrath and the Airtraq laryngoscopes: a manikin study. Eur J Anaesthesiol 2009; 26: 554–558.
3. Tourtier JP, Forsans E, Leclerc T, et al. Acute severe asthma: performance of ventilator at simulated altitude. Eur J Emerg Med 2011; 18: 77–80.
4. Johannigman JA. Critical care aeromedical teams (CCATT): then, now and what’s next. J Trauma 2007; 62 (Suppl 6): 35.
5. Laennec RT. De l’auscultation
mediate, ou Traité du diagnostic des maladies des poumons et du coeur, fondé principalement sur ce nouveau moyen d’exploration. Paris, France: JA Brosson & JS Chaude; 1819.
6. Tavel MT. Cardiac auscultation
. A glorious past—but does it have a future? Circulation 1996; 93: 1250–1253.
7. Tavel MT. Cardiac auscultation
. A glorious past—and it does have a future! Circulation 2006; 113: 1255–1259.
8. Bishop LC. Aviation auscultation
. JAMA 1990; 263: 233.
9. Cottrell JJ, Kohn GM. Aviation ausculation. JAMA 1990; 263: 233.
10. Garner DC. Noise in medical helicopters. JAMA 1991; 266: 515.
11. Gasaway DC. Noise levels in cockpits of aircraft during normal cruise and considerations of auditory risk. Aviat Space Environ Med 1986; 57: 102–112.
12. Poulton TJ, Worthington DW, Pasic TR. Physiologic chest sounds and helicopter engine noise. Aviat Space Environ Med 1994; 65: 338–340.
13. Hunt RC, Bryan DM, Brinkley VS, et al. Inability to assess breath sounds during air medical transport by helicopter. JAMA 1991; 265: 1982–1984.
14. Stone CK, Stimson A, Thomas SH, et al. The effectiveness of oesophageal stethoscopy in a simulated in-flight setting. Air Med J 1995; 14: 219–221.
15. Tourtier JP, Fontaine E, Coste S, et al. In flight auscultation
: comparison of electronic and conventional stethoscopes. Am J Emerg Med 2011; 29: 932–935.
16. Tourtier JP, Libert N, Clapson P, et al. Auscultation
in flight: comparison of conventional and electronic stethoscopes. Air Med J 2011; 30: 158–160.
17. Issenberg SB, McGaghie WC, Gordon DL, et al. Effectiveness of a cardiology review course for internal medicine residents using simulation
technology and deliberate practice. Teach Learn Med 2002; 14: 223–228.
18. Barrett MJ, Kuzma MA, Seto TC, et al. The power of repetition in mastering cardiac auscultation
. Am J Med 2006; 119: 73–75.
19. Butter J, McGaghie WC, Cohen ER, et al. Simulation
-based mastery learning improves cardiac auscultation
skills in medical students. J Gen Intern Med 2010; 25: 780–785.