Article, Ultrasound

Ultrasound detection of the sliding lung sign by prehospital critical care providers

Unlabelled imageultrasound detection of the sliding lung”>American Journal of Emergency Medicine (2012) 30, 485-488

Brief Report

Ultrasound detection of the sliding lung sign by prehospital critical care providers

Matthew Lyon MD, Perry Walton DO, Valori Bhalla MD, Stephen A. Shiver MD?

Department of Emergency Medicine, Medical College of Georgia, Augusta, GA 30912-2800, USA

Received 20 October 2010; revised 8 January 2011; accepted 9 January 2011

Abstract

Background: The presence of the sonographic sliding lung sign is a sensitive indicator for the absence of a pneumothorax.

Objective: The aim of this study was to determine if prehospital critical care providers (PHCPs) can acquire and maintain the necessary skills to determine the presence or absence of the SLS following a brief tutorial.

Methods: This was a blinded randomized observational trial using a cadaveric model. The model was randomized to Esophageal intubation (negative SLS) or tracheal intubation (positive SLS), and a SonoSite 180 plus (Bothel, WA) machine was used for the examination. After a 9-month period, the PHCPs were reevaluated without additional instruction.

Results: There were 8 PHCPs. A total of 6 intubations were performed yielding a total of 48 trials. The presence or absence of the SLS was correctly identified in 46 of the 48 trials, resulting in a sensitivity and specificity of 96.9% (95% confidence interval [CI], 89.6%-99.1%) and 93.8% (95% CI, 93.8%-79.3%), respectively. At the 9-month follow-up, 7 of the original PHCPs were available to participate. A total of 8 intubations were performed yielding a total of 56 trials. The presence or absence of the SLS was correctly identified in all 56 trials, resulting in a sensitivity and specificity of 100% (95% CI, 93.6%-100%).

Conclusion: Prehospital critical care providers can accurately determine the presence or absence of the sonographic SLS following a brief tutorial and retain the skill set following a 9-month interval.

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Introduction

Prehospital care providers (PHCPs) are of paramount importance in rapidly recognizing and treating life-threaten- ing conditions such as Tension pneumothorax (PTX). Fortunately, this condition can be effectively treated with needle decompression or tube thoracostomy [1]. If a critically injured patient is going to survive, however, PHCPs must

* Corresponding author. Tel.: +1 706 721 2613.

E-mail address: [email protected] (S.A. Shiver).

recognize the presence of a Tension PTX and treat appropriately. Historically, decisions to decompress the chest have been made based on physical examination, but physical examination skills are often compromised when working in noisy and at times austere environments [2]. A suboptimal physical examination may lead to delays in chest decompression or result in unnecessary treatment when a PTX is not present [3,4].

Ultrasound (US) technology via the Focused assessment with sonography in trauma (FAST) examination has empowered clinicians with additional tools to more rapidly evaluate and disposition trauma patients [5]. As a result of

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486 M. Lyon et al.

more recent studies evaluating US detection of the sliding lung sign (SLS), increasing numbers of clinicians are now incorporating presence or absence of SLS into their FAST examinations [6,7].

The SLS is the sonographic image of the pleural surfaces moving relative to one another within the thorax. On ultrasonography, it appears as 2 echogenic lines sliding with respiration. When PTX is present, the air will prevent the deeper pleural surface from being visualized and the sliding motion will not be seen. Using US, the absence of a PTX is determined through the detection of a SLS [8,9]. Accuracy can be enhanced with the addition of secondary techniques found on most US, including M-mode and power Doppler. The presence and absence of the SLS in M-mode are visualized as the seashore sign and stratosphere sign, respectively. On power Doppler, color will be visible at the pleural interfaces due to the relative motion of the pleural surfaces in the absence of PTX, but no color will be present at the pleural interface when a PTX is present. The presence of the SLS, signifying the absence of PTX, has been shown to have a sensitivity of 95% to 100%, which is superior to chest x-ray and comparable with computed tomography [6,8,9].

Ultrasound should be a useful tool in ruling out the presence of PTX in the prehospital setting. It has many characteristics that make it desirable including portability, safety, and reproducibility. In addition, US, unlike auscul- tation, may be performed effectively in noisy environments [10]. We seek to determine whether PHCPs can learn and retain the skill set necessary to recognize the presence or absence of the SLS following a brief instructional session.

Methods

This study was a blinded randomized observational trial assessing the ability of PHCPs to identify the SLS using bedside US. It was conducted at a large, urban tertiary care medical center and was approved by the institutional review board. Informed consent was obtained from all participants before participation. Prehospital care providers, all part of an active helicopter critical care transport team, were chosen as study subjects. The critical care transport teams at our institution consist of critical care paramedics and/or nurses with significant critical care experience.

A 25-minute instructional session, including both a didactic portion and hands-on practice, was given to all participants. The session focused solely on the detection of the presence or absence of the SLS, and secondary US techniques for the detection of the SLS, including power Doppler US and M-mode US, were also introduced. The equipment consisted of a SonoSite 180 PLUS (Bothell, WA) US machine with a 4- to 2-MHz microconvex broadband transducer.

A fresh warmed cadaver was used as a model for demonstrating the presence or absence of the SLS. The

technique used consisted of evaluating the visceral and parietal pleura by positioning the transducer perpendicular to the ribs at the most anterior portion of the chest wall lateral to the sternum. With bag valve ventilation and endotracheal intubation, the pleural movements of the cadaver result in the appearance of the SLS. When intubated in the esophagus, bag valve ventilation results in no pleural movement and, thus, no SLS. This model of demonstrating SLS was chosen because it accurately represents the presence or absence of SLS including M-mode and Doppler characteristics seen in clinical practice and has been validated in other research projects [11].

The cadavers were randomly intubated, using a random number generator, in the trachea or in the esophagus. The intubations were accomplished using direct laryngoscopy and fiber optic confirmation when necessary. The presence or absence of the SLS was confirmed before each trial by the investigators. Participants were excluded from the room during the intubations, and the cadaver was completely covered except for the chest area, thus blinding the participant to the location of intubation (Fig. 1). Each trial consisted of the evaluation of the right hemithorax for the presence or absence of the SLS.

The participants were also isolated from one another during the data collection process, with each participant evaluating the cadaver independently. No time limits were placed on the participants for performing the US evaluation,

Fig. 1 Cadaver was completely covered except for the focal area of examination.

US detection of the sliding lung sign by PHCPs 487

and the use of M-mode and power Doppler US was available at the participant’s discretion. The data were collected on a standard collection sheet and subsequently analyzed using descriptive techniques. Statspages.net, a commercially available Web-based program, was used for calculations.

After a 9-month period of clinical usage, the PHCPs were reevaluated using the same cadaveric model and research protocol used in the prior training session. No further instruction was given concerning the technique.

Results

Eight PHCPs were enrolled in the study, with 4 being registered nurses and 4 being critical care paramedics. Clinical experience ranged from 10 to 22 years, with an average of 11.75 years. Two of the PHCPs had previous, limited exposure to US, none had used US in clinical practice, and none had been exposed to US usage in the detection of SLS for the evaluation of possible PTX.

A total of 6 intubations, yielding a total of 48 trials, were performed by the PHCPs. The presence or absence of the SLS was correctly identified in 46 of the 48 trials, for a sensitivity and specificity of 96.9% (95% confidence interval [CI], 89.6%-99.1%) and 93.8% (95% CI, 93.8%-79.3%),

respectively. Sixteen trials were randomized to no SLS, whereas the remaining 32 displayed a SLS. In 1 instance, a critical care paramedic misidentified a SLS when there was none present. The second error occurred when a registered nurse failed to visualize the SLS when present. In conjunction with B-mode imaging, power Doppler US and M-mode US were used in 2 (4.2%) of 48 trials and 18

(37.5%) of 48 trials, respectively.

In the 9-month follow-up study, 7 of the original PHCPs were still used by the aeromedical service and agreed to participate in the study. All 7 reported clinical usage of US for detection of SLS at a rate of less than 1 occurrence/month. A total of 8 intubations were performed yielding a total of 56 trials. The presence or absence of the SLS was correctly identified in all 56 trials, with 28 trials each showing SLS or no SLS. The sensitivity was 100% (95% CI, 93.6%-100%), and the specificity was 100% (95% CI, 93.6%-100%). Power Doppler US was not used by any of the participants, and M- mode US was used in 3 (5.4%) of 56 trials.

Discussion

Since the introduction of US into emergency medicine in the 1980s, its role has been greatly expanded. Most emergency applications of US involve the rapid and accurate detection of life-threatening medical conditions [5]. With the extended FAST, multiple studies have shown that US can accurately determine either the presence or absence of the SLS, which correlates to the presence or absence of PTX [6,7]. Although this use of US is interesting

and accurate, its clinical utility is somewhat limited because there are other diagnostic methods available in the ED. Other methods such as auscultation and chest x-ray are less sensitive, but diagnostic modalities such as computed tomography are as sensitive and give other diagnostic information [6,12]. In out-of-hospital settings, these com- peting modalities, except for auscultation, are not feasible, making detection of the SLS very useful to the clinician [10]. In some instances, such as helicopter transport, even auscultation is severely limited due to excessive noise, vibration, limited work space, and others. The inability to make an accurate diagnosis can lead to delays in treatment or potentially inappropriate treatments such as Needle thoracostomy when a PTX is not present [3,4].

Although clinical US by nonradiologists is becoming more accepted, the use of US by nonphysicians is a new frontier [13]. Typically, nurses and paramedics are the personnel responsible for critical care transport. Their training is limited in regard to diagnostic radiology, and their Scope of practice is limited to specific life-threatening diagnoses, such as PTX. Although complex diagnostic applications using US may not become part of the PHCPs skills in the near future, this study shows that all members of a critical care transport team can quickly acquire and retain the skills necessary for use of US to detect a SLS.

Limitations

Limitations of this study include the use of a cadaver model and the fact that the study was performed in a controlled environment. Even though the cadaveric model demonstrates the SLS accurately, evaluation of the critically ill patient, particularly during transport, may yield different results. In addition, a lack of a SLS has been demonstrated in the setting of chronic obstructive pulmonary disease and pulmonary blebs in prior studies [6]. Further studies will be necessary to evaluate the effects of vibration, motion, visibility, and so on, that may be encountered during active transport as they may impact the accuracy of the SLS in the evaluation of PTX. In addition, the relative small number of participants may limit the ability to generalize the results.

Conclusion

This study suggests that PHCPs with limited to no prior US experience can acquire the US skill set necessary to detect the SLS following a brief tutorial session. They can detect the SLS with a high degree of sensitivity and specificity, and the skill set is retained following a 9-month interval.

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