Which ultrasound transducer type is best for diagnosing pneumothorax?

Abstract

Background: An accurate physical examination is essential in the care of critically ill and injured patients. However, to diagnose or exclude a pneumothorax, chest auscultation is unreliable compared to lung ultrasonography. In the dynamic prehospital environment, it is desirable to have the best possible ultrasound transducer readily available. The objective is to assess the difference between a linear-array, curved-array, and phased-array ultrasound transducer in the assessment for pneumothorax and to determine which is best.

Methods: In this double-blinded, cross-sectional, observational study, 15 observers, experienced in lung ultrasonography, each assessed 66 blinded ultrasound video clips of either normal ventilation or pneumothorax that were recorded with three types of ultrasound transducers. The clips were recorded in 11 adult patients that underwent thoracoscopic lung surgery immediately before and after the surgeon opened the thorax. The diagnostic accuracy of the three transducers, elapsed time until a diagnosis was made, and the perceived image quality was recorded.

Results: In total, 15 observers assessed 990 ultrasound video clips. The overall sensitivity and specificity were 98.2% and 97.2%, relatively. No significant difference was found in the diagnostic performance between transducers. A diagnosis was made slightly faster in the linear-array transducer clips, compared to the phased-array transducer (p = .031). For the linear-, curved-, and phased-array transducer, the image quality was rated at a median (interquartile range [IQR]) of 4 (IQR 3-4), 3 (IQR 2-4), and 2 (IQR 1-2), relatively. Between the transducers, the difference in image quality was significant (p < .0001).

Conclusions: There was no difference in diagnostic performance of the three transducers. Based on image quality, the linear-array transducer might be preferred for (prehospital) lung ultrasonography for the diagnosis of pneumothorax.

Keywords: Emergency medical services; Pneumothorax; Transducer; Ultrasonography.

Fig. 1

A typical uncropped image of the pleural interface, acquired with the phased-array transducer. On the right, the cropped version is displayed as is was played back to the observers

Fig. 2

The surgeon performs lung ultrasonography in a patient with a confirmed pneumothorax and the videoscope in situ. The video screen displays an image of the inside of the right hemi-thorax and the collapsed right lung. The surgeon is handling the wrapped-up ultrasound transducer. The ultrasound device is shown in the back of the image

Fig. 3

A typical uncropped and cropped image of the pleural interface, acquired with the phased-array transducer. On the right, the cropped version is displayed as it was played back to the observers

Fig. 4

A cropped 15-s clip played in a random order to the observers

Fig. 5

Boxplot of the elapsed time until a diagnosis was made compared between transducer types and diagnoses. The elapsed time until a diagnosis was stated by the observers. The time is represented in median seconds. The box represents the 25–75% interquartile range. The whiskers indicate the 95% confidence interval. There is a significant difference in the elapsed time until a diagnosis was made between normal ventilation and pneumothorax within all three transducers (p < .0001)

Fig. 6

Clustered bar count of the image quality rating per transducer type. The Wilcoxon signed-rank test showed a significant difference in image quality between all three transducers (p < .0001)