Page 78 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 3
Methods
We performed a double-blinded, cross-sectional, observational study to compare three types of ultrasound transducers for the diagnosis of two conditions: normal ventilation, and pneu- mothorax. Ethical approval was obtained from the institutional ethics review board of the Radboud university medical center, Nijmegen. Written informed consent was asked and obtained from every patient and from every observer.
At the preoperative outpatient evaluation clinic of the Radboud university medical center, Nijmegen, the Netherlands, from September to October 2017, we recruited a consecutive series of eleven eligible patients that were scheduled for video-assisted thoracoscopic surgery (VATS) for pulmonary, mainly neoplastic, pathology. The inclusion criteria were a body mass index < 30 kg m-2 and the absence of pathology of the chest wall, visceral or parietal pleura.
Lung US is a valuable test for the detection or exclusion of a pneumothorax.13,14 A US trans- ducer is positioned on the chest wall perpendicular to two adjacent ribs. Between the acous- tic shadows of two ribs, a hyperechoic line is visible representing the interface of the pari- etal and visceral pleura. With normal ventilation, lung sliding is observed as a to-and-fro movement at the pleural line as a result of the sliding of the visceral pleura against the inner chest wall. B-lines may be observed as hyperechoic lines radiating down from the pleural line. Their presence excludes pneumothorax (at the transducer position). Horizontal repe- titions of the pleural line appearing below at multiples of the skin-pleural line distance are called A-lines. Their appearance is more prominent in the presence of a pneumothorax when B-lines are absent and no longer obscuring the A-lines.
We used a portable X-Porte ultrasound system (Fujifilm SonoSite Inc., Bothell, WA, USA) equipped with three transducers: a high-frequency linear-array 15–6 MHz (HFL50xp), a curved-array abdominal 5–2 MHz (C60xp) and a phased-array cardiac 5–1 MHz (P21xp) transducer. The footprints of the transducers are 5 cm, 6 cm, and 2.1 cm, respectively.
For the VATS procedure, isolated ventilation of the dependent lung via a double-lumen en- dotracheal tube was necessary. First, all patients underwent general anesthesia, were intubat- ed and ventilated, and placed in a lateral decubitus position. The ventilator was set to deliver a tidal volume of 5 ml kg-1 at a rate of 20 min-1. The anesthesiologist verified the position and depth of the double-lumen endotracheal tube with fiberoptic bronchoscopy.
Secondly, the linear array, curved-array, and phased-array transducer were positioned over the 4th or 5th intercostal space at the axillary line in a cranio-caudal orientation. 15-second