Cx50 ultrasound system

Carotid-femoral PWV was determined by applanation tonometry of the right carotid and femoral artery pulsations using a SphygmoCor system (AtCor Medical, Inc., Lisle, IL, USA) as described previously. Brachial artery reactivity testing for measurement of FMD was performed using the lower-arm occlusion technique, a linear array vascular ultrasound transducer (L12-3), and a Phillips Cx50 ultrasound system as described previously [25 (link),26 (link)]. The right and left carotid arteries were imaged using a Siemens S2000 ultrasound system with a 9L4 transducer as described previously. Carotid plaques were defined as a discrete, focal wall thickening ≥1.5 cm or focal thickening at least 50% greater than the surrounding IMT and summed to create a score of 0–12 [25 (link),26 (link)].

LUS was performed using the Philips CX50 ultrasound system (Philips Medical Systems, Bothell, WA, USA) with a 3.5 MHz convex probe at a depth of 15–18 cm adjusted to the patient's chest wall thickness. The LUS was performed by an investigator (J.H.) who was trained in a standard protocol recommended by the international guideline (14 (link)). All patients were examined with LUS immediately before extubation in a semi-recumbent position and without the support of any positive pressure on a T-piece. B-lines were measured by scanning eight regions of the thorax in a longitudinal plane between two ribs with a distance of adjacent two B-lines <7 mm (14 (link), 15 (link)). B-lines were defined as linear, vertical hyperechoic artifacts that start from the pleura moving synchronously with respiration. Each hemithorax was divided into upper and lower regions, which were further divided into medial and lateral regions by the anterior axillary line. The scanned images were independently adjudicated by two investigators (J.H. and A.K.) who were blinded to the clinical information. A positive region was defined as the presence of three or more B-line count in each area scanned. A positive LUS examination was defined as having two or more positive regions in both hemithoraces.

Transthoracic echocardiography (with the CX50 ultrasound system and an S5–1 Sector Array Transducer, Philips Medical System, Suresnes, France) was performed by a physician blinded to the study outcomes. Left ventricular ejection fraction (LVEF), end-systolic volume (ESV), and end-diastolic volume (EDV) were measured using Simpson’s method on a four-chamber view. The aortic velocity-time integral (VTIAo), pre-ejection time and systolic time were measured by pulsed Doppler at the left ventricular outflow tract on a five-chamber view. Stroke volume (SV; mL) was calculated as VTIAo×SAo, and was expressed as indexed SV (SVi) = SV/body surface area (ml.m^− 2). Cardiac output (CO) was calculated as SV × heart rate (HR), and was expressed as indexed CO (CI) = CO/ body surface area (ml min^− 1 m^− 2). Mean echocardiographic parameters were calculated from five measurements (regardless of the respiratory cycle) and analysed retrospectively.

Extracranial high-resolution sonography of the carotid arteries was performed with Philips iU22 and 9–3 MHz linear array transducer. Two patients were examined at the intensive care unit with a portable Phillips CX50 ultrasound system and 12–3 MHz linear array transducer (both systems Philips Medical Systems, Bothell, WA, USA). Patients and controls were examined by two sonographers (AF, UWA), which both are trained and certified for the NOR-SYS duplex sonography research protocol in collaboration with the Vascular Imaging Centre, University Medical Centre, Utrecht, The Netherlands.

Transthoracic echocardiography (with the CX50 ultrasound system and an S5-1 Sector Array Transducer, Philips Medical System, Suresnes, France) was performed by a physician who was blinded to the study outcomes. The left ventricular ejection fraction was measured using Simpson’s biplane method with a four-chamber view. The aortic surface area (SAo, in cm²) was calculated as π×(diameter of the left ventricular outflow tract)²/4. The aortic velocity-time integral (VTIAo), was measured with pulsed Doppler at the LVOT on a five-chamber view. The SV (mL) was calculated as VTIAo×SAo. Cardiac output (CO) was calculated as SV×heart rate (HR) (ml min^-1) and was expressed as an indexed CI, i.e. CO/body surface area (ml min^-1 m²). Mean echocardiographic parameters were calculated from five measurements (regardless of the respiratory cycle) and analysed off lines.