Study subjects
Patients who were admitted to the Emergency Intensive Care Unit of Shanghai Tenth People's Hospital (Shanghai, China) from April to June 2020 were recruited. This study was approved by the Ethics Committee of Shanghai Tenth People's Hospital, and the written informed consent was obtained from all the study subjects.
Inclusion and exclusion criteria
Inclusion criteria were as follows: patients who aged over 14 years old with hemodynamic instability, unknown volume status, increased extravascular lung water, septic shock, cardiogenic shock, traumatic shock, acute respiratory distress syndrome (ARDS), severe burn, acute pancreatitis, high-risk surgery, etc. Exclusion criteria were as follows: contraindications for use of PiCCO (allergy to heparin, existence of infection in puncture site, severe hemorrhagic disease or thrombolysis, anticoagulation with high-dose heparin, arteritis, arterial stenosis, treatment with intra-aortic balloon counterpulsation, severe pneumothorax, massive pulmonary embolism, pulmonary space-occupying lesion, intracardiac shunt, ventricular septal defect, severe mitral regurgitation, aortic stenosis, or aortic aneurysm), diseases associating with great errors in ultrasonic imaging (e.g., malignant arrhythmias, atrial fibrillation, non-sinus rhythm, lesions associated with aortic root abnormalities, aortic valve replacement), refuse to perform PICCO or ultrasound examination, or refuse to participate in this study.
Study protocol
Two-Lumen Central Venous Catheterization Set (CS-27702-E; Arrow International Inc., Reading, PA, USA), PiCCO Monitoring kit (PULSION Medical Systems SE, Feldkirchen, Germany), CVP pressure sensor and its accessories (MX9505T; Smiths Medical ASD Inc., Dublin, OH, USA) were used. The vital signs of the patients who met the criteria were stable for 5 to 10 min after implantation of PiCCO. The central venous pressure (CVP) when venous return equals zero is the Pmcf. CO and ELWI of the patients were monitored via repeated measurements for 3 times, and then, their average values were accordingly calculated.
At the same time, an AI-powered ultrasound machine (GE Medical Systems, Milwaukee, WI, USA) was used for measurement, which was equipped with phased array probe (3Sc-RS Wide Band Phased Array, 1.6-4.5 MHz), convex array probe (C1-5-RS Wide Band Convex, 1.5-6 MHz), automatic VTI measurement software, and automated B-line scoring on thoracic sonography (Fig. 1). After successfully performing the experiments by two critical care physicians, the following parameters were obtained according to the 2016 guideline presented by the American Echocardiography Society.
First, to measure LVOT, scan the parasternal left ventricular long axis, and measure the LVOT within the 5 mm side of the aortic valve (Fig. 2a).
Secondly, we attempted to automatically identify and quantify VTI and CO; scan the standard section of the apical five-chamber heart. The ultrasound system uses artificial intelligence technology to automatically optimize the position of the pulsed Doppler sampling frame, record the Doppler spectrum, automatically track and trace VTI spectrum, automatically calculate the average VTI spectrum, and automatically calculate the HR, and its built-in calculation formula was as follows: LVOT area (cm2) = π × (LVOT Diam (cm)/2) 2, SV (ml) = LVOT area (cm2) × VTI (cm), CO (L/min) = SV (L) × HR (beats/minute, bpm); CO can be calculated automatically (Fig. 2b,c,d).
Thirdly, total number of B lines was calculated as follows: B lines were defined as discrete laser-like vertical hyperechoic reverberation artifacts extending from the pleural line to the bottom of the screen without fading and moving synchronously with the lung slide. The probe was placed in the intercostal space using the 8-zone method, that is, from the parasternal to the anterior axillary line as the anterior wall, from the anterior axillary line to the posterior axillary line as the lateral wall, while the anterior wall was bounded. In brief, the measurement point of the anterior region was located at the second intercostal space (area 1) and the fourth intercostal space (area 2) behind the midline of the clavicle, and the lateral area was located at the fourth intercostal space (area 3) and the sixth intercostal space (area 4) behind the level of the midline of the armpit. Each chest wall was divided into 4 regions, with 8 areas on both sides.
After each probe was placed and stabilized in each intercostal gap, the automatic counting software was run, which could automatically detect B-lines, select an image with the greatest number of B-lines from the 6-second sequence, and provide the number of B-lines from 0 to ≥ 5. The specific criteria of the built-in scoring system are as follows: 0 point: normal lung volume (that is, normal lung or 1-2 well-separated B lines); 1 point: moderately decrease of lung gas content, the presence of pulmonary interstitial syndrome (3-4 isolated B lines) or focal pulmonary edema (fusion of B lines during vertical scanning < 50% of the intercostal space); 2 points: severe decrease of lung gas content with alveolar edema, that is, ≥ 5 or diffuse fusion B lines, occupying all intercostal spaces; 3 points: complete disappearance of lung gas content and lung consolidation, that is, hepatoid change of lung tissue with or without bronchial inflation sign. The lowest score is 0, and the highest is 24; 0 is normal, otherwise, it is abnormal, the higher the score, the more serious the disease (Fig. 3). The measurements of PiCCO and AI-powered ultrasound were completed by two professionally trained physicians.
Statistical analysis
Herein, SPSS 23.0 software (IBM, Armonk, NY, USA) was used to perform statistical analysis. The measured data were expressed as mean ± standard deviation ( ± s), and t-test was used to compare data between the groups. P < 0.05 was considered statistically significant.