A Cross-Sectional Study of Acute Cor Pulmonale in Acute Respiratory Distress Syndrome Patients in China
Acute respiratory distress syndrome (ARDS) is a severe and life-threatening form of respiratory failure characterized by acute inflammatory lung injury, progressive dyspnea, and refractory hypoxemia. Despite advances in protective ventilation strategies, the mortality rate of ARDS remains high. One of the critical complications associated with ARDS is acute cor pulmonale (ACP), which is caused by increased right ventricular afterload due to pulmonary vascular dysfunction. ACP is an independent risk factor for poor prognosis in ARDS patients, making its early identification and management crucial. This study aims to investigate the morbidity and mortality rates of ACP in ARDS patients in intensive care units (ICUs) across mainland China and to assess the severity and prognosis of ACP using a novel ultrasound protocol called TRIP.
Background and Rationale
ARDS leads to pulmonary vascular dysfunction, which increases pulmonary arterial pressure and right ventricular afterload. This can result in ACP, characterized by right ventricular dilation and dysfunction. The development of ACP is influenced by several factors, including the severity of lung injury, hypoxic pulmonary vasoconstriction, pulmonary microthrombosis, and the use of positive pressure mechanical ventilation. Positive end-expiratory pressure (PEEP), while essential for preventing alveolar collapse, can also increase right ventricular afterload, further exacerbating ACP.
The incidence of ACP in ARDS patients has been reported to range from 22% to 60%, depending on the diagnostic criteria and patient population. Mechanical ventilation settings, such as high airway pressures, have been shown to significantly increase the risk of ACP. For instance, airway pressures greater than 26 cm H2O have been associated with a higher incidence of ACP and mortality. Early identification of ACP is critical for tailoring appropriate therapeutic strategies, such as adjusting mechanical ventilation parameters to reduce right ventricular strain.
Echocardiography has emerged as a rapid, non-invasive, and effective tool for diagnosing ACP. It allows for the assessment of right ventricular size, function, and hemodynamics, which are essential for identifying ACP and guiding treatment. However, there is a lack of large-scale epidemiological data on ACP in ARDS patients in China, and the exact morbidity and mortality rates remain uncertain. This study seeks to address this gap by conducting a multicenter, cross-sectional investigation of ACP in ARDS patients in Chinese ICUs.
Study Design and Methods
This study is a multicenter, cross-sectional investigation conducted across more than 20 hospitals in China. The study population includes patients diagnosed with moderate-to-severe ARDS according to the Berlin definition. ARDS is classified as mild (200 mmHg < PaO2/FiO2 ≤ 300 mmHg), moderate (100 mmHg < PaO2/FiO2 ≤ 200 mmHg), or severe (PaO2/FiO2 ≤ 100 mmHg) with a PEEP value of at least 5 cmH2O. Patients with cardiogenic pulmonary edema, chronic pulmonary hypertension, or other conditions that could cause chronic right heart dysfunction are excluded from the study.
The sample size was calculated based on an estimated ACP incidence of 22%, with an allowable error of 0.05 and a significance level of 0.05. After accounting for a 10% loss to follow-up, the final sample size was determined to be 355 patients.
Ultrasound Protocol: TRIP
The TRIP protocol is a novel ultrasound-based approach designed to assess the severity and prognosis of ACP in ARDS patients. TRIP stands for Tricuspid regurgitation velocity (T), Right ventricular size (R), Inferior vena cava diameter fluctuation (I), and Pulmonary regurgitation velocity (P). The protocol includes the following parameters:
- Tricuspid Regurgitation Velocity (T): A velocity greater than 2.8 m/s indicates elevated pulmonary arterial pressure.
- Right Ventricular Size (R): A right ventricular/left ventricular basal diameter ratio greater than 1.0 suggests right ventricular dilation.
- Inferior Vena Cava Diameter Fluctuation (I): An IVC diameter greater than 2 cm with decreased inspiratory collapse indicates elevated right atrial pressure.
- Pulmonary Regurgitation Velocity (P): A velocity greater than 2.2 m/s suggests pulmonary hypertension.
The TRIP protocol also includes additional echocardiographic parameters, such as tricuspid annular plane systolic excursion (TAPSE), systolic eccentricity index (sEI), and pulmonary artery diameter, to further stratify the severity of ACP. Each parameter is scored based on its deviation from normal values, with a total TRIP score calculated for each patient. This scoring system allows for a comprehensive assessment of ACP severity and its impact on patient outcomes.
Data Collection and Outcomes
Data collection includes detailed demographic and clinical characteristics, such as age, sex, primary diagnosis, comorbidities, and medication history. Clinical and laboratory data, including vital signs, blood tests, and radiological imaging, are recorded within two hours of ARDS diagnosis. Mechanical ventilation parameters, such as tidal volume, peak pressure, plateau pressure, PEEP, and FiO2, are also documented.
Hemodynamic parameters, including central venous pressure (CVP), central venous-arterial blood carbon dioxide partial pressure difference (Pv-aCO2), and lactate concentration, are collected to assess right heart function. The primary outcomes of the study are 28-day mortality, ICU mortality, and hospital mortality. Secondary outcomes include the length of stay in the ICU, mechanical ventilation days, and the association between ACP-related factors and ICU mortality.
Statistical Analysis
Continuous variables are presented as mean ± standard deviation (SD), and comparisons between groups are made using Student’s t-test. Qualitative variables are expressed as percentages and compared using the Chi-square test. The morbidity and mortality rates of ACP in ARDS patients are calculated, and the TRIP score is used to stratify ACP severity. Receiver operating characteristic (ROC) curves are used to evaluate the predictive value of the TRIP score for mortality. Univariate logistic regression is performed to identify factors associated with poor outcomes in ACP patients.
Discussion
ARDS is a complex and heterogeneous condition with limited effective therapeutic options. The development of ACP in ARDS patients is associated with increased mortality, making its early detection and management essential. The TRIP protocol offers a convenient and effective tool for assessing ACP severity and guiding treatment decisions. By combining multiple echocardiographic parameters, the TRIP protocol provides a comprehensive evaluation of right heart function and pulmonary hemodynamics.
The study highlights the importance of individualized mechanical ventilation strategies to minimize right ventricular strain in ARDS patients. High airway pressures and excessive PEEP can increase pulmonary vascular resistance and right ventricular afterload, leading to ACP. Early identification of ACP using echocardiography allows for timely adjustments in ventilation settings, potentially improving patient outcomes.
The findings of this study are expected to provide valuable epidemiological data on ACP in ARDS patients in China. The TRIP protocol may serve as a potential tool for rapid ACP stratification and differential diagnosis, enabling clinicians to tailor therapeutic interventions based on the severity of right heart dysfunction.
Conclusion
This multicenter, cross-sectional study aims to investigate the morbidity and mortality rates of ACP in ARDS patients in Chinese ICUs and to assess the severity and prognosis of ACP using the TRIP protocol. The study is expected to provide detailed epidemiological information on ACP, including clinical factors associated with its development. The TRIP protocol offers a novel approach to evaluating ACP severity, which may help improve the management of ARDS patients in the future. By identifying factors associated with poor outcomes, this study aims to guide the development of personalized therapeutic strategies to reduce the burden of ACP in ARDS patients.
doi.org/10.1097/CM9.0000000000000531
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