Acute respiratory distress syndrome Diagnosis

Acute respiratory distress syndrome is suspected by significant symptoms, including dyspnea and hypoxia, if results of the chest X-ray examination and arterial blood gas analysis is consilient with ARDS, in addition to cause pulmonary edema, hypoxia, then ARDS can be diagnosed.

Some tests use to diagnosis for Acute respiratory distress syndrome:

1. Chest X-ray examination:
Show the vague edge of lung, and appeared patchy, and integration of the shadow of large infiltration, can see the shadow of large inflatable bronchial symptoms.

2. Pulmonary function test:
1) Spirometry measured: lung capacity and vital capacity, residual gas, and reduced functional residual gas. Respiratory dead space increase, if the dead space volume / tidal volume (VD / VT)> 0.6, prompted the need of mechanical ventilation.

2) Determination of lung compliance: in bedside chest often measured total compliance, the application of positive end-expiratory pressure in patients with the following formula can be dynamic compliance (Cdyn) compliance testing not only for diagnosis, to determine efficacy, but also for monitoring the availability of pneumothorax or atelectasis and other complications have practical value.

3) Analysis of arterial blood gas: PaO2 decreased, the ARDS diagnosis and monitoring of commonly used indicators. According to analysis of arterial oxygen can be calculated alveolar arterial oxygen difference (PA-aO2), resting arterial shunt (Qs / Qt), respiratory index (PA-aO2/PaO2), oxygenation index (PaO2/FiO2) and other derivative indicators, the diagnosis and evaluation of the severity of the disease very helpful. If the Qs / Qt increased the disease has been advocated for the classification to be higher than 15%, 25% and 35% were classified as mild, moderate and severe, ranging in severity. Respiratory index reference to the range of 0.1 ~ 0.37,> 1 indicates that significantly decreased oxygenation. > 2 often need mechanical ventilation. Oxygenation index by reference to the range of 53.2 ~ 66.7kPa (400 ~ 500mmHg), ARDS when to 26.7kPa (20mmHg).

3. Pulmonary vascular permeability and hemodynamic determination:

1) Determination of pulmonary edema fluid protein: increased pulmonary capillary permeability, water and protein molecules into the interstitial or alveolar, so that the protein content of edema fluid and plasma protein concentration ratio increased, if the ratio> 0.7, consider the ARDS, <0.5 for cardiogenic pulmonary edema.

2) Alveolar - capillary membrane permeability (ACMP) Determination: Application of dual-isotope labeling in vivo to 113 indium (113In) autologous transferrin marker for determination of the volume of lung protein accumulation, while 99m Tc (99mTc ) marked autologous red blood cells, correction of thoracic blood flow distribution. 113, respectively, calculated indium, 99m Tc heart lung count ratio of radiation to observe the changes in 2-hour accumulation of plasma protein derived index. Reference value of healthy 0.138 × 10-3/min.

3) Hemodynamic monitoring: four-chamber through the access to Swan-Ganz catheter, can be measured and calculated pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), pulmonary vascular resistance (PVR), PVO2, CVO2, Qs / Qt and thermal Determination of rare cardiac output (CO) and so on, not only for diagnosis, differential diagnosis value, but also for the treatment of mechanical ventilation, in particular the impact of PEEP on circulatory function, the monitoring indicators are also important. ARDS patients with higher average pulse pressure pulse> 2.67kPa, pulmonary artery pressure and pulmonary capillary wedge pressure (PAP-PCWP) increased (> 0.67kPa), PCWP general <1.18kPa (12cmH2O), if> 1.57kPa (16cmH2O), while for acute left heart failure, can be excluded from ARDS.

4) Extravascular lung water content determination: The use of dual-tracer dye dilution method from central venous or right heart catheter tube into 5cm indocyanine green dye glucose 10ml, and then in the femoral artery through a catheter connected thermistor records thermal dilution curve, and the density of detection dye dilution curve, and then dealt with through the computer calculation of lung water, can be used to determine the extent of pulmonary edema.