We studied prospectively 65 patients who were admitted into the intensive care unit (ICU) with severe respiratory failure. Forty patients were male with mean (SD) age 44 ± 21 years (range, 21–77, median 55) and 25 were female with mean (SD) age 47 ± 18 years (range, 18–78, median 56). The patients were classified into 4 groups: The first group (group A) included 23 patients (14 male, 9 female; median age 53, range 18–78 years) fulfilling the criteria of ARDS . All these patients were supported mechanically for their respiratory failure (PaO2/FiO2 127 ± 11, APACHE II 19.6 ± 1.1). The cause of ARDS was trauma (9), pneumonia (3), sepsis (5), transfusions (2), pancreatitis (2), intoxication (1), and burns (1).
The second group (group B) included 14 patients (8 male, 6 female; median age 56; range 19–77 years) on mechanical respiratory support who had at least one condition from those suggested by Fowler et al as risk factors for ARDS development. All patients (PaO2/FiO2 235 ± 23, APACHE II 20.9 ± 1.3) in this group developed ARDS within 48 hours. The cause of ARDS was sepsis (3), pneumonia (4), trauma (6), and pancreatitis (1).
The third group (group C) included 28 patients at high risk for ARDS development who did not develop ARDS (18 male, 10 female; median age 51; range 19–73 years; PaO2/FiO2 277 ± 21; APACHE II 17.1 ± 1.9). The cause of disease was trauma (15), sepsis (5), pneumonia (2), transfusions (2), intoxication (2), arrest (1), and pancreatitis (1).
The control group (group D) included 40 healthy individuals who had minimal surgery (e.g. lymph node biopsy, nasal diaphragm correction, tonsillectomy, etc.) and received anesthesia for a short period of time. Twenty-six were male, median age 35 years (range 19–70) and 14 were female, median age 38 years (range 25–73).
For patients' classification, the following criteria were employed:
1. the ARDS criteria of the American-European Consensus Conference on ARDS : (a) acute onset; (b) bilateral chest radiographic infiltrates; (c) pulmonary artery occlusion pressure of ≤ 18 mmHg, or no evidence of left atrial hypertension, and (d) impaired oxygenation regardless of the positive end-expiratory pressure (PEEP) concentration, with a PaO2/FiO2 ratio of ≤ 300 torr for acute lung injury (ALI) and ≤ 200 torr for ARDS;
2. the high risk criteria for ARDS development according to Fowler et al ;
3. the criteria for pneumonia according to the EPIC study , and
4. the criteria for septic syndrome according to Bone et al .
The Acute Physiology And Chronic Health Evaluation-II (APACHE II) scoring system was used for grading disease severity .
The protocol was approved by the Ethics Committee of our institution.
After admission to the ICU, blood samples were obtained from a central venous line within 2 hours. APACHE II score and PaO2/FiO2 values were obtained at the time of sample collection. The samples were obtained through a Swan-Ganz catheter.
The blood was collected in a heparinized vacutainer tube and kept immediately at 4°C. After centrifugation at 1500 g at 4°C, the plasma was kept at -80°C until measurement. At the same time BALF was obtained by fiberoptic bronchoscopy. The fluid was filtered through nylon net to remove the mucous secretions, and centrifuged at 500 g for 10 min to remove cells. The supernatant was kept in cryotubes at -80°C in aliquots of 0.5 ml. The method of microlavage was used as described previously . The following criteria were used for an acceptable sample:
(a) the procedure should be shorter than 1 min, while the time of saline staying in the lungs should be less than 20 s;
(b) recovery of more than 50% of the saline used for the lavage;
(c) absence of obvious blood contamination in the BALF, and
(d) the level of urea in the BALF should be more than 0.4 mmol. The urea level was used as an index of BALF dilution [25, 26].