Pleural effusion in patients with acute lung injury: a CT scan study.

OBJECTIVES: Pleural effusion is a frequent finding in patients with acute respiratory distress syndrome. To assess the effects of pleural effusion in patients with acute lung injury on lung volume, respiratory mechanics, gas exchange, lung recruitability, and response to positive end-expiratory pressure. DESIGN, SETTING, AND PATIENTS: A total of 129 acute lung injury or acute respiratory distress syndrome patients, 68 analyzed retrospectively and 61 prospectively, studied at two University Hospitals. INTERVENTIONS: Whole-lung CT was performed during two breath-holding pressures (5 and 45 cm H2O). Two levels of positive end-expiratory pressure (5 and 15 cm H2O) were randomly applied. MEASUREMENTS: Pleural effusion volume was determined on each CT scan section; respiratory system mechanics, gas exchange, and hemodynamics were measured at 5 and 15 cm H2O positive end-expiratory pressure. In 60 patients, elastances of lung and chest wall were computed, and lung and chest wall displacements were estimated. RESULTS: Patients were divided into higher and lower pleural effusion groups according to the median value (287 mL). Patients with higher pleural effusion were older (62±16 yr vs. 54±17 yr, p<0.01) with a lower minute ventilation (8.8±2.2 L/min vs. 10.1±2.9 L/min, p<0.01) and respiratory rate (16±5 bpm vs. 19±6 bpm, p<0.01) than those with lower pleural effusion. Both at 5 and 15 cm H2O of positive end-expiratory pressure PaO2/FIO2, respiratory system elastance, lung weight, normally aerated tissue, collapsed tissue, and lung and chest wall elastances were similar between the two groups. The thoracic cage expansion (405±172 mL vs. 80±87 mL, p<0.0001, for higher pleural effusion group vs. lower pleural effusion group) was greater than the estimated lung compression (178±124 mL vs. 23±29 mL, p<0.0001 for higher pleural effusion group vs. lower pleural effusion group, respectively). CONCLUSIONS: Pleural effusion in acute lung injury or acute respiratory distress syndrome patients is of modest entity and leads to a greater chest wall expansion than lung reduction, without affecting gas exchange or respiratory mechanics.

Nitrogen washout/washin, helium dilution and computed tomography in the assessment of end expiratory lung volume.

INTRODUCTION: End expiratory lung volume (EELV) measurement in the clinical setting is routinely performed using the helium dilution technique. A ventilator that implements a simplified version of the nitrogen washout/washin technique is now available. We compared the EELV measured by spiral computed tomography (CT) taken as gold standard with the lung volume measured with the modified nitrogen washout/washin and with the helium dilution technique. METHODS: Patients admitted to the general intensive care unit of Ospedale Maggiore Policlinico Mangiagalli Regina Elena requiring ventilatory support and, for clinical reasons, thoracic CT scanning were enrolled in this study. We performed two EELV measurements with the modified nitrogen washout/washin technique (increasing and decreasing inspired oxygen fraction (FiO2) by 10%), one EELV measurement with the helium dilution technique and a CT scan. All measurements were taken at 5 cmH2O airway pressure. Each CT scan slice was manually delineated and gas volume was computed with custom-made software. RESULTS: Thirty patients were enrolled (age = 66 +/- 10 years, body mass index = 26 +/- 18 Kg/m2, male/female ratio = 21/9, partial arterial pressure of carbon dioxide (PaO2)/FiO2 = 190 +/- 71). The EELV measured with the modified nitrogen washout/washin technique showed a very good correlation (r2 = 0.89) with the data computed from the CT with a bias of 94 +/- 143 ml (15 +/- 18%, p = 0.001), within the limits of accuracy declared by the manufacturer (20%). The bias was shown to be highly reproducible, either decreasing or increasing the FiO2 being 117+/-170 and 70+/-160 ml (p = 0.27), respectively. The EELV measured with the helium dilution method showed a good correlation with the CT scan data (r2 = 0.91) with a negative bias of 136 +/- 133 ml, and appeared to be more correct at low lung volumes. CONCLUSIONS: The EELV measurement with the helium dilution technique (at low volumes) and modified nitrogen washout/washin technique (at all lung volumes) correlates well with CT scanning and may be easily used in clinical practice. TRIAL REGISTRATION: Current Controlled Trials NCT00405002.

Relationship between gas exchange response to prone position and lung recruitability during acute respiratory failure.

PURPOSE: To clarify whether the gas exchange response to prone position is associated with lung recruitability in mechanically ventilated patients with acute respiratory failure. METHODS: In 32 patients, gas exchange response to prone position was investigated as a function of lung recruitability, measured by computed tomography in supine position. RESULTS: No relationship was found between increased oxygenation in prone position and lung recruitability. In contrast, the decrease of PaCO(2) was related with lung recruitability (R(2) 0.19; P = 0.01). Patients who decreased their PaCO(2) more than the median value (-0.9 mmHg) had a greater lung recruitability (19 +/- 16 vs. 8 +/- 6%; P = 0.02), higher baseline PaCO(2) (48 +/- 8 vs. 41 +/- 11 mmHg; P = 0.07), heavier lungs (1,968 +/- 829 vs. 1,521 +/- 342 g; P = 0.06) and more non-aerated tissue (1,009 +/- 704 vs. 536 +/- 188 g; P = 0.02) than those who did not. CONCLUSIONS: During prone position, changes in PaCO(2), but not in oxygenation, are associated with lung recruitability which, in turn, is associated with the severity of lung injury.