Evaluation of lung infiltration score to predict postural hypoxemia in ventilated acute respiratory distress syndrome patients and the lateralization of skin pressure sore

Context: Mechanical ventilation with positive end expiratory pressure (PEEP) is associated with unequal aeration of lungs in acute respiratory distress syndrome (ARDS) patients. Therefore, patients may develop asymmetric atelectasis and postural hypoxemia during lateral positioning. Aims: To validate proposed lung infiltration score (LIS) based on chest x-ray to predict postural hypoxemia and lateralization of skin sores in ARDS patients. Settings and Design: University hospital ICU. Prospective, observational study of consecutive patients. Materials and Methods: Sixteen adult patients of both genders on mechanical ventilation with PEEP for 24 to < 48 hours. On chest x-ray, 6 segments were identified on each lung. The proposed LIS points (0- normal; 1- patchy infiltrates; 2- white infiltrates matching heart shadow) were assigned to each segment. Without changing ventilation parameters, supine, left and right lateral positions at 45° tilt were randomly changed. At the end of 20 minutes of ventilation in each position, we observed arterial oxygen saturation, hemodynamic and arterial blood gases. Later, position change protocol (4 hourly) was practiced in ICU, and skin pressure sore grading was noted within a week of ICU stay. Statistical Analysis Used: Nonparametric Bland and Altman correlation analysis, ANOVA and Student t test. Results: Arterial oxygenation (PaO 2 /FiO 2 = 313± 145.6) was significantly (P< 0.01) higher in better lung (lower LIS)-down position than supine (PaO 2 /FiO 2 = 199± 70.2) or a better lung-up position (PaO 2 /FiO 2 = 165± 64.8). The positioning-related arterial oxygenation was significant (P< 0.05) at LIS asymmetry ≥3 between two lungs. Conclusions: The LIS mapping on chest x-ray was useful to differentiate between asymmetric lung disease and postural hypoxemia in ICU patients, which predisposed patients to early skin sore changes on higher LIS side.