Correlation of sonographic and radiographic scores of lung edema and metrics of shunt, dead space, and respiratory mechanics in invasively ventilated patients

Objective: To investigate the relationship between sonographic and radiological scores of lung edema with metrics of shunt, dead space, and respiratory mechanics in critically ill patients under invasive ventilation for greater than 24 hours. Methods: This is a secondary analysis of a prospective observational study involving invasively ventilated critically ill patients. The radiographic assessment of lung edema score and the global lung ultrasound score were utilized to evaluate pulmonary edema. Measurements for assessing shunt and dead space included the ratio of partial pressure of oxygen to fraction of inspired oxygen ratio, ventilatory ratio, and corrected minute volume, respectively. Respiratory mechanics were assessed through dynamic respiratory system compliance, driving pressure, and mechanical power of ventilation. Results: A total of 364 invasively ventilated patients were included; one-third of them were classified as having acute respiratory distress syndrome. Median radiographic assessment of lung edema and global lung ultrasound scores were 15 [8 to 20] and 7 [3 to 13], respectively. Both scores explained little of the variance in partial pressure of oxygen to fraction of inspired oxygen ratio, ventilatory ratio, corrected minute volume, respiratory system compliance, driving pressure, and mechanical power (R2 = 0.05-0.12). Patients without acute respiratory distress syndrome exhibited a stronger association between the radiographic assessment of lung edema score and partial pressure of oxygen to fraction of inspired oxygen ratio, as well as between the global lung ultrasound score and respiratory system compliance. In contrast, patients with acute respiratory distress syndrome demonstrated stronger associations between the radiographic assessment of lung edema score and mechanical power and between the global lung ultrasound score and dead space metrics. A positive interaction of positive end-expiratory pressure was found only for the association between partial pressure of oxygen to fraction of inspired oxygen ratio and the radiographic assessment of lung edema and global lung ultrasound scores. Conclusion: The radiographic assessment of lung edema score and the global lung ultrasound score poorly correlate with shunt, dead space, and respiratory mechanics metrics in invasively ventilated patients. A counterintuitive moderation effect of acute respiratory distress syndrome status is observed in some of these associations.