Mechanical Power in Decelerating Flow versus Square Flow Ventilation in Pediatric Acute Respiratory Distress Syndrome

Mechanical power is a summary variable quantifying the risk of ventilator-induced lung injury. The original mechanical power equation was developed using square flow ventilation. However, most children are ventilated using decelerating flow. It is unclear whether mechanical power differs according to mode of flow delivery. This study compared mechanical power in children with acute respiratory distress syndrome who received both square and decelerating flow ventilation.

This was a secondary analysis of a prospectively enrolled cohort of pediatric acute respiratory distress syndrome. Patients were ventilated on decelerating flow and then placed in square flow and allowed to stabilize. Ventilator metrics from both modes were collected within 24 h of acute respiratory distress syndrome onset. Paired t tests were used to compare differences in mechanical power between the modes.

This study enrolled 185 subjects with a median oxygenation index of 9.5 (interquartile range, 7 to 13) and median age of 8.3 yr (interquartile range, 1.8 to 14). Mechanical power was lower in square flow mode (mean, 0.46 J · min-1 · kg-1; SD, 0.25; 95% CI, 0.42 to 0.50) than in decelerating flow mode (mean, 0.49 J · min-1 · kg-1; SD, 0.28; 95% CI, 0.45 to 0.53) with a mean difference of 0.03 J · min-1 · kg-1 (SD, 0.08; 95% CI, 0.014 to 0.038; P < 0.001). This result remained statistically significant when stratified by age of less than 2 yr in square flow compared to decelerating flow and also when stratified by age of 2 yr or greater in square flow compared to decelerating flow. The elastic contribution in square flow was 70%, and the resistive contribution was 30%.

Mechanical power was marginally lower in square flow than in decelerating flow, although the clinical significance of this is unclear. Upward of 30% of mechanical power may go toward overcoming resistance, regardless of age. This is nearly three-fold greater resistance compared to what has been reported in adults.