Gas exchange, specific lung elastance and mechanical power in the early and persistent ARDS

Abstract

Purpose: Aim of this study was to evaluate the effect of acute respiratory distress syndrome (ARDS) duration on gas-exchange, respiratory mechanics, specific lung elastance and mechanical power.

Materials and methods: In a single center prospective study 28 ARDS patients (66.4 ± 10.0 years, BMI 23.6[21.3-28.8] kg/m², PaO₂/FiO₂ 148.9[99.6-173.5]) who still presented ARDS criteria after 7-days of mechanical ventilation were studied in early and persistent phase of the disease (day-1 and after 7-days). Each patient underwent PEEP trial at 5-15 cmH₂O in both phases.

Results: At both PEEP levels the PaO₂ was similar in both phases (early: 70.7[65.1-84.4] vs 102.0[85.5-131.8] mmHg; persistent 70.7[63.0-76.2] vs 97.4[86.5-117.1] mmHg, 5-15 cmH₂O respectively), the PaCO₂ was significantly higher in the persistent phase at both PEEP levels (early 50.6 ± 10.2 vs 52.1 ± 10.5 mmHg; persistent 57.7 ± 13.4 vs 56.9 ± 12.8 mmHg). Specific lung elastance was not different in the early compared to the persistent phase 12.5 ± 3.1 vs 12.2 ± 3.8 cmH₂O. The mechanical power normalized for the functional residual capacity increased with PEEP and was similar in both phases (early 23.4[12.8-32.8] vs 34.3[25.3-47.9], persistent 16.3[10.9-24.1] vs 26.7[19.9-46.0] J/min/L, 5-15 cmH₂O respectively).

Conclusions: The persistent phase of ARDS for 7-days did not affect the respiratory mechanics while significantly impaired the PaCO₂ exchange.

Keywords: Mechanical power; Pulmonary gas exchange; Respiratory distress syndrome; Respiratory mechanics.