External chest-wall compression in prolonged COVID-19 ARDS with low-compliance: a physiological study

Area of Science:

• Critical Care Medicine
• Respiratory Physiology
• Pulmonary Disease

Background:

• External chest-wall compression (ECC) is an intervention sometimes applied to Acute Respiratory Distress Syndrome (ARDS) patients, but its efficacy remains unproven.
• The specific benefits of ECC in COVID-19 ARDS (C-ARDS) with low respiratory system compliance (Crs < 35 mL/cmH2O) are not well understood.

Purpose of the Study:

• To evaluate if ECC using a 5 L-bag can decrease driving pressure (DP) and enhance gas exchange in low-compliance C-ARDS.
• To elucidate the underlying physiological mechanisms of ECC's effects in this patient population.

Main Methods:

• Eleven patients with low-compliance C-ARDS underwent a protocol including baseline measurements, 60 minutes of ECC, and subsequent discontinuation and PEEP reduction.
• Respiratory mechanics, gas exchange, hemodynamics, and electrical impedance tomography were monitored.
• Animal studies in pigs with acute ARDS were conducted using pleural pressure transducers to assess ECC's impact on the pleural pressure gradient.

Main Results:

• ECC acutely reduced DP from 14.2 ± 1.3 to 12.3 ± 1.3 cmH2O (P < 0.001), attributed to improved lung compliance.
• Changes in DP induced by ECC strongly correlated with those from PEEP reduction (R² = 0.82, P < 0.001).
• The initial DP reduction benefit diminished over 60 minutes (DP = 13.3 ± 1.5 cmH2O, P = 0.03 vs. baseline); gas exchange and hemodynamics remained unchanged. Animal studies showed ECC decreased the end-inspiratory pleural pressure gradient.

Conclusions:

• In C-ARDS patients with low compliance, ECC provides an acute reduction in driving pressure.
• ECC serves as a tool to identify hyperinflation by improving Crs and reducing the pleural pressure gradient, though it does not enhance oxygenation.
• The benefits of ECC appear to be transient, and its effects on DP are comparable to PEEP reduction.