Heart-lung interactions during neurally adjusted ventilatory assist.

Area of Science:

• Critical Care Medicine
• Cardiopulmonary Physiology
• Mechanical Ventilation

Background:

• Mechanical ventilation can negatively impact right ventricular function.
• Neurally Adjusted Ventilatory Assist (NAVA) aims to mitigate these effects by synchronizing with patient effort.
• Understanding NAVA's impact on heart-lung interactions is crucial for optimizing ventilator strategies.

Purpose of the Study:

• To compare the effects of NAVA and Pressure Support Ventilation (PSV) on right ventricular function in intubated patients.
• To evaluate how different levels of NAVA and PSV influence hemodynamic parameters and right ventricular performance.
• To investigate the mechanisms behind observed differences in right ventricular function between NAVA and PSV.

Main Methods:

• 10 intubated patients with cardiac dysfunction were studied using invasive monitoring (pulmonary artery catheter, esophageal balloons) and echocardiography.
• Ventilation was applied using NAVA and PSV at various levels (e.g., NAVAlow, NAVAal, NAVAhigh; PSVlow, PSVal, PSVhigh) for 20 minutes each.
• Key parameters assessed included esophageal pressure, pulmonary artery pressures, and right ventricular outflow tract velocity time integral (a surrogate for stroke volume).

Main Results:

• NAVA, across all tested levels, maintained negative esophageal pressure deflections during inspiration, unlike PSV which reversed this pattern.
• Right ventricular stroke volume (outflow tract velocity time integral) was preserved during NAVA but decreased with increasing PSV levels.
• Right ventricular systolic pressure increased significantly with higher PSV levels, indicating increased outflow impedance, whereas NAVA did not alter this parameter.

Conclusions:

• Right ventricular performance is less impaired with NAVA compared to PSV in mechanically ventilated patients.
• NAVA may preserve right ventricular function by maintaining cyclic intrathoracic pressure variations and limiting inspiratory right-ventricular outflow impedance.
• These findings suggest NAVA offers a potential advantage in managing patients with compromised cardiac function requiring mechanical ventilation.