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      This weeks review is related to the use of recruitment maneuvers for moderate to severe ARDS guided by echo cardiography.

Moderate and Severe Acute Respiratory Distress Syndrome: Hemodynamic and Cardiac Effects of an Open Lung Strategy With Recruitment Maneuver Analyzed Using Echocardiography.
Mercado et al
Crit Care Med 2018; 46:1608–1616

 Moderate to severe ARDS is still a therapeutic challenge. Achieving acceptable goals of oxygenation among these patients is offset quite often by the fear of hemodynamic compromise. Recruitment maneuvers have not found strong evidence based backing. However, there might be yet some subset of patients who need and benefit from recruitment maneuvers. Identifying the optimum PEEP also remains a tricky proposition.
        Mercado et al in a prospective observational study attempted to evaluate a decremental PEEP strategy combined with echocardiographic assessment of LV and RV function and strain. Their hypothesis was based on a premise that recruitment maneuvers and high PEEP applied during the expiratory limb of the PV curve is safer for both the lung and the heart.
        They identified patients with moderate to severe ARDS as per the Berlin definition. They ensured euvolemia by using the PLR maneuver and correcting it prior to application of the recruitment maneuver. All patients had invasive arterial pressure as well as CVP monitoring. They applied the principle of coronary perfusion pressure as defined by MAP - CVP. RV and LV strain were also measured along with End Diastolic Volumes and TAPSE/MAPSE.
          All the study patients were paralysed. Recruitment was started by applying a PEEP of 25 cm H2O with a driving pressure of 15 cm H2O. PEEP was then incrementally increased by 5 cm H2O every 2 minutes with a constant driving pressure until a PEEP of 40 cm H2O was reached. Once this level of PEEP was reached, PEEP was reset to 25-15 and decrement strategy started. Decrement was achieved at 5 cm H20 of PEEP every 4 minutes. Oxygen saturation and compliance were measured to identify the point of termination of decreasing PEEP. A fall in SpO2 by > 2% or compliance by > 2 ml /cm H2O were the triggers to stop PEEP. From this point recruitment as described above was repeated again and PEEP was reduced to a level higher than previous start level.
          Hemodynamics were assessed by MAP, CVP, Coronary Perfusion Pressure and Echocardiography both at peak recruitment as well as at optimum PEEP.
             The effects of recruitment maneuvers were dramatic. The Systolic pressure fell by 17% , DBP by 14%, MAP by 15 % SV by 19% and CO by 20% between optimum and peak PEEP levels. The CVP rose significantly to cause a fall of Coronary Perfusion Pressure by 37%. These changes were transient and reverted to baseline within a hour of downsizing the PEEP. LV strain and RV strain were also noted.
         Non responders were identified by several parameters. Non responders had higher RVEDA/LVEDA ratios. All hemodynamic parameters had far greater decrements in non responders than amongst responders.

What the authors say:
       This study demonstrates that in patients with moderate to severe ARDS, a slow stepwise RM is associated with oxygenation improvement  and transient and reversible right and left cardiac dysfunction. Furthermore, setting a higher PEEP after this RM dramatically improved both oxygenation and lung function without any deterioration in either LV or RV function.
       An open lung strategy achieved by a slow stepwise RM appears to be beneficial for the lung while not resulting in negative effects on the heart.

My views:
1. This study shows the value of hemodynamic monitoring during recruitment.
2. Recruitment maneuvers are not hemodynamically neutral
3. Hemodynamic assessment could identify those who may not benefit from RM
4. This is a small study of 20 patients each. May not find favor as EBM, but has a sound physiological basis