Influence of a Personalized Lung Volume Optimization Maneuver on Lung Aeration and Cardiac Performance in Mechanically Ventilated Children

1) The objective of the CHD study is to define the impact of a LVOM after cardiac surgery with CPB on hemodynamics and lung mechanics in children with congenital heart disease (CHD) undergoing surgery.

The Specific Aims of this work are:

Specific Aim 1:

Evaluate hemodynamics and lung mechanics during and after a LVOM:

In cases of children undergoing cardiac surgery all measurements will be performed with closed chest conditions.

Specific Aim 2:

Evaluate a potential benefit of lung volume optimization by performing PEEP titration on hemodynamics and lung mechanics compared to standard care without PEEP titration to optimize end-expiratory lung volume while maintaining same tidal volume targets in cases and controls.

Hypotheses:

1. Hemodynamics and lung mechanics will be significantly different before and after LVOM. We expect that there will be little difference between intervention and control group before performing PEEP titration in the interventional group.
2. Once the PEEP titration has been performed in the interventional group, we hypothesize that patients who received the intervention will have improved hemodynamics and lung mechanics with modest PEEP while receiving the same tidal volume than the control group (U-shaped curves).

Rationale: Surgery with cardiopulmonary bypass typically involves an interruption of mechanical ventilation while CPB is running. This is oftentimes associated with atelectasis formation and impaired gas exchange due to reduced end-expiratory lung volume. While there have been few studies in adults that have shown that optimization of lung volume by performing PEEP titration after CPB can significantly improve Cardiac Index and right ventricular function, there have been only very few prospective pediatric studies which assessed the impact of different PEEP settings on hemodynamics, and lung mechanics after cardiac surgery in children. Because these patients are generally among the most fragile postoperative patients, it is critical to understand if specific ventilator strategies can help mitigate any negative hemodynamic consequences after surgery. The purpose of this study is to understand the critical cardiopulmonary interactions that occur with changes in lung volumes, and to determine optimal approaches to mechanical ventilation under these different circumstances.

Cardiopulmonary interactions differ based on the underlying cardiac anatomy and physiology. Most studies of cardiopulmonary interactions following surgery for congenital heart disease have examined the difference between positive and negative pressure ventilation. This work consistently showed improvement in cardiac output and pulmonary blood flow with negative pressure ventilation, while positive pressure ventilation was associated with decreased cardiac output. However, these studies have been conducted in the 1990's and positive pressure ventilation has changed significantly in the meantime.

Similarly, while patients with left ventricular dysfunction generally benefit from positive pressure ventilation, there is little data regarding the hemodynamic effects of positive pressure ventilation on right ventricular performance.

Modulating pulmonary vascular resistance by optimizing lung volumes might be a promising approach to improve both lung mechanics and hemodynamics. Studies in this population have focused more on the effects of FiO2 and hyperventilation than on respiratory mechanics and cardiopulmonary interactions.

2) The objective of the ECMO study is to evaluate if a LVOM in children and infants with ARDS at risk or need for ECMO has an impact on ECMO prevention or shortening of ECMO duration.

Specific aims:

• assess the effect of LVOM on lung aeration and perfusion assessed with EIT
• assess the effect of LVOM on hemodynamics with (primarily VV-ECMO) and without ECMO
• evaluate if LVOM can prevent the need for ECMO
• evaluate if LVOM can shorten ECMO duration

Rationale:

Children with NARDS or PARDS usually have reduced lung volumes. Typically ECMO is initiated when oxygenation index approaches 40 with further deterioration of hypercarbia, hemodynamics and worsening hypoxemia. Current treatment strategies include reducing ventilatory support on ECMO ("rest settings") which is typically followed by a "whiteout" of the lungs reflecting lung collapse and fluid infiltration. Usually within 10 days of ECMO support invasive ventilation is gradually increased to re-open the lung and allow for ECMO weaning. Optimizing lung volumes by performing a LVOM early on in the disease process might be beneficial to wean ECMO faster or even prevent its need by avoiding massive lung collapse during rest settings in patients that have high potential for lung recruitability.