Does High Frequency Oscillatory Ventilation Combined With Intermittent Sigh Breaths Improve Oxygenation Compared to High Frequency Oscillatory Ventilation Without Sigh Breaths in Neonates?

High frequency oscillatory ventilation (HFOV) has been used in neonatal respiratory care for more than three decades. HFOV provides effective gas exchange with minimal pressure fluctuation around a set mean airway pressure (MAP) functioning as a continuous distending pressure (CDP), and low tidal volume compared to conventional ventilation (CV). HFOV was therefore thought to be able to reduce the risk of bronchopulmonary dysplasia in ventilated preterm babies. However results from randomized controlled trials comparing HFOV with conventional ventilation have been conflicting and meta-analyses have not shown clear evidence that HFOV is safer or more effective than conventional ventilation neither when used as initial strategy nor as rescue strategy in preterm babies with respiratory distress syndrome (RDS). Consequently there are no absolute indications for HFOV in preterm babies and most neonatologists today use HFOV as a rescue mode when conventional ventilation is failing in the acute setting of RDS as well as in the baby with bronchopulmonary dysplasia.

Maintaining adequate functional residual capacity (FRC) together with the fraction of inspired oxygen FiO2 are the main determinants of oxygenation. The larger the FRC, the larger is the volume of available oxygen in the alveoli for gas transport. Adequate oxygen saturation (SAT) of the blood in room air or an improvement in oxygen-saturation without changing the fraction of inspired oxygen can be seen as an indirect indicator of normal or normalized FRC, and most neonatologists use oxygenation as an indirect marker for lung volume during HFOV.

The CDP or set-MAP is the main determinant of lung-aeration during HFOV. A too low MAP may cause non-homogenous aeration and atelectasis leading to atelectotrauma and redirection of airflow to more compliant alveoli leading to localized hyperinflation.

Accordingly, early animal studies showed that recruitment and maintenance of FRC during HFOV could reduce lung injury. Lung recruitment was initially achieved by superimposing conventional ventilation (CV) breaths on top of HFOV with lower MAP than used today, either as recurrent sustained inflations lasting 15-20 seconds about every 20 minute, as intermittent sigh breaths (3-5 tidal breaths pr minute) delivered as normal conventional breaths or as conventional ventilation at normal rate combined with HFOV.

Today most neonatologists perform this so-called "open lung" concept by adjusting the set-MAP using oxygenation as an indirect guide of lung recruitment. Different approaches are used explained by difficulties in direct bedside monitoring of FRC. Some initiate HFOV with MAP 2-3 cm H2O above the MAP needed during conventional ventilation subsequently adjusting MAP until the fraction of inspired O2 (FiO2) <0.25-0.6 providing no signs of over inflation of the lungs on x-ray. Others go through a more complex step-wise increase in MAP till FiO2 cannot be reduced further, and then gradually decrease MAP until FiO2 again needs to be increased to maintain a predefined SAT and then continues ventilations with a MAP set at 2 cm H2O above this point, thereby placing ventilation on the more compliant deflation limb of the pressure-volume relationship of the lung.