A Narrative Review on the Past, Present, and Future of Small-Bore Ventilation, Expiratory Ventilation Assistance, and Flow-Controlled Ventilation

The first description of oxygenation through a transtracheal cannula comes from half a century ago. Ventilation through a small diameter airway mandates a high-pressure differential, and as a result passive expiration is impeded. Safe normoventilation through a cannula could therefore only be performed if the upper airway was open. Expiratory ventilation assistance (EVA) with Ventrain® has overcome this problem. In fact, ventilation and oxygenation improve if no leakage occurs through the upper airway. This has led to the development of Tritube®, an ultrathin endotracheal tube with cuff, and Evone®, an automated ventilator for use with Tritube®.Ventrain®, Tritube®, and Evone® have much improved possibilities in airway management, especially for narrow airways. Also, flow-controlled ventilation (FCV) with Evone® has been shown to be a promising form of ventilation. During inspiration and expiration, flow is constant (square waveform) and continuous (no pauses or plateau pressure phases). Furthermore, flow can be set very low. These properties lead to a slow and gradual in-and expiration, which lead to a more homogeneous distribution of air and an increase in ventilation efficiency. The low and continuous flows are lung protective as energy dissipation into the lungs and airways is minimised. This narrative review describes the development of Ventrain® and its derivatives: Tritube®, Evone®, and flow-controlled ventilation; their current use, and the possibilities they can bring in the (near) future.