Neue Veröffentlichung

01.09.2006 

The Novalung® iLA membrane ventilator: technical aspects.

By Stefan Fischer, MD MSc, PhD and Martin Strueber, MD The Novalung Interventional Lung Assist (iLA) device is a membrane ventilator that allows for oxygen and carbon dioxide gas exchange to occur by simple diffusion. It has been used in patients with severe acute lung failure due to ARDS, inhalation injury, severe pneumonia, chest injury, foreign body aspiration, and after thoracic surgical interventions [1]. The concept of “protective ventilation” was described decades ago, but with the introduction of extracorporeal ventilation devices such as the Novalung it may reach new dimensions [2]. It potentially helps to avoid or reduce ventilator associated lung injury and remote secondary organ failure, which is related to injurious mechanical ventilation [3, 4].

Technical aspects of the equipment

The iLA consists of a plastic gas exchange module with diffusion membranes made from polymethylpentene (PMP). These PMP fibers are woven into a complex configuration of hollow fibers. The PMP material is woven to bundles in a low resistance configuration mat arranged in well defined stacks, which provides maximum blood/gas mixing. Gas transfer takes place without the direct contact with blood. In addition, the PMP membrane surface in contact with blood is treated with a heparin coating to provide a biocompatible and non-thrombogenic surface. Blood flows over the exterior surface of the device’s fibers; the ventilating gas (commonly O2) flows inside these fibers (Figure 1). In this way the Novalung iLA mimics the native lung. This allows for the blood exiting the device to have the normal amount of oxygen and carbon dioxide that exits the normal lung. In the arterio-venous portion of this pumpless shunt carbon dioxide exchange is the primary function due to arterial inflow blood, while a veno-venous attachment, which requires the support of a mechanical pump, additionally allows full oxygenation support [5]. The Novalung iLA is a low gradient device, designed to operate without the help of a mechanical pump in an arterio-venous configuration. Based on this principle, adequate mean arterial blood pressure is mandatory. This device is attached to the systemic circulation (preferred access sites are the femoral vessels by percutaneous cannulation using Seldinger’s technique) and receives only part of the cardiac output (1-2 L/min) for extracorporeal gas exchange (Figure 2). This allows complete CO2 removal, which can be controlled by varying the rate of gas flow. Oxygenation, however, depends on the degree of shunt, arterial oxygenation saturation, and other variables. The native lung in this situation also contributes to oxygenation. The limited increase in oxygenation provided by the Novalung might potentially be life saving in some patients with oxygenation deficiency. However, it has to be underscored that patients with a primary oxygenation disorder may not necessarily benefit from the pumpless iLA mode. As Figure 3 demonstrates, the blood enters the device through the inlet connector [1]. The blood flows into the pre-chamber. Any micro air bubbles that may have entered the device are removed through the de-airing ports [3]. The blood flows into the main chamber where gas exchange takes place. The oxygenated and decarboxylated blood is returned to the patient via the device outlet connector [2]. Two de-airing membranes [3] are integrated at the top apex on both sides of the device. These de-airing membranes allow gas bubbles, but not liquids (such as blood), to cross. The de-airing membranes facilitate priming and de-airing of the device, and are also used to eliminate any air trapped in the device during support. An oxygen supply is connected to the upper gas connector [4] and provides the medium for respiration to take place. The lower gas connector [5] is open to the atmosphere in all instances and is the place where gas is exha

mehr Artikel