From Baghdad to Germany: Use of a New Pumpless Extracorporeal Lung Assist System in Two Severely Injured US Soldiers

Abstract

The authors describe a new extracorporeal pumpless interventional lung assist system (iLA) that was implemented in two US soldiers with severe acute respiratory distress syndrome received from enemy action in Iraq, who were at risk for critical hypoxemia/hypercapnia. The system is characterized by a new low-resistance gas exchange membrane that is integrated in an arterial-venous bypass established by cannulation of the femoral artery and vein. Cardiovascular stability is essential to produce sufficiently high blood flow rates over the gas exchange unit. After implantation of the interventional lung assist, oxygenation increased and carbon dioxide elimination improved rapidly. Ventilator settings were able to be adjusted to the decreased pulmonary gas exchange needs, making protective lung strategies possible. Air transport of both patients with the running iLA system was uneventful. The iLA was removed after 15 and 8 days of continuous operation, respectively, and both soldiers were successfully weaned from mechanical ventilation. Interventional, extracorporeal pump-free pulmonary support opens up new possibilities for pulmonary protection due to ease of use, effectiveness, and low costs; however, there is concern of distal limb ischemia. Experiences to date are encouraging, although randomized studies are lacking, and the procedure carries significant risks.

CASE REPORT

Even after the end of major combat, US soldiers in Iraq find themselves frequently targeted by sniper fire, land mine detonation, and improvised explosive devices. Vastly improved emergency medicine is saving an unprecedented number of lives, although survivors recurrently have grave injuries requiring immediate surgical treatment and intensive care support. However, facilities for invasive organ replacement techniques such as extracorporeal pulmonary support are limited, as is the option for transferring unstable, critically wounded patients on long distance flights to Europe or the United States.

The authors report the treatment and transportation of two US soldiers with life-threatening injuries sustained during two different casualties in Iraq using a new system for extracorporeal, pump-free pulmonary support.

Technical Data

The interventional lung assist (iLA) (Novalung GmbH, Hechingen, Germany) is a single-use ultracompact extracorporeal gas exchange system perfused by the patient’s circulation without the use of a mechanical blood pump. Apart from an oxygen supply, the system does not require additional energy or substrate sources. After cannulation of the femoral artery and vein, a passive femo-femoral shunt flow over an oxygenator generated by the arterial-venous pressure gradient produces an effective CO₂ extraction and moderate improvement in arterial oxygenation. The oxygenator is the central element of the system, which is characterized by a new low-resistance poly-(-4-methyl-1-pentene) diffusion membrane. Cardiovascular stability is essential to produce sufficiently high blood flow rates (1.0 to 2.5 L/min) over the gas exchange unit.¹ To connect the iLA to the patient, two large-bore cannulas (13F to 17F) are inserted into both the femoral artery and vein by the Seldinger technique before the intravenous administration of a bolus dose of unfractionated heparin (5000 IU). The prefilled system (250 mL normal saline) is then connected to the cannulas and the arteriovenous shunt is released. Oxygen inflow to the oxygenator is up to 12 L/min, which both oxygenates the blood and effectively “blows off” carbon dioxide. A continuous low-dose heparin infusion (200 to 600 IE/h) is sufficient to achieve a mild prolongation of aPTT between 40 and 50 seconds, given that the system is entirely homogeneously coated with heparin to optimize hemocompatibility. Functional control and shunt flow can be monitored by transit time ultrasound technology.

Soldier One

A 22-year-old US soldier sustained traumatic amputation of both lower legs when his armored vehicle was struck by several land mine explosions. After initial resuscitation, including generous circulatory volume replacement and stump tourniquets, the patient was rushed to the Baghdad emergency room. Before admission, intubation became necessary as the patient complained of increasing shortness of breath. The following injuries were diagnosed: severe, rapidly developing pulmonary failure due to blast exposure; acute abdominal trauma with laceration to the liver parenchyma as well as bilateral renal contusions; traumatic amputation of both lower legs; massive blood loss with consecutive severe hemorrhagic shock.

Immediate management included wound debridement, stump hemostasis, transfusion of blood and coagulation products, and exploratory laparotomy with abdominal packing followed by tensionless abdominal closure. After initial stabilization, acute pulmonary deterioration progressed rapidly while the patient had development of acute renal failure. It became increasingly difficult to secure pulmonary gas exchange despite constant increase in ventilation support. Chest radiographs revealed signs of acute respiratory distress syndrome (ARDS) with patchy diffuse bilateral infiltrates. Ventilation setting combined with the resulting blood gas values suggested hypoxic and hypercapnic decompensation despite maximum ventilatory support available under the prevailing condition. Neither extracorporeal pulmonary support nor pump- based renal replacement, e.g., hemodialysis, were available in Baghdad. In this critical, life-threatening situation, the implementation of a new, pump-free interventional lung assist system (iLA), was considered a therapeutic option.

Immediately after implantation of the iLA, oxygenation increased markedly, and carbon dioxide elimination improved (Table 1). Ventilator settings were adjusted to decreased pulmonary gas exchange needs. The patient was stabilized and then transferred on day 5 with military Medevac transport first to Landstuhl, Germany, and from there by ambulance helicopter to the intensive care unit of Regensburg University Hospital. There were no major complications reported during transport, requiring only a portable ventilator and oxygen supply for the iLA system. The authors took over care of the patient in a critical and restricted but steady condition. The soldier received vasopressors continuously and remained hemodynamically stable. Because of markedly impaired renal function, pump-driven hemodiafiltration was started, creating a partial bypass within the venous iLA line. Antibiotic treatment, which had been commenced in Baghdad, was continued. Due to the efficient gas exchange afforded by the iLA system, ventilation support was able to be reduced considerably and ARDS resolved gradually. The abdomen was closed definitively, and the clinical, radiologic, and laboratory signs of infection continued to decline. The iLA process was discontinued after 15 days, and the cannulas were removed uneventfully. The patient was extubated a few days later, with satisfactory gas exchange during spontaneous breathing. The soldier was transferred back home, where he made a swift recovery and was fitted with prostheses (Figure 1).

Table 1: Ventilation and Blood Gas Values of Soldier One Before and After Implementation of the Interventional Lung Assist System

Figure 1.: (a) Soldier one on admission to ICU, University Hospital Regensburg. The iLA system with its gas exchange unit is visible, along with the ultrasound clip for the measurement of blood flow. (b) During rehabilitation after fitting with prostheses (photographs with patient’s permission).

Soldier Two

A 30-year-old US Army special forces medic received a gunshot wound to his right thorax and then fell out of his moving vehicle. The patient was brought to the emergency room with stable vitals. CT scan demonstrated right pulmonary hemorrhage, pulmonary contusion, and multiple rib fractures. A chest tube was placed followed by the drainage of approximately 1300 mL fresh blood, with a persistent air leak. The patient was transported the next day by Critical Care Air Transport Team to Landstuhl US Forces Regional Medical Center, Germany. En route, the patient had worsening respiratory distress with increasing hemoptysis requiring intubation shortly after arrival. A contrast CT showed a small pulmonary embolus (PE) on the side of the chest opposite the trauma. In addition, complete consolidation of the right lower lobe and infiltration of the remaining right lung as well as a small residual pneumothorax was described. Due to concerns that the PE was from a lower extremity source and full heparin anticoagulation was not suitable because of the still-active pulmonary bleeding, an inferior vena cava filter was implanted. Subsequently, he was given multiple blood and plasma products to control the pulmonary bleeding. The following days, the patient required increasing ventilatory support. Cardiac status was normal, but the patient’s blood gases revealed rising hypercapnic decompensation despite maximal ventilatory support. In this critical situation, consistent with ARDS, the implementation of a pulmonary assist system was considered necessary. Due to the excellent CO₂ removal capability and the reduced need for anticoagulation, the iLA system was chosen.

Implantation of the assist system was uneventful, as was the following transport by ambulance helicopter to Regensburg University Hospital, Germany, for further treatment. Artificial ventilation with high positive end-expiratory pressure (16 to 20 cm H₂O) in a lung-protective, low-tidal-volume mode was continued; CO₂ removal by the iLA was excellent. Pulmonary gas exchange improved rapidly with long-time prone position and lung recruitment maneuvers performed. Antibiotic regime adjustment, fluid restriction, and integration of spontaneous breathing into ventilation support led to substantial pulmonary function improvement. The iLA system was able to be stopped after 8 days of continuous uncomplicated operation, and cannulas were removed. After extubation (the following day) intermittent noninvasive continuous positive airway pressure ventilation support was enforced until the fully conscious patient was able to be transferred back to Landstuhl Regional Medical Center for further recovery.

Discussion

Treatment in specialized centers using extracorporeal lung assist is required for patients with hypoxia or hypercapnia due to severe acute respiratory failure or ARDS that have not responded to conventional therapy.² The transfer of these patients is associated with a high incidence of potentially life-threatening complications. Conventional extracorporeal gas exchange (ECMO) is characterized by a high demand on technical and staff support and may be limited by available resources. In addition, patients are exposed to the anticoagulation-related risk of bleeding. The extracorporeal iLA has been described as an alternative treatment option.³ We report the use of iLA in two US soldiers with acute pulmonary failure due to a blast exposure and a gunshot injury, respectively. After implementation, iLA allowed rapid and effective elimination of carbon dioxide and a moderate increase in oxygenation. Although oxygen exchange capacity of iLA is limited⁴ in comparison with pump-driven ECMO, substantial improvement of oxygenation was observed in our two patients. We assume that this is, to a larger extent, due to changes in ventilation strategies rather than to the iLA device. The system is valuable not only as a means of reducing the need for aggressive ventilation but also for the safe inter hospital transport of the critically compromised pulmonary patient, due to ease of use, effectiveness, and relatively low costs.⁵ Cardiovascular stability is mandatory. Despite using relatively small cannulas, critical ischemia of the distal limb or bleeding at the site of cannulation are possible adverse effects.⁴ Interventional, extracorporeal pump-free pulmonary support opens up new possibilities for pulmonary protection. Experiences to date are encouraging, although randomized studies are lacking, and the procedure carries significant risks. Robust studies in larger populations are needed.