[Venovenous extracorporeal membrane oxygenation (ECMO) with a heparin-lock bypass system. An effective addition in the treatment of acute respiratory failure (ARDS)].
Mortality of severe acute respiratory distress syndrome (ARDS) in Germany is about 60%. Respiratory therapy can make the lung injury worse by high positive airway pressures, high tidal volumes and high inspiratory oxygen concentrations. Extracorporeal membrane oxygenation (ECMO) was employed to reduce aggressive mechanical ventilation, but it has not been proved to be superior to conventional ventilation. However, encouraged by recently developed improvements in the technique and concept of ECMO, we introduced this therapy into our program for the treatment of ARDS. PATIENTS AND METHODS. All patients with severe ARDS (lung injury score > 2.5) admitted to our multidisciplinary intensive care unit from March 1992 to March 1995 were evaluated prospectively. After admission, the patients first underwent a conventional therapeutic approach, including pressure-controlled inverse-ratio ventilation, permissive hypercapnia, changes in body position (in particular, the prone position), negative fluid balance, anti-biotics, and low-dose hydrocortisone infusion. ECMO via a covalently heparin-coated, venovenous bypass-system with a vortex pump and two membrane lungs was performed if ARDS did not improve after 24-96 h of conventional therapy and if two of three of the slow-entry criteria for ECMO were fulfilled: (1) PaO2/FiO2 < 150 mmHg at PEEP > 5 mbar; (2) semistatic compliance < 30 ml/mbar; (3) right-left shunt > 30%. Only in cases of life-threatening hypoxemia (PaO2 < 50 mmHg at FiO2 1.0 and PEEP > 5 mbar for > 2 h (fast-entry criteria) was ECMO instituted immediately. RESULTS. Sixty patients fulfilled the entry criteria for our study. Thirty-nine patients were treated with a conventional protocol, 37 after improvement of ARDS and 2 who had not improved but in whom there were contraindications to the use of ECMO. ECMO was performed in 10 patients who had not improved, but who fulfilled the slow-entry criteria and in 11 primarily hypoxemic patients who fulfilled the fast-entry criteria. The survival rate was 30/39 (77%) for the conventional therapy group, 6/10 (60%) for the slow-entry group, and 11/11 (100%) for the fast-entry group. The onset of ECMO allowed a significant decrease in peak and mean airway pressures, tidal volume, ventilatory rate, minute volume and inspiratory oxygen concentration. Sufficient gas exchange was provided, and pulmonary artery pressures significantly decreased on bypass. The most frequent complications on bypass were pneumothorax (15/21 patients) and bleeding (7/21 patients). CONCLUSION. In comparison with the historical results at our own institution, the present study demonstrates an improvement in the survival rate from 56% to 78% since ECMO has become available. We conclude that venovenous ECMO with a heparin-bonded bypass circuit is an effective additional option for the treatment of patients with severe ARDS.