VENOVENOUS EXTRACORPOREAL MEMBRANE-OXYGEN ATION USING A HEPARIN-BONDED BYPASS CIRCUIT - AN EFFECTIVE ADDITIONAL OPTION FOR THE TREATMENT OFSEVERE ACUTE RESPIRATORY-DISTRESS SYNDROME

Mortality of severe acute respiratory distress syndrome (ARDS) in Germ any is about 60%. Respiratory therapy can make the lung injury worse b y high positive airway pressures, high tidal volumes and high inspirat ory oxygen concentrations. Extracorporeal membrane oxygenation (ECMO) was employed to reduce aggressive mechanical ventilation, but it has n ot been proved to be superior to conventional ventilation. However, en couraged by recently developed improvements in the technique and conce pt of ECMO, we introduced this therapy into our program for the treatm ent of ARDS. Patients and methods. All patients with severe ARDS (lung injury score >2.5) admitted to our multidisciplinary intensive care u nit from March 1992 to March 1995 were evaluated prospectively. After admission, the patients first underwent a conventional therapeutic app roach, including pressure-controlled inverse-ratio ventilation, permis sive hypercapnia, changes in body position (in particular, the prone p osition), negative fluid balance, antibiotics, and low-dose hydrocorti sone infusion. ECMO via covalently heparin-coated, venovenous bypass-s ystem 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 th ree of the slow-entry criteria for ECMO were fulfilled: (1) PaO2/FiO(2 ) <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 FiO(2) 1.0 and PEEP >5 mbar for >2 h (fast-entry crit eria) was ECMO instituted immediately. Results. Sixty patients fulfill ed 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 o f ECMO. ECMO was performed in 10 patients who had not improved, but wh o fulfilled the slow-entry criteria and in 11 primarily hypoxemic pati ents who fulfilled the fast-entry criteria. The survival rate was 30/3 9 (77%) for the conventional therapy group, 6/10 (60%) for the slow-en try group, and 11/11 (100%) for the fast-entry group. The onset of ECM O allowed a significant decrease in peak and mean airway pressures, ti dal volume, ventilatory rate, minute volume and inspiratory oxygen con centration. Sufficient gas exchange was provided, and pulmonary artery pressures significantly decreased on bypass. The most frequent compli cations on bypass were pneumothorax (15/21 patients) and bleeding (7/2 1 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 seve re ARDS.