Surfactant therapy and extracorporeal life support

I read with great interest the article by Hermon and coworkers [1], who reported that surfactant application in children with severe respiratory failure treated with extracorporeal membrane oxygenation was associated with improved lung volume and pulmonary mechanics. Although these findings must be confirmed in prospective studies, they are very promising. Based on a series of animal studies, more than 10 years ago we advocated use of a combination of surfactant therapy and extracorporeal life support in the treatment of severe respiratory failure. We found that one effective option is to combine intratracheal instillation of a large fluid volume with diluted surfactant and LFV-ECCO2R (low frequency ventilation and extracorporeal carbon dioxide removal).

In animal studies using ¹⁴¹Ce-labelled microspheres mixed with the surfactant [2, 3], we observed that, following endotracheal administration, this surfactant preparation was distributed inhomogeneously in the lungs. However, significantly improved distribution was achieved when this dose of surfactant (100 mg/kg body weight) was diluted with normal saline to a concentration of 6.25 g/l. In order to apply this dose, intratracheal fluid administration of 16.0 ml/kg body weight was required. Subsequently, we evaluated the effect of large volume fluid installation in lung lavaged rabbits while applying two gas exchange techniques, namely continuous positive pressure ventilation and LFV-ECCO2R [4]. We observed significantly higher arterial oxygen tension in the LFV-ECCO2R group than in the control group in the normocapnic state.

Based on these promising findings we further explored weaning possibilities [5]. Four hours after surfactant instillation in lung lavaged rabbits, the inspired fraction of oxygen could be decreased to 40% in a stepwise manner, such that arterial oxygen tension could easily be maintained within the normal range. Extracorporeal flow rates during perfusion ranged from 20 to 35 ml/kg per min and were sufficient to keep the arterial carbon dioxide tension and pH within normal limits. After 4 hours, the lung lavaged rabbits could breathe spontaneously with continuous positive airway pressure and 40% oxygen, and normal blood gas values were maintained. Using LFV-ECCO2R we required flow rates of only 20–35 ml/kg per min and were able to use a small, compact circuit, thereby minimizing the additional adverse effects of an extracorporeal circuit [6, 7]. Our findings indicate that barotrauma/volutrauma due to mechanical ventilation and oxygen toxicity due to high fraction of inspired oxygen can be minimized in an animal model of acute severe respiratory failure using combined LFV-ECCO2R and surfactant therapy.

I hope that this additional information will stimulate the authors to explore further the clinical application of surfactant and extracorporeal life support.