Veno‐venous extracorporeal blood phototherapy increases the rate of carbon monoxide (CO) elimination in CO‐poisoned pigs

Background and objectives: Carbon monoxide (CO) inhalation is the leading causeof poisonrelated deaths in the United States. CO binds to hemoglobin (Hb),displaces oxygen, and reduces oxygen delivery to tissues. The optimal treatmentfor CO poisoning in patients with normal lung function is the administration ofhyperbaric oxygen (HBO). However, hyperbaric chambers are only available inmedical centers with specialized equipment, resulting in delayed therapy. Visiblelight dissociates CO from Hb with minimal effect on oxygen binding. In a pre-vious study, we combined a membrane oxygenator with phototherapy at 623 nmto produce a “mini” photoECMO (extracorporeal membrane oxygenation) de-vice, which improved CO elimination and survival in CO-poisoned rats. Theobjective of this study was to develop a larger photoECMO device (“maxi”photo-ECMO) and to test its ability to remove CO from a porcine model of CO poisoning.

Study design/materials and methods: The “maxi” photoECMO device and thephoto-ECMO system (six maxi photo-ECMO devices assembled in parallel), were tested in an in vitro circuit of CO poisoning. To assess the ability of the photo-ECMO device and the photoECMO system to remove CO from CO-poisonedblood in vitro, the half-life of COHb (COHb-t1/2), as well as the percent COHbreduction in a single blood pass through the device, were assessed. In the in vivostudies, we assessed the COHb-t1/2in a CO-poisoned pig under three conditions:(1) While the pig breathed 100% oxygen through the endotracheal tube; (2) whilethe pig was connected to the photo-ECMO system with no light exposure; and (3)while the pig was connected to the photo-ECMO system, which was exposed to red light.

Results: The photo-ECMO device was able to fully oxygenate the blood after asingle pass through the device. Compared to ventilation with 100% oxygen alone,illumination with red light together with 100% oxygen was twice as efcient inremoving CO from blood. Changes in gas flow rates did not alter CO eliminationin one pass through the device. Increases in irradiance up to 214 mW/cm2wereassociated with an increased rate of CO elimination. The photo-ECMO devicewas effective over a range of blood flow rates and with higher blood flow rates,more CO was eliminated. A photo-ECMO system composed of six photo-ECMOdevices removed CO faster from CO-poisoned blood than a single photo-ECMOdevice. In a CO-poisoned pig, the photo-ECMO system increased the rate of CO elimination without significantly increasing the animal's body temperature orcausing hemodynamic instability.

Conclusion: In this study, we developed a photo-ECMO system and demonstrated its ability to remove CO from CO-poisoned 45-kg pigs. Technical modificaitons of the photo-ECMO system, including the development of a compact, portable device, will permit treatment of patients with CO poisoning at the scene of their poisoning, during transit to a local emergency room, and in hospitals that lack HBO facilities.