Utilizing a Modified Oxygenator for Enhanced CO 2 Scrubbing in Low-Volume Lung Protective Ventilation

By Brian Lupish, CMI Fellow

An in vitro prototype for a new type of CO 2 scrubber for mechanical low-volume protective ventilation devices has been designed at the University of Pittsburgh through the collaboration of University of Pittsburgh Physicians and Engineering Faculty. Once fully developed, it holds the potential to reduce incidence and severity of hypercapnia (abnormally high CO 2 concentration in the blood), one of the greatest drawbacks of mechanical ventilation therapies.

For patients suffering from severe lung failure, mechanical ventilation is often required. Up to 140,000 American adults per year require mechanical ventilation, at a cost of $57,000 each. Despite the immense costs, mechanical ventilation has a mortality rate as high as 45%, largely due to hypercapnia.

Hypercapnia occurs due to the low volumetric limitations of effective mechanical ventilation. It leads to blood acidification, de-synchronization between the ventilator and the patient, and pulmonary hypertension.  Furthermore, chronic obstructive pulmonary disease (COPD) patients often require mechanical ventilation to assist with CO 2 removal, as opposed to less invasive methods which would otherwise be adequate. 

Several approaches to dealing with hypercapnia have been investigated. Extracorporeal carbon dioxide removal (ECCO2R) involves filtering a patient's blood through an external artificial lung.  Unfortunately, this is a specialized and rarely available method.  An alternative method, continuous renal replacement therapy (CRRT), has the potential for effective CO 2 removal by removing bicarbonate ion.  However, existing variants of CRRT further acidify the blood.  Unfortunately, it requires high dialysis flow rates, which creates the risk of unacceptable mineral loss in the dialysate. 

In order to address difficulties with CRRT, a team of engineers and physicians created a modified bubble oxygenator capable of recycling dialysate fluid and scrubbing it of CO 2 . It was subsequently determined that for the device to be effective, converting the bicarbonate ion in the dialysate back into CO 2 gas that could be vented off would need to occur. Several parameters, including temperature, vacuum pressure, and pH were analyzed to identify ways to do so.  Ultimately the inventors determined that the bubble oxygenator used for recycling the dialysate fluid would require an additional enzyme as part of the design. More recently, based on literature review the team will also be exploring electrochemical methods that could be incorporated into the bubble oxygenator to convert bicarbonate ion rapidly to CO 2 gas.

The researchers who developed the system were:

Their research was funded through an $18,000 grant from CMI in 2013.