'Dialysis' for the lungs

The way the Hemolung Respiratory Assist System works is similar to a kidney dialysis machine. It collects the patient's blood, removes carbon dioxide and then returns the blood back to the patient.

A new machine is being tried out at a hospital here, which could save the lives of patients on mechanical ventilators.

The ventilator that helps patients breathe, thus keeping them alive, is also the device that could make them worse.

The machine is needed for patients who have moderate to severe acute respiratory distress syndrome, a life-threatening condition which prevents enough oxygen from reaching the lungs.

But the ventilator changes the way air is delivered to the lungs.

It pushes air into a patient's airway, instead of relying on air being sucked in through breathing, said Dr Matthew Cove, an intensivist and consultant at the division of respiratory and critical care medicine at National University Hospital (NUH).

The airway then reacts to the increased pressure by releasing inflammatory substances that further injure the lungs and worsen acute respiratory distress syndrome.

Up to half of these patients can die when this happens.

Doctors now reduce the amount of air that is pushed into the lungs, called the tidal volume, but this has created other problems.

As less carbon dioxide is removed through the ventilator with a lower tidal volume, it accumulates in the patient's blood, turning it acidic.

High levels of carbon dioxide in the blood causes hypercapnia, which impairs the function of the heart and puts a patient at risk of a cardiac arrest. It also appears to slow down or impair bacterial killing, preventing patients from fighting infections properly.

Dr Cove and his team are now testing a new machine that collects blood from the body and removes the carbon dioxide before returning it back to the patient.

He said it is similar to a dialysis machine, which takes over the function of an impaired kidney by removing toxins from the blood.

The machine, called the Hemolung Respiratory Assist System, is easier to operate than other carbon dioxide-removal machines, he added.

In the next 11/2 years, up to 50 patients with acute respiratory distress syndrome who are on ventilators will be randomly assigned to either Hemolung or standard care. Consent for the study will be sought from their next-of-kin.

Their rate of recovery and number of days on the ventilator will be tracked, among other things.

Dr Cove said: "Our goal is to halt the progression of acute respiratory distress syndrome and facilitate lung recovery, while avoiding more invasive treatments."

Acute respiratory distress syndrome affects critically ill patients and is typically triggered by pneumonia, sepsis (blood poisoning) or trauma. Up to 60 in every 100,000 people will be affected, according to overseas studies.

joanchew@sph.com.sg


This article was first published on May 21, 2015.
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