University of Iowa researchers eye safest way to share ventilators between patients

IOWA CITY - Although treating multiple patients with one ventilator is a medical measure of last resort, there is a safer way to do it - if you must - according to new research involving the University of Iowa.

A desperate NewYork-Presbyterian Hospital - at the epicenter of this country's COVID-19 outbreak - just weeks ago began, in some cases, treating two patients with one ventilator, according to the New York Times. Before that, the practice had been tried just twice in crisis situations - including the 2017 Las Vegas shooting and more recently for coronavirus patients in Italy.

The New York ventilator tactic in March was the first attempt to multitask ventilators as a longer-term strategy, according to the Times.

And new research from the UI, Boston University and University of Cincinnati found one method of ventilator sharing to be safer than an alternative.

'We looked at what the exact dangers are of doing it,” said David Kaczka, associate professor in the UI departments of anesthesia, biomedical engineering and radiology, and a researcher on the study. 'And then what we could do to make it safer.”

The peer-reviewed paper, 'Shared Ventilation in the Era of COVID-19: A Theoretical Consideration of the Dangers and Potential Solutions,” was published online Wednesday in Respiratory Care, the official science journal of the American Association for Respiratory Care.

The scientists - who received help via 3D-printing from UI-based Protostudios - began their research in mid-March, according to Kaczka, who said the team continuously wrote the manuscript as data came in, allowing them to produce findings in under a month.

'There was anecdotal evidence that this could be done after the mass shooting in Las Vegas in 2017,” Kaczka said. 'But there was nothing in the literature about its safety or effectiveness.”

Nailing that down, according to the research team, was paramount - as shared ventilation has become of 'considerable interest for addressing the severe shortage of mechanical ventilators available during the novel coronavirus pandemic.”

'We highlight the potentially disastrous consequences of naive ventilation, in which patients are simply connected in parallel to a ventilator without any regard to their individual ventilatory requirements,” according to the paper.

The New England Journal of Medicine reported a broad range of estimated ventilator needs in the United States - from hundreds of thousands to a million.

Safest method

Although researchers investigating shared ventilation said the tactic can be deadly and should only be considered under desperate circumstances, they found the safest way to do it uses a method they call 'pressure-controlled ventilation.”

That method allows a patient to continue getting support even if a blockage or other change occurs, while the alternative method - 'volume-controlled ventilation” - gives other unaffected patients more support under such circumstances.

Pressure control, essentially, lowers the risk of catastrophic lung damage by providing more control over gas flow and the tidal volume each patient receives, according to the research.

'If you do have to share a ventilator, volume control is probably the least safe way to do it,” Kaczka told The Gazette. 'But pressure-control, if it does have to be done, that's the safest way to do it.”

Researchers tested both methods in computer simulations and on mechanical test lungs.

'The actual simulations were done in Boston,” Kaczka said. 'The experiment on the ventilator was done at the University of Iowa.”

The study provides important information for this specific crisis, which - unlike the Vegas trauma involving patients with similar profiles - has presented patients with varying lung mechanics. Even when patients are chosen to share a ventilator because of their closely matched needs, their circumstances often change.

'Any substantial alteration of one patient's respiratory system - for better or for worse - could be catastrophic for all connected patients if you don't have a way to control individual pressure and tidal volumes,” Kaczka said.

Weighing decision

Several professional societies - like the Society for Critical Care Medicine, the American Society of Anesthesiologists, and the Anesthesia Patient Safety Foundation - have spoken out against the practice, in March issuing a statement that, 'Sharing mechanical ventilators should not be attempted because it cannot be done safely with current equipment.”

'It is better to purpose the ventilator to the patient most likely to benefit than fail to prevent, or even cause, the demise of multiple patients,” according to the statement.

But Kaczka said the expected and dire need for ventilator options demanded further investigation - and the first question they asked was whether it's safe.

'In this case, it has to be safe for every patient you connect to the ventilator,” he said. 'Then it has to be effective. The patient has to be better off than if you didn't connect them to a ventilator.”

Although he reiterated sharing ventilators is never ideal, the researchers did find controlling for pressure mitigated many concerns flagged when controlling by volume.

'With PCV, each patient is exposed to a constant inspiratory pressure and will receive a tidal volume commensurate with their own respiratory compliance,” Kaczka said. 'In our method, each patient receives an independent (positive end-expiratory pressure), so we are able to customize the treatment for each patient as if they each had their own ventilator.”

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