A team of researchers from the Royal Women’s Hospital, Monash University and the Alfred Hospital has successfully tested, in a simulated environment, the potential to ventilate two lungs of different compliances from a single ventilator using only commonly available hospital equipment. While the authors do not condone the practice of ventilator splitting and say the findings must be interpreted and applied with caution, the experiments demonstrate the hope of simultaneously ventilating two test lungs of different compliances and modify the pressure, flow and volume of air in each lung, in case of extreme emergencies.
“Patients with COVID-19 may develop progressive viral pneumonitis leading to severe respiratory failure,” said lead author Dr. Alexander Clarke, a researcher in the Department of Anaesthesia at the Royal Women’s Hospital.
“The combination of unprecedented disease burden and global supply chain disruption has resulted in worldwide shortages of medical equipment.”
“Despite our advances in the practical application of ventilator splitting, the practice is unregulated and under tested. But as the COVID-19 pandemic continues to grow, some countries, like the USA, may consider ventilator splitting on compassionate grounds. The U.S. FDA has passed emergency use authorization for the splitting of ventilators.”
“While ventilator splitting has, at face value, validity in addressing ventilator shortages, we agree that on sober reflection, it is a solution that needs to be weighed up carefully as it may cause more harm than good.”
The basic principle of ventilator splitting is simple — two or more patients are connected to one ventilator and both are exposed to the same circuit dynamics.
This presents many challenges including ventilator and patient synchronicity — ventilation requirements are different for a 100 kg male and a 50 kg female, cross-infection from inter-patient gas exchange, oxygen concentration, and the lack of monitoring for individual tidal volume, flow and pressure. Irregularly pressurized air supply can kill patients.
To counter this, Dr. Clarke and colleagues connected a flow restrictor apparatus, which consisted of a Hoffman clamp and tracheal tube, to the inspiratory limb of the ventilator to the high compliance test lungs.
The breathing circuit ran from the humidifier to a hospital-commodity Y-connector splitter.
From the splitter, two identical limbs were created, simulating the ventilation of two pairs of patient lungs.
The resistance was modified to achieve end-tidal volumes of 500 ml ± 20 ml.
“The addition of the flow restrictor was critical to the way this setup works — without the restrictor, we weren’t able to control air flow to each simulated patient,” said co-author Dr. Shaun Gregory, a scientist in the Department of Mechanical and Aerospace Engineering at Monash University.
While the findings are exciting for crisis and trauma medicine, they need to be interpreted and applied with caution.
“Our experiment has demonstrated that in order to deliver a safe tidal volume and airway pressure, a resistance mechanism is required on at least one inspiratory limb of the circuit,” Dr. Gregory said.
“One way of achieving this is through the use of a tracheal tube and Hoffman clamp — common, practical items found in hospitals.”
“While the discovery is promising, the use of this method in the clinical context has not been validated and we don’t recommend its wider use without further trials.”
“We are hopeful of one day being able to get great surety with this approach to ventilator splitting so we can help save lives in dire cases of emergency.”
The team’s paper was published in the journal Anaesthesia.
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