IIT-Bombay designs prototype to reuse oxygen for patients on ventilators

A team of alumni and researchers at the Indian Institute of Technology-Bombay (IIT-B) have built a breathing device that can reduce wastage of oxygen when a Covid-19 patient is put on assisted breathing support such as ventilators.

The prototype, called ‘reBreather’, is a semi-closed circular breathing system that will allow patients to breathe in unused exhaled oxygen. Covid-19 patients with severe breathing trouble are put on ventilators that can supply oxygen through a combination of nasal cannula and mask at a flow rate of up to 50 litres per minute.

However, the lung can only absorb one litre of oxygen in a minute. The rest of the 49 litres (L) are breathed out or wasted. The researchers have used an existing technology of reusing exhaled oxygen— commonly used in diving and mountaineering systems — to cut down on this wastage.

“At a time when oxygen is in short supply across the country, this mode of recirculating oxygen can help save lives,” said Santosh Noronha, assistant professor, department of chemical engineering, IIT-B, who is one of the 15 members of the team behind reBreather.

The prototype has been designed by the staff, students and alumni affiliated with Tata Centre for Technology and Design, department of chemical engineering, and Nex Robotics—a start-up by alumni of the institute.

According to the calculations by the team, this recirculation of oxygen can reduce the number of cylinders required by a critical patient from nine to almost one per day. This calculation is based on the assumption that a cylinder holds 7,800L of pure oxygen.

“It is a good system on paper and we [doctors] are quite excited about it. However, it has to be put into use in a hospital set up before we can be sure of its working,” said city-based infectious diseases specialist Om Shrivastav, who was not a part of the project.

A healthy human inhales 5L of air in a minute, of which one-fifth or a litre is oxygen. The human lungs can absorb only a quarter of this, which is 250 millilitres (ml). This may increase when the person is performing an activity or is ill. For every 250ml of oxygen absorbed, the lungs breath out 225ml of carbon dioxide.

reBreather is a semi-closed circular breathing system with an inlet section which pumps in fresh oxygen from an oxygen cylinder or a centralised oxygen system in hospitals. The oxygen flow rate is set on the cylinder with a flow meter. An adjustable venturi valve is given at the input to allow for external air to be automatically pulled in based on the desired oxygen flow rate. A one port mask is attached to the patient. The exhaled air is fed to a container which has medical-grade soda lime. This soda lime selectively absorbs carbon dioxide from the exhaled output and allows the rest of the air to pass through to the inlet section of the system. The soda lime changes colour once it has exhausted its capability to absorb carbon dioxide and can be replaced.

“Soda lime is the only consumable item in the system. We are working on modifying the designs further so that this can also be regenerated,” said Noronha.

The technical details of the system have been made public under Creative Commons to grant access to healthcare workers across the country.

“So far the system has been tested on healthy volunteers. We are planning to start a clinical trial soon. However, as approvals for clinical trials take time, we have made our system public so that if anybody wants to use it in the meantime, they can do so. It is an existing technology used in diving and mountaineering systems,” Noronha added.

A single unit of reBreather cost the team around ₹50,000.

“As most of it is plastic, the unit can be sanitised and reused. So it is mostly a one-time expense,” Noronha said.

City-based pulmonologist Lancelot Pinto said, “When we breathe ambient air, we breathe air with a concentration of oxygen that’s about 21%. The air we exhale tends to have an oxygen concentration of 17%. This applies to healthy lungs. When lungs are affected [by infections or chronic lung diseases], they become inefficient at transferring oxygen, and we add supplemental oxygen so that the higher concentration of inspired air will create a steeper gradient for the oxygen to move across damaged alveolar membranes. However, this extraction is likely to be sub-optimal, resulting in a reasonably high concentration of oxygen in the exhaled air [higher than room air]. If an efficient method were created to reuse this oxygen, enrich it further to match the need while removing the carbon dioxide exhaled, it would be a very promising step in conserving the use of supplemental oxygen, which has become a precious resource.” Hindustan Times