Diving rebreather technology has been applied to saving the lives of intensive-care patients – thanks to scuba diver Martin Stanton, managing director of the Vobster Quay inland diving site in Somerset.
The first order for 1000 of his 3CPAP ventilators has just been placed by the NHS to help patients with severe breathing difficulties.
Stanton came up with the idea of applying the century-old principle of recycling oxygen through use of a rebreather – first used by naval divers in World War One – to the NIV (Non Invasive Ventilation) device that is so important in hospital intensive-care units.
Such ventilators are used for some 60% of patients with acute pneumonia – the main reason Covid-19 patients become hospitalised – as well as other conditions such as acute influenza. However, when hospitals started reporting a shortage of ventilators as well as oxygen for patients in the early days of the pandemic, Stanton set about finding a solution.
A software engineer by trade, and having previously owned and run Vobster Marine Systems (VMS), he already had many years of experience in the design and manufacture of rebreathers under his belt.
“What 3CPAP does that is different – and it truly is a first – is to make a rebreather perform CPAP,” Stanton told Divernet. CPAP stands for Continuous Positive Airway Pressure. “The oxygen-saving capabilities of a rebreather are well understood, but the trick is: how do you maintain both breathable volume and pressure automatically?
“On a rebreather, adding volume is easy – we usually use an ADV [Automatic Diluent Valve]. But getting rid of it is harder. We as divers generally vent the volume out through our nose or mouth.
“We can’t expect a patient to do that, and actually during CPAP this is impossible because you’re wearing a sealed mask. So the first invention, which I patented, was an automatic volume-control valve that maintains the ideal volume in the breathing loop.”
Maintaining pressure
Stanton’s second challenge was to find a way of maintaining pressure in the device. “CPAP requires us to apply a constant pressure in the airway, but a rebreather operates at ambient pressure,” he explained. “So I had to develop a way to generate above-ambient pressure, but within a closed system.
“That wasn’t too bad, and with the help of the Cabinet Office and a few friends, I had a system up and running in April, 2020.
“However, the pressure needs to stay as close as possible to target throughout the breathing cycle, but when you breathe in and out you need to have a way of altering the supplied pressure in real time, to compensate for the changes in pressures delivered.” Stanton says he had perfected that aspect of the system by January, 2021.
The result, his easily transportable 3CPAP ventilator, has a sodalime canister attached to recycle the exhaled oxygen and costs about £3,300 – a huge saving when compared to the £12,000 cost of a typical VC70 ICU ventilator.
The saving in oxygen required is also marked. A standard CPAP system might use 50 litres of oxygen per minute which, with an average UK general hospital delivery rate of around 3,000 litres per minute, allows only 60 patients to be treated.
“Using a rebreather-based system, we can treat over 1,000,” said Stanton. “This is pertinent, because the average UK hospital has 300-400 beds, and if you exceed the limits of the oxygen system it tends to shut down – leaving the patients with no oxygen at all.”.
Treatment anywhere
An NHS report in late 2021 showed that CPAP reduced the likelihood of a patient being intubated by 18%, and improved the outcome for those who did need intubating by around 16%, said Stanton. The chances of surviving intubation for patients with acute pneumonia are around 50-50.
A further advantage of 3CPAP is that it can even be run on an oxygen concentrator, commonly used in care homes to deliver O2 to patients at low volumes but usable in a clinical environment only in conjunction with a rebreather.
“This allows us to give this life-saving treatment anywhere, as long as we have sodalime to remove the CO2, and power,” said Stanton. “Sodalime is still a consumable, but it’s a lot easier to transport than high-pressure oxygen.”
Regulatory testing of the 3CPAP is almost complete, he said, with UK patient trials due to start in August. After completing the NHS order, applications will begin for the various certifications needed to export 3CPAP.
The new system “has the very real potential to allow acute CPAP to be delivered using oxygen concentrators, during transport and in countries where oxygen supplies are limited,” says the Medical Devices Testing Evaluation Centre.
Stanton, who exhibited the product last week at the Cheltenham Science Festival, was awarded £130,000 in development funding by Innovate UK and Millfield Medical Electronics.
Also on Divernet: Guidance Relaxed on Post-Covid Scuba, Divers & Covid: A Doctor Needs Your Help
