Low-cost ventilators

A group of UK anaesthetists has designed and tested three prototype low-cost ventilators that could provide vital support during major healthcare emergencies involving large numbers of patients or casualties.

It is claimed the devices could also be used where resources are limited, such as in developing countries, remote locations or by the military.

‘Our research has demonstrated that it is possible to make a gas-efficient ventilator costing less than £200, for use where 2-4 bar oxygen is available, with no pressurised air or electrical requirements,’ said consultant anaesthetist Dr John Dingley from Morriston Hospital, Swansea.

‘Such a device could be mass produced for crises where there is an overwhelming demand for mechanical ventilation and a limited oxygen supply.’

Problems with limited oxygen supply date back to the First World War when medical professionals had to deal with the large numbers of casualties affected by poisoned gas.

‘The physiologist J S Haldane developed a delivery system that provided a high flow of oxygen from a modest fresh gas flow,’ added Dr Dingley, who is also a reader in anaesthetics at Swansea University.

‘Our aim was to extend Haldane’s concept of maximally efficient oxygen delivery to include pneumatic gas-powered ventilator designs.

‘The initial design was envisaged as a ventilator for difficult environments, especially military scenarios, where large oxygen cylinders would be impractical or in short supply, and electrical power would be unavailable.

‘This led to two variants that are suited to emergency construction in bulk for mass deployment prior to a respiratory failure pandemic or other major healthcare situation.’

All three designs operate on the principle that the energy is taken from compressed oxygen at a supply pressure of 2-4 bar to provide the motive force to ventilate the lungs.

‘After the stored energy has been used to provide motive power in this way, the waste oxygen – which is now at atmospheric pressure – is then re-used to enrich the air being drawn into the ventilator before it is delivered to the lungs,’ explained Dr Dingley.  

‘In this way, most of the breathable oxygen is obtained from ambient air.’

A mechanical test lung was used to test the three devices and this showed that they would provide effective ventilation for patients who were unable to breathe unaided. The devices were also tested over a range of lung volumes and compliances, which the researchers said indicated that the oxygen consumption was considerably lower than that of the commercially available gas-powered ventilators currently on the market.

The team concluded that this means even if the devices had to be used over an extended period of time, they would use less than conventional units. The team also claimed the devices would provide a viable and financially attractive alternative to buying extra critical care ventilators, which are expensive, complex microprocessor-driven devices.   

‘These devices could be used anywhere that 2-4 bar oxygen is available, such as a converted ward with no piped air or electricity,’ said Dr Dingley. ‘In extreme circumstances, they could even run on hospital compressed air, using very little air from the hospital’s compressor reservoir.’

Dingley added that the mechanism could possibly be made as a single-use device and stockpiled for crises where there is an overwhelming demand for mechanical ventilation, such as a pandemic.