ON HIS first night as a trainee paediatrician in Sylhet, Bangladesh, Mohamad Chisti (pictured above) watched three children die of pneumonia. Oxygen was being delivered to them, through a face mask or via tubes placed near their nostrils, using what is called a basic “low-flow” technique which followed World Health Organisation (WHO) guidelines for low-income countries. But it was clearly failing. He decided to find a better way.

Last year 920,000 children under the age of five died of pneumonia, making it the leading killer of people in that age group. This figure is falling (in 2011 it was 1.2m), but it still represents 16% of all infant deaths. Such deaths are not, however, evenly distributed. In Bangladesh pneumonia causes 28% of infant mortality.

Pneumonia is a result of bacterial, viral or fungal infection of the lungs. Its symptoms of breathlessness result from a build-up of pus in the alveoli. These are tiny sacs, found at the ends of the branching airways within the lungs, that are richly infused with capillary blood vessels. They are the places where oxygen enters the bloodstream and carbon dioxide leaves it. Stop the alveoli doing their job and a patient will suffocate.

Pneumonia is particularly threatening to malnourished children—which many in Bangladesh are. First, malnourishment debilitates the immune system, making infection more likely. Second, to keep its oxygen levels up and its CO 2 levels down, a child with pneumonia breathes faster and faster. But this takes a lot of energy, so undernourished infants do not have the ability to keep such an effort up for long. Dr Chisti’s device is designed to reduce the effort required to breathe, and to do so cheaply. (The reason for the WHO’s recommended approach in poor countries is that the sort of ventilator routinely available in the rich world costs around $15,000. But low-flow oxygen delivery does not reduce the effort required to breathe.)

His invention was inspired by something he saw while visiting Australia. On this trip he was introduced to a type of ventilator called a bubble-CPAP (continuous positive airway pressure), which is employed to help premature babies breathe. It channels the infant’s exhaled breath through a tube that has its far end immersed in water. The exhaled breath emerges from the tube as bubbles, and the process of bubble formation causes oscillations of pressure in the air in the tube. These feed back into the child’s lungs. That improves the exchange of gases in the alveoli and also increases the lungs’ volume. Both make breathing easier.

At about $6,000, standard bubble-CPAPs are cheaper than conventional ventilators. But that is still too much for many poor-country hospitals. However, after a second piece of serendipitous inspiration, when he picked up a discarded shampoo bottle that contained leftover bubbles, Dr Chisti realised he could probably lash together something that did the same job. Which he did, using an oxygen supply (which is, in any case, needed for the low-flow oxygen delivery method), some tubing and a plastic bottle filled with water. And it worked.

In 2015 he and his colleagues published the results of a trial that they had conducted in the institution where he practises, the Dhaka Hospital of the International Centre for Diarrhoeal Disease Research. This showed that the method had potential. The hospital now deploys it routinely and the number of children who die there from pneumonia has fallen by three-quarters. That means the survival rate in the Dhaka Hospital is today almost on a par with that of children treated in rich-world facilities, using conventional ventilators.

Dr Chisti says that, as well as saving lives, his device has cut the hospital’s spending on pneumonia treatment by nearly 90%. The materials needed to make his version of a bubble-CPAP ventilator cost a mere $1.25. The device also consumes much less oxygen than a conventional ventilator. In 2013 the hospital spent $30,000 on supplies of the gas. In 2017 it spent $6,000.

The idea is spreading. Dr Chisti and his team are about to start trials of the new ventilator in a group of hospitals in Ethiopia. If it works as well there as it does in Dhaka, it will surely be taken up elsewhere. All in all, the Chisti bottle-based ventilator shows what can be achieved by stripping an idea down to its basic principles. Effectiveness, it neatly demonstrates, need not always go hand in hand with high tech.