ICU ventilators are surprisingly complicated machines, we've just brought some HAMILTON-C6 machines at work if you want an idea of the top of the line. Ventilating sick COVID patients, or indeed anyone with ARDS, is one of the most challenging things we do in intensive care. Even with high end commercial ventilators, the mortality rate for intubated COVID patients is >70%.
I would consider the following a bare-minimum feature set for a COVID patient ventilator, any less and it would do more harm than good:
- cycle between an inspiratory and expiratory phase
- during the inspiratory phase, deliver an adjustable volume of gas (in the region of 6 ml per kg of patient's body weight) using as little pressure as possible, with an adjustable upper limit of pressure (in the region of 30 cmH2O)
- during the expiratory phase provide an adjustable pressure against exhalation (in the region of 0-30 cmH2O)
- allow blending of air and oxygen to deliver an adjustable inspired oxygen fraction
- allow the timing of the inspiratory and expiratory phases to be independently varied, thereby allowing the respiratory rate and the ratio of inspiration to expiration time to be controlled. Permit respiratory rates in the range of 8-60 breaths per minute
- measure and display the pressures and volumes within the respiratory system
- allow adjustable alarm-limits for pressures and volumes, and provide clear audible and visual alarms if these values are exceeded
For added patient safety and benefit, the following would be helpful
- measure inspired and expired oxygen and carbon dioxide content, and display both on a continuous waveform graph
- allow the patient to initiate the inspiratory phase by sensing patient inspiratory effort and providing pressure support for inhalation; ie sense when the patient inhales and deliver 10-15 cmH2O pressure for 0.5 seconds to augment inhalation