The issue is that with the kind of ventilation required you need to sedate the patient with gasses and you need to recycle those gasses and unused oxygen. With the length of time patients have to be on this you don't want to lose those gasses and also pump it out into the atmosphere. The Manley design could be a good starting point I suppose, you just have to replace the weight system with controllers and add a carbon scrubbing stage to feed back the gasses. The carbon scrubbing stage is the tricky one, it's something that requires good chemistry and not mechanics and electronics.

Physician here; this isn't true for the ventilation of COVID patients, or ICU patients in general.

There's a difference between simple ventilator [1], and an anesthesia machine [2] that adds gas mixing, scavenging, etc.

ICU patients are anesthetized using IV sedation (a common regimen in the US is fentanyl/propofol), not inhalational anesthetics. Most vents only have simple inline filters to reduce contamination.

[1] A classic vent in the US is the Puritan Bennett 840. Here's its manual showing filters: https://www.medtronic.com/content/dam/covidien/library/us/en...

[2] https://en.wikipedia.org/wiki/Anaesthetic_machine

I suppose that's good news then for potential emergency use of unapproved makeshift alternatives to ventilators, I guess it also makes hand ventilation viable if you have enough volunteers available to do the bagging.

Bagging is hard to do for extended periods.

Anesthesiologist here - true, I was a Stanford medical student on an ICU rotation when a Tesla employee crashed his plane into high voltage power lines while attempting to land at San Carlos airport. Electrical power on the peninsula was out for an extended period of time. Battery backups eventually failed, then gas powered generators started failing so everyone with a pair of hands took turns manually ventilating the patients. If push comes to shove, we could get by with a Jackson-Reese circuit and a pair of hands. Obviously we don’t want to find ourselves in this situation.

Why is it relevant he was a Tesla employee?

Do you think a simple design like the Manley would pass muster today?

Seriously thinking about putting together a group of people to start producing these locally. Around campus we have a significant capacity in manufacturing precision mechanical devices.

I have an MTV (manually triggered ventilator) in my O2 kit for a scuba diving emergencies. Of course my O2 supply is only good for about 15 minutes. Would this be of any assistance while waiting for an ENT to arrive?

I am ignorant as far as the use of inhalable medications is concerned. However, I find it weird that you'd want to recycle oxygen: carbon dioxide removal is either hard or requires consumables, while oxygen can be concentrates from air using a simple process that consumers only energy (by adsorbing nitrogen on surfaces of particular minerals).

FWIW: in the kind of disaster these kind of home brew devices are targetted at, they're unlikely to be used on sedated patients.

I read this as "how to save a life with a vaccuum cleaner in extremis", and not "here's a good ventilator design". Is it a good idea? I dunno. I'll check on the vaccuum today just in case.

Also FWIW: the air path doesn't seem like the critical piece here. My (amateur) intuition tells me that the number of lives saved by amateur ventilators will be rather less than the number killed by amateur intubation devices.

If amateur ventilators are only used when ventilation is required and standard ventilators are not available, that still may be a good answer.. still, I am sure that there are better and worse designs for amateur ventilators, it would be best if someone who knew they were doing reviewed various designs and could recommend the best of the bad situations.

More amateur intuition: there are probably more available trained health care providers (e.g. radiologists who put tubes in as med students) than there are devices. These things aren't going to be needed by "us", but by them. They need to be the ones coming up to speed.

Again: I'd be sort of OK with a ventilator manufactured by a HN reader. Under no circumstances do I want a software geek putting a tube in me.

Anesthesiologist here - sedation is ideal for managing patients in respiratory failure, though volatile anesthesia is not commonly used in an ICU setting (at least not in the US). It is more common to use IV drugs such as dexmedetomidine, fentanyl, or dilaudid.

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

None of what you're describing seems particularly hard except the actual ventilation (inspiratory and expiratory), and the detection of patient inhalation (which may need tuning). The rest is just normal programming of an LCD microcontroller.

I proposed a design on the slack group based on a centrifugal blower and airflow and pressure sensors.. I think this is the principle modern hospital ventilators use. You do the logic and control system in C code rather than mechanical linkages and valves.. very few moving parts, and pcbs/pcb assembly are quick and cheap. just don't make any bugs..

It’s cooler if you roll your own.

Ask programmers, they’ll get you up to speed.