Connecting 2-4 Patients to the Same Ventilator

[berkeman]

TL;DR

How do you parallel up Patients on one ventilator? What are the risks?

How does this work? Do you just parallel the tubing to the ET tubes? Or is there more to it? Seems like a risky move, but in these times, it may be necessary...

https://abc7news.com/new-york-to-allow-hospitals-to-treat-two-patients-with-one-ventilator/6052788/

From the link in the article:

March 26, 2020: The Society of Critical Care Medicine (SCCM), American Association for Respiratory Care (AARC), American Society of Anesthesiologists (ASA), Anesthesia Patient Safety Foundation (APSF), American Association of Critical‐Care Nurses (AACN), and American College of Chest Physicians (CHEST) issue this consensus statement on the concept of placing multiple patients on a single mechanical ventilator.

The above‐named organizations advise clinicians that sharing mechanical ventilators should not be attempted because it cannot be done safely with current equipment. The physiology of patients with COVID‐19‐onset acute respiratory distress syndrome (ARDS) is complex. Even in ideal circumstances, ventilating a single patient with ARDS and nonhomogenous lung disease is difficult and is associated with a 40%‐60% mortality rate. Attempting to ventilate multiple patients with COVID‐19, given the issues described here, could lead to poor outcomes and high mortality rates for all patients cohorted. In accordance with the exceedingly difficult, but not uncommon, triage decisions often made in medical crises, it is better to purpose the ventilator to the patient most likely to benefit than fail to prevent, or even cause, the demise of multiple patients.

Note that the last part of the quote about triaging Patients in life-and/or-death situations is one of the more difficult issues we deal with in EMS.

 

[Vanadium 50]

My first thought was "in series or in parallel"?

 

[BillTre]

My thoughts were:

1. what is the pumping mechanism like?
2. what is its pressure profile (vs. time) applied to the patient?
3. does the person running the unit have to dial it into each patient or does one set of settings fit all?
4. Is air only pumped in, or both in and out (maybe good for emphysema)?
5. is there any feedback regulation of the pressure being applied based on the patient's response (like resistance) to the pressure (this would seem to make it difficult to put several individuals on one machine)

Guess I don't know that much about ventilators.

This Wikipedia article kind of answers a some of those questions.

 

[berkeman]

Guess I don't know that much about ventilators.

Yeah, same with me. I'm wondering if ETCO2 is part of the monitoring loop...

 

[chemisttree]

This paper is a preliminary evaluation. It looks like pressure control or volume control. Pressure setting was 25 cm H2O and volume was set to 2L tidal volume (whatever that is) or 500 mL per test lung. Respiratory stacking was monitored but not CO2. Looks like it is just mechanical breathing. Probably the patient would be put completely under. Sounds dangerous.

Here is a discussion of how it will be accomplished. Definitely sub-optimal.

 

[berkeman]

This paper is a preliminary evaluation.

Yikes, it looks like they are skipping any animal studies and going straight to humans now. Or we are the animal study, I guess.

And the cross-infection issue seems significant. Sure, all the Patients have COVID-19, but if one has developed pneumonia and the others on the same ventilator haven't yet...

 

[Vanadium 50]

I have serious concerns about the ethics of this. Maybe this is effective, maybe it isn't, and maybe as you say, it will make things worse. And even "effective" has a lot of gray to it: do we know the prognosis of a patient who has advanced far enough to require a ventilator? I know "triage" is a dirty word, but before performing medical experiments on our populace, it would be good to have some idea that it would help.

 

[berkeman]

Note that the last part of the quote about triaging Patients in life-and/or-death situations is one of the more difficult issues we deal with in EMS.

And here is one of the first public statements about such triage with respect to ICU in general and ventilators in particular...

https://www.cnn.com/2020/03/27/health/michigan-henry-ford-letter-coronavirus/index.html

"Because of shortages, we will need to be careful with resources," reads the letter, which is addressed to patients, families and the community. "Patients who have the best chance of getting better are our first priority."

"Patients who are treated with a ventilator or ICU care may have these treatments stopped," it says, "if they do not improve over time."

The letter goes on to say patients with severe heart, lung, kidney or liver failure, severe trauma or burns, or terminal cancers may be ineligible for a ventilator or ICU care. These patients will instead receive "pain control and comfort measures."

"This decision will be based on medical condition and likelihood of getting better," the letter says

 

[BillTre]

tidal volume (whatever that is)

Tidal volume is the volume of air inhaled and exhaled. Similar to tides going in and out of an estuary.
Total lung volume is larger. Not all the air in the lungs is exchanged in each breath.
There is also something like dead space (can't remember the exact term) which is the volume of inhaled air which fills the tubes leading to the lungs. It is part of the tidal volume, but does not get to the lung and partake in gas exchange.

 

[BillTre]

Other than the potential for spreading pathogens among a group of patients in one ventilator, my concern is that pumping air into different patients (linked up in parallel) would have similar issues to current flow through parallel resistors.
The flow would be determined by the relative resistances of the set of patients rather than what each individual patient's diseased physiolgy would be best getting.
This would be especially problematic if it is standard to either individualize the settings of a ventilator for particular patients or if the were feedbacks from patient's physiology controlling the pumping. Which patient's feedback would be used, or would they be combined in some way?

 

[Vanadium 50]

This is fixable by putting a restriction (per patient tunable, ideally) upstream.

The problem I see is that the more you MacGyver this to make it work in a way other than what it was designed to, the more likely some unintended undesirable consequence will pop up. If you hook up 4 patients per ventilator on Monday, congratulate yourself on Tuesday, and they all break under the increased load on Wednesday, you're no better off.

And while you might be able to order as few more ventilators because they are "essential", I am sure they are filled with parts that are "non-essential", or are made by machines that are non-essential, if you go far enough up the chain.

 

[chemisttree]

This would be especially problematic if it is standard to either individualize the settings of a ventilator for particular patients or if the were feedbacks from patient's physiology controlling the pumping. Which patient's feedback would be used, or would they be combined in some way?

As the paper I quoted stated, this would require all patients be matched so that their physiology was similar. They would likely all be sedated as this type of respiration is supposed to be “uncomfortable.”

 

[berkeman]

I wonder if they will staff these setups with respiratory therapists (RTs), or if it will require a full anesthesiologist to deal with it all. Wow, what a work load.

 

[BillTre]

I wonder if they will staff these setups with respiratory therapists (RTs), or if it will require a full anesthesiologist to deal with it all. Wow, what a work load.

I heard a radio report that they were people that normally work in non-medical aspects of hospitals to do simple medical things in hospitals (perhaps like orderlies?). This might free up real nurses to deal with ventilators. It didn't sound like they could quickly make fully trained respritory techs at the drop of a hat. I would expect a bunch of people sliding around among different jobs to get those best suited to the most important jobs doing them and the least trained for the simplest ones.
I really don't expect them to find a lot of respiratory tech or anesthesiologists very quickly.

Some well trained people maybe coming out of retirement to help out with the crisis.
Some places also want to get med. students out of med school early, which makes sense to me.

 

[Ygggdrasil]

Based on published data from China, it's not actually clear to me how much ventilators are helping at this point. Here are statistics from two studies in China that look at critically ill cases of COVID-19:

32 patients required invasive mechanical ventilation, of whom 31 (97%) died.

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30566-3/fulltext

29 (56%) of 52 patients were given non-invasive ventilation at ICU admission, of whom 22 (76%) required further orotracheal intubation and invasive mechanical ventilation. The ICU mortality rate among those who required non-invasive ventilation was 23 (79%) of 29 and among those who required invasive mechanical ventilation was 19 (86%) of 22.

https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30110-7/fulltext

Of course, other studies have shown ventilators can more generally be helpful against acute respiratory distress syndrome (a study of 178 H1N1 cases from 2009, which shows a 46% mortality of patients on mechanical ventilation, and a wider meta-analysis of treatments for ARDS finds a 34.6% mortality of patients with severe ARDS treated with mechanical ventilation or ECMO). However, there is reason to think that COVID-19 is different: 1) Ventilators treat the symptoms but not the cause of the problems. If the virus is still active in the body, ventilators ultimately won't solve that problem. 2) It has been reported that the virus could infect other organs of the body, so while ventilation could solve issues with lung function, the virus may cause death due to damage to other organs such as the heart, liver or kidneys.

In both cases, it seems like the best candidates for ventilators would be those whose bodies seem to be getting the infection under control, whereas ventilation may not be so helpful to those whose immune systems have not been able to control the virus. This would suggest that better triage of cases rather than sharing ventilators would be a better strategy (though I don't know if it's possible to assess how well patients' immune systems are fighting the virus).

Ventilators would likely have higher effectiveness once good antiviral therapies that can control the infection are identified, so there is still good reason for the country to mass produce ventilators for treating COVID-19 patients.

 

[chemisttree]

A good discussion of sharing ventilators here.

Confirms much of what has been discussed already.

Also reports that Prisma Health is 3D printing valves for use in a manifold to enable multiple patients per respirator. You can download the specs and print one yourself (if you are a hospital). www.prismahealth.org/VESper