The story began in early March. With COVID-19 bearing down upon us, it became clear that we could run out of ventilators. This sparked interest in the concept of splitting ventilators between several patients. Some articles and videos were circulated on twitter describing how this could be done. These mostly described splitting a ventilator set in volume control mode.
Upon seeing this, two things were apparent to me:
- Splitting a ventilator in volume control mode would be a disaster. This could lead to all sorts of dangerous interactions between the patients. There are many ways to turn a ventilator into an assault weapon, and this is one of them. At risk of being pedantic, I would not ever consider splitting ventilators in a volume control mode.
- Using pressure-cycled ventilation with continuous mandatory ventilation could overcome most of these problems. This might allow splitting the ventilator in a reasonably safe manner (not perfect, but not an assault weapon either).
I described the fundamental concepts of how this might be done here. Subsequently Drs. Mergeay and Pinson led a team in Belgium to develop this idea much, much further. Almost simultaneously with Dr. Pinson’s report, the team at Columbia Presbyterian in NYC released a detailed protocol for split ventilation and began using it.
At nearly the same time that Dr. Pinson’s and Columbia’s reports surfaced, a joint statement from multiple professional societies was released admonishing us against splitting a ventilator. This is a unique statement which seems to have been derived via spontaneous generation:
- It contains no actual evidence.
- It lacks any defined methodology.
- It lists no authors.
- It cannot legitimately claim to be a “guideline,” so instead it's labelled a “joint statement.”
The statement seems to be directed primarily towards the concept of splitting ventilators in a volume cycled mode (which, as described above, is indeed an idea that would not work). As such, the statement is already obsolete. Based on the work done by the Belgian team & the Columbia protocol, many of the concerns listed in the joint statement are now demonstrably incorrect. Some examples include the following:
#1) Joint statement says: “Attempting to ventilate multiple patients would likely require arranging the patients in a spokelike fashion around the ventilator as a central hub… Spacing the patients farther apart would likely result in hypercarbia.”
- One of the concerns commonly raised with split ventilation is that the tubing would increase the amount of dead space. However, one-way valves could prevent patients from re-breathing exhaled gas. With the use of one-way valves, it shouldn’t matter how long the tubes are between the patient and the ventilator.
#2) Joint statement says: “Spontaneously breathing by a single patient sensed by the ventilator would set the respiratory frequency for all the other patients.”
- Any sane approach to split ventilation would be designed to avoid this. This could be managed by “locking out” the ventilator trigger (reducing trigger sensitivity so that patients would not trigger the ventilator – effectively achieving a controlled mandatory ventilation mode). Additionally, patients would need to be rendered passive on the ventilator (either using paralytic or high-dose respirolytic sedation).
#3) Joint statement says: “Patients may also share gas between circuits in the absence of one-way valves”
- Yep, that’s why modern protocols for doing this involve one-way valves.
#4) Joint statement says: “Volumes would go to the most compliant lung segments.”
- Yep, that’s why you need to set the ventilator in a pressure cycled mode.
#5) Joint statement says: “Positive end-expiratory pressure, which is of critical importance in these patients, would be impossible to manage.”
- There is some truth to this, but not necessarily much. Patients with obstructive lung disease could develop AutoPEEP – and this couldn’t be managed on an individual basis. However, most patients with COVID don’t have airway obstruction and don’t develop AutoPEEP.
#6) Joint statement says: “Alarm monitoring and management would not be feasible.”
- Again, a bit of truth here, but this is an overstatement. Please see the Columbia Protocol part G on how to set ventilator alarms. This isn’t perfect, but it’s not flying blind.
#7) Joint statement says that in the event of a cardiac arrest, if a patient were disconnected from the ventilator this “would alter breath delivery dynamics to all of the other patients.”
- Not in a pressure-cycled mode. As long as the tubing to the patient was clamped, ventilation of other patients attached to the ventilator wouldn’t be changed.
#8) Joint statement says “The greatest risks occur with sudden deterioration of a single patient (e.g. pneumothorax, kinked endotracheal tube), with the balance of ventilation distributed to the other patients.”
- Again, this problem exists only with a volume-cycled mode. Using a pressure-cycled mode, if one patient deteriorated that wouldn’t affect the other patients attached to the ventilator.
So, overall, the Joint Statement is a laundry list of reasons why split ventilation could be dangerous if done poorly. However, there are solutions to many of these problems. It doesn’t appear that the authors of the statement anticipated the ingenuity of the teams in Belgium and Columbia at avoiding these issues.
The safety and efficacy of split ventilation remains an intensely controversial issue. Further evidence is required to answer this, possibly in the form of outcomes from actual case series at various hospitals. At this point, it is premature for anyone to claim to know the answer with certainty.
In this context, the Joint Statement represents a classic over-reach by professional societies which seek to infantilize front-line clinicians. The statement might be right, but it might also be disastrously wrong. In the absence of any solid evidence, this opinion statement writ large does little more than stymie innovation and expose well-intentioned physicians to excess liability.
more on split ventilation
- Splitting ventilators (PulmCrit)
- Columbia Presbyterian protocol for splitting ventilators here.
- More advanced and granular exploration about how to hook everything up here.
- Alternatives to vent splitting and the safest vent splitting methods in COVID-19 (EMCrit RACC with Scott Weingart and Marco Garrone.
- Should we put multiple COVID-19 patients on a single ventilator? Jack Iwashyna on LITFL
Opening image from YouTube video of Buddy Breathing.
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