I've received several questions on twitter about this. There are a variety of ways to do it, depending on available materials…
(1) Filter attached directly to the mask
The simplest way to achieve this is to attach the filter directly to the mask, as shown below.
This should work well – provided that the filter and mask are adaptable to one another.
https://twitter.com/doctormromeo/status/1245158922467577856
(2) Two-limb closed system with a full-featured mechanical ventilator
This involves attaching the BiPAP mask to a traditional mechanical ventilator (with both inflow and outflow tubing). Filters are placed on both the inflow and outflow limbs, generating a completely closed system.
The advantage is that this generates a 100% closed system (assuming no mask leak, of course).
The disadvantage of this approach is that it involves using a full-featured mechanical ventilator to perform CPAP or BiPAP. Since the ventilator isn't designed for this purpose, it may have inferior leak compensation and trigger sensitivity, when compared to a dedicated BiPAP unit (e.g. a Respironics V60 units).
(3) One-limb system with a specialized noninvasive machine (e.g. Respironics V60)
This involves the following:
- BiPAP mask is connected to a specialized noninvasive machine.
- One viral filter is attached to the inflow limb.
- A second viral filter is attached to the exhaust port, as shown below:
Here's a similar setup (image from tweet by Armstrong Medical).
Advantages:
- A dedicated noninvasive machine (e.g. Respironics V60) may have superior triggering capacity and leak compensation, compared to a traditional mechanical ventilator.
- Using a V60 for non-intubated patients will free up a full-featured ventilators for use with intubated patients.
Disadvantages:
- Some BiPAP devices do have a built-in one-way valve (example below). This is designed to allow air into the tubing if there is negative pressure. This valve is intended to prevent the patient from asphyxiating in the event of catastrophic device failure (e.g. if the BiPAP machine stopped functioning or the tubing became occluded).
- So this isn't a 100% closed system. However, as long as the BiPAP machine is working, there should be positive pressure within the tubing – so this one-way valve should remain closed.
And make sure you're using the right filters!
- Not everything that looks like a viral filter is a viral filter (heat and moister exchangers shouldn't be confused with viral filters).
related…
- Webinar by Weingart on avoiding intubation.
- Section in IBCC COVID chapter on noninvasive ventilation.
How long do filters function if you have to use a humidifier ie delivery through a tracheotomy
This is how I have set up the disposable CPAP and BILevel masks here. Down side is that My clinical directors boss, said NO WAY because, she believes that the filters don’t work to stop exhalation aerosolization. I have tried showing them evidence. But I don’t seem to have enough puppets and crayons. I don’t know how to add a pic of my rig’s here. We don’t have ventilators, and now we don’t have CPAP. So, for now I teach my Doc’s how to get a bit of CPAP with the BVM. That, I can at least do for now.
Nurses aren’t putting people on CPAP or BIPAP because they are not closed systems so they are afraid to get the virus. This might make them less afraid to do the right thing. See https://youtu.be/mUWwsHY2wss
Pretty much all CPAP/BiPAP masks have exhalation ports which is why they are an aersolization risk (not just from mask leak). For any of these interfaces you generally have to use a well fit anesthesia mask and have some other expiratory valve (a dual limbed circuit or a whisper swivel) to avoid this problem and appropriately filter exhaled gas.
disagree, in some cases you can put a filter on the exhalation port
I’m wondering how you attach the filter to the exhalation port.
What is the purpose of the viral filter on the inflow limb? At least with CPAP, I would expect that the constant positive pressure would prevent exhalation from travelling to the machine. Is this precaution BiPAP specific?
It is meant to be used as a “debris” filter….to stop any material that may be sent in to the inspiratory circuit. there is wear and tear on the NIV just like any other machine, its meant to stop it from reaching the patients airway.
We use the filter on the Whisper Valve, this creates a closed system as long as the patient can tolerate the mask. Has anyone transported on Bipap? Looking for suggestions ,input on how it is being done
Yes
Bacteria filter at machine as well as BEFORE exhalation port on circuit.