Commit f52b9179 authored by Zach Fredin's avatar Zach Fredin
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added background documentation

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# Negative Pressure Covid Box
An isolation tent/box that prevents aerosols from spreading beyond the patient's immediate area. Allows caregivers to use currently-prohibited respiratory aides, such as CPAP/BiPAP/nebulizers.
This to-be-better-named project is an isolation box that prevents aerosols from spreading beyond the patient's immediate area. It allows caregivers to use currently-prohibited respiratory aides, such as CPAP, BiPAP, and nebulizers. This rough CAD render shows the general idea:
The box covers the patient from the torso up so they can be covered while prone or sitting up. The circular port at the back is connected to a HEPA filter and a blower inlet, while the cutout at the front has a flexible skirt to provide a reasonable seal.
## status
Early development/exploration.
## need
As discussed in an [issue I posted]( in mid-April, covid-19 has dramatically curtailed the support toolkit available to respiratory specialists. To recap:
>Briefly, hospitals have updated protocols to essentially ban these common respiratory interventions on any patient that presents with COVID-19 symptoms to avoid putting hospital staff at risk. Eric said that currently ~10% of these patients end up testing positive; the remaining 90% are thus being deprived critical treatment for COPD, congestive heart failure, and many other ailments. He believes in the short and long-term such a design could be a game-changer, since it frees up PPE, reduces caregiver risk, and opens up mid-range treatment options prior to pushing doctors to rely on invasive ventilation.
In short, a system that makes BiPAP, CPAP, and nebulizers viable again has great deal of leverage:
- reduced pressure on dwindling ventilator stockpiles
- better patient outcomes through less-invasive interventions
- less need for PPE during non-physical patient interactions
- improved caregiver safety due to reduced aerosol contamination risk
## plans
While it is tempting to simply bolt a blower onto our [Covid Isolation Box](, one must remember the ubiquitous warning sticker present on most fume hoods:
In order to scavenge hazardous vapors, fume hoods need laminar flow and adequate velocity; the aforementioned sticker reminds users that raising the sash above a marked point disrupts airflow enough to prevent the system from functioning properly. Similarly, we must understand the airflow in our system and design the exhaust mechanism accordingly if we want it to protect caregivers. As such, we are starting with simulation using Dassault's [Simulia platform](, building on their work simulating sneezing, coughing, and breathing for our mask and face shield design efforts. The simulation results will feed into [blower sizing and selection](, at which point we will build our first physical prototype.
Due to the inherent uncertainty in sealing around the perimeter of the box, it is likely that we will need to implement some kind of active blower control to maintain sufficient aerosol scavenging. Since the exhaust will pass through a safety-critical filter, we should also monitor filter performance online and alert caregivers when replacement is needed. In both cases, we will likely instrument the box with low-cost PCB-mounted differential pressure sensors such as [these models]( from Amphenol (~$30 each single-lot from Digi-Key and in stock). Again, simulation results should point us to the needed pressure differential range we need to maintain to produce good flow conditions, eliminating the need for airflow sensors.
## other efforts
Harvard's GSD is working on a [similar concept]( a disposable folded box and a negative pressure system to reduce aerosol risk.
A public group called PreVent (link to be added), based out of Cleveland, is also working on a similar effort. They plan to extend the concept to a portable isolation hood for ambulatory patients.
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