POD: a Bay Treatment Concept
COVID-19 exposed a sudden and unexpected patient management crisis for those working in ESRD facilities. Whenever possible, we attempt to avoid management crisis and instead, practice crisis management, which under the circumstances of the situation during the virus SARS-CoV2 (COVID-19) in the U.S. was actually handled fairly well. But the challenges that had to be addressed exposed some very substantive shortcomings of the facilities where kidney dialysis is delivered.
As data starts to become more vigorous, we are starting to see interesting facts that suggest that less than 10% of the transmission is from fomite (touching objects and transmitting to our mouth, nose or eyes). That means over 90% is by air transmission if data continues along the course. We know people are getting infected in their homes. This happens when a household member drags the infection back to the house enclosure and sustained contact with the virus increases the dosage to the point of infection. Like the house, other enclosed spaces with concentrations of people have surfaced as places of concern for high transmission. Transmission from outdoor activities where close and high concentrations of people ARE NOT apparent have proven relatively benign, with much lower probabilities of exposure to infection. Of course, in these types of outdoor situations the probability of gaining high dosages of infection is much lower.
In order to get infected by a virus there is typically some viral load that must happen, however in the case of COVID-19 the dosage is not yet determined. This is a real technical threshold that needs to be established, but in theory, we can already determine some practices that might be beneficial within ESRD facilities, where we have dense concentration of highly susceptible individuals. We know that even the act of breathing has the potential of releasing some dose of virus. Sneezing and coughing throws higher doses of aerosols creating a variation of sustained distance and time. Most extensive data has been done with influenza viruses. The National Institute of Health has a number of studies each pointing to some basic facts. In these studies, they know some virus aerosols stay in the air for a period of time, some fall to a surface, and some to the ground. How long the virus stays active is dependent on where it is, where it lands, or even how quickly it evaporates. Published data have suggested that sneezing may produce as many as 40,000 droplets between 0.5–12 μm in diameter (1)(2) that may be expelled at speeds up to 100 meters/second (1).
Patients lying in bed, breathing or sleeping, may produce exhaled airflow that can reach the airspace of a patient in the neighboring bed, and even farther in the presence of certain types of ventilation systems (3). Unavoidable air movement into neighboring airspace may occur during the most innocuous daily activities, such as walking, or even arm movement. We know a door opening creates eddy currents of air which is another example of the issue. Moving a cubical curtain could create incredible particulate turbulence. The extent to which these currents can be understood and mitigated is a benefit to diminishing aerosol movement. We know the ESRD facility needs and requires direct observation of the patient at the treatment headwall. To accomplish this, open treatment floors have been the preference for some time. The challenges with these situations have been obvious during the COVID-19 crisis. Realizing the importance of the direct observation cannot be diminished, we must look at contributing factors that might influence future treatment floor designs.
This issue lies with air filtration or other air treatment remedies where they disinfect air at the source of distribution, but after that interaction the air is free to circulate and attract articulate whenever it is exposed. There are many filtration or disinfection means that can be and should be considered for the air stream where healthcare interactions are to occur. This is not an inexpensive solution, nor does it really address the open treatment floor typically utilized in ESRD, or for that matter many PACU recovery bays, infusion therapies, physical therapies and other large room treatment areas. Filtering particulate via HEPA filtration or basic UV coil cleaning device that is added to many air handling units cleanse at the source.
In this conceptual diagram we see a typical air filter flowing along three station locations – the lower diagram illustrates a normal condition were infection aerosols are not a challenge – the upper diagram shows the center station having infectious exhalations and eventually loading the three station with infectious load – notice the air filter again at the supply end of the air.
There is probably no silver bullet at this juncture for a reasonable solution to the open bay treatment floor. However, there are some basic concepts that can be considered to tamp down the challenging impacts realized during COVID-19, if operational adjustments can be accommodating. Currently it is not uncommon to see eighteen to thirty patients in a single treatment room. If each of the persons diagrammed above represented nine patients, one can easily see the illustration showing a potential for ten to eighteen patients being directly impacted by airflow in a negative manner just by the direct flow of air.
Now imagine the treatment floor split into three 9-person compartments.
In this conceptual diagram each person represents three patient stations. By considering a POD concept we are able to limit direct systemic exposure to one to six persons in the situation illustrated.
What has the modification done? From a patient care point of view we now have to look at small nursing teams. You may be able to keep the same staffing ratios, but the training of the team would likely be much different. The support rooms may be able to stay the same distribution if adjacency is carefully addressed. By having the small areas, each being served with individual POD clean air, managing the development of a disease can be easier to stage. In the instance illustrated the center POD would be designated an infectious POD and non-infected patients would be removed from the POD. This certainly increases the HVAC cost of the facility which must be taken into account. Certainly, fomite transmission at places like the toilet rooms will not be assisted by this configuration concept.
Addressing indeterminable eddy currents within each POD is a matter of limiting cross circulation, the number of door swings, and other disruptive movements of air. This cannot be totally eliminated. Much of mitigating this has to do with proper staff training. In laboratories we know not to locate laminar flow hoods in direct circulation pathways but in an open treatment floor. The issues are not so simplified as a considerable amount of additional traffic can be anticipated. Still, careful consideration of how nurse stations are placed, and where clean areas and soiled area are placed can have a significant impact.
We have not addressed the small environment and virus transmission, as might be the case in bathrooms. This becomes a much different concern which should be addressed separately. As for the large treatment areas, maybe some discussion would be valuable about going to nine to 12-person POD configurations. Expressing this to persons who have been on the front lines may enable them to offer other features to improve how we are able to handle future concerns of this type.
(1) Cole EC, Cook CE. Characterization of infectious aerosols in health care facilities: an aid to effective engineering controls and preventive strategies. American Journal of Infection Control. 1998;26(4):453–464.
(2) Tang JW, et al. Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises. Journal of Hospital Infection. 2006;64(2):100–114.
(3) Qian H, et al. Dispersion of exhaled droplet nuclei in a two-bed hospital ward with three different ventilation systems. Indoor Air. 2006;16(2):111–128.