Saturday, April 12, 2008

Why There is a Need for the Pandemic Ventilator

The World Health Organization, (WHO) is concerned that the H5N1 strain currently circulating in birds, may mutate so that it may readily infect and spread in humans. The current WHO pandemic status is level 3, which is a pandemic alert.

Pandemics vary widely in severity. Some mild pandemics do not cause much more illness than the normal seasonal flu strains and can be handled by the existing medical care system with minimal problems. The flu pandemics of 1957-58 and 1968-69 were like this. Other pandemics were very severe and caused many deaths. The 1918 pandemic was very severe and caused more deaths than World War One did. It is estimated by some, that the 1918 Spanish Flu pandemic may have killed between 50 and 100 million people.

Pandemics occur because a virus mutates to a new form that the current living population has not been exposed to before. It has been 40 years since the last pandemic, and today most people in the world have never been exposed to a pandemic influenza strain. Many experts say it is not just a matter of “if” another pandemic occurs, but “when”. Because of the high lethality of the current H5N1 strain in birds and the humans it has infected, many health experts are concerned that if a pandemic arises from this strain, it may cause very serious illness in the people it affects and may cause many deaths.

Many of the deaths caused by pandemic (and seasonal) influenza are due to reduced lung function caused either directly by the influenza virus or by opportunistic pneumonia infections that result from additional secretions in the lungs and the flu’s effects on the persons immune response. The lung injury condition that results is called ARDS (Acute Respiratory Distress Syndrome). For seasonal influenza, most deaths are in the very old or very young. Pandemic influenza causes many deaths in young adults. Medical treatment, including the use of a ventilator is the only way to save these young lives if they are afflicted with ARDS from pandemic influenza.

The WHO, the CDC, HHS and many other national and international health organizations take the threat of another pandemic in the future very seriously. They are actively monitoring the spread of H5N1 and doing every thing they able to minimize the chance that it will infect human populations. There is also research ongoing into developing vaccines for any emerging pandemic influenza, and also stockpiling of antiviral medications that can be used to control and limit the spread of the virus if it starts spreading from human to human. Many governments also have plans to control people’s individual freedoms, alter standards of care, and impose tight controls on freedom of movement of the population in the event of a pandemic so as to reduce the number of deaths.

There are not enough ventilators available right now to treat the number of people that will develop ARDS in a moderate or severe pandemic. Many people will die from pandemic flu that could have been saved if they had access to medical treatment with a ventilator. In the US, there are about 105,000 ventilators in hospitals. Of that number, only about 20,000 or less are available and not being used at any given time. There are also a number of ventilators in strategic stockpiles and there may be other ventilators that can be diverted from anesthesia machines. No one has done a strict inventory of availability, but these numbers suggest that there could be 30,000 to 40,000 ventilators made available from this existing stock for use in a pandemic. It is very difficult to know exactly how many ventilators will be required ahead of time. This depends on how many people get the pandemic influenza and also how severe the resulting illness is. Estimates for the number of people needing a ventilator for a moderate pandemic range from 100,000 to 200,000. Estimates for a severe pandemic range upwards of 700,000. Most pandemic plans acknowledge that a shortfall will occur, and will use triage protocols to ration the available ventilators.

Triage means that someone will determine who gets the opportunity to survive by getting one of the few available ventilators. Everyone needing a ventilator, whether he or she has pandemic flu or another condition will be assessed using a Sequential Organ Failure Assessment (SOFA) score. People who are very sick and are judged to have a lower chance of survival will be refused a ventilator. As the need increases, this threshold will be lowered. Many people who could have survived will then be refused a ventilator as well. Most triage plans do not discriminate based on age, so many of the deaths will be young people. It will not be possible to purchase enough commercially made ventilators during a pandemic to alleviate this crisis once it begins.

The Pandemic Ventilator is a design for a ventilator that can be constructed from readily available materials even after a pandemic begins. The design will try to have as many alarms and required features as is feasible. The idea of the public building homemade ventilators in the face of a shortfall to augment existing supplies is not without precedent. Home built ventilators were used to save lives in the 1940s and 1950s during the polio epidemic. Popular Mechanics even published plans for one in 1952. (See my other posting on this.) Using modern computerized control systems, we can build much more capable devices than they did.

2 comments:

Anonymous said...

While there may be a need for additional ventilators during a severe influenza pandemic, some of ur numbers are a bit misleading (although I doubt intentionally).

1) ~ 70,000 full feature US vents...the 105K number has not been able to be verified.

2) The utilization rate of devices is not as high as everyone reports. It is likely 40-55% on avg and a bi higher during winter. There has not been any reported data otherwise. Hence there are likely about 25-30K vents not being attached to pts on a given day. The problem is that patients and vents distribution will be uneven during any event and it is not logisitically easy to move pts or vents throghout large regions or the entire country.

3) While a total of ~750K of additional pts in te US may require mech vent during pandemic severity index 5 (like 1918-1919) this does not mean we require 750K additional vents. This is a cumulative number and not a concurrent number. The actual peak demand has been estimated at about 1/10 of 750K, but again recall these are all predictions based on many assumptions and from data before modern critical care was being practiced. Also the impact of antivirals, less perfectly atched vaccine, social distancing etc on peak ventilator demand are not known and only best guess predcitions with unclear accuracy are available.

Anonymous said...

We really don't know how many ventilators may be needed. The numbers are more guestimates than estimates. You MIGHT be right but you MIGHT be wrong - and you get triaged to death. Right now, the virus is using migratory birds as an air transport network, making connecting flights as multiple species of birds use the same summer, winter, or "refuelling" airbase. For example, Canada geese use Alaska as a summer airbase but some use Russia and others use North America as winter airbases.

Plus, the virus reproduces while making connecting flights - unlike an airline passenger. So, it spreads. After several years from discovery, it's got to be all over, increasing the danger of mutation to a human to human form. If it has the right incubation time, H5N1 can then use OUR air transportation system, spreading at 500mph with minutes between connecting flights instead of weeks with the avian transportation network.

The virus is racking up the frequent flier miles! Working at an airport, I realised this with the "avian transport network" a couple years before the scientists made the same thing public.

Result? We don't know when or where the jump will occur. They have a LOT of frequent flier miles.

If things get really bad, it can get REALLY bad, overloading a healthcare system designed to maximise utilisation of resources for the sake of the bottom line. There is little to no "excess capacity" to handle a huge surge of patients. The hospitals are too busy milking insurance companies and feeding CEOs and stockholders to have readiness for a pandemic that hasn't happened since polio.