Flu Pandemic - a doctors point of view

[wacki]

If the strain acquires better human-to-human transmission, we are in for some tough times. Conservative worst-case puts the kill rate at 2% in the U.S. Both young and old will die.

There are about 25,000 ventilators in the U.S. but up to a million people would require ventilation, and several hundred thousand certainly would in an almost-worst-case scenario.

The very first major public health step should be to close all schools and day cares to prevent sick children from interacting with the healthy. This is the best method of preventing the spread of a flu epidemic. There is no mechanism to do this in place and politicians will likely delay. The decision, for the most part, relies on state governments.

If schools close, nurses will end up in short supply due to the lack of daycare for their children. The capacity of health centers will be affected.

Even at full capacity, the health care system cannot handle a major pandemic. Thousands would simply not get seen, even people who are dying.

This is a very real threat although it's probability is low.

With virulent strains adults can drown in their own fluids, essentially the lungs fill with reactive inflammation. One of the biggest life saving tools in a situation like this would be a respirator. If someone is infected with a virulent strain they could require respiration for 24 hours a day for a week. With possibly millions requiring respiration when there are only 25,000 respirators this could be a real problem.

Due to trial lawyers, the FDA, and general politics, low cost emergency respirators will not become a reality or will atleast not be released in time. The good news is homemade respirators may not be that difficult to make and I believe I can make one from an ambu bag and parts found at a home depo.

This is the summary of a conversation I've had w/ a few doctors.

I've been asked by some doctor friends if this situation occurs to post plans on the Internet. Well an ounce of prevention is worth a pound of cure.

My personal plans would be to attach a rheostat controlled motor to a crankshaft of sorts (aka a wheel with a an attachment point for a rod on the perimeter) that pushed a piston (the rod connected to the wheel) up and down. The piston would compress and depress a normal hospital ambu bag. The ambu bag would be altered by having a tube connecting the bag and mouth piece for relatively remote use. Talking about it and getting it done are 2 completely different scenerios though.

It would be cheap, ~ $100, use readily available parts, and easy to make. Just my thoughts but if anyone else here has better ideas I'm all up for hearing about them.

 

[soccerballtux]

Can you explain the need for a respirator? I have no idea why they would need an "acne iron lung" or whatever.

Also, if my lungs fill with fluid, why not just have my friend hold my feet up against the wall while I cough up into a bowl or on the floor?


One other thing.....I know its just the young and old affected, but due to some odd physical property of my body (terrible circulation?) It takes me forever to get over a cold. For instance I got sick last friday and still have a sore throat. Granted I haven't gotten much sleep (such is the nature of college life) but I don't think that would affect my sickness that much. So my question is, would I be more likely to be one to die, simply because of my circulation issues? Or is that even a problem? Or what would be keeping me from getting over my cold? My metabolism is fine (I eat whatever I want [but do eat healthily, just extra crappy stuff on top ] and have not been gaining weight), so wtf?

Could it be some healing mechanism that goes slowly in my body? I'm thinking that whatever it is that is causing the slow recovery would be something that could closen my encounter with death.

 

[Mark R]

In case of severe lung disease, e.g. pneumonia, viral infection, then the natural response of the body is to breath harder. Normally, supplemental oxygen would be all that's needed to get enough oxygen into the body. However, if things get very severe, then the body becomes unable to keep up the effort of breathing even with supplemental oxygen - the muscles get tired (you're doing heavy exercise, while unwell with fever and dehydration) and once that point is reached, death follows very quickly.

The idea of a ventilator is to do some of the work of breathing - so more oxygen can get into the lungs and therefore the blood. So, if someone with a lung problem is beginning to tire, they need some sort of mechanical help.

The fluid that builds up in the lungs can be of 2 types:
Inflammatory fluid: In pneumonia (which may occur with influenza) it can be a thick gunge, essentially like the pus you get in an infection elsewhere. Imagine the minute 0.1mm little air sacs in your lungs filled with the thickest nastiest green phlegm you had when you had bronchitis.
Fluid: In some cases of lung injury, you can get 'pulmonary oedema' which is where excessive fluid from the blood leaks into the lungs. Because of water's surface tension it coats the entire surface of the air sacs. This coating prevents oxygen getting in, but it so thin that it remains stuck to the inside of the lungs - like water remains stuck to the inside of a sponge.

There are a number of methods of providing assisted respiration, but there is one way that is extremely simple (although not as effective as the more complex methods). This is a technique called 'continuous positive airways pressure' or CPAP. And it's name describes it exactly.

Essentially, you provide oxygen to the lungs at very slightly higher pressure (about 0.5 kPa) than the air in the room. You make sure that the slightly higher pressure is maintained all the way through inhalation and exhalation. This same technique is used with lower pressures and air (instead of oxygen) to treat sleep apnoea (in the case of sleep apnoea, it's intended to stop the throat from collapsing, rather than do anything with the lungs).

The more astute people would probably think that CPAP does precisiely nothing - what is a constant pressure going to do? Well, the answer lies in the lungs. The high pressure blows up the air sacs in the lungs like balloons - so diseased ones, which may have collapsed completely, can partially inflate and start moving oxygen. The high pressure can also push the fluid that leaked into the air sacs, back through the leaks, back into the blood (essentially, reverse osmosis). Finally, the increased diameter of the air sacs reduces the overall stiffness of the lungs, so they are easier to inflate/deflate (due to Laplace's law).

The problem with CPAP (and other forms of assisted ventilation) is that the high pressure isn't all good. It can disturb blood flow through the lungs, and reduce the blood flow to the heart. It can be uncomfortable (it needs a tightly fitting mask strapped to the face, and a gale force wind of oxygen coming through it). More seriously, diseased lungs are fragile, and can be punctured by the high pressure air. While a punctured lung is a not particularly good at any time, with assisted ventialtion it is an absolute disaster, unless it is immediately recognised. (This is the major reason why the pressures have to be adequately controlled).

Because of the very high oxygen flow required (you have to be able to keep the pressure up during inspiration which can be 40 litres/min), you need:

a) A humidifier and warmer. Pumping such a large volume of dry gas past face and nose can cause skin injury, and pumping large volumes of dry gas through the lungs will cause dehydration and massive heat loss due to evaporation. It will also need to be warmed to reduce heat loss from the face and to improve comfort.

b) Careful pressure control - You need enough pressure to be useful, but not so much that you cause injury. It should be adjustable so that it can be adjusted to suit. There needs to be a failsafe pressure relief valve. Ideally, you should have a pressure guage so you know what's actually being delivered.

c) A compressor that won't spontaneuosly combust when compressing pure oxygen, but which can maintain the necessary flow rates/pressures, and never be able to generate a harmful pressure (2 kPa or greater). (If you have your oxygen at pressure, you won't need this)

d) Some way of ensuring that the humidifier remains sterile. Nice warm fluids are excellent breeding grounds for nasty bugs, as are injured lungs.

e) A very large oxygen source - the only practical way I can see of obtaining pressure control is to use a spring controlled pressure relief valve which opens into the general air. This means your source needs to be able to supply 40 l/min constantly, and the relief valve needs to be able to discharge the whole 40 l/min to the room air.

If you want a device that has seperate inspiration/expiration phases, then that gets complicated.

 

[Eeezee]

There are only 25,000 respirators???

 

[Mark R]

There are only 25,000 respirators???

The demand for fully featured automatic ventilators is not high. Most hospitals will only have a few (maybe 5 in a 'normal' sized hospital). They are only needed for the sickest of sick patients. They require the a breathing tube to be inserted (very uncomfortable, so requires heavy sedation +/- paralysis with a muscle relaxant drug), and such patients require 24-hour 1 to 1 nursing (sometimes 1 patient to 2 24-hour nurses).

Artifical ventilation is not simply a matter of pushing air into the lungs and letting it out again. It requires careful pressure control, careful volume control, sensing of the patient's own breathing (so the ventilator doesn't attempt to push a breath in, when the lungs are already full), etc.

It's one thing to buy a ventilator. It's another entirely to pay for the skilled 24-hour staff to operate and supervise it.

 

[DrPizza]

Wow, from all the doctor's and nurse's points of view that I've listened to (wife is a nurse, I spend a lot of time in the hospital while waiting for her shift to end) is that the media is going to great lengths to sensationalize the avian flu story. They're blowing it way out of proportion, and getting people unnecessarily worried.

 

[bendixG15]

The last flu killer was in 1918 when an estimated 40 million people died worlwide.

Here's a quick read.....http://www.stanford.edu/group/virus/uda/