Oxygen does harm ?

[Ridryder 911]

thought this spark some debate...

Studies Trials Abstracts

Giving oxygen may do more harm than good, new report shows

By

Jul 11, 2005, 12:13

Courtesy the EMS House of DeFrance http://www.defrance.org

Doctors and paramedics who give their patients oxygen – the most commonly administered "drug" in the world – may be doing more harm than good, a Queen's University researcher contends.

And although there's a simple solution – adding carbon dioxide to the mix – it isn't being used by most Canadian hospitals and emergency services networks, says Dr. Steve Iscoe, a respiratory physiologist. This has implications for treating a number of serious health conditions, including heart disease, stroke, diabetes, difficult labour and delivery, and wound healing.

Dr. Iscoe's commentary, based on his own and other researchers' findings, is published in the July issue of CHEST, the Cardiopulmonary and Critical Care Journal. Co-author of the article is Dr. Joseph Fisher, from the Toronto General Hospital's Department of Anesthesia.

"Pure oxygen can reduce blood flow to organs and tissues by increasing ventilation," Dr. Iscoe explains. "The increase in ventilation, which is almost never considered, 'blows off' carbon dioxide, and this fall constricts blood vessels. When carbon dioxide is added, however, the blood vessels dilate, increasing blood flow and causing more oxygen to reach tissues in key areas like the brain and heart."

Researchers in the early 1900s observed that breathing pure oxygen increased ventilation and lowered carbon dioxide levels. Based on their observations, several tried adding carbon dioxide and claimed success in resuscitating people and infants and treating carbon monoxide poisoning.

But the practice of using expired air – even before it was known to contain carbon dioxide – dates back much further. The use of mouth-to-mouth resuscitation on infants was recorded in a 1754 book by Benjamin Pugh, A Treatise of Midwifery, and there are biblical references to the custom. Yet modern medical texts do not mention that inhalation of oxygen decreases carbon dioxide levels and the effects on blood flow; consequently it is not part of standard practice.

"It's puzzling that a simple idea like this has received so little attention from clinicians," says Dr. Iscoe. Although there has been some concern about the possibility of patients receiving too much carbon dioxide (which can cause discomfort), he points out that new designs for oxygen masks allow precise monitoring of levels delivered or, in fail-safe mode, prevent inhalation of carbon dioxide. One can even use the patient's own expired carbon dioxide, the researcher adds.

"The reduction in oxygen delivery to the fetus, the brain, the heart, and other body tissues that might be induced by oxygen administration is, as this paper points out, largely unrecognized even by respirologists such as myself," says Dr. Peter Macklem, professor emeritus of medicine at McGill University and 1999 recipient of the prestigious Gairdner Foundation Wightman Award for outstanding leadership in medicine and medical science.

"If we respirologists are unaware, then internists, surgeons, obstetricians, pediatricians and family physicians who are at the front line of treatment for most of the clinical conditions they describe are unlikely to be better informed," Dr. Macklem continues. "The magnitude of the risk now needs to be quantified by appropriate clinical trials. While it will take a few years before we will know for sure, the wisest course of action in the interim is to administer low concentrations of carbon dioxide along with oxygen therapy."

Among the areas where Drs. Iscoe and Fisher see particular benefits for patients from improved oxygen delivery are:

heart attack;

stroke;

carbon monoxide poisoning;

wound healing in hospitals, where drug-resistant infections are on the rise;

cerebral blood flow to fetuses during difficult birth procedures; and

treating foot ulcers and gangrene in people with type 2 diabetes.

Dr. Iscoe hopes to evaluate the promise of the new technique in a study of diabetic patients. As the incidence of obesity rises, diabetes is expected to affect a growing number of people and exert increasing demands on the health care system.

"I think it's incumbent on health professionals to consider carbon dioxide when administering oxygen, since we know that carbon dioxide levels control blood flow to so many parts of the body," Dr. Iscoe says. "We should look at carbon dioxide not as an enemy, but as an ally."

###

Funding for Dr. Iscoe's research comes from the Canadian Institutes for Health Research, the Canadian Lung Association and Ontario Thoracic Society, and from the Wm. M. Spear Foundation and the R.K. Start Memorial Fund.

First of all, Dr. there has been masks invented before you were probably a physician called venturi.. that allowed ambient room air to mix. Also do you really ever get "pure" oxygen if with non-rebreather mask, that mixes C02 .. hmm, never seen that study either. Also they do have oxygen therapy for diabetic ulceration using oxygen... it's called hyperbaric chambers (HBO) duh... Looks like another scientist spending Canada's $$$ to make a name for himself...

without really investigating products used or out there. Where are we getting these so-called scientist ?

Be safe,

Ridrder 911

[Summit]

"In conclusion, no more BVM, but 15L via pocket mask so you can give them CO2!!!!!" :wink:

[emt_hound]

Interesting...

Does anyone know how much CO2 a person gets on 15L O2 via NRB? I'm assuming its a negligible amount (since its a "non-rebreather") but I wonder if a Pt gets any at all.

[Margaret]

I guess that will fall into the category with all the "we all know the same thing but lets see how much it takes to say the same thing over and over again . "

I am sure if someone gave me thousands of dollars i could tell you why every nursing home should do away with the beds that crank and if you give me more then that ill try to find out why the fattest most biggest people are in them .

There are so many points about just about every topic , I don't think there will ever be a "right way" to be able to get the good and bad out of one thing we need to learn how to balance .

[Summit]

Probably not much since ambient CO2 is negligable (atmospheric ppCO2 0.27mmHg @ STP, ie inhaled RA). The pressure gradient of atmospheric ppCO2 is physiologically hardly different from a ppCO2 of zero, right?

ppCO2 in exhaled breaths is usually around 30mmHg.

[Ridryder 911]

I am sure Steven, will be able to fill in the guess work on this one...

Ridryder 911

[THE_DITCH_DOCTOR]

OK....time for respiratory physiology 101:

Normal PaCO2 (and ETCO2 which correlates with PaCO2) is 35-45 mm Hg (you don't want to go below 30 in a head trauma or stroke victim (i.e. someone with signs of increased ICP or other intracranial pathology) for the very reason discussed in the article, but this guy is taking it a bit too far (although the author of the article is partly to blame).

Normally a NRB at 15 L/min will deliver a fraction of inspired O2 (FiO2) of ~60-80%. The exact amount depends on how well the mask fits the face and the also varies with the patient's minute ventilation- at excessively high minute ventilations tend to get lower FiO2 while on masks because they will entrain outside air in an effort to pull in as much air as they need (remember an adult male is capable of moving >120 liters of air per minute at maximal effort under extreme circumstances). 100% by NRB is a pipe dream in 99.9% of cases.

As a reminder, you can get a rough idea of the FiO2 by using the following formula:

FiO2 = 0.21 + (4 x Oxygen flow rate in LPM)

FYI 0.21 is 21% (the amount of O2 in our atmosphere)

[buddha]

An interesting perspective, to say the least. Makes you think about the simple stuff. With respiratory failure, we are finding that the true measure of success in treatment lies not in how much oxygen you can load into a patient but in how well you can regulate CO2 levels - oximetry vs. capnography.

[Guest]

Hmmm, just for clarification ... NRBs are suppose to deliver a FiO2 of 80 - 95% I thought?

Simple face masks 60% - 80%?

Nasal Cannula 24% to 44%?

What's with the 60 - 80% for NRBs Steve?

All of the above dependent on liter flow ...

Zach

[THE_DITCH_DOCTOR]

No, it's all a matter of mask seal, minute ventilation and a myriad other issues.

According to most textbooks, a nasal cannula SHOULD deliver approximately:

1- 24%

2L- 28%

3L- 32%

4L- 36%

5L- 40%

6L- 44%

Now what they fail to mention is that these are:

a. Rough estimates

b. based upon healthy volunteers with normal RR, minute ventilation and tidal volumes

c. based upon people with no nasal anatomical malformations (septal deviations, etc), no obstruction to flow (stuffy nose being an example)

The following factors affect FiO2 in a low flow system (such as a nasal cannula)

Increase FiO2

Higher O2 input (increase O2 flow)

Closed mouth breathing/pt not talking

Low inspiratory flow (slow inhalations)

Low tidal volume

Slow respiratory rate

Low minute ventilation

High I:E ratio (longer inhalation than exhalation)

Decreases FiO2

Lower O2 input (decrease O2 flow)

Mouth open breathing/pt talking

Higher inspiratory flow (rapid inhalation)

Larger tidal volume

Higher minute ventilation

Fast respiratory rate

Short inspiratory time

High I:E ratio

(Taken from Table 34-4, Page 748, Egan's Fundamentals of Respiratory Care)

Basically the point is that most O2 delivery systems (with notable exceptions being correct ventilation with a BVM, or via a CPAP mask, or via an ET tube) do not approach high concentrations- or even reliably produce the stated FiO2's at the level of the alveoli.