Giving oxygen may do more harm than good

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."