Archive for the ‘Pulse Oximeter’ Category

Replace the PulseOx test for CHD!

September 30, 2010

Just a few weeks ago the Pulse Oximetry test (also known as PulseOx) became part of the Newborn Screening Uniform Panel. In a post on this blog, we discussed how the PulseOx was a good test, but not perfect.

But what if we could discard the PulseOx, in favor of a better test?

Hot off the press – really, it hasn’t even been printed yet, it was electronically published before a print version is available – is a study by the University Medical Center in the Netherlands. Appearing in the European Journal of Clinical Investigation is a study (CLICK HERE to read the abstract) showing that certain biological markers do show up more often in children with Congenital Heart Defects! In the study, higher concentrations of S-adenosylmethionine, S-adenosylhomocysteine, and folate RBC were observed in children with heart defects.

(Don’t ask me to explain all that; it’s DNA and Molecular Biology with a little Chemistry thrown in for good measure!)

Could this test replace PulseOx? Perhaps… but not tomorrow. The study was a relatively small study, with only 329 children participating. (143 CHDers with 186 heart healthy children as a control group) The researchers themselves even stress that more research needs to be done.  But we could very well be looking at the first steps to a foolproof, 100% accurate “GOTCHA!” test for heart defects. And by studying the DNA changes that occur with a CHD, we could unlock the secret to how heart defects occur… and stop them before they begin!

Special thanks to Amy Basken for bringing this research to my attention. Amy is tireless, working for several different CHD groups. Today she represents Mended Little Hearts!

The PulseOx test – not perfect, but good

September 21, 2010

If you have been reading Facebook or Twitter this past weekend, you’ve probably seen the news: The Health and Human Services’  Secretary’s Advisory Committee on Heritable Disorders in Newborns and Children (SACHDNC) voted to recommend pulse oximetry screening for critical congenital heart disease be added to the newborn screening uniform panel.

According to what I have read, the Health and Human Services Secretary now has 180 days in which to consider the recommendation and decide to either accept it or reject it. Historically the Secretary acts fairly quickly and usually accepts the recommendations given by her advisors, so the major hurdle could well have been cleared. It could only be a matter of time before the Pulse Oximetry becomes standard practice.

No PulseOx testing protocol exists yet. The official recommendation by the Health Resources and Services Administration addresses this issue, by stating “The Health Resources and Services Administration shall guide the development of screening standards…

This will delay the process – with no testing protocol, the recommendation can’t be accepted on a Tuesday and the program begin at 12:01 AM Wednesday. For the results to mean anything, a medical test must be administered in the exact same manner each and every time it is given. For example, I need to have some blood drawn this week. The nurse will apply a tourniquet to my arm, inset a needle into a vein in the crook of my elbow, and draw three vials of blood. Everyone else, no matter where they are, who has those tests done will go through the same process. Protocols are an essential part of medical testing. As this 2008 report notes, “Nursing staff received in-service training in the screening protocol and performed the pulse-oximetry procedure.”

In this study the type of  Oximeter is specified (under the heading “Methods”). This is also an important part of the protocol – perhaps not the exact same type of testing equipment, but a standard that must be met, and probably an agreed on calibration procedure. If you step on and off a manual scale enough times, the pointer will no longer return to zero… and your weight will be inaccurate until the scale is “zeroed out.” A pound or two won’t make much difference, but a point or two difference on a PulseOx reading could mean alarmed parents and unneccessary testing. A proper testing protocol would even specify a testing location, as studies have shown slightly lower PulseOx readings when the test is performed on the foot. Fussy or crying babies also produced lower saturation numbers.

Despite what you may have heard, the PulseOx test isn’t that accurate when performed on heart defects that do not cause Cyanosis. Cyanosis (medical term: Hypoxemia) comes from the root word Cyan, meaning “blue,” and is caused by low levels of oxygen in the blood. Cyanosis can be hard to detect, as the oxygen level has to drop below 90% before it begins to appear. Cyanosis will cause the lips, fingers, and toes to have a blueish tinge. (SEE THIS ILLUSTRATION) Non-Cyanotic (also known as “acyanotic”) Heart Defects account for 70% of all defects. When these defects are present, blood oxygenation (and therefore the PulseOx reading) is usually normal. In fact, the recommendation is only meant for CCCHDs, or Critical (sometimes the word Complex is used) Cyanotic Congenital Heart Defects.

While the Pulse Oximetry screening test is not the complete answer for detecting Congenital Heart Defects; it is certainly part of the answer – another piece of the puzzle; another arrow in our quiver. My idea – and I don’t know if it is just a pipe dream, or a discovery we haven’t made yet – is to find a “bulletproof” test that indicates the presence of a heart defect. Does a defective heart release a gene, an enzyme, or any kind of biomarker into the bloodstream?   If we could find that marker and learn how to detect it… Gotcha!

But until that day comes – if it ever comes – you throw everything but the kitchen sink into the fight.

She blinded me with SCIENCE!

April 5, 2010

A recent Funky Heart! post has been included in the 24th edition of Scientia Pro Publica, a blog carnival dedicated to scientific subjects written for the layman. Scientia Pro Publica is being hosted this week at 360 Degree Skeptic, the blog of a former professor of psychology at Daytona State College.

Pulse Oximetry explained

March 30, 2010

A Pulse Oximeter (PulseOx) is a useful tool, but exactly how does one work? Obviously, it’s not magic, though it might as well be. Very few people can tell you what happens in the couple of seconds that occur after you place it on your finger.

Pulse Oximeters were invented in the 1940’s by scientist Glen Milliken, who published his ideas in a research paper titled The oximeter: an instrument for measuring continuously oxygen-saturation of arterial blood in man. But it looked nothing like the Oximeters we have today: those wouldn’t appear until the Japanese refined the technology in 1972.

But the average person still wouldn’t have been able to purchase a Pulse Oximeter. Biox made it into a commercial product in 1981, and it was the late 1980’s before they really began to catch on in the United States.

So how do they work? A Pulse Oximeter emits light from two different sources: a red light that you can see, and an infrared light that you can’t see. As the PulseOx is placed on your finger or ear the lights activate automatically.

The red light (which has a wavelength of 660 nm) shines through the finger and is absorbed by hemoglobin. The problem is, everything else in the body absorbs light, also. So the infrared light is used too – it has a higher wavelength and is absorbed at a different rate than the red light. A receiver picks up the light waves from both sources as they leave the body, and the Oximeter’s computer chip compares the two. The comparison values are entered into a mathematical formula (CLICK HERE and page down to see the formula that makes Pulse Oximetery possible) and the answer is displayed on the screen – all in a matter of moments!

If I had to do the math to figure out the Oxygenation level, It would take all day to get one reading!

Oximetery does have its limitations: while most people think it is a beat to beat accurate measurement, it is not. It is an average over time. Another big drawback is that it can be fooled by Carbon Monoxide poisoning. hemoglobin mated with Carbon Monoxide responds like oxygen mated Hemoglobin, so a patient dying of Carbon Monoxide poisoning will give a PulseOx reading of 90% or higher.  Also, dark skin could cause inaccurate readings. This 2007 report contends that it does; later reports either report no effect or draw inconclusive results.