The PulseOx test – not perfect, but good

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.

Tags: PulseOX, Research