Sunday, April 20, 2014

When Your Pulse Ox Won't Read Properly

Kristoff, why isn't my pulse ox working?
Pulse oximetry is one of the most indispensable tools anesthesiologists use to maintain the safety of the anesthetized patient. Though it has become widely used only since the 1980's, it is now one of the monitors that is required by the ASA whenever sedation is being given. Prior to its invention, anesthesiologists could only tell if a patient was hypoxic from an intubation of the esophagus when the patient became cyanotic, which by then could be too late. Giving anesthesia without a pulse ox is like driving a car in the rain without any windshield wipers; it can be done but the picture of the road is much less clear and more dangerous.

I'll leave it to somebody else to go through the technical details of how pulse ox monitors work. I will tell you that it doesn't always operate as well as we would like. The most common cause of a malfunction is if the patient is cold. Inside the frigid operating rooms, a patient can easily lose body heat. When that happens, the body compensates by shutting down circulation to the extremities, preserving the heat for the heart and the brain. This poor circulation to the limbs, particularly the fingers, makes it difficult for the pulse ox to read well.

Likewise if a patient is on some sort of pressors because of low blood pressure from sepsis or hypovolemia, the arterial constriction induced by the drugs will prevent an adequate circulation to the small arteries in the fingers. This will again prevent the pulse ox from operating properly. Some other common conditions that will lead to false pulse ox readings include any pressure on the arm. If the patient's arms are tucked to his side during an operation, a surgeon can easily lean on the arm, preventing an adequate blood flow to the fingers. If the pulse ox reading drops periodically, say every three to five minutes, that probably means the pulse ox monitor was accidentally placed on the same arm as the blood pressure cuff, causing the circulation to fall every time the cuff inflates.

Some patients have a condition called Raynaud's Disease. This manifests itself as poor circulation in the fingers and toes leading to cyanosis when the patient gets cold. This causes the pulse ox signals to degrade. If a patient is shivering or moving his fingers, the pulse ox won't work either. African Americans with dark fingernail beds can throw off the monitor, making it almost useless.

So what can be done to make sure this essential monitor functions properly? First of all, an adequate circulation to the fingers is absolutely mandatory. Therefore if the patient is cold, warm up the room if possible or use a heating blanket and IV fluid warmer to increase the patient's body temperature. If the patient's poor circulation to the extremities is due to hypovolemia, give more fluids. If you suspect the blood flow is inadequate due to the surgeon leaning or sitting on the arm, tell him gently to back off. Remember they don't want any complications to their patients as much as you do.

If none of those measures work, it's time to try something else. Every anesthesiologist always tries a second pulse ox. Some put it on a different finger of the same hand, like the thumb, because it has a bigger nail bed for the monitor to read through. If that doesn't work, another pulse ox may be placed on the opposite hand. Since both upper extremities usually receive the same amount of circulation, this rarely works but we all do it.

When you run out of fingers to place the pulse ox monitor, the next step maybe to try the earlobe. Some people have larger ear lobes than others. If a patient has very small ear lobes, it can be difficult to position the pulse ox light just right to pick up the pulsatile blood flow. There are also special small pulse ox clips that can be applied to the earlobe, negating the need for large stickers that can stick to the patient's hair and which usually fall off anyway. I've also seen people use these clips on a patient's nose too which also works.

Finally always try placing the pulse ox sticker on the patient's forehead, centering it over the bridge of the nose. I used to scoff at the usability of this application, since the light emitting end of the sticker is so far away from the receiving end. But it functions surprisingly well. Even when a patient is cold, there is usually preserved circulation to the head allowing the pulse ox to read the blood flow. The pulse ox waveform may not be as strong as on the fingers, but sometimes any waveform is all we can ask for. Of course when all else fails, and you just have absolutely no idea how well a patient is getting oxygenated, bite the bullet and draw an arterial blood gas. That is ultimately the most definitive answer for how well the patient is receiving oxygen.

Pulse oximetry has truly revolutionized the practice of anesthesia. This noninvasive monitor, along with capnography, has exponentially increased the safety of patients under sedation. No cases should be started without a functioning pulse ox monitor in the room. Any surgery center that skimps on this essential component while lavishing its surgeons with 75 different types of sutures is not a facility any reasonable anesthesiologist should seek employment. A patient's life, along with your medical license, is too precious to risk any sedation without a fully working pulse ox.

3 comments:

  1. I've used the clip or a pedi pulse ox on the lip before, the bridge of the nose is a great idea as well!

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  2. I have a friend who does a digital block with bupivacaine and a TB syringe when this happens. Vasodilates and pulse ox signal returns!

    I'm not saying it's a good idea or not, just sharing.

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  3. "Placing a pulse oximeter finger clip sensor on an ear does not provide clinically reliable SpO2 readings." Source: http://www.rcjournal.com/contents/06.07/06.07.0727.pdf

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