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Home>Topics>>EMS: Using Pulse Oximetry

EMS: Using Pulse Oximetry

Tue, 10 Apr 2012|

FIre Engineering EMS Editor Mike McEvoy discusses using pulse oximetry, a method of determining the oxygen level in your patient. Mike also discusses some tips and issues with readings on pulse oximetry devices.



[MUSIC] Hi, welcome to Training Minutes. Today we're going to talk about using pulse auxsemitry, which has been added to the first responder and the EMT curriculum. Pulse [INAUDIBLE] is a method of determining the oxygen level in the patient. It has many limitations. First thing that we're going to do is place the probe on the patient. So we have a finger probe that we're using with this device and we're going to choose a finger that has the best blood flow. Of the fingers on your hand your ring finger tends to be the finger that has the highest blood flow. So we'll place the probe on the patients ring finger, we could put it on any one of the other fingers, preferentially, one of the three middle fingers, not the thumb, not the pinky. And then we'll. Watch the pulse oximeter as it boots up. It's going to collect a pulse-ox reading, which you see is 100% here, and the heart rate from the patient. Now, some of the issues with pulse oximetry have to do with. Things that it may detect other than oxygen that's in the patient. It's looking at the hemoglobin and determining the saturation of the hemoglobin with oxygen. It could be fooled, as firefighters know, by carbon monoxide. It's unable, in conventional pulse oxymeters. Like this device to be able to tell the difference between oxyhemoglobin and carboxyhemoglobin. So if this patient was pulled from a fire and had a 20% carboxyhemoglobin carbon monoxide level, the Pulse Ox would still read 100%, not recognizing. That 20 percent of that was carbon monoxide. So that's the first caveat about using Pulse Oximetry. Clearly, if a patient's pulled from a fire and has a pulse oximiter using a conventional pulse oximiter that can't tell the difference between Oxyhemoglogin and Carboxyhemoglobin then. the saturation was low, we would say, well there's a problem with that patient. The other question that people often ask is cyanide. If a patient was poisoned with cyanide, with the pulse [INAUDIBLE] have an effect from the cyanide? The answer to that seems to be not. Pulse [INAUDIBLE] do not seem to be effected in their readings by cyanide levels in the blood stream. Next question is, what's the strength of the blood flow to the digit where you placed the probe? Now we chose what we believe to be the best blood flow by using the ring finger on this patient. If for some reason we weren't getting a good signal, if he had low profusion, we may need to place the probe on another digit on his hand, or perhaps on a toe. There are probes that are specially made to put on the ear. There are probes that are made to go on the nose. There are probes that are make to go on the forehead. You need to use a probe that is designed for whatever application you are using. In this case, a finger probe on a finger. On this particular oximeter, which is made by Masimo, as well as oximeters that are made by Datex-Ohmeda. And by Phillips we have an indicator of the actual perfusion on the patient that's called perfusion index. If you are using a brand of oximeter that has perfusion index, in an adult patient one point four is a cut off for a reliable versus a unreliable signal. In this instance. His profusion index is well over four and so his profusion to the extremity that we have the probe on is excellent. If you're doing it on a neo-nate, 1.27 is the threshold for good versus bad profusion. The other question is nail polish. Can nail polish interfere with pulse asymmetry and in fact, three colors of nail polish actually do throw the pulse asymmetry signal off. Black, blue, and green nail polish. So if your patient is wearing nail polish, you may use a nail polish remover, a prep pad similar to an alcohol pad that's designed to remove nail polish has acetone on it and the acetone would be used to wipe the nail polish off the patients nail. You could also position the probe so that it reads sideways through the finger, avoiding the nail bed completely. Reading sideways would eliminate the effect of black, blue or green nail polish that the patient had. Another question is, what about ambient light? And there are certain forms of ambient light that could interfere with the pulse ox signal. Sun light is one, and very bright sun light may require you to put a towel over the extremity that you have the pulse ox probe on. Lights that's indoor, such as fluorescent light, which you may have in the back of your ambulance or your rescue. Or Xenon light, which may be in a sports stadium or a place where that sort of light is used could interfere with pulsocks [sp?] signal. And again, putting a towel over the extremity will eliminate that interference from the readings. That are being taken. Some people question whether sickle cell crisis or sickle cell anemia effects pulse ox readings. The answer to that is no, sickle cell does not affect a pulse ox reading. The other question is what about dark pigmented skinned patients. So people who are, for example, African American or Indian who have a darker pigmentation to their skin. Pulse ox is not effected by darkly pigmented patients. And finally hyperbilirubinemia, patients who for some reason have an elevated level of bilirubin in their bloodstream, perhaps they're in liver failure or perhaps they have some other condition that's causing excessive levels of bilirubin. Those patients typically have a yellow appearance to their skin. That does not interfere with pulsox. So we talked in another fire engineering video series about using pulse ox imagery to take blood pressure and again if you are trying to assess a blood pressure you could place the probe on the extremity pump the blood pressure on the same and watch for the pulsation. As you let the air out of the blood pressure cup. And get a rough idea of the systolic blood pressure. So those are some tips for using pulse oximetry, a common tool. Something that's been added into our curriculum in the new first responder, NEMT curriculum. And a very helpful device to determine what the oxygenation status of your patient is. And as oxygen becomes more important, and we start to realize some of the detriments of giving oxygen to patients who have traumatic conditions, such as trauma, acute myocardial infarction. or stroke. Where excessive levels of oxygen make actually hurt the injury to those patients and make their conditions worse, pulse asymmetry is a valuable tool for assessing the patients in the EMS field. Thanks for watching training minutes, I'm Mike Mackavore the EMS editor for fire engineer.

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