I thought it was a pretty cool tool if it could tell you when to intubate! How many new tools do we purchase and put on patients without a full understanding of how the thing works? We have providers today who think the only reason to use capnography is for tube confirmation, and many are reprimanded for using special nasal cannulas to read end-tidal carbon dioxide EtCO 2 because of their cost. But I digress. In my 40 years in EMS, I have seen this cycle play out many times: New device with limited training leads to poor understanding resulting in misuse that turns into a distraction from patient care.
Pulse oximetry has been used routinely in the medical setting longer than capnography. However, many providers may not fully understand how a pulse oximeter works. This article will give you a better understanding about how a pulse oximeter works, what the readings mean, and what role a pulse oximeter plays in emergency medicine.
Before we dive into pulse oximetry, first we must review basic relevant anatomy and physiology of the respiratory system. The medulla controls the ventilatory effort. This diffusion occurs across the alveolar capillary membrane where CO 2 in the blood is exchanged for O 2 from air. As O 2 travels across the respiratory membranes, it seeks out and binds to hemoglobin molecules on red blood cells. A pulse oximeter is a noninvasive means of measuring both pulse rate and the arterial oxygen saturation of hemoglobin at the peripheral capillary level.
The photoelectrical sensing probe measures the amount of red and infrared light being absorbed as arterial oxygen reaches the capillary beds during systole, when more light is absorbed, and diastole, when less light is absorbed. The monitor calculates the time between the peaks of light absorption and displays a pulse rate in beats per minute.
It also calculates a value based on the ratio of light absorbed at systole and diastole to display a peripheral oxygen saturation percentage SpO 2. See Figure 1. The better the sampling, the greater the difference between systolic and diastolic blood pressure in the capillary beds. A great difference makes for a more accurate reading. In normal perfusion states, a pulse ox SpO 2 and SaO 2 from blood gas readings should be very close.
Oxygen has to be carried from the lungs and be released to the cells. Recall that the respiratory system supplies oxygen to the tissues for cellular metabolism i. See Figure 2, p. Oxygenation and ventilation are two separate physiological processes; however, ventilation can effect oxygenation. Oxygenation i. The oxyhemoglobin dissociation curve defines the point that oxygen can release dissociate from hemoglobin to be used by the cells and is based on normal pH and normal body temperature.
See Figure 3, p. A high pH i. In this state, the cells are deprived of oxygen and can become hypoxic. Conversely, a low pH acidosis or high body temperature hyperthermia will cause a right shift of the curve, which in turn makes it more difficult for oxygen to bind very tightly to hemoglobin making oxygen more readily available to the cells.
A photoplethysmograph PPG is a plethysmograph that uses optical techniques. It can measure the change in the volume of arterial blood with each pulse beat. This change in blood volume can be detected in peripheral parts of the body such as the fingertip or ear lobe using a technique called photoplethysmography.
The pulse oximeter that detects the signal is called a plethysmograph or 'Pleth' for short. Because of the nature of pulse oximeter, measuring the pressure from a pleth waveform has not been possible. However, the information has shown to be useful in diagnosis and in gauging the severity of illness in newborns.
Many doctors use the pulse oximeter's pleth waveform as an early indication for cyclic changes in physiology. The blood flow is normally shown as a waveform using a bar or graph. It can provide useful information regarding the heart condition. Heart rhythm. Avoid focusing too much on one number alone. Can you please check? Do you think he might be cold? Contact a nurse or medical professional if the machine starts to beep.
However, these sounds are usually nothing to worry about. If the monitor or another piece of equipment starts beeping, call a nurse to come check it. Can you please come and check it? Ask your healthcare provider if you have any questions or concerns. Doctors and nurses use them to identify problems in conjunction with other signs and symptoms.
If you are worried about something you see on the screen, ask a doctor or nurse. Include your email address to get a message when this question is answered. Spending some time away from the hospital will give you a chance to recharge and allow the person time to rest and recover as well. Helpful 3 Not Helpful 0. Related wikiHows How to. How to. More References 3. About This Article. Medically reviewed by:. Danielle Jacks, MD. Co-authors: 4. Updated: April 24, Categories: Caregiving.
Medical Disclaimer The content of this article is not intended to be a substitute for professional medical advice, examination, diagnosis, or treatment. Thanks to all authors for creating a page that has been read 73, times.
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