Pulse oximetry | Diseases and conditions: Medical tests.

What is a Pulse oximetry

Pulse oximetry is a diagnostic test which is used constantly in hospitals and medical emergencies. With it we can know how much oxygen there is in the blood without performing an extraction of blood, unlike what happens in the arterial blood gases.
Oxygen passes into the blood through the alveoli of the lung and is transported within red blood cells, hemoglobin-joined. Hemoglobin is a protein with a molecule of iron, which is where the oxygen attaches, and when that happens the proteins change shape. Pulse oximetry takes advantage of this feature to measure the blood oxygen.
The device that is used is a Pulse Oximeter, a small clip that is placed on the tip of any finger of hand. At one end it has a light and transmitter in the receiver front end. Light through the finger and is altered with oxygenated hemoglobin, in such a way that there are many more molecules of hemoglobin occupied with oxygen over the beam of light is altered.
Alterations of the beam of light is collected by the receiver of the Pulse Oximeter, there are interpreted, and give a numeric value that represents the percentage of oxygen in the blood. The ordeal a few moments, does not represent any discomfort to the patient, and can help to initiate treatment or perform other tests quickly.

When a pulse oximetry is made

Pulse oximetry is a test that is used every day in medicine of patients admitted, in emergency situations, or in outpatient consultations. It does not imply any invasion for the patient and can bring much useful information. It is the first step to testing more annoying as an arterial gas. The situation where the gases is an important utility is respiratory failure.
Although respiratory failure can only be diagnosed through an arterial blood gases, pulse oximetry allows you to decide the realization of this technique. If pulse oximetry is normal, not worth a gas analysis, and the patient saves is a blood collection something annoying. Respiratory failure situations can be diverse, some of them would be asthma, COPD, pulmonary fibrosis, acute Lung edema, etc.
Other metabolic alterations such as acidosis, alkalosis, or problems such as hyperventilation and renal failure, cannot diagnose is via pulse oximetry. In these cases is you must perform an arterial blood gas that allows not only know the levels of oxygen in blood, but also the levels of ions in blood and carbon dioxide.
An exception would be carbon monoxide poisoning, a very toxic molecule that forms in combustion of low quality (homemade bonfires, stove, living room, etc.), and which binds to hemoglobin disabling it. In that case the blood gases would oxygen levels in normal blood, but pulse oximetry would detect this abnormality in hemoglobin, being the only way to diagnose it.

Preparation for a pulse oximetry

If you will perform a pulse oximetry , these are the issues that you must take into account:
Duration: lasts very little. The time that passed since you put the Pulse Oximeter in any finger until the results is just a few moments.
Admission: admission is not needed. It can be in a hospital or an outpatient, even in the House. Some people chronically neumologicos have their own Pulse Oximeter at home and use it on a daily basis.
Is it necessary to be accompanied?: no.
Drugs: don't need to take any prior medication. It must be said to the doctor all medications are taken at the time, although they do not usually affect the amount of oxygen in the blood.
Food: is a test that is not altered by eating in the hours before, so it is not necessary to save fast.
Clothes: don't need special clothes. The Pulse Oximeter is placed on a finger and do not need to undress so they put it.
Documents: it is advisable to carry your health card, but at the time of you pulse oximetry not usually ask you for any identification.
Pregnancy and breast-feeding: the test can be taken without modifying any attitude. It is better to let the doctor know that you're pregnant, because pulse oximetry may be slightly different.
Contraindications: there are no contraindications.

How a pulse oximetry

Arriving to the inquiry or to the emergency room doctor will make you some general questions about your state of health (important diseases, risk factors, lifestyle, work place...), and above all insist the symptoms that have led you to consult. The symptom that is associated with respiratory failure is shortness of breath, fatigue , or shortness of breath.
After perform you a general physical examination, and assess the realization of a pulse oximetry if it believes it may be useful for diagnosis and treatment. To be a simple test is usually done on all persons directly.
At the same time, a doctor or a nurse will proceed to put the Pulse Oximeter. Is usually placed on the fingers of the hand; somebody is invalid. But there are situations in which the blood does not well to the tip of your fingers. Some of them are physiological, as exposure to the cold, and others are pathological situations, such as sepsis, Raynaud's disease, etc. In those cases, you can try placing the Pulse Oximeter in other locations, such as for example the earlobe.
Few second after placing the Pulse Oximeter will begin to detect the blood pulse, then light will cross the finger and deform according to the hemoglobin molecules that are occupied with oxygen. A number, that the doctor be construed to take clinical attitudes according to the result appears on the display of the Pulse Oximeter.

Complications of pulse oximetry

There are no complications when the pulse oximetry. What if there are complicated situations in which this technique cannot be used. Some of them are sepsis, cardiogenic shock, arterial ischaemia, Raynaud's disease, freezing or cryoglobulinemia. All of them have one factor in common: decrease or absence of blood flow to the extremities.

Results of pulse oximetry

Pulse oximetry results consist of a percentage representing the amount of oxygen in the blood attached to hemoglobin; It is what is known as saturation of oxygen (SatO2). This information can also be obtained with a gas analysis, but pulse oximetry allows to obtain it directly, without estimates.
Oxygen saturation is not the established method for diagnosing respiratory failure, only the partial pressure of oxygen (pO2) is the valid data for this purpose, and it can only be obtained through an arterial blood gas. However, oxygen saturation has a very strong correlation.
Levels of between 98 and 100% oxygen saturation are considered normal. With age, it is usual that the passage of oxygen is not optimal, so it also can be accepted as normal up to 95%. In chronic pulmonary patients to 90% can be considered normal. The reason for considering 95% as the limit of normalcy is that it corresponds with a partial pressure of oxygen of 60 mmHg, limit to diagnose respiratory failure.
If a pulse oximetry is normal the doctor will take care of other problems, but if it is less than 95% it will be his priority. It will first ask an arterial blood gas, to confirm the data and observe exactly the level of oxygen in the blood and other metabolic disorders. Then you put oxygen through nasal glasses or mask, depending on the seriousness of the situation.
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