Generality
Hypoxemia means reduced amount of oxygen available in the blood. Often, but not always, this condition is associated with hypoxia, ie a reduced amount of oxygen available in the tissues.
The most classic symptom of hypoxemia is dyspnea, or breathing difficulty.
The hypoxaemic patient must be treated with oxygen and, in severe cases, with assisted ventilation.
What is hypoxemia
Hypoxemia is a condition in which arterial blood contains less oxygen (or less available for use) than normal. In other words, it means that the oxygen contained in the arterial blood is scarce or not very usable.
Hypoxemia is a potentially very serious condition, as poorly oxygenated blood does not properly nourish the tissues and organs present in the body. The insufficient oxygenation of the latter can lead to the establishment of a condition known as hypoxia .
An organ or tissue affected by hypoxia works inadequately or no longer completely fulfills all its functions.
The main organs of the body, for which hypoxemia and, subsequently, hypoxia represent the greatest danger, are the brain and the liver .
According to another definition, hypoxemia is also the decrease in the partial pressure of oxygen in the blood (PO 2 ). To learn more about the meaning of the O 2 partial pressure, read the dedicated article.
IPOSSIEMIA E IPOSSIA ARE SYNONYMS?
Although hypoxemia and hypoxia are not the same thing, we often tend to confuse the terms and use them improperly; this error originates from the fact that from the first (hypoxemia) the second (hypoxia) very often derives.
Hypoxemia is exclusively related to blood and the suffix -emia indicates this.
Hypoxia, on the other hand, concerns the oxygen available at the tissue level, whose deficiency is not always due to a state of hypoxemia. For example, imagine that you are holding the base of a finger with a lace; this, little by little, will begin to become pale and no longer receive blood. The lack of blood supply results in a process of localized hypoxia, limited to the tissues of the finger and not dependent on the oxygen levels available in the blood (which are completely normal).
Causes
To better understand: what are alveoli?
Pulmonary alveoli are small cavities in the lungs, where gas exchange between the blood and the atmosphere occurs. Inside them, in fact, the blood is enriched with the oxygen contained in the inhaled air and "frees" itself of the carbon dioxide discarded by the tissues, after their spraying.
Hypoxemia occurs when gas exchange between blood and atmosphere is reduced or, worse still, impossible. The conditions for which this deficit exchange can occur are:
- An obstruction in the airways that carries air inspired by the pulmonary alveoli. To block the passage of air, they can be, for example, the excess mucus produced by severe attacks of asthma or the presence of a foreign body accidentally inhaled.
- ARDS, or acute respiratory distress syndrome . It is a serious disease of the lungs, caused by damage to the alveolar capillaries (ie the blood vessels of the alveoli); these, once damaged, are no longer adequately reached by the blood to be oxygenated. The main causes of ARDS are: sepsis, severe chest trauma, inhalation of harmful substances and severe pneumonia.
- Some drugs that depress the activity of respiratory centers . Classic examples of such medicines are narcotics (such as morphine) and anesthetics (such as propofol).
- Congenital heart defects . These are diseases of the heart, present from birth, such as the so-called interatrial defect or the so-called interventricular defect.
- COPD, or chronic obstructive pulmonary disease . It is a disease of the bronchi and lungs, due to which reduced pulmonary function occurs.
- Pulmonary emphysema . It is a disease of the lungs due to an anatomical alteration of the alveoli. Pulmonary emphysema is considered, in certain aspects, a form of chronic obstructive pulmonary disease, but given some characteristics that distinguish it, it is often treated separately.
- Mountain sickness . The dangerous effects of high altitudes begin to appear around 2, 500 meters. At this altitude, in fact, due to low atmospheric pressure (attention: pressure, not the presence of oxygen!), Gas exchange between blood and atmosphere is reduced.
- Interstitial lung disease . It refers to a morbid state of the lung, in which the lung tissue is replaced by scar tissue. The presence of scar tissue prevents normal breathing, therefore also oxygenation of the blood.
- Pneumonia . It is the medical term used to indicate inflammation of the lungs. It usually has a bacterial origin ( Streptococcus pneumoniae, Staphylococcus aureus or Mycoplasma pneumoniae ) or viral (influenza virus, Adenovirus or Herpes simplex ), but can also be caused by some fungi ( Pneumocystis jirovecii ).
- A pneumothorax . It is the expression of an anomalous infiltration of air inside the pleural cavity that is found all around the lung. The lung becomes smaller (collapse) and the patient struggles to breathe.
- Pulmonary edema . It is a very serious pathological condition, due to the fact that the bronchioles and alveoli are filled with liquid. This liquid comes from the alveolar capillaries and is the element responsible for the lack of gas exchange.
- Pulmonary embolism . It is a highly dangerous circumstance, characterized by the presence, in the arterial vessels directed to the lung, of a blood clot, also called an embolus. An embolus hinders direct blood flow to the alveoli, thus reducing the amount of blood being oxygenated.
- Pulmonary fibrosis . It is due to the formation, instead of the normal lung tissue, of scar-fibrotic tissue, which compresses the lungs, reducing the functionality of the alveoli.
- Sleep apnea . It is a sleeping sickness, so those who suffer from it temporarily interrupt their breathing while they are sleeping.
Symptoms
Hypoxemia and what it can entail, that is hypoxia, manifest themselves with a different symptomatology from person to person, based on the triggering pathological conditions.
In general, the observable signs and symptoms are:
- dyspnea (that is, the feeling that you are out of breath) both under stress and at rest;
- change in skin color, which can become cyanotic blue or cherry red;
- state of confusion ;
- cough and hemoptysis (ie blood emission from the respiratory tract);
- increase in heart rate, aimed at greater tissue oxygenation;
- increased respiratory rate, in response to lower blood oxygenation in the lungs;
- intense sweating ;
- exhaustion;
- drumstick fingers ;
- low oxygen saturation;
- low partial pressure of oxygen in the blood.
HOW ARE THE OXYGEN SATURATION AND PARTIAL PRESSURE OF OXYGEN IN THE BLOOD MEASURED?
Oxygen saturation ( SpO 2 ) and partial oxygen pressure in arterial blood ( PaO 2 ) are two fundamental parameters for establishing the state of hypoxemia.
Figure: oximetry tool. From the site: normalbreathing.com
The oxygen saturation, or the percentage of oxygen molecules linked to hemoglobin, is measured with a particular instrument, called an oximeter (NB: the examination is the oximetry ), which is applied on a finger of the hand or on a lobe of the ear (in both cases these are highly vascularized anatomical regions). Values of oxygen saturation higher than 95% are considered normal, while values equal to or less than 90% begin to become life-threatening.
The partial pressure of oxygen in arterial blood, on the other hand, is measured by the so-called blood gas analysis, at the end of which there is a complete picture of the partial pressures of all the gases contained in the blood.
The normal values of the partial pressure of oxygen in the blood and its values in case of hypoxemia are reported in the tables below.
| Normal values of partial oxygen pressure in arterial blood (PO2). | |
| Age (years) | PO2 mmHg |
| 20-29 | 94 (84-104) |
| 30-39 | 91 (81-101) |
| 40-49 | 88 (78-98) |
| 50-59 | 84 (74-94) |
| 60-69 | 81 (71-91) |
| Values of oxygen partial pressure in arterial blood, in case of hypoxemia. | |
| Degree of hypoxemia | PO2 mmHg |
| Mild hypoxemia | 60-80 |
| Moderate hypoxemia | 40-60 |
| Severe hypoxemia | <40 |
PLEASE NOTE: SpO 2 values are related to those of PaO 2 . For example, a SpO 2 value of 90% (which we have seen is dangerous) correlates to a value of PaO 2 lower than 60mmHg.
WHEN TO REFER TO THE DOCTOR?
The most characteristic sign of hypoxemia is dyspnea. In less severe cases, it appears only under stress (that is when an increase in respiratory rate is required); while, in the most serious cases, it also appears at rest.
Treatment
In the event of overt hypoxemia and hypoxia, the therapeutic intervention must be immediate and based on the administration of oxygen through special medical instruments ( oxygen therapy ).
Therefore, once the oxygen levels are restored, it is necessary to understand the triggering causes and intervene accordingly on these. To cite an example, in the case of severe asthma, the patient should be given specific drugs, such as bronchodilators or inhaled corticosteroids, whose purpose is to make the airways open again (that is, open).
SERIOUS CASES
The patient suffering from severe hypoxaemia and hypoxia may need a breathing support, represented by an artificial ventilation machine .
SOME ADVICES
Patients with dyspnea and other respiratory problems are usually advised to:
- stop smoking, because active smoking is one of the main causes of pulmonary emphysema and COPD;
- avoid passive smoking, because it is as dangerous as active smoking;
- practice regular physical activity (obviously appropriate to your age and your state of health), as it improves tolerance to efforts and breathing.
Such advice, for obvious reasons, is also often given to those who suffer from hypoxemia and hypoxia.
