Generality
Hypoxemia means reduced amount of available oxygen in the blood. Often, but not always, this condition is associated with hypoxia, i.e. a reduced amount of available oxygen in fabrics.
The most classic symptom of hypoxemia is dyspnea, or difficulty in breathing.
The hypoxemic patient should be treated with oxygen administration and, in severe cases, also with assisted ventilation.
So is hypoxemia
Hypoxemia is a condition in which arterial blood contains less (or less available for use) oxygen than normal. In other words, it corresponds to saying 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 onset of a condition known as hypoxia .
An organ or tissue affected by hypoxia is functioning inadequately or no longer fulfilling all of its functions completely.
The main organs of the body, for which hypoxemia and, subsequently, hypoxia represent the greatest danger, are the brain and liver.
According to another definition, hypoxemia is also the decrease in the partial pressure of oxygen in the blood (PO2). To learn more about the meaning of the partial pressure of O2, read the dedicated article.
ARE HYPOXYMIA AND HYPOXIA SYNONYMOUS?
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 the second (hypoxia) very often derives from the first (hypoxemia).
Hypoxemia only affects the blood and the suffix -emia indicates just that.
Hypoxia, on the other hand, concerns the oxygen available in the tissues, the lack of which is not always due to a state of hypoxemia. For example, imagine tightening the base of a finger with a lace; this, little by little, will begin to turn pale and no longer receive blood. Failure to supply blood determines a process of localized hypoxia, confined 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 the alveoli?
The pulmonary alveoli are small cavities in the lungs, where gas exchanges between the blood and the atmosphere take place. Inside them, in fact, the blood is enriched with the oxygen contained in the inhaled air and is "freed" of the carbon dioxide discarded by the tissues, after their spraying.
Hypoxemia arises when the gaseous exchanges between blood and atmosphere are reduced or, worse still, impossible. The conditions under which this deficient exchange can occur are:
- An obstruction in the airways that lead inspired air to the pulmonary alveoli. For example, the excess mucus produced by severe asthma attacks or the presence of a foreign body accidentally inhaled can obstruct the passage of air.
- ARDS, or acute respiratory distress syndrome. It is a serious lung disease, 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 trauma to the chest, inhalation of harmful substances and severe pneumonia.
- Some drugs that depress the activity of the respiratory centers. Classic examples of such drugs are narcotics (such as morphine) and anesthetics (such as propofol).
- Congenital heart defects. These are heart diseases, present from birth, such as the so-called atrial defect or the so-called interventricular defect.
- COPD, or chronic obstructive pulmonary disease. It is a disease of the bronchi and lungs, as a result of which reduced lung function occurs.
- Pulmonary emphysema. It is a disease of the lungs, due to an "anatomical alteration of the alveoli." Pulmonary emphysema is considered, in some respects, a form of chronic obstructive pulmonary disease, but, given some characteristics that distinguish it, it is often treated separately.
- Altitude sickness. The dangerous effects of high altitudes begin to appear around 2,500 meters. At this altitude, in fact, due to the low atmospheric pressure (attention: the pressure, not the presence of oxygen!), The gaseous exchanges between blood and atmosphere are reduced.
- Interstitial lung disease. It refers to a morbid state of the lung, in which lung tissue is replaced by scar tissue. The presence of scar tissue prevents normal breathing, therefore also the 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 it 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 which is all" around the lung. The lung becomes smaller (collapses) and the patient struggles to breathe.
- Pulmonary edema. It is a very serious pathological condition, due to the fact that the bronchioles and alveoli fill with fluid. 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 obstructs blood flow to the alveoli, thereby reducing the amount of blood that is oxygenated.
- Pulmonary fibrosis. It is due to the formation, instead of normal lung tissue, of scar-fibrotic tissue, which compresses the lungs, reducing the functionality of the alveoli.
- Sleep apnea. It is a sleeping sickness, whereby sufferers temporarily stop breathing while they are sleeping.
Symptoms
Hypoxemia and what it can entail, ie hypoxia, manifest themselves with different symptoms from person to person, based on the triggering pathological conditions.
In general, the observable signs and symptoms are:
- dyspnoea (i.e. the sensation of shortness of breath) both during exertion and at rest;
- change in skin color, which may become cyanotic blue or cherry red;
- state of confusion;
- cough and hemoptysis (i.e. blood from the respiratory tract);
- increased heart rate, aimed at greater tissue oxygenation;
- increased respiratory rate, in response to decreased 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 THE PARTIAL PRESSURE OF THE OXYGEN IN THE BLOOD MEASURED?
The oxygen saturation (SpO2) and the partial pressure of oxygen in the arterial blood (PaO2) are two fundamental parameters to establish 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 special instrument, called an oximeter (NB: the test is the oximetry), which is applied to a finger or a lobe of the ear (in both cases they are highly vascularized anatomical regions). Oxygen saturation values above 95% are considered normal, while values of 90% or less begin to become life-threatening.
The partial pressure of oxygen in arterial blood, on the other hand, is measured by means of 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 the values of the same in case of hypoxemia are shown in the tables below.
PLEASE NOTE: SpO2 values are correlated to PaO2 ones. For example, an SpO2 value of 90% (which we have seen to be dangerous) correlates with a PaO2 value of less than 60mmHg.
WHEN TO SEE THE DOCTOR?
The most characteristic sign of hypoxemia is dyspnea. In less severe cases, it appears only under exertion (ie when an increase in respiratory rate is required), while, in more severe cases, it also appears at rest.
Treatment
In case 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 have been restored, it is necessary to understand the triggering causes and consequently intervene on these. Just to cite an example, in case of severe asthma, it is advisable to have the patient take appropriate drugs, such as bronchodilators or inhaled corticosteroids, whose purpose is to make the airways open again.
SERIOUS CASES
The patient suffering from severe hypoxemia and hypoxia may need a breathing support, represented by an artificial ventilation machine.
SOME ADVICES
Patients with dyspnoea and other breathing problems are usually advised to:
- quitting smoking, because active smoking is a major cause of pulmonary emphysema and COPD;
- avoid passive smoking, as it is as dangerous as active smoking;
- regularly practice physical activity (obviously appropriate to your age and state of health), as it improves exercise tolerance and breathing.
Such advice, for obvious reasons, is also often given to those suffering from hypoxemia and hypoxia.
