Generality
Mechanical ventilation, or artificial ventilation, is the support to breathing that doctors reserve to people totally, or partially, unable to breathe spontaneously.
A cornerstone of intensive therapy, mechanical ventilation is clinically indicated in the case of: severe acute lung diseases (eg: ARDS), apnea associated with respiratory arrest, severe and acute asthma, acute or chronic respiratory acidosis, severe hypotension, moderate / severe hypoxemia, excessive respiratory work, neurological diseases such as muscular dystrophy etc.
There are two types of mechanical ventilation: mechanical pressure negative ventilation, which is the oldest type, and positive pressure mechanical ventilation, which represents the most modern and currently popular type.
The use of mechanical ventilation, together with the most appropriate medical therapies, can save an individual's life.
Mechanical ventilation is not without risks.
Brief review of spontaneous breathing
Spontaneous breathing is that fundamental autonomous process for the life of the human being, which involves the introduction of oxygen-rich air into the lungs and the subsequent expulsion of carbon dioxide.
The introduction of oxygen-rich air is known as inspiration ; inspiration takes place through the nose or mouth .
Once inspired, the air travels through the so-called respiratory tracts (in order, pharynx, larynx, trachea, bronchi and bronchioles) up to the pulmonary alveoli, or the site where the organism “captures” the oxygen from the air, in exchange for carbon dioxide.
Once the oxygen has been captured, the expulsion of the air containing carbon dioxide, now no longer necessary, takes place through a process called expiration .
Within this framework, the so-called respiratory muscles, which are: the diaphragm and the intercostal muscles, play a fundamental role.
During inspiration:
- The intercostal muscles contract . Their contraction lifts the ribs and favors the expansion of the rib cage.
- The diaphragm contracts . Its contraction compresses the abdominal organs downwards, guaranteeing a greater expansion space for the lungs contained in the rib cage.
During exhalation:
- The intercostal muscles relax . Their relaxation draws the ribs down and reduces the volume of the rib cage.
- The diaphragm relaxes . Its relaxation involves its upward movement, the upward movement of the abdominal organs and a reduction in the volume of the rib cage.
What is mechanical ventilation?
The mechanical ventilation, or artificial ventilation, is the support to the respiration realized through a special device - the so-called mechanical fan - and reserved for people unable to breathe spontaneously, due to particular critical conditions.
Therefore, mechanical ventilation is a life-saving or potentially medical support, capable of compensating / replacing spontaneous breathing, where it is difficult or impossible.
IN WHICH HOSPITAL DEPARTMENT HAS A PLACE?
The hospital ward, where mechanical ventilation is generally held, is intensive care .
Intensive care, or intensive care unit, is the hospital ward reserved for the hospitalization of patients in serious health conditions, who need continuous treatment, monitoring and support, in order to maintain their vital functions normally.
WHO IS TAKING CARE OF PATIENTS SUBJECT TO MECHANICAL VENTILATION?
Mechanical ventilation is a method that involves several health professionals, including:
- A doctor with a specialization in anesthesia - intensive care - intensive care (anesthesiologist - resuscitation - intensive care) or in pneumology (pneumologist). It is a professional figure with specific training in the implementation of mechanical ventilation.
- A professional nurse with a specific preparation in anesthesia, intensive care and intensive care techniques . It supports the doctor in evaluating the patient and provides for the implementation of the prescribed drug therapies.
- Team of general nurses prepared in mechanical ventilation and in the needs of those subjected to it . The task of this team is to take care of the patient.
- A respiratory therapist . He is a professional figure with specific training in the diagnosis and treatment of diseases of the respiratory system and in the realization of mechanical ventilation.
operation
Mechanical ventilation works by replacing or supplementing the activity of the respiratory muscles. The respiratory muscles are the muscles that guarantee the processes of inhaling and exhaling air, respectively, in and from the lungs.
Indications
Mechanical ventilation is indicated for all those who have serious difficulties in spontaneous breathing .
Severe spontaneous breathing difficulties may depend on:
- A severe and acute lung disease . The most representative example of such a condition is ARDS, which stands for Acute Respiratory Distress Syndrome ;
- State of apnea associated with respiratory arrest . Such a circumstance may derive from severe intoxication;
- Severe and acute asthma ;
- Acute or chronic respiratory acidosis, resulting for example from conditions such as COPD (chronic obstructive pulmonary disease), myasthenia gravis, Guillain-Barré syndrome, motor neuron disease, etc .;
- Excessive respiratory work, which induced the phenomena of tachypnea and respiratory distress ;
- Arterial hypoxemia of moderate / severe degree . Arterial hypoxemia whose oxygen partial pressure (PO2) values are less than 60 mmHg is moderate / severe;
- Severe hypotension . Examples of conditions that are at the origin of severe hypotension are: sepsis (or septicemia), shock and congestive heart failure;
- Neurological diseases such as muscular dystrophy or amyotrophic lateral sclerosis ( ALS ).
Types
There are two types of mechanical ventilation: negative pressure mechanical ventilation and positive pressure mechanical ventilation .
MECHANICAL VENTILATION WITH NEGATIVE PRESSURE
Conceived around the 1920s, negative pressure mechanical ventilation is the oldest method of supporting spontaneous breathing.
Today less and less in vogue, it involves the use of a mechanical fan in the shape of a large tank, capable of containing the body of a human being (head and neck excluded) and creating a pressure difference between the inside and the outside of the patient's chest, such as to induce the expansion of the thoracic cage and the entry into the lungs of the air outside the chest.
The method in question is called "negative pressure", since the mechanical fan favors the entry of air into the lungs, through the creation, around the patient's chest, of a negative pressure environment .
The mechanical negative pressure fan effectively mimics the functions performed by the respiratory muscles: it replaces them in expanding the thoracic cage (it is the moment when air enters the lungs) and in bringing it back to normal conditions (it is the moment in which the expiration of carbon dioxide occurs).
The mechanical negative pressure fan is known in the medical-scientific field as an iron lung .
The steel lung represented, for years, one of the main polio treatments in its acute phase, when the patient is unable to breathe autonomously.
MECHANICAL VENTILATION WITH POSITIVE PRESSURE
Designed around the 1950s, positive pressure mechanical ventilation is the modern method of supporting spontaneous breathing.
The mechanical fan necessary for its realization is an adjustable electronic device, which pumps air into the patient's respiratory tract at regular intervals (12-25 pumps per minute), effectively mimicking the breaths of inspiration.
The current mechanical positive pressure fans are such technologically advanced instruments that are able to:
- Record internal airway pressure;
- Calculate, based on the pressure present inside the airways, the exact volume of air to be pumped;
- Understanding whether the patient has a minimal capacity for spontaneous breathing (at this juncture, it would act as an aid to breathing) or if, instead, the patient is completely unable to breathe spontaneously (in this circumstance, he would act as a real substitute for spontaneous breathing) .
- Notify if the pumping action is ineffective.
The air pumping in the respiratory tract can be done in two different ways: through a special mask, applicable on the face of the patient, or through a tube to be introduced into the trachea by mouth ( endotracheal tube ) or through an opening on the neck ( tube for tracheotomy ).
The choice to resort to the mask or the tube in the trachea depends on the patient's condition: if the latter has completely free airways, the circumstances exist to make use of the mask (as there is no impediment to the passage of air ); if instead the patient has some obstruction along the first respiratory tract, it is necessary to insert a tube into the trachea, to be sure of bypassing the obstruction.
Clearly, the use of the mask makes positive pressure mechanical ventilation a non-invasive method, while the application of a tube in the trachea makes it an invasive method .
Finally, the last note concerns the expiration of carbon dioxide : the expulsion of the oxygen-depleted air takes place at the end of the pumping phase, due to the elasticity of the lungs and respiratory muscles.
Positive pressure mechanical ventilation is so called because it works by increasing the pressure inside the airways, through the mask, the endotracheal tube or the tracheotomy tube.
| Table. Summary of some characteristics of negative pressure and positive pressure mechanical ventilation. | |||
Type of ventilation | History | Advantages | Disadvantages |
| With negative pressure | Designed around the 1920s. | It proved very useful in the treatment of patients with poliomyelitis. |
|
| With positive pressure | Designed around the 1950s, it has since become the most widely used method for supporting spontaneous ventilation. | Useful during major surgery operations, when the patient is subjected to general anesthesia and needs help with breathing. | If the support for spontaneous breathing must last a long time, it is necessary to resort to tracheotomy and to insert a tube into the trachea through the neck (a very invasive technique). |
Duration and monitoring
The use of mechanical ventilation ends in the presence of a clear recovery by the patient and in the presence of clear signs of a spontaneous breathing ability.
To understand when to suspend mechanical ventilation, doctors use specific diagnostic tests, which verify the ability of spontaneous breathing in an individual.
PATIENT MONITORING
People subjected to mechanical ventilation are continuously monitored by the medical personnel who are treating them.
Continuous monitoring allows to have the situation under complete control and to notice possible changes (both in better and worse) of the health conditions of the patients.
Benefits
Mechanical ventilation has several benefits and advantages.
First of all, it provides the patient with the oxygen necessary for maintaining the health and proper functioning of the most important organs of the human body (brain, heart, liver, etc.).
Secondly, it is a form of medical life support without any interaction with drugs and other substances, which can help the patient.
Finally, it can be carried out for long periods of time, waiting for a significant improvement in the patient's condition and a signal that certifies the new-found capacity for spontaneous breathing.
IMPORTANT NOTE
Mechanical ventilation is not a treatment that heals, as for example a surgical intervention or a drug therapy could be; it is rather a more or less long-term temporary remedy, which allows the patient's health to remain stable, until any pharmacological treatment has had any effect or until a surgical operation is carried out that is suited to the patient's needs.
Risks and complications
Mechanical ventilation has certain risks.
Indeed, its realization may involve:
- Barotrauma with involvement of the lungs (pulmonary barotrauma) . As a result of pulmonary barotrauma, the patient may be a victim of pneumothorax, pneumomediastinum, pneumoperitoneum and / or subcutaneous emphysema.
Pulmonary barotrauma is one of the best known complications of positive pressure mechanical ventilation.
- Acute injuries of the lungs . They are characterized by damage to the pulmonary alveoli, damage from which they may depend: the formation of pulmonary edema, the loss of surfactant, alveolar blood loss and alveolar collapse.
- Diaphragm muscle atrophy . The diaphragm is a muscle on a par with the muscles of the legs or arms: its non-use (which is a typical consequence of the absence of spontaneous breathing) leads to a loss of tonicity and a weakening of the muscle fibers.
- Reduction of cilia motility in the respiratory tract and consequent tendency to develop pulmonary infections (pneumonia) . The respiratory tract uses a mucociliary system to capture germs and bacteria inside them and transport them to the mouth for their elimination.
Mechanical ventilation affects the health of the aforementioned mucociliary system and compromises its functional effectiveness.
