Acute respiratory failure

Acute respiratory failure is a condition characterized by disruption of the normal gas composition of arterial blood: delivery of a sufficient amount of oxygen to arterial blood and removal of the corresponding amount of carbon dioxide from venous blood into the alveoli. Disruption of pulmonary gas exchange leads to a decrease in p _a O ₂ (hypoxemia) and an increase in p _a CO ₂ (hypercapnia). The diagnostic criterion for acute respiratory failure is a decrease in p _a O ₂ below 50 mm Hg and / or p _a CO ₂ above 50 mm Hg in the absence of intracardiac shunting. However, even with normal blood gas parameters, acute respiratory failure can develop due to the strain of the external respiratory apparatus; in such cases, the diagnosis is made only on the basis of clinical data. Respiratory failure is a syndrome characteristic of various diseases. Certain anatomical and physiological features of the respiratory organs in children predispose to the development of acute respiratory failure syndrome.

Anatomical and physiological features of the respiratory system in children:

• "expiratory" structure of the chest;
• low absolute values of respiratory volume and “dead space”;
• physiological tachypnea;
• narrow airways;
• weakness of the respiratory muscles;
• relatively lower surfactant activity.

Three types of acute respiratory failure:

• hypoxemic;
• hypercapnic;
• mixed.

Hypoxemic (shunto-diffusion) acute respiratory failure - insufficient blood oxygenation with relatively adequate ventilation: low p a _O 2 _in combination with normal or slightly reduced p _a CO ₂. The main feature is a violation of alveolar-capillary perfusion with intrapulmonary shunting of blood without changing alveolar ventilation. The alveolar-capillary difference in oxygen is increased.

Hypercapnic (ventilation) acute respiratory failure - a decrease in p _a O ₂ with an increase in p _a CO ₂ as a result of primary hyperventilation with a subsequent sharp decrease in the volume of ventilation and severe hypercapnia. The basis is a pathological increase in ventilation-perfusion relations with sharp alveolar hypoventilation.

Mixed acute respiratory failure is manifested by hyperventilation, an increase in the alveolar-capillary difference. Hypoxemia is less pronounced than in hypoxemic acute respiratory failure.

Pathophysiological mechanisms of acute respiratory failure.

• Insufficient ventilation.
• Violation of ventilation-perfusion relationships.
• Intrapulmonary right-to-left shunt.
• Violation of alveolar-capillary diffusion.

In pediatric practice, the most common disorder is ventilation-perfusion relationships, and rarely, alveolar-capillary diffusion.

Each age has its own most common causes of acute respiratory failure. Among newborns, acute respiratory failure is most often observed in premature babies and children with congenital heart and lung defects. In children aged 1 to 2 years, the most common causes of acute respiratory failure are respiratory infections and heart disease, and in children aged 7 to 12 years, bronchial asthma.

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Emergency care for acute respiratory failure

Acute subcompensated and decompensated laryngeal stenosis, often occurring with mechanical trauma, is a critical condition that, if emergency care is inadequate, can lead to fatal consequences. As a rule, problems that arise when performing a particular therapeutic action aimed at restoring the patency of the upper respiratory tract most often occur in conditions that are poorly suited for providing emergency care, that is, at the pre-hospital stage.

According to the St. Petersburg Bureau of Forensic Medicine, 4,474 people died from mechanical asphyxia in 1995-1997, which was more than 20% of the total number of violent deaths. Directly from aspiration of foreign bodies, 252 patients died in three years, which was approximately 6% of the total number of asphyxia cases caused by mechanical factors.

One of the possible causes of respiratory failure in victims with mechanical injuries may be tongue retraction due to a comatose state, drug-induced sleep, and other reasons. To ensure airway patency in this case, it is necessary to perform Safar's techniques:

• head extension (performed with caution, since injury may cause damage to the cervical spine);
• traction of the lower jaw forward and upward;
• head turn.

If these simple techniques do not fully restore the airway, then, with sufficient depth of anesthesia, an oropharyngeal airway with a rigid mouthpiece is installed in the victim.

A frequent cause of acute respiratory failure that occurs with mechanical injuries is aspiration syndrome. The flow of acidic gastric contents into the tracheobronchial tree poses a real threat to the lives of victims with shock-producing trauma. Emergency measures to prevent aspiration include: gastric probing, performing the Selik maneuver - giving the victim's head an elevated position, carefully removing contents from the oral cavity, and, finally, quickly performed intubation. The latter allows, firstly, to protect the airways from repeated entry of oral contents into them, and secondly, creates favorable conditions for artificial ventilation of the lungs and sanitation of the tracheobronchial tree.

When blood, cerebrospinal fluid and gastric juice flow into the trachea and bronchi, they are washed with a 1% soda solution and, if possible, the washing solution is completely removed from the lungs (sanation bronchoscopy) followed by the introduction of antibiotics and glucocorticoid hormones into the tracheobronchial tree.

In those rare cases when tracheal intubation fails for some reason (traumatic deformation of the laryngeal cartilages, difficulties in identifying the location of the glottis due to severe edema, anatomical features, etc.), it is necessary to resort to emergency conicotracheostomy, which, in conditions of time constraints, is most conveniently performed using a conicotracheostomy device. It is a thin-walled cannula bent at an angle of 90 0 with an internal diameter of at least 4 mm and a mandrin located in its lumen, the double-edged end of which protrudes beyond the cannula by 8-10 mm.

As can be seen, even small diameter cannulas used in pediatric practice can be suitable for restoring upper airway patency in situations considered resuscitative. Reasonable choice of cannula diameter is crucial for ensuring adequate spontaneous as well as forced ventilation, and should be as minimal and least traumatic as possible for performing conicotracheocentesis. A universal set for conicotracheostomy consists of five instruments of different diameters (from 2 to 8 mm) placed in a container in which an abacterial environment is maintained.

Conicotracheotomes are placed in a container around the circumference on special support platforms that perform protective functions and allow the cutting properties of the lancet-shaped tip of the mandrin to be preserved for a long time. The container is hermetically sealed with a lid with a fastener that ensures the sterility of the device during transport. The reliability of this part of the device is also extremely important for maintaining the integrity of the instrument during transportation.

The influence of the internal diameter on the magnitude of the gas mixture pressure during inhalation

Cannula diameter, mm	Inspiratory pressure, cm H2O
2	20-22
4	10-12
6	5-6
8	3-4

The technique of puncturing the conical ligament or interannular space is simple, and the entire manipulation takes a few seconds. The sequence of actions is as follows: after treating the puncture site with an antiseptic solution, the trachea is fixed between the first and second fingers of the left hand. Then a notch is made on the skin in the longitudinal direction about 4-5 mm long and the trachea is punctured strictly along the midline with a mandrel perforator inserted into the cannula (the instrument in the assembled state). After the perforator tip penetrates the lumen of the trachea, a sensation of "failure" appears and then, as the instrument advances, when the "entry" part of the mandrel and the cannula are in the lumen of the trachea, the mandrel is removed.

The correct position of the cannula is checked by the sound caused by the air flow when the mandrin is removed from it. Then the cannula is advanced (already without the mandrin with the perforator) until the flange stops at the surface of the neck, after which it is fixed with a bandage or adhesive plaster.

The Conicotracheotome Kit expands the caregiver's options by allowing the ventilation opening to be enlarged by successive use of devices of different diameters, with each successive size Conicotome used as a dilator.

The use of the device in acute upper respiratory tract obstruction has significant advantages over tracheostomy surgery, especially in conditions unsuitable for its implementation (pre-hospital stage).

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Respiratory support in patients with restored airway patency

The choice of respiratory therapy for patients with restored patency of the upper respiratory tract suffering from hypoxic hypoxia depends on many factors, the main ones being:

• degree of respiratory distress;
• presence of other types of damage;
• conditions for providing emergency assistance;
• qualification of medical personnel;
• equipped with breathing equipment.

Along with traditional methods of hypoxic hypoxia correction, high-frequency ventilation (HF ALV) can be used. Its introduction into emergency medical care has significantly increased the effectiveness of resuscitation measures at the pre-hospital stage, i.e. in the most difficult conditions and the least suitable for providing qualified care.

A significant obstacle to the spread of this type of artificial lung ventilation is the lack of mass-produced devices, the design of which must meet requirements that take into account the operating conditions and the volume of assistance provided at the pre-hospital stage. The device must be easy to operate, fairly compact, have a universal power source and low oxygen consumption.

The results of arterial blood gas analysis indicate normalization of carbon dioxide tension and a significantly greater increase in oxygen tension (more than 1.5 times) with HF ALV compared to the traditional method. Based on this, the prospects for using the HF ALV method in providing emergency care at the pre-hospital stage consist of adequate elimination of hypoxemia and thereby creating favorable conditions for the restoration and normalization of cardiac function during resuscitation measures.

Correction of breathing disorders in thoracic trauma

The most severe components of thoracic trauma (according to their clinical course) are contusions and ruptures of the lungs, which are often accompanied by pneumothorax and hemothorax. Tension pneumothorax is especially life-threatening due to the increase in intrapleural pressure, leading not only to compression of the lung, but also to displacement of the mediastinal organs with subsequent rapid development of pulmonary-cardiac insufficiency.

If it is necessary to transfer the victim to artificial respiration (for vital indications) and he has tension pneumothorax, the first emergency measure according to the Belau method is drainage of the pleural cavity in the second intercostal space along the midclavicular line with a needle with a valve or a plastic tube, the free end of which is immersed in a vessel with liquid. The procedure for draining the pleural cavity in case of tension pneumothorax should be performed regardless of the type of ventilation, but invariably before or simultaneously with the start of artificial ventilation.

Severe respiratory disorders are also characteristic of open pneumothorax. In this case, the severity of the injury is due to rapidly increasing hypoxemia, which develops as a result of gas exchange disorders, mainly in the collapsed lung. The intrapleural pressure drop that occurs during the act of breathing leads to flotation of the mediastinum and the movement of air from the collapsed lung to the functioning one during inhalation and in the opposite direction - during exhalation.

The disorders that arise in these cases require emergency drainage of the pleural cavity with two drains in the second and sixth intercostal spaces, respectively, along the midclavicular and posterior axillary lines, followed by active aspiration until the collapsed lung is completely straightened and respiratory therapy is performed.

A common cause of post-traumatic respiratory failure in closed chest trauma are multiple fractures of the ribs and sternum. Violations of the rib cage framework lead to significant changes in the biomechanics of the breathing act, limitation of the rib cage mobility, and, as a result, to gas exchange disorders manifested in rapidly increasing hypoxemia. That is why restoration of the disrupted rib cage framework is one of the most important therapeutic measures aimed at correcting gas exchange disorders and normalizing ventilation-perfusion relations in the lungs. One of the effective methods for eliminating the costal valve is extramedullary osteosynthesis.

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Epidural and retropleural anesthesia in patients with thoracic trauma

The severity of the condition of victims with thoracic trauma is aggravated by severe pain syndrome, which significantly disrupts ventilation-perfusion relationships in the lungs. Pain that occurs in victims with multiple rib fractures and pleural damage is especially difficult to bear.

Various analgesics and their combinations with sedatives, as well as various types of blockades, are traditionally used to relieve pain. In case of fractures of 1-2 ribs, it is advisable to use intercostal blockades, and in victims with multiple rib fractures - epidural blockades, which provide effective pain relief and help normalize ventilation-perfusion relations in the lungs. However, anesthesia performed in the early period of traumatic disease (against the background of infusion therapy and stabilization of hemodynamic parameters) cannot be considered safe due to the probable development of arterial hypotension, the cause of which may be relative hypovolemia, even in cases where the dose of local anesthetic is selected strictly individually, taking into account the severity of the patient's condition.

Retropleural anesthesia (RPA) has a good therapeutic effect in these conditions. As with epidural anesthesia, the anesthetic introduced into the retropleural space affects the sensory and motor roots of the spinal cord, as well as the sympathetic ganglia, thereby having a beneficial effect on the function of external respiration, without significantly changing the indicators of systemic hemodynamics.

The active introduction of this type of conduction anesthesia into intensive care practice was determined not only by its good analgesic effect and fairly simple technique of implementation, but also by the minimal number of complications, the risk of which can be quite significant in victims with shock.

The use of retropleural anesthesia as a method of pain relief in closed combined chest trauma has an obvious clinical effect, which consists of less pronounced, but quite sufficient analgesia and a softer hemodynamic effect compared to epidural blockade, which undoubtedly indicates the priority of this method in the treatment of victims with shock-producing trauma.

In clinical situations in which (despite the restoration of the rib cage framework, adequate pain relief and rational oxygen therapy) the symptoms of respiratory failure continue to increase, it is necessary to resort to prolonged artificial ventilation of the lungs as an inevitable means of stabilizing the rib cage.

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