CPAP - spontaneous breathing with constantly positive airway pressure

Currently, there are various devices and apparatus with which you can create excess pressure in the airways both during the entire breathing cycle and in its individual phases. When performing spontaneous breathing with constantly positive pressure (CPAP), pressure fluctuations inevitably occur, but it always remains above atmospheric pressure. This method is widely used in neonatology, since it does not require tracheal intubation, it is well tolerated by newborns and not only improves pulmonary gas exchange, but also stimulates the respiratory center.

[1], [2], [3], [4], [5]

Indications for use of CPAP

Indications for the use of CPAP are arterial hypoxemia (paO2 <50 mm Hg, with a fractional oxygen concentration (FiO2> 0.5) associated with impaired ventilation-perfusion ratios and intrapulmonary shunting, as well as with central or obstructive apnea in neonates. Mandatory condition - a satisfactory level of alveolar ventilation (PaCO2 <60-65 mm Hg and pH> 7.25) Therefore, CPAP is usually effective at the following conditions:

• light and moderate forms of ARDS of newborns,
• transient tachypnea of newborns,
• central and obstructive apnea of newborns,
• ablation from mechanical ventilation, 
• prevention and treatment of respiratory failure after extubation.

The method of carrying out svvtvnogo respiration with a constant positive pressure in the airways

CPAP can be performed by connecting pressure-regulating devices to the endotracheal tube, nasal or nasopharyngeal catheters.

For CPAP, neonatal infants usually use a double nasal cannula. They are easy to fix, they do not bother the child and provide satisfactory tightness. As the child breathes through the natural airways, air conditioning of the respiratory mixture is usually not required. The main disadvantage of this method is injury to the nasal mucosa. Approximately every 2 hours, it is necessary to clean the cannula and sanitize the nasal passages. To prevent the accumulation of air in the stomach, the introduction of a gastric probe is required.

As a single nasopharyngeal catheter, a conventional intubation tube can be used. The stability in maintaining the pressure with this method is even less than with the use of the cannula. When sputum enters the catheter, the aerodynamic resistance and the work of breathing increase sharply.

Through the endotracheal tube CPAP is usually performed when the patient is weaned from the ventilation. This is the most reliable way of maintaining pressure, conditioning the respiratory mixture and monitoring ventilation monitoring, since all the capabilities of the respirator are involved. Possible combination of CPAP and assisted ventilation or other methods of respiratory support Disadvantages of this method are associated with the need for endotracheal intubation.

When CPAP is performed, children usually use a pressure of 3 to 8 cm of water. Art. This pressure in most cases ensures the stability of pulmonary volumes, without causing pronounced hyperinflation of normally functioning alveoli. Starting pressure values:

• 4-5 cm of water in the treatment of newborns weighing <1500 g,
• 5-6 cm of water in the treatment of ARDS in newborns with a mass> 1500 g,
• 3-4 cm of water during the weaning from the ventilation or after extubation.

The concentration of oxygen in the respiratory mixture is usually set at 40-50%. In the event of discomfort, the appointment of sedatives is acceptable, except when the method is used to combat central apnea.

In 20-30 minutes after the beginning of CPAP and stabilization of the patient's condition, it is necessary to examine the gas composition of the blood. If hypoxemia persists with satisfactory ventilation, increase airway pressure by 2 cm of water. Art. However, do not routinely use a pressure above +8 cm of water. Since this usually does not give a tangible increase in p0O2, but it can lead to a significant drop in CB.

Acceptable is the pressure at which the rhythm and respiration rate normalizes, the traction of the compliant places of the chest decreases, and p02 stabilizes in the range of 50-70 mm Hg (paO2 - 90-95%) in the absence of respiratory acidosis.

Further, with the improvement of the child's condition, gradually (by 5%) oxygen concentration is reduced, bringing it to a nontoxic level (40%). Then, too slowly (1-2 cm of water), under the control of the gas composition of the blood, reduce the pressure in the airways. When it is possible to bring the pressure to 3 cm of water. Article, the conduct of CPAP is terminated. Oxygenation is continued in the tent, setting the oxygen concentration 10% higher than with CPAP.

If, despite CPAP at a pressure of +8 cm H2O and an oxygen concentration above 60%, hypoxemia (paO2 <50 mmHg) persists, hypoventilation and acidosis (PaCO2> 60 mmHg and pH <7.25) increase or cardiovascular insufficiency is increased, it is necessary to transfer the child to mechanical ventilation.

Contraindications to the use of CPAP

• congenital malformations (diaphragmatic hernia, tracheoesophageal fistula, atresia of the hoan),
• Respiratory acidosis (paco2> 60 mm Hg and pH <7.25),
• severe cardiovascular failure,
• Attacks of apnea, accompanied by bradycardia and non-treatable methylxanthines.

[6], [7], [8]

Dangers and Complications

• The use of CPAP increases the risk of the onset and progression of air leakage syndromes from the lungs (interstitial emphysema, pneumothorax). In addition, an excessive level of pressure can cause hyperinflation of the lungs and a decrease in extensibility.
• An increase in intrathoracic pressure can lead to a marked decrease in venous return and CB. These effects are most pronounced in patients with hypovolemia.
• Most methods of conducting CPAP creates the prerequisites for ingression and accumulation of air in the stomach. In the absence of decompression, not only vomiting and aspiration is possible, but also a rupture of the hollow organ.
• Fluctuations of MC in newborns as a result of changes in hemodynamics and gas composition of blood can create prerequisites for the development of periventricular hemorrhages.

[9], [10], [11]

Physiological effects of high blood pressure 

• prevents the early expiratory closure of the airways and promotes the expansion of hypoventilated alveoli, which leads to an increase in the functional residual capacity of the lungs, 
• improves ventilation-perfusion ratio, reduces intrapulmonary venous-arterial discharge and as a result increases paO2, 
• increasing initial low lung volumes, increases the extensibility of lung tissue, therefore, with the right pressure in the respiratory tract, the work of breathing is reduced, 
• stimulates the respiratory center through the baroreceptors of the lungs, as a result of which the breathing becomes more rhythmic and deep, its frequency decreases.