CPR - spontaneous breathing with continuous positive airway pressure

Currently, there are various devices and apparatuses that can be used to create excess pressure in the respiratory tract both during the entire respiratory cycle and in its individual phases. When performing spontaneous breathing with constant positive pressure (CPAP), pressure fluctuations inevitably occur, but it always remains higher than atmospheric pressure. This method is widely used in neonatology, as it does not require tracheal intubation, is well tolerated by newborns and not only improves pulmonary gas exchange, but also stimulates the respiratory center.

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Indications for the use of CPAP

An indication for the use of CPAP is arterial hypoxemia (paO2 <50 mm Hg, with a fractional oxygen concentration (FiO2 >0.5) associated with impaired ventilation-perfusion relationships and intrapulmonary shunting, as well as with central or obstructive apnea in newborns. A mandatory condition is a satisfactory level of alveolar ventilation (paCO2 <60-65 mm Hg and pH >7.25). Therefore, CPAP is usually effective in the following conditions:

• mild and moderate forms of ARDS in newborns,
• transient tachypnea of the newborn,
• central and obstructive apnea of the newborn,
• weaning from artificial ventilation,
• prevention and treatment of respiratory failure after extubation.

Method of performing continuous positive airway pressure breathing

CPAP can be delivered by connecting pressure-regulating devices to an endotracheal tube, nasal catheter, or nasopharyngeal catheter.

Double nasal cannulas are usually used for CPAP in newborns. They are easy to fix, cause little discomfort to the child, and provide a satisfactory seal. Since the child breathes through the natural airways, conditioning of the breathing 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 cannulas and sanitize the nasal passages. To prevent air accumulation in the stomach, a gastric tube must be inserted.

A regular endotracheal tube can be used as a single nasopharyngeal catheter. The stability in maintaining pressure with this method is even less than when using cannulas. When sputum enters the catheter, aerodynamic resistance and breathing work increase sharply.

CPAP is usually performed through an intubation tube when weaning a patient off artificial ventilation. This is the most reliable way to maintain pressure, condition the breathing mixture, and monitor ventilation, since all the capabilities of the respirator are used. It is possible to combine CPAP with assisted ventilation or other methods of respiratory support. The disadvantages of this method are related to the need for endotracheal intubation.

When performing CPAP in children, pressure from 3 to 8 cm H2O is usually used. In most cases, such pressure ensures stability of lung volumes without causing pronounced hyperinflation of normally functioning alveoli. Starting pressure values:

• 4-5 cm H2O when treating newborns weighing <1500 g,
• 5-6 cm H2O in the treatment of ARDS in newborns weighing >1500 g,
• 3-4 cm H2O when weaning from mechanical ventilation or after extubation.

The oxygen concentration in the breathing mixture is usually set at 40-50%. If discomfort occurs, sedatives may be prescribed, except in cases where the method is used to combat central apnea.

Blood gas analysis should be performed 20-30 minutes after the start of CPAP and stabilization of the patient's condition. If hypoxemia persists with satisfactory ventilation, the airway pressure should be increased by 2 cm H2O. However, pressure above +8 cm H2O should not be used routinely, as this usually does not result in a noticeable increase in paO2, but can lead to a significant drop in CO.

Acceptable pressure is considered to be the one at which the rhythm and frequency of breathing are normalized, the retraction of the pliable areas of the chest is reduced, and PaO2 is stabilized in the range of 50-70 mm Hg (PaO2 - 90-95%) in the absence of respiratory acidosis.

Later, as the child's condition improves, the oxygen concentration is gradually reduced (by 5%), bringing it to a non-toxic level (40%). Then, just as slowly (by 1-2 cm H2O), under the control of the blood gas composition, the pressure in the respiratory tract is reduced. When the pressure is brought to 3 cm H2O, CPAP is stopped. Oxygenation is continued in the tent, setting the oxygen concentration 10% higher than with CPAP.

If, despite the use of CPAP at a pressure of +8 cm H2O and an oxygen concentration above 60%, hypoxemia persists (paO2 <50 mm Hg), hypoventilation and acidosis increase (paCO2 >60 mm Hg and pH <7.25), or cardiovascular failure worsens, the child must be transferred to mechanical ventilation.

Contraindications to the use of CPAP

• congenital malformations (diaphragmatic hernia, tracheoesophageal fistula, choanal atresia),
• respiratory acidosis (paCO2>60 mmHg and pH <7.25),
• severe cardiovascular failure,
• attacks of apnea accompanied by bradycardia and not amenable to treatment with methylxanthines.

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Dangers and complications

• The use of CPAP increases the risk of the development and progression of pulmonary air leak syndromes (interstitial emphysema, pneumothorax). In addition, excessive pressure levels can cause hyperinflation of the lungs and decreased compliance.
• Increased intrathoracic pressure may result in marked reductions in venous return and CO. These effects are most pronounced in patients with hypovolemia.
• Most methods of CPAP administration create conditions for air to enter and accumulate in the stomach. Without decompression, not only vomiting and aspiration are possible, but also rupture of the hollow organ.
• Fluctuations in MC in newborns as a result of changes in hemodynamics and blood gas composition can create preconditions for the development of periventricular hemorrhages.

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Physiological effects of high blood pressure

• prevents early expiratory closure of the airways and promotes the straightening of hypoventilated alveoli, which leads to an increase in the functional residual capacity of the lungs,
• improves ventilation-perfusion relationships, reduces intrapulmonary venous-arterial shunt and as a result increases raO2,
• by increasing the initially low lung volumes, it increases the elasticity of the lung tissue, therefore, with correctly selected pressure in the airways, the work of breathing decreases,
• stimulates the respiratory center through the baroreceptors of the lungs, as a result of which breathing becomes more rhythmic and deep, and its frequency decreases.