Artificial ventilation

Traditional artificial ventilation of the lungs

Controlled ventilation is performed when the patient does not have spontaneous breathing or it is undesirable in a given clinical situation.

In neonates, controlled and assisted artificial ventilation of the lungs is performed exclusively by pressure-oriented ventilators, switching on time, with a continuous gas flow in the breathing circuit. These devices allow easy compensation of gas leaks in the breathing circuit, which usually occur during ventilation in small children. High gas flow rates in the circuit of such respirators ensure rapid delivery of the required gas volumes when spontaneous inspirations occur, which minimizes the work of breathing. In addition, the slowing inspiratory flow ensures better gas distribution in the lungs, especially when there are areas with non-uniform mechanical properties.

Indications for artificial ventilation

Indications for artificial ventilation should be determined individually for each newborn. It is necessary to take into account the severity of the condition and the nature of the disease, the gestational and postnatal age of the child, clinical manifestations of respiratory and cardiovascular failure, X-ray data, acid-base balance and blood gas composition.

The main clinical indications for mechanical ventilation in newborns:

• apnea with bradycadia and cyanosis,
• refractory hypoxemia,
• excessive work of breathing,
• acute cardiovascular failure.

Additional criteria may include the acid-base balance and blood gas composition indicators:

• paO2 <50 mm. rt. Art. at FiО2 >0.6,
• рАО2 <50 mm Hg with CPAP >8 cm H2O,
• paCO2 >60 mmHg and pH <7.25

When analyzing laboratory test data, both absolute values and dynamics of the indicators are taken into account. The blood gas composition can remain within acceptable limits for a certain time due to the stress of compensatory mechanisms. Considering that the functional reserve of the respiratory and cardiovascular systems in newborns is much lower than in adults, it is necessary to decide on the transition to artificial ventilation before signs of decompensation appear.

The goal of artificial ventilation is to maintain paO2 at a level of at least 55-70 mm Hg (SO2 - 90-95%), paCO2 - 35-50 mm Hg, pH - 7.25-7.4.

Modes of artificial ventilation

Normal mode

Starting parameters:

• FiO2 - 0.6-0.8,
• ventilation frequency (VR) - 40-60 per 1 min,
• inspiratory duration (ID) - 0.3-0.35 s,
• PIP - 16-18 cm water. st,
• PEEP - 4-5 cm water. Art.

Having connected the child to a respirator, first of all pay attention to the chest excursion. If it is insufficient, then every few breaths increase PIP by 1-2 cm H2O until it becomes satisfactory and VT reaches 6-8 ml/kg.

The child is provided with a comfortable state by eliminating external irritants (stop manipulations, turn off bright lights, maintain a neutral temperature regime).

Tranquilizers and/or narcotic analgesics are prescribed: midazolam - saturation dose of 150 mcg/kg, maintenance dose of 50-200 mcg/(kg h), diazepam - saturation dose of 0.5 mg/kg, trimeperidine - saturation dose of 0.5 mg/kg, maintenance dose of 20-80 mcg/(kg h), fentanyl - 1-5 mcg/(kg h).

After 10-15 minutes from the start of artificial ventilation, it is necessary to monitor the blood gas composition and adjust the ventilation parameters. Hypoxemia is eliminated by increasing the average pressure in the respiratory tract, and hypoventilation is eliminated by increasing the respiratory volume.

"Permissible hypercapnia" mode

The “permissible hypercapnia” regime is established if there is a high risk of development or progression of baro- and volutrauma.

Approximate gas exchange rates:

• p CO2 - 45-60 mm Hg,
• pH >7.2,
• VT- 3-5 ml/kg,
• SpO2 - 86-90 mm Hg.

Hypercapnia is contraindicated in intraventricular hemorrhage, cardiovascular instability, and pulmonary hypertension.

Weaning from artificial ventilation begins when the state of gas exchange improves and hemodynamics stabilizes.

Gradually decrease FiO2 <0.4, PIP <20 cm H2O, PEEP >5 cm H2O, VR <15/min. After this, the child is extubated and transferred to CPAP via nasal cannula.

The use of trigger modes (B1MU, A/S, RBU) during the period of weaning from the ventilator allows for a number of advantages, primarily related to a reduction in the frequency of baro- and volumetrauma.

High-frequency oscillatory artificial ventilation of the lungs

High-frequency oscillatory ventilation (HFOV) is characterized by frequency (300-900 per 1 min), low tidal volume within the dead space, and the presence of active inhalation and exhalation. Gas exchange during HFOV is carried out both by direct alveolar ventilation and as a result of dispersion and molecular diffusion.

Oscillatory artificial ventilation of the lungs constantly maintains the lungs in a straightened state, which contributes not only to the stabilization of the functional residual capacity of the lungs, but also to the mobilization of hypoventilated alveoli. At the same time, the efficiency of ventilation is practically independent of regional differences in the mechanical properties of the respiratory system and is the same with high and low compliance. In addition, at high frequencies, the amount of air leakage from the lungs decreases, since the inertia of fistulas is always higher than that of the respiratory tract.

The most common indications for HFOV in newborns:

• unacceptably strict parameters of traditional mechanical ventilation (MAP>8-10 cm H2O),
• the presence of air leak syndromes from the lungs (pneumothorax, interstitial emphysema).

Parameters of HFV

• MAP (mean airway pressure) directly affects the level of oxygenation. It is set 2-5 cm H2O higher than with traditional mechanical ventilation.
• The oscillation frequency (OF) is usually set in the range of 8-12 Hz. A decrease in the ventilation frequency leads to an increase in the respiratory volume and improves the elimination of carbon dioxide.
• The AP (oscillation amplitude) is usually selected so that the patient has visible vibration of the chest. The higher the amplitude, the greater the respiratory volume.
• BYu2 (fractional oxygen concentration). It is set the same as with traditional artificial ventilation.

Correction of the parameters of the HF mechanical ventilation should be made in accordance with the blood gas composition indicators:

• in hypoxemia (pa02 <50 mm Hg),
• increase the MAP by 1-2 cm of water column, up to 25 cm of water column,
• increase B102 by 10%,
• apply the lung straightening technique,
• in hyperoxemia (pa02>90 mm Hg),
• reduce BYu2 to 0.4-0.3,
• in hypocapnia (paCO2 <35 mm Hg),
• reduce AR by 10-20%,
• increase the frequency (by 1-2 Hz),
• in hypercapnia (paCO2>60 mm Hg),
• increase AP by 10-20%,
• reduce the oscillation frequency (by 1-2 Hz),
• increase MAR.

Termination of HF mechanical ventilation

As the patient's condition improves, SO2 is gradually (in increments of 0.05-0.1), bringing it to 0.4-0.3. MAP is also gradually (in increments of 1-2 cm H2O) reduced to 9-7 cm H2O. After this, the child is transferred either to one of the auxiliary modes of conventional ventilation, or to CPAP via nasal cannulas.