When it is used in mechanical assisted ventilation (AMV), when the patient breathes weakly, the airway pressure drops to zero or negative pressure when inhaling, which triggers breathing to do work, thus triggering the ventilator to synchronously deliver air for auxiliary breathing.
When exhaling, the ventilator stops working, and the gas in the lungs is discharged from the body by the elastic retraction of the chest and lungs.
Auxiliary/Controlled Ventilation (A/C) This mode combines the characteristics of AMV and CMV. When the patient breathes spontaneously and can trigger the ventilator to deliver air, it is AMV. Ventilation frequency is determined by the patient's spontaneous breathing. When the patient does not spontaneously breathe or the inspiratory negative pressure cannot reach the preset trigger sensitivity, the machine automatically switches to CMV to deliver air according to the preset breathing frequency and tidal volume.
It is the most commonly used ventilation method at present.
When patients with pressure support ventilation (PSV) inhale, the ventilator provides predetermined positive pressure to help patients overcome airway resistance, expand lungs, reduce inspiratory muscle strength and increase tidal volume.
At the end of inhalation, the positive airway pressure disappears, and the patient can exhale without obstacles.
Intermittent Command Ventilation (IMV) Synchronous Intermittent Command Ventilation (SIMV) IMV is a combination of spontaneous breathing and controlled breathing.
On the basis of spontaneous breathing, patients are given regular intermittent ventilation instructions, and gas is forced into the lungs to provide partial ventilation needed by patients.
Its tidal volume and ventilation frequency are preset by the ventilator, and any ventilation support level of 0- 100% can be delivered through commanded ventilation.
Increasing the frequency and tidal volume of IMV will increase the proportion of ventilation support until ventilation is completely controlled.
If spontaneous breathing is strong, the level of ventilation support can be gradually reduced, and patients can easily transition to complete spontaneous breathing and finally evacuate the ventilator.
This mode is usually used to empty the ventilator.
Positive end-expiratory pressure (PEEP) can increase the trans-pulmonary end-expiratory pressure, enlarge alveoli, re-expand collapsed alveoli, and increase compliance, thus improving ventilation and oxygenation, making V/Q appropriate, increasing oxygen partial pressure, reducing oxygen concentration, and effectively preventing lung injury caused by oxygen poisoning.
Generally speaking, when the mechanical ventilation mode and parameters are properly selected, the oxygen concentration reaches 50% or above, and the oxygen partial pressure is still less than 60mmHg, PEEP can be appropriately added.
At 5- 15cmH2O, patients with continuous positive airway pressure (CPAP) spontaneously breathed, and positive airway pressure was delivered during inspiration and expiration. The expiratory air flow is greater than the inspiratory air flow, and the air flow and positive pressure can be adjusted according to the patient's specific conditions, which has similar physiological effects to PEEP, but CPAP increases the functional residual capacity more than PEEP.
Deep inhalation (sigh sigh) Every 50- 100 breaths, the machine will automatically strengthen deep inhalation, and the tidal volume is 65438+ 0.5-2 times of the set tidal volume. Its physiological function is to make the alveoli expand regularly to prevent atelectasis and alveolar collapse. BIPAP is a noninvasive ventilation method developed in recent ten years, namely CPAP plus PSS.
When patients inhale, BIPAP ventilator provides higher inspiratory pressure to help patients overcome airway obstruction, thus increasing ventilation and reducing the work of breathing.
When exhaling, the machine automatically reduces the pressure, making it easier for patients to exhale gas and providing appropriate positive end-expiratory pressure.
The advantage is that ventilation is supported by the mask, and no artificial airway is needed.
Arterial blood gas analysis is the main basis of mechanical ventilation regulation.
Therefore, arterial blood gas analysis should be measured regularly during mechanical ventilation.
PaO2 is an index reflecting arterial oxygenation.
After 30 minutes of effective mechanical ventilation, PaO2 _ 2 should rise to above 60 mmHg, otherwise it should be regarded as ineffective mechanical ventilation.
If PaO2 _ 2 _ 2 can't reach the ideal level, the following methods should be adopted: a, appropriately increase the oxygen concentration; B. adding PEEP C to prolong the inhalation time; PaCO2 PaCO2 _ 2 is an index reflecting the ventilation effect.
Under ideal ventilation conditions, the PaCO _ 2 of patients should be maintained at 40-50mmHg. After a period of ventilation, the PaCO _ 2 of the patient is still significantly higher than the normal value, indicating that the ventilation volume is insufficient, which should be corrected by appropriately increasing the ventilation volume, ventilation frequency, prolonging the expiration time and ventilation volume per minute.
If PaCO2 _ 2 _ 2 is too low after ventilation, it means that patients are hyperventilated, which may lead to metabolic alkalosis and respiratory alkalosis in patients with chronic respiratory failure. The tidal volume, air exchange times and air exchange per minute should be reduced to adjust.
Hemodynamic monitoring
1 bedside monitoring temperature, pulse, blood pressure, urine volume.
2 arterial pressure monitoring
3 Central venous pressure monitoring is not commonly used.
Application of pulmonary artery catheter
The humidifier needs 350-500ml of water every day, with intermittent injection of 20-60 ml each time, dropping 3-5 ml each time during sputum suction, or dropping 4-6 ml of wetting agent continuously. It is best to use distilled water or cold boiled water. Normal saline is not recommended at present.
Handling of common problems
Man-machine confrontation
1 easy to appear in the early stage.
In the middle stage, oxygenation and ventilation are not improved, especially when the lungs are severely humidified and the compliance is reduced, the blood flow ratio is unbalanced during severe ventilation, and hypoxemia and respiratory acidosis often lead to obvious respiratory asynchronism.
3 poor synchronization performance, artificial airway obstruction and air leakage.
Treatment: carefully check the position of tracheal intubation, whether there is secretion retention, whether the rear airbag leaks, and the reasons for treatment.
Sedatives can be used, such as intravenous diazepam.
The life-threatening problem of alarm is that the pressure of alarm air source is too high, exhalation valve and timer fail, and power failure should be dealt with immediately. The low-pressure alarm is out of touch with the patient, and the high-pressure alarm for air leakage blocks the machine with phlegm.
Pointer: The general condition is improved, the respiratory function is obviously improved, the blood gas analysis is stable, and there is no acid-base imbalance and electrolyte disorder. After mechanical ventilation, the vital signs are stable, and the lung function indexes meet the following conditions, so you can go offline (vital capacity ≥ 10 ~ 15 ml/kg). FEV 1.0 ≥ 10 ml/kg maximum inspiratory negative pressure.