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9. Noninvasive Ventilation
Noninvasive ventilation (NIV) refers to mechanical ventilation without invasive artificial airways. There have been many noninvasive methods of assisted ventilation in the past, including negative pressure ventilator, rocking bed, pneumobelt, diaphragm pacing, and high-frequency oscillatory ventilation. However, in comparison to other noninvasive methods, noninvasive positive pressure ventilation (NIPPV) has become the dominant positive pressure ventilation method in the world due to its effectiveness and convenience, the use of a mask (or interface) to transfer gas from a positive pressure ventilator to the nose or mouth.
9.1 Noninvasive Positive Pressure Ventilation (NIPPV)
Mechanical ventilation that delivers gas to the airway through a mask or “interface” is called noninvasive positive pressure ventilation (NIPPV). It allows air leaks through the mouth or around the mask. The optimization of patient comfort and acceptance and effective management of air leaks are the keys to NIPPV’s success .
Indications for noninvasive positive pressure ventilation :
Acute exacerbations of COPD
To facilitate weaning in COPD
Acute cardiogenic pulmonary edema (use of CPAP)
Postoperative respiratory failure
Not intubating patients
Obstructive sleep apnea
Restrictive lung diseases
Upper airway obstruction
Acute respiratory distress syndrome
Life-threatening myocardial ischemia
Patients who do not cooperate
9.2 Human-Ventilator Interface
Interfaces are devices that connect ventilator tubing to the face, facilitating the pressurized gas into the lung through the entry of the airway. Appropriate interfaces can provide accurate target airway pressure, optimize patient comfort, and achieve the best treatment results. In determining the optimal pressure level, patients should be encouraged to try several different interfaces to determine the one with the best overall comfort and effect, that is, the most comfortable mask may not be the most suitable, and the most suitable mask may not be the most comfortable.
Currently available interfaces include a nasal mask, nasal pillow, full face mask (oronasal mask), and oral interface. An oronasal mask for acute and short-term diseases, and in cases of chronic and prolonged cases, a nasal mask; and if the patient does not cooperate well, full face masks are recommended. For some patients, an oronasal mask usually requires higher pressure and poorer control than a nasal mask, and in practice, the best choice of the interface varies from person-to-person. Many experts agree that the best interface is “the one the patient is willing to use” [3, 4].
9.3.1 Mask Intolerance
Mask intolerance is the most common problem encountered by patients in adapting to NIPPV. Trying different types of interfaces can help. Do not force patients to wear a mask for longer than they can tolerate, and encourage patients to try at least weeks or months to get used to noninvasive ventilation before considering giving up.
9.3.2 Nasal Congestion and Dry Nose
These symptoms are often seasonal. Increasing humidity and heat often improve the comfort and acceptance of airflow through the airways. The application of saline or nasal gel may also be effective for dry nose.
9.3.3 Redness or Ulcers on the Bridge of the Nose
When the mask puts too much pressure on the bridge of the nose causes the symptoms. Minimizing the tension of the straps or use another type of mask can often alleviate this problem. Some patients experience a rash where the mask comes in contact with the skin. It may be helpful to use glucocorticoid cream or to wash your face with a mild cleansing soap before using the mask.
The symptom is usually tolerable and transient without the need to adjust the settings.
9.3.5 Oral Leak
Patients are usually well ventilated in the presence of air leaks, and no special measures are required. The pressure-limited ventilation can maintain mask pressure by maintaining airflow to compensate for leaks. While volume-restricted ventilation, tidal volume needs to be adjusted to up to the compensation for leaks.
9.3.6 Failure to Improve Daytime Gas Exchange
If the gas exchange did not improve within a few weeks, considering the following factors: application time, air leaks accidentally, obstructive pulmonary diseases, human–ventilator asynchronization, and insufficient minute ventilation. By adjusting the inspiratory pressure or tidal volume, the frequency and the application time, or these parameters in combination, gas exchange may be improved. If there is evidence that the patient cannot trigger the ventilator, adjusting the trigger sensitivity or increasing the backup rate may be helpful .
9.3.7 The Deterioration of Gas Exchange after Initial Stabilization
In cases of progressive neuromuscular disease, the deterioration of gas exchange after initial stabilization often occurs. Pulmonary function tests and arterial blood gas analysis should be done periodically to assess the conditions. The frequency of follow-up depends on whether the patient has just started the treatment (every few weeks), or in a stable period of treatment (twice a year), or is experiencing clinical deterioration (more frequent follow-up). To improve the worsening of the lung function, it is often necessary to gradually increase inspiratory pressure, tidal volume, respiratory rates, or the application time of the ventilator.
9.4 Main Ventilation Techniques
9.4.1 CPAP (Continuous Positive Airway Pressure)
By delivering constant pressure during both inspiration and expiration, the variation ranges within 1–2 cm H2O, CPAP can increase functional residual capacity and prevent the alveoli from collapsing. CPAP can also decrease afterload and increase cardiac output. This method does not provide additional pressure above the CPAP level, the patients must trigger the ventilator spontaneously.
9.4.2 BiPAP (Bilevel Positive Airway Pressure)
BiPAP provides different levels of positive airway pressure during inspiration and expiration. The pressure level during inspiration is called inspirational positive airway pressure (IPAP), and the pressure level during expiration is called expiratory positive airway pressure (EPAP) .