Noninvasive Ventilation Procedures

Noninvasive ventilation (NIV) can be defined as a ventilation modality that supports breathing by delivering mechanically assisted breaths without the need for intubation or surgical airway.[1] It is a popular method of adult respiratory management in both the emergency department (ED) and the intensive care unit (ICU), and it is increasingly used in the care of pediatric patients.[2]  Besides avoiding the adverse effects of invasive ventilation, NIV has the added advantage of patient comfort. It has become an important mechanism of ventilator support both inside and outside the ICU.[3, 4, 5]

NIV is divided into two main types, negative-pressure ventilation (NPV) and noninvasive positive-pressure ventilation (NIPPV); the latter is further subdivided into several subtypes, including continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), and volume-assured pressure support (VAPS). This article addresses these methods and briefly discusses heliox adjunct therapy.

NIV is indicated in neonates and infants as follows:

• Weaning from the ventilator
• Preventing collapse of the lung
• Minimal need for respiratory support, with good respiratory drive
• Bronchiolitis

NIV is indicated in children as follows:

• Impending respiratory muscle fatigue
• Asthma
• Bronchiolitis
• Pneumonia
• Obstructive sleep apnea syndrome
• Chronic conditions (eg, Duchenne muscular dystrophy, other myopathies)
• Cystic fibrosis ^[6]

NIV is indicated in adults as follows:

• Obstructive sleep apnea syndrome
• Chronic obstructive pulmonary disease with exacerbation
• Bilateral pneumonia
• Acute congestive heart failure with pulmonary edema
• Neuromuscular disorders
• Acute lung injury
• Weaning from ventilator - A 2009 meta-analysis indicated that NIV, as a method of weaning critically ill adults from invasive ventilation, was significantly associated with reduced mortality and ventilator-associated pneumonia ^[7] ; although NIV is currently employed for weaning from invasive ventilation in the acute setting, its use for weaning from prolonged ventilation is still occasional and has not been standardized ^[8]

A systematic review and meta-analysis by Glenardi et al compared NIV with high-flow nasal oxygen therapy in COVID-19 patients with acute respiratory failure (ARF).[9]  NIV was found to have a higher success rate but also a significantly higher mortality. The authors suggested that high-flow nasal oxygen therapy should be considered before NIV in ARF associated with COVID-19 but noted that larger studies would be needed for better definition of the benefits of the former in this setting.

Absolute contraindications for NIV are as follows:

• Respiratory arrest or unstable cardiorespiratory status
• Uncooperative patients
• Inability to protect airway (impaired swallowing and cough)
• Trauma or burns involving the face
• Facial, esophageal, or gastric surgery
• Apnea (poor respiratory drive)
• Reduced consciousness
• Air leak syndrome

Relative contraindications for NIV are as follows:

• Extreme anxiety
• Morbid obesity
• Copious secretions
• Need for continuous or nearly continuous ventilatory assistance
• Lack of respiratory drive
• Diseases with air trapping (eg, asthma) - In a child on CPAP, periodic monitoring is required; if the clinical condition and arterial blood gases deteriorate despite CPAP support, intubation should be considered

A large retrospective cohort study by Lindenauer et al found that patients with severe COPD exacerbations who were treated with NIV at the time of hospitalization had lower inpatient mortality, shorter length of stay, and lower costs than patients who were treated with invasive mechanical ventilation.[10]

Another large retrospective cohort study found that in 1254 patients hospitalized with asthma exacerbation and receiving ventilatory support in the form of NIV or invasive mechanical ventilation, those successfully treated with NIV appeared to have better outcomes than those treated with invasive mechanic ventilation.[11]  However, it is possible that NIV may have been used selectively in a lower-risk group. 

Ventilating devices that may be used in noninvasive ventilation (NIV) include the following:

• Ventilators (see the first and second images below)
• Negative-pressure ventilator

Bilevel positive airway pressure (BiPAP) vision ventilator.

NIPPY ventilator (B&D Electromedical, Warwickshire, UK).

Interface appliances that may by used in NIV include the following:

• Nasal/nasopharyngeal prongs (see the first image below)
• Nasopharyngeal tube for continuous positive airway pressure (CPAP)
• Nasal mask (see the second image below)
• Face mask (see the third, fourth, and fifth images below)
• Head mask
• Cuirass (see the sixth image below)

Nasal and nasopharyngeal prongs for continuous positive airway pressure (CPAP).

This cushioned nasal mask (least invasive mask available) provides comfort by covering only nostrils. Stretchable strap around neck helps secure mask in place. Pressure over nasal cartilages and nasal septum should be preventing by checking frequently.

Noninvasive ventilation face mask that covers nose and mouth is shown with attachments, prior to fixation on patient’s face. Straps help secure mask tightly onto forehead and along sides of cheeks going around head, thereby maintaining tight seal.

This whole-face mask for noninvasive ventilation is very useful, especially with pediatric patients, in that it covers entire face while maintaining transparency so that children can appreciate presence of parents or caregivers. It helps improve compliance and reduce anxiety.

This full-face mask is suitable for noninvasive ventilation in that it provides seal over nose and mouth with minimal tension. Forehead cushion helps stabilize mask over front of forehead, thereby releasing pressure over nasal bridge.

Cuirass.

Anesthesia

Mild sedation and analgesia may be required to keep the patient comfortable. Anxiolytics may be helpful for patients experiencing claustrophobia from the face mask or for patients with increased respiratory rates secondary to anxiety. However, extreme caution must be exercised in using sedative agents in the setting of respiratory difficulty; these agents may depress respiratory drive and lead to hypercarbia or respiratory failure, thereby necessitating intubation. The respiratory effort of the patient must be maintained.

Patients generally are cooperative and do well with explanation of the application procedure.

Positioning

In noninvasive positive-pressure ventilation (NIPPV), positioning for face mask or nasal mask application is as follows[12] :

• Seat the patient in a bed or chair in a 30-90º upright position.
• Position the mask so that the nasal portion of the mask fits just above the junction of the nasal bone and cartilage
• A strap is needed to maintain correct positioning of most interfaces and is important for patient comfort; simple disposable Velcro straps are most often used, and these should be fastened so that one or two fingers can pass between the headgear and the face; it should be noted that erosion of the nasal bridge and nasal cartilage can occur with long-term use

Positioning for nasal prong application is as follows:

• Nasal prongs should fill the nasal openings completely without stretching the skin or putting undue pressure on the nares, and the corrugated tubing should not be touching the patient’s skin
• No lateral pressure should be exerted on the septum; such pressure could pinch or twist the septum

Consider the following when setting up the machine:

• Humidifier - Use a disposable humidifier top with a 1-L bag of water attached; adequate humidity prevents drying of secretions
• Oxygen flow - A gas flow of 6-10 L/min is delivered via a blender; this amount of gas flow provides adequate pressure to wash out carbon dioxide in the system, compensate for normal air leakage from tubing connections, and generate adequate pressure
• Occlude the pressure line connection port with the white plug provided; this completes the NIPPV circuit
• For CPAP, set the default pressure at 4-6 cm H ₂O; pressures of 10 cm H ₂O or higher may be used on an individual basis, depending on the patient's pathophysiology; remember to check the water level and adjust for evaporation, as necessary
• For bilevel positive airway pressure (BiPAP), common settings are about 15 cm H ₂O for inspiratory positive airway pressure (IPAP) and about 5 cm H ₂O for expiratory positive airway pressures (EPAP); for more details, see Noninvasive Positive-Pressure Ventilation
• Suction the airway, if necessary, before applying the face mask

Noninvasive ventilation (NIV; see the video below) is a popular method of adult respiratory management in both the emergency department (ED) and the intensive care unit (ICU), and it is increasingly used in the care of pediatric patients. NIV is divided into two main types: negative-pressure ventilation (NPV) and noninvasive positive-pressure ventilation (NIPPV). NIPPV is further subdivided into several subtypes, including continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), and volume-assured pressure support[13] (VAPS).

The following should be kept in mind in the provision of NIV:

• NIV should ensure maintenance of functional residual capacity (FRC)
• NIV should be the first line of respiratory therapy for carefully selected clinical problems
• NIV helps avoid associated adverse side effects of invasive ventilation (eg, ventilator-associated pneumonia, excessive sedation, barotrauma, and volutrauma)
• Vital signs, clinical profile, and blood gases should be monitored carefully, especially in the first few hours after initiation of NIV; this allows early recognition of signs of lack of improvement and timely consideration of the need for intubation in selected cases
• NPV mimics physiologic ventilation
• Heliox therapy may be useful in patients with a selected group of obstructive airway diseases (eg,  reactive airways disease)

In the context of the COVID-19 pandemic, it is important to remember that there is a risk of dispersion of aerosolized particles to the healthcare environment with poorly fitting masks; particular caution is therefore required when NIV is used in the critical care setting.[14, 15]

Because of its versatile applications, NIPPV is currently used for respiratory diseases, neuromuscular diseases, chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF), and diaphragmatic weakness.[16, 17, 18, 19, 20, 21, 22, 23]  It should be used to help buy time while other modalities are used to correct underlying medical problems. It may be used to delay or avoid tracheal intubation in some patients with acute respiratory distress.[24, 25]  Ease of administration and portability, as well as the ability to eliminate obstructive sleep apnea (OSA), make NIPPV the first choice among NIV modes.

NIPPV is most often begun in the ED, and acute pulmonary edema and exacerbation of COPD are the most common indications.[26]  However, NIPPV is also used in the ICU setting for acute respiratory failure. Additional uses have included weaning patients from invasive ventilation. NIPPV with BiPAP in patients who have undergone cardiac bypass or valve repair surgery has been shown to improve oxygenation after extubation as compared with nasal oxygen alone.[27, 28]

Continuous positive airway pressure

Ventilator mode

A CPAP ventilator delivers air at a constant pressure during inspiration and expiration. The patient must be able to breathe spontaneously.

Use

CPAP is mainly used for hypoxemic respiratory failure (eg, in acute pulmonary edema). It prevents alveolar collapse and facilitates oxygen delivery to pulmonary capillaries. CPAP increases the FRC and opens collapsed alveoli, and this, in turn, enhances gas exchange and oxygenation.

CPAP reduces left ventricular transmural pressure, thereby increasing cardiac output. Hence, it is very effective for treatment of acute pulmonary edema and is considered the modality of first choice in these patients. Pressures usually are limited to 5-15 cm H2O. Each patient’s requirements must be reviewed in light of his or her disease process and disease pathophysiology. Caution is advised in patients with borderline low blood pressure, who may become hemodynamically unstable; one of the disadvantages of CPAP is reduced venous return.

In the ED and the ICU, CPAP is generally administered via a face mask, with a seal created over the mouth and nose (see the images below). In some cases, however, a smaller mask can be used that covers just the nose. For patients who require CPAP at home on a nightly basis because of nocturnal hypoxemia due to episodes of OSA, nasal prongs provide a pneumatic splint that holds the upper airway open. CPAP provides positive airway pressure throughout all phases of spontaneous ventilation.

Continuous positive airway pressure (CPAP) administered on adult patient.

Continuous positive airway pressure (CPAP) administered on child.

Bilevel positive airway pressure

Ventilator mode

BiPAP is pressure-limited ventilation. Predetermined inspiratory pressure is delivered, which can cause different tidal volumes, depending on the resistance of the respiratory system. BiPAP has the advantage of leak compensation. It is preferred for most short-term applications because pressure-limited modes are better tolerated than volume-limited modes.

BiPAP involves the following three modes:

• Pressure support - The ventilator delivers air at a set pressure during inspiration each time a patient initiates a breath
• Pressure control - The ventilator automatically delivers a set number of breaths per minute at a set pressure
• BiPAP - The ventilator delivers different pressures during inspiration and expiration; if necessary, this mode can fully ventilate the patient

Use

BiPAP provides two forms of positive pressure: inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP). This is highly beneficial in patients with respiratory fatigue or failure. During exhalation, pressure is variably positive. Airflow in the circuit is sensed by a transducer and is augmented to a preset level of ventilation. Cycling between inspiratory and expiratory modes may be triggered by the patient's breaths or may be preset. BiPAP helps in improving patient comfort.

BiPAP is a particularly effective respiratory modality when patients are not improving sufficiently on CPAP alone. Not only does it provide the benefit of CPAP by providing increased airway pressure during expiration, but it also adds inspiratory assistance that may further reduce the work of breathing and assist with augmenting the ventilator in patients at risk for hypercapnia (eg, patients with COPD).

Patients may tire from breathing against resistance, even as it helps prevent alveoli from closing.

A common practice is to use initial settings of 10-12 cm H2O for IPAP and 5-7 cm H2O for EPAP and then to adjust IPAP to 15-20 cm H2O, depending upon the response over the next hour or so.

In conditions such as lung collapse or pulmonary edema, the initial EPAP may have to be high. However, an EPAP that is too high can lead to reduced preload. Hence, a balance in adjusting the ventilatory settings is desirable. Backup rates can be chosen according to the age of the patient. The fraction of inspired oxygen (FiO2) is another useful variable in titrating the response to oxygenation.

Volume-assured pressure support

VAPS is a mode of NIV that automatically adjusts inspiratory pressure in order to maintain a constant respiratory volume. In patients with chronic respiratory failure, its effects do not appear to differ significantly from those of BiPAP.[13, 29]

Volume-limited ventilation

Ventilator mode

In volume-limited ventilation, a predetermined tidal volume or minute volume is delivered each time a patient takes a breath. This leads to varying peak inspiratory pressures, depending on the resistance of the respiratory system.

Use

In this mode, ventilators usually are set in assist-control mode with high tidal volume (10-15 mL/kg) to compensate for air leaks. Interfaces can be selected to suit the comfort of the patient.

This mode is suitable for obese patients or patients with chest-wall deformities (ie, patients who need high inflation pressure) and for patients with neuromuscular diseases who need high tidal volumes for ventilation.

The prototypical NPV device was the iron lung which was first used in 1928, but is best known for its role during the polio epidemics of the 1950s.

The Hayek oscillator (see the image below) is a subsequently developed NPV device that applies high-frequency oscillation by using an airtight cuirass (a jacket of flexible foam sealed to fit around the chest and abdomen).[30]  It is designed to provide negative pressure during inspiration and positive pressure during expiration, creating controlled ventilation, including high-frequency chest-wall oscillation.

Hayek oscillator.

The medical use of heliox (a low-density misture of helium and oxygen) as a breathable gas in the treatment of respiratory disease was first introduced in 1934 by Barach. Since then, heliox has been studied in various upper- and lower-airway conditions by many investigators. Vineet et al conducted a computerized bibliographic search of available clinical material on the properties of helium and its applications in pediatric intensive care.[31]

NIPPV can be used to treat patients with upper-airway obstructions such as those caused by glottic edema following extubation. In this situation, NIPPV can be combined with aerosolized medication, heliox, or both.

Heliox administration is most effective in conditions involving density-dependent increases in airway resistance, especially when used early in an acute disease process. Substituting helium for nitrogen in a gas mixture changes the physical properties of the inhaled gas, decreasing gas density and increasing laminar air flow in the airway.

Heliox therapy also appears to be beneficial in COPD exacerbations. Jaber et al demonstrated that administering heliox during noninvasive pressure-support ventilation led to improvements in pH level, arterial oxygen tension (PaCO2), and work of breathing in patients with acute exacerbation of COPD.[32]  It may also improve clinical tolerance and potentially further reduce the need for invasive ventilation in selected patients.

Gainnier et al reported that in their randomized, prospective study in adults, the helium-oxygen mixture decreased the work of breathing in patients with COPD who were mechanically ventilated.[33]  Hence, the helium-oxygen mixture may be useful in reducing the burden of ventilation.

For effective results, heliox should be used in a combination ratio of 60 parts helium to 40 parts oxygen or 79 parts helium to 21 parts oxygen.

Heliox can be administered as a nebulization or via ventilator, though not all ventilators have the ability to add heliox.

Some of the medical conditions in which heliox may be useful include the following:

• Croup
• Bronchial asthma
• COPD
• Acute airway obstruction
• Epiglottitis
• Laryngitis
• Tracheitis
• Stridor
• Foreign body aspiration
• Tracheomalacia/stenosis
• Cystic fibrosis
• Bronchiectasis

Continuing heliox therapy for hours has significant cost implications, in that the heliox cylinders (see the images below) run out reasonably quickly. Any beneficial effect of heliox should become evident in a relatively short period.

Heliox cylinders.

NIPPV has relatively few complications when compared with invasive ventilation. Patients must be monitored carefully for worsening respiratory distress, tachypnea, and deteriorating blood gas values. Inadequate clearance of respiratory secretions may pose a problem, especially because the seal must be maintained.

NIV should be used with extreme caution in patients with pulmonary processes (eg, a lobar pneumonia) that affect only one side of the lungs. In such cases, NIV primarily ventilates the good lung, producing increased pressure on that side, which leads to decreased blood flow to the healthy lung and increased pulmonary blood flow to the affected lung, or area of lower pressure. This can lead to a relative decrease in gas exchange.

It is extremely important for the air seal to be tight, and the skin may be affected. Most complications are related to local skin effects, especially with long-term use. These include ulceration and pressure necrosis at the application sites of appliances such as masks, straps, or nasal prongs. Protective synthetic coverings (eg, CombiDERM ACD, ConvaTec DuoDERM CGF control gel formula dressing) may help prevent skin breakdown and ulceration on the bridge of the nose. Eye irritation and pain or congestion of the nasal sinuses may occur.

Distention of the stomach due to aerophagia and aspiration secondary to vomiting during NPV are additional concerns. When gastric distention occurs, a nasogastric tube can be used to relieve the distention while still allowing the mask to seal.

Adverse hemodynamic effects from NPV are unusual, though preload reduction and hypotension may occur.[34, 33]