Noninvasive ventilation techniques augment alveolar ventilation without an indwelling artificial airway. This is accomplished with either negative (subatmospheric) or positive pressure administered via an external interface. Mechanical ventilation emerged first with negative pressure ventilation in 1830, predating the development of artificial airways. It had a long history of success in treating polio patients in respiratory failure. The concept of body ventilation later evolved to include positive pressure ventilation delivered via external masks covering some combination of the nose and mouth.

Noninvasive positive pressure ventilation (NPPV) has several advantages when compared with negative pressure ventilation. Its system components are small and portable, are easy to use and easy to fit, and cause less discomfort and avoid upper airway obstruction, unlike negative-pressure ventilators. In recent years, new technologies have become available that allow both short- and long-term use of NPPV in children.

These devices allow delivery of airflow under pressure, with or without supplemental oxygen, for gas exchange without an invasive airway. With the increased level of acuity seen in many pediatric hospitals as well as increasing numbers of technology-dependent children, hospitalists need to familiarize themselves with the indications and the technologies available in the hospital, delivery room, and emergency department, during transport, and in the special care and intensive care units.

A number of different devices are available, each with advantages and disadvantages. In general, most devices for noninvasive ventilation are pressure (rather than volume) controlled, with limited adjustment options.

CONTINUOUS POSITIVE AIRWAY PRESSURE

Devices for continuous positive airway pressure (CPAP) provide a continuous flow of delivered air to generate a preset pressure throughout the entire respiratory cycle. As illustrated in Figure 195-1, CPAP provides a constant airflow at a set supra-atmospheric pressure, superimposed on a patient’s spontaneous breaths. The additional airflow raises inspiratory pressures and applies a positive end-expiratory pressure, overall increasing mean airway pressure. The additional end-expiratory distending pressure helps prevent airway collapse and resultant atelectasis, in turn increasing the patient’s functional residual capacity. These effects have been shown to improve oxygenation and lessen work of breathing. CPAP does not directly increase tidal volume, however, and as such it provides respiratory support but not truly assisted ventilation.^1,2

BILEVEL POSITIVE AIRWAY PRESSURE

Bilevel positive airway pressure devices (e.g. BiPAP, Respironics Corporation) can provide different set pressures during inspiration and expiration.³ The pressure difference between expired positive airway pressure (EPAP) and inspired positive airway pressure (IPAP) serves to increase tidal volume and hence minute ventilation (see Figure 195-1).

Bilevel NPPV is commonly delivered in either the spontaneous (S) or spontaneous-timed (S/T) mode. In S mode, each patient breath is assisted by machine-delivered IPAP when the machine senses the change in airflow triggered by the inspiratory effort of the patient. Because there is no background respiratory rate set on the machine, a child must initiate each breath on his or her own.

In S/T mode, a respiratory rate can be set to provide a backup rate in the event that the child slows or ceases respiratory efforts. In this mode, the device responds to inspiratory and expiratory flow rates to cycle machine-initiated breaths between the patient’s inhalation and exhalation. It reliably senses a patient’s breathing efforts even when moderate air leaks are present in the circuit.

Since the degree of ventilation delivered is largely determined by the IPAP, tidal volume support is maintained despite the presence of significant air leaks. However, it is important to remember that with this pressure-determined modality, ventilation will fall in the presence of increasing airway resistance or reduced lung compliance.²

NASAL INTERMITTENT POSITIVE-PRESSURE VENTILATION

Nasal intermittent positive-pressure ventilation, also sometimes referred to as nasal intermittent mandatory ventilation (NIMV), is a form of bilevel noninvasive support administered to neonates, primarily in the neonatal intensive care unit (NICU) setting. Most commonly this is used in respiratory distress syndrome (RDS) secondary to prematurity, but other indications include other causes of respiratory distress in the neonate as well as apnea of prematurity. NIMV differs from previously discussed bilevel support primarily in that it is an exclusively unsynchronized method of ventilation, providing positive inspiratory pressure (analogous to IPAP) at a desired respiratory rate. Neonates with RDS often have patchy atelectasis secondary to insufficient or inactivated surfactant, retained fetal lung fluid, inflamed, weaker respiratory musculature, and/or obstructed airways. The positive end-expiratory pressure (analogous to CPAP/EPAP) provided by NIMV recruits atelectatic alveoli. Additionally, mandatory, timed machine-generated breaths help generate tidal volumes, which is important because premature neonates often have weak central respiratory drive as well as increased surface tension in the alveoli, making it difficult to expand the lungs on inspiration. Because of premature neonates’ small size and weaker respiratory musculature, they generate smaller negative inspiratory pressures that are not adequate to trigger NPPV flow sensors. The guaranteed assistance in minute ventilation provided by both mandatory respiratory rate and IPAP delivery makes NIMV preferable in neonates to bilevel NPPV. NIMV has been shown to prevent failure of extubation when compared to nasally-administered CPAP.⁴

HIGH-FLOW NASAL CANNULA

An additional delivery system gaining popularity is heated, humidified high-flow nasal cannula (HFNC), also known at some institutions by its brand name Vapotherm (Vapotherm, Inc). This system, which is not categorized as a form of NPPV by some, delivers heated and humidified oxygen via nasal prongs. Its use in hospitals has increased because it is easily tolerated, frequently more so that NPPV masks. Delivering humidified air directly into the nose has been beneficial in that it offers convenience for the patient in resuming activities, such as eating and speaking, and potentially avoids complications of NPPV masks such as skin breakdown of the nasal bridge, difficult mask fits, and headgear or strap discomfort. HFNC is not simply a different way to generate CPAP; it works through five distinct mechanisms to assist with respiration: (1) causes changeover of nasopharyngeal dead space gases, decreasing the waste of this area’s inspired volume, (2) decreases nasopharynx inspiratory resistance, (3) uses warmed and humidified air, leading to improved conductance in airways and improved pulmonary compliance, especially in neonates, (4) decreases metabolic work of humidifying and warming inspired air was well as decreasing insensible losses, and (5) increases flow rates through the cannula, which when transmitted to the distal airways lead to increases in positive end-expiratory distending pressure and lung recruitment.^1,5

HFNC systems allow for oxygen delivery to be titrated according to the patient’s respiratory status independent of the flow of air delivered. In addition, different combinations of gas can be given, such as helium–oxygen (heliox), which is a combination of helium and oxygen instead of nitrogen mixed with oxygen. Because of its lower density, helium makes the inspired gas lighter and thus enhances laminar air flow in airways which may be partially obstructed. It has been successfully used in bronchiolitis, asthma, and croup.⁶ Further discussion of the uses of HFNC in middle respiratory tract infections and bronchiolitis is included in Chapter 101.

OTHER MODALITIES

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  The Infant Flow SiPAP Comprehensive (CareFusion, San Diego, CA) ventilator includes an abdominal motion sensor which synchronizes the delivery of positive inspiratory pressure with the baby’s inspiratory effort.⁷

  
  
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  The SERVO-i ventilator (Maquet, Solna, Sweden) offers a neurally adjusted ventilatory assist by using the electrical activity of the diaphragm as a trigger for a machine breath; this can be used for both invasive and noninvasive ventilation.

  
  
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  When using the mouthpiece or “sip” ventilator, a cooperative, usually older child can breathe through a large straw-like device placed in the mouth, triggering a pressure-supported breath from a portable ventilator.

Indications for NPPV or HFNC include short-term and chronic conditions, some of which are listed in Table 195-1. Short-term use of NPPV or HFNC can be used when the disease state requiring positive pressure is reversible and resolution of the state is expected. Chronic use of NPPV may be indicated in disease states in which the respiratory failure is progressive or not expected to resolve.⁸

Initiation of NPPV for patients with an acute illness or exacerbation of subacute disease processes typically occurs in an intensive care unit (ICU) setting, although the initiation and use of HFNC is increasing outside of ICU settings at many institutions. Typically, strict guidelines for the amount of flow and oxygen are followed, and escalation above specified levels necessitates prompt transfer to an ICU. With the growing number of patients chronically on NPPV for some part of the day, some general wards are allowing for patients at stable home settings to be cared for outside an ICU.

ACUTE USES OF NONINVASIVE VENTILATION

Neonatal Support

Uses of NPPV in the newborn have increased with improved delivery devices and understanding of its effectiveness in neonates. Some of the most common indications include support in the delivery room, primary therapy for RDS (surfactant deficiency) or meconium aspiration syndrome, post-extubation support and weaning, avoidance of reintubation, and treatment of apnea. The most important goal of introducing noninvasive ventilation has been to decrease the need for intubation and mechanical ventilation, theoretically limiting the risk of barotrauma and volutrauma⁹ to newborn lungs.

Nasal CPAP and other modes of noninvasive ventilation have been used successfully to avoid intubation in RDS for some premature infants. The COIN trial examined whether early CPAP versus intubation led to significant decreases in chronic lung disease (bronchopulmonary dysplasia); by 36 weeks’ gestational age, there was no difference in rates of need for oxygen therapy between the two groups.¹⁰ Therefore the use of CPAP seems to be a valuable option that allows clinicians to avoid some of the risks of intubation in the preterm neonate (such as volutrauma, barotrauma, and airway trauma) without increasing the likelihood of the long term consequences of chronic lung disease.^7,10

Bronchiolitis

Bronchiolitis makes up a significant proportion of pediatric admissions to the general wards and ICUs. The use of NPPV is common and is used in both hypoxemic and hypercarbic respiratory failure as a modality to help prevent intubation or as a bridge off ventilatory support after extubation. More recently, heated, humidified HFNC has also been introduced as a support device for these children. HFNC is generally seen as safer, more comfortable to the patient, and applies lower flow levels than CPAP and bilevel NPPV, which has led to it being used on some general pediatric wards as an intermediary step, in an effort to prevent need for escalation to CPAP or bilevel NPPV and transfer to an ICU.¹¹

Pneumonia

In children with acute hypoxic respiratory failure resulting from pneumonia, NPPV has been shown to decrease rates of intubation in an ICU setting. Success of NPPV in these patients is manifested by decreased respiratory rates and heart rates as well as improved gas exchange. NPPV is being used in the treatment of mild to moderate pediatric acute respiratory distress syndrome, but data is limited on its effectiveness and comparability to standard treatment with invasive mechanical ventilation. NPPV has also been successfully used in the treatment of other conditions affecting the lower airways and lung parenchyma, such as the acute chest syndrome in sickle cell disease, cardiogenic pulmonary edema, and postoperative atelectasis. HFNC has also been used successfully for pneumonia and acute chest syndrome. It is actively being explored as an option for use in other lung diseases, but further studies on its effectiveness and optimal use in all of these indications is needed.