644 • The wide availability, ease of use, and low risk profile of nonin vasive ventilation (NIV) make it an attractive alternative to intu bation and invasive mechanical ventilation Consequently, its[.]
55 Noninvasive Ventilation in the Pediatric Intensive Care Unit OMAR ALIBRA HIM AND KATHERINE N SLAIN PEARLS • The wide availability, ease of use, and low-risk profile of noninvasive ventilation (NIV) make it an attractive alternative to intubation and invasive mechanical ventilation Consequently, its use is increasing in the pediatric intensive care unit Practitioners should be familiar with the variety of available technologies and patient interfaces • Although the successful use of NIV in parenchymal lung diseases has been described for decades, there are currently no acute disease processes in children for which the initial application of NIV is considered standard of care • The primary goal of NIV is to stabilize the critically ill patient through provision of adequate gas exchange and decreased work of breathing in a disease process expected to be self- limited • Careful patient selection is paramount for the success of NIV in critically ill children • Intubation should be considered in patients with acute respiratory failure receiving NIV who not show clinical improvement or have signs and symptoms of worsening disease process within a few hours of NIV implementation • Long-term use of NIV in children has been increasing over the last decades especially in patients with chronic respiratory failure Concordant with its rise in popularity, the benefits of noninvasive ventilation (NIV) in pediatric respiratory failure are increasingly being established The first widely relevant noninvasive mode of ventilation was developed in 1929 by Drinker and Shaw; the “iron lung” revolutionized treatment of acute poliomyelitis,1,2 but its size, expense, and challenges with patient accessibility, immobility, and comfort limited its practicality While invasive mechanical ventilation (IMV) remains the predominant mode of respiratory support for children with acute respiratory failure, the associated risks—including airway complications, ventilatorassociated lung injury and infections, and the need for potentially harmful sedatives and neuromuscular blockade—make consideration of alternative modes of respiratory support important.3,4 In the hospital setting, indications for NIV include respiratory failure anticipated to be quickly reversible, postextubation respiratory support, and for those patients with limitations of care Acutely ill children successfully managed with NIV have shorter hospital lengths of stay, shorter duration of ventilatory support, and decreased mortality compared with children treated with invasive ventilation.5,6 The wide availability, ease of use, and low-risk profile of NIV make it an attractive alternative to IMV Consequently, it is being used with increasing frequency in the pediatric intensive care unit (PICU).3 Therefore, practitioners should be familiar with the variety of available technologies and patient interfaces There are four basic types of NIV: high-flow nasal cannula (HFNC), continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), and negative-pressure ventilation (NPV) While HFNC does not augment tidal volume or mean airway pressure, it is another form of noninvasive support that is quickly rising in popularity and will be covered as well This chapter will review the epidemiology, physiology, clinical application, patient selection, monitoring, complications, and failure of NIV 644 Epidemiology The rising use of NIV in the PICU is primarily due to the popularity of noninvasive positive-pressure ventilation (NIPPV; i.e., CPAP and BiPAP) and HFNC As many as 23% of children admitted to the PICU receive HFNC,5 and many clinicians consider it a firstline therapy for treatment of acute respiratory failure.7,8 The popularity of HFNC is primarily due to its role in the treatment of bronchiolitis, with other common indications including asthma, postextubation respiratory support, and respiratory distress associated with congenital heart disease.5,9 The popularity of CPAP and BiPAP is also rising in the PICU A multicenter Italian study described an increase in use from 11.6% to 18.2% over a 7-year period,10 while another study including more than 3000 critically ill children showed an increase in BiPAP use from less than 1% to nearly 7% over a 5-year CHAPTER 55 Noninvasive Ventilation in the Pediatric Intensive Care Unit period.11 Practice surveys and smaller, single-center studies show similar trends.3 Common indications for CPAP and BiPAP include asthma, bronchiolitis, acute hypoxemic respiratory failure, pneumonia, and postoperative respiratory failure.10,11,13 Despite conflicting data to support its routine use in pediatric acute respiratory distress syndrome (PARDS), many practitioners express a willingness to use noninvasive positive pressure ventilation as treatment,3 and it is frequently employed as a first line respiratory modality.14 In a recent international, multicenter, prospective observational study including 708 children with PARDS, NIPPV was used in 22.6% of patients This is an increase from a decade prior, when an international cross-sectional study of 59 pediatric intensive care units (ICUs) showed that 8.5% of children meeting criteria for acute lung injury/ARDS criteria were treated with NIPPV.15 Physiology and Application of Noninvasive Ventilation While all modes of NIV can improve respiratory effort and pulmonary gas exchange, the respiratory support provided by HFNC, CPAP, BiPAP, and NPV differ in important ways Thus, understanding the physiology of these respiratory support modalities informs appropriate patient selection A proper understanding of the physiology is paramount in selecting the most appropriate NIV modality for a particular patient High-Flow Nasal Cannula The use of HFNC in pediatric acute hypoxemic respiratory failure has increased over the last decade, with nearly one-quarter of all children admitted to the PICU receiving this form of respiratory support.4 The popularity of HFNC is likely related to its ease of use, portability, tolerability, and its success in treating perinatal lung disease and viral bronchiolitis.17,18 Recent randomized controlled trials including children with bronchiolitis suggest that HFNC may be superior to the standard low-flow nasal cannula18,19 and equivalent to CPAP20 in prevention of treatment failure requiring escalation of care Clinicians may also choose to use HFNC in children at risk for development of PARDS, although data are limited in this subset of patients.21 Although incompletely understood, the benefits of HFNC are undoubtedly multifactorial In a tachypneic patient with diminished tidal volumes, the bulk movement of oxygen-rich gas past the nasopharyngeal dead space results in improved alveolar ventilation The increased flow rates provided by HFNC may also provide enough low-level positive pressure to overcome subtle upper airway obstruction Additionally, provision of conditioned inspiratory gas at high flow rates likely reduces inspiratory resistance through the nasal passages, improves mucociliary clearance, and reduces metabolic work associated with heating and humidifying the inspiratory gas.22–24 Together, these mechanisms often improve respiratory mechanics and gas exchange in children with acute respiratory failure (Fig 55.1).25–27 The HFNC system includes the following basic elements: (1) a source of pressurized and blended oxygen and air, (2) a water reservoir attached to a heated humidifier, (3) a heated circuit that maintains gas temperature and humidity, and (4) a nonocclusive cannula interface With initiation of HFNC, the clinician sets the gas temperature, fraction of inspired oxygen (Fio2), and flow rate We recommend an initial gas temperature 1°C to 2°C below 645 body temperature for comfort The initial HFNC Fio2 should be chosen based on patient need and physiology and adjusted to target a desired peripheral capillary oxygen saturation (Spo2) While there is no consensus regarding the ideal gas flow rate, there is evidence to support weight-based dosing, at least in infants.28 Modest respiratory support is provided with flow rates between 0.5 and 1.0 L/kg per minute, while increasing the flow to 1.5 to 2.0 L/kg per minute further attenuates intrathoracic pressure swings associated with work of breathing.29 Flows greater than L/kg per minute may not provide additional clinical benefit.30 Noninvasive Positive-Pressure Ventilation Modes of NIPPV, such as CPAP and BiPAP, are beneficial in patients with upper airway obstruction, neuromuscular disease, diseases of increased airway resistance (i.e., asthma or viral bronchiolitis), and in restrictive diseases, such as pneumonia and PARDS.31,32–34 In acute bronchospasm, expiratory resistance is greater than inspiratory resistance The increased lower airway resistance prolongs the expiratory time constant, leading to carbon dioxide retention and tachypnea A vicious cycle ensues whereby the increased respiratory rate precludes complete exhalation, causing air trapping, increased functional residual capacity (FRC), and intrinsic positive end-expiratory pressure (PEEP) Intrinsic PEEP is an additional load that the fatigued patient with respiratory embarrassment must work against This may be particularly problematic in small children, whose smaller airway caliber and more compliant chest wall make them vulnerable to an obstructive process, such as bronchiolitis and asthma.35 For these infants and children, NIPPV can unload fatigued respiratory muscles and prevent collapse of peripheral small airways to allow for a more complete exhalation and reduced work of breathing In patients with restrictive lung disease, compliance is decreased and chest wall expansion is limited Acute processes (including infection, effusion, alveolar or interstitial edema) and chronic processes (such as neuromuscular dysfunction or thoracic cage abnormalities) can all contribute to restrictive lung disease The resultant decreased FRC and decreased tidal volume lead to a compensatory increase in respiratory rate necessary to maintain minute ventilation The decreased FRC can also lead to further alveolar collapse and progressively worsening lung compliance from atelectasis The application of positive pressure in these patients decreases the inspiratory work of breathing, allowing generation of higher tidal volumes, subsequently increasing FRC.36 CPAP raises expiratory pressures above atmospheric pressure, making it appropriate for use in hypoxic respiratory failure in the acute setting.36 CPAP does not generate inspiratory flow, nor does it directly increase tidal volume It improves FRC by overcoming inspiratory work produced by elastic forces.37,38 Improved FRC can, in turn, decrease atelectasis and improve ventilation/perfusion (V/Q) matching Furthermore, the reduction in inspiratory work provided by CPAP allows the respiratory muscles to generate higher tidal volumes, indirectly improving ventilation In the CPAP mode, devices provide a constant flow with resultant constant positive pressure throughout the respiratory cycle while the patient breathes spontaneously CPAP is usually well tolerated in children,20,39,40 but some patients may need sedation at initiation or throughout the implementation to improve tolerance of the device-patient interface.41 With BiPAP, the clinician sets an expiratory positive airway pressure (EPAP), an inspiratory positive airway pressure (IPAP), inspiratory time, back-up respiratory rate, and Fio2 The IPAP assists with inspiration, while the EPAP maintains airway patency throughout 646 S E C T I O N V Pediatric Critical Care: Pulmonary Gas blender Humidifier Heater Cannula Heated circuit A B Breathing gas Warm water flow Warm water return Cross-section of tubing C • Fig 55.1 Commonly used devices for delivery of heated humidified gas mixtures via high-flow nasal cannula (HFNC) (A) HFNC system assembled using a blender heater/humidifier and wire heated circuit (B) Airvo-2 HFNC system (Fisher & Paykel Healthcare); (C) Precision Flow high-velocity nasal insufflation HFNC system (Vapotherm, Inc.) CHAPTER 55 Noninvasive Ventilation in the Pediatric Intensive Care Unit 647 • BOX 55.1 Goals of Noninvasive Positive Pressure Ventilation (NIPPV) A Short-Term NIPPV Long-Term NIPPV Decrease work of breathing Relieve dyspnea Improve gas exchange Avoid intubation Symptomatic relief Improve gas exchange Improve sleep duration and quality Prolong survival Improve quality of life it an attractive first-line support therapy However, care should be taken in patients with persistent hypoxemia and elevated respiratory rates, as both have been associated with failure of BiPAP.44,45 Goals of NIPPV are given in Box 55.1 Negative-Pressure Ventilation B C • Fig 55.2 Various interfaces for delivery of noninvasive ventilation support (A) Nasal pillows (Medical Innovations PedFlow and ResMed Swift FX) (B) Nasal (Sleepnet MiniMe 2) and oronasal (Respironics AF531) masks (C) Full face mask (Respironics FitLife) and helmet (arol NIV10301/X) (Images courtesy of the manufacturers.) expiration The difference between these two pressures assists in the generation of tidal volume; thus, BiPAP is an appropriate mode of ventilation for both hypoxic and hypercarbic respiratory failure A well-fitted patient interface is essential for effective CPAP and BiPAP use (Fig 55.2) Air leaks around an ill-fitting mask will prevent generation of adequate mean airway pressure However, masks that are too tight can lead to skin breakdown and pressure ulcers that will preclude prolonged use There are multiple patient interfaces available, including nasal pillows, nasal masks, oronasal masks, total face masks, helmets, and mouthpieces.42,43 The nasal, oronasal, and total face masks are most commonly used in the PICU With an appropriately fitting mask and patient-device synchrony, BiPAP can effectively provide mean airway pressure, improve oxygenation, and unload fatigued respiratory muscles in children with acute respiratory failure BiPAP is generally well tolerated in patients, and its low-risk profile makes The original negative-pressure iron lung ventilator used a large chamber enclosing the entire body save for the head (Fig 55.3) Advances in intubation and mechanical ventilation combined with the cumbersome nature of the iron lung led to the widespread use of invasive PPV as the main support modality in patients with respiratory failure While invasive PPV can improve outcomes in these patients, it is not free of morbidity and potential complications, particularly those related to airway injury, ventilator-associated lung injury, use of sedation and muscle relaxation, and increased hospital stay This has resulted in a renewed interest in NPV devices (e.g., RTX Biphasic Cuirass Ventilator, Hayek Medical) with new technology that overcomes some of the inadequacies of the traditional iron lung47–56 (Fig 55.4) The cuirass interface is a plastic shell that covers the anterior chest wall to deliver either continuous negative pressure or biphasic ventilation (Fig 55.5) In continuous negative extrathoracic pressure (CNEP) mode, negative pressure is maintained at a constant level throughout the respiratory cycle while the patient breathes spontaneously Conversely, during biphasic cuirass ventilation (BCV), inspiratory and expiratory phases are fully controlled (control mode) by modifying the negativity of the air pressure applied to the cuirass During inspiration, NPV creates subatmospheric (negative) pressures within the cuirass applied to the anterior chest wall, creating negative intra-alveolar pressures that allow air to flow into the lungs During expiration, the NPV device delivers less negative pressure (set on the ventilator as a positive number), creating positive intra-alveolar pressure that facilitates air movement out of the lungs This is physiologically very similar to spontaneous breathing, with the main exception that expiration in the NPV device is active, unlike restful spontaneous breathing in which expiration is passive and dependent on the elastic recoil of the chest wall The cuirass is available in seven pediatric and four adult sizes The cuirass and connecting tubing to the ventilator are reusable, but the disposable foam liners are for individual use only The foam liner is essential to create a seal between the cuirass and anterior chest wall that allows for generation of negative pressure CNEP is usually chosen as the initial support mode in patients undergoing NPV It is the NPV equivalent of CPAP The minimum CNEP support is 28 cm H2O; this level is then adjusted until the work of breathing improves (in increments of cm H2O) A pressure of 214 cm H2O generally is sufficient, but 648 S E C T I O N V Pediatric Critical Care: Pulmonary Pressure Negative pressure control manometer Positive pressure Negative Positive control Inspiration Exhalation Bellows Rotating wheel B A • Fig 55.3 Tank respirator (“iron lung”) During inspiration (A), a negative pressure is created in the cham- ber using a bellows system (shown in figure) or a piston Expiration (B) can be either passive or assisted with positive pressure (so-called biphasic ventilation) • Fig 55.4 Hayek RTX cuirass ventilator The chest cuirass is made of flexible plastic This ventilator is capable of conventional negative pressure ventilation as well as high-frequency chest wall oscillations support can be escalated to higher negative pressures (e.g., 220 cm H2O) as needed throughout the treatment course Escalation of support to control mode is warranted in cases of persistent respiratory distress or apnea unresponsive to CNEP Control mode is the NPV equivalent of synchronized intermittent mandatory ventilation (SIMV) pressure control, in which the patient is able to take spontaneous breaths in between ventilator mandatory breaths Inspiratory and expiratory pressures are set on the ventilator as negative and positive numbers, respectively, while maintaining inspiratory to expiratory pressures as a 3:1 ratio (e.g., 215, 15) The pressure differential, which is the mathematical number between inspiratory (I) and expiratory (E) pressures, determines the chest wall excursion and, ultimately, the tidal volume The I:E ratio is usually set at 1:1 but can be changed as needed The ventilator mandatory rate is set slightly above the patient respiratory rate but preferably not to exceed 60 breaths/ (e.g., set ventilator rate at 42 breaths/min if patient respiratory rate is 40 breaths/min) NPV may improve cardiac output by lowering intrathoracic pressure and increasing venous return to the heart (right ventricular preload) It also improves alveolar recruitment and FRC optimization, which decreases the pulmonary vascular resistance and right ventricle afterload, thereby increasing pulmonary blood flow These features make NPV a potentially advantageous modality in patients with right-sided heart failure, passive pulmonary circulation (Fontan circuit), or restrictive physiology (post–tetralogy of Fallot repair) and have been associated with increased pulmonary blood flow.51,53,57 To date, there is a paucity of data describing the use of NPV in pediatric acute respiratory failure In 1996, Samuels et al performed a prospective randomized controlled trial in 244 neonates comparing CNEP of 24 to 26 cm H2O with standard therapy, which included CPAP of cm H2O.58 Despite not reaching statistical significance, the study showed that the need for intubation was lower in the NPV group compared with the group that received standard therapy (86% vs 91%) The NPV group also received oxygen for fewer days compared with the control group (18.3 days vs 33.6 days, respectively).58 Al-Bakhi retrospectively compared the use of NPV to invasive PPV in infants with recurrent apnea secondary to acute bronchiolitis NPV was associated with a reduced rate of intubation, shorter PICU stay, and reduced sedation use.54 In an animal study of surfactant-depleted rabbits comparing NPV and PPV, Grasso and colleagues50 showed that NPV was associated with improved gas exchange, greater lung perfusion, better lung expansion, and decreased lung injury A ... out of the lungs This is physiologically very similar to spontaneous breathing, with the main exception that expiration in the NPV device is active, unlike restful spontaneous breathing in which... It is the NPV equivalent of CPAP The minimum CNEP support is 28 cm H2O; this level is then adjusted until the work of breathing improves (in increments of cm H2O) A pressure of 214 cm H2O generally... also choose to use HFNC in children at risk for development of PARDS, although data are limited in this subset of patients.21 Although incompletely understood, the benefits of HFNC are undoubtedly