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Respiratory Failure

Phuong Vo, MD,* Virginia S. Kharasch, MD† *Division of Pediatric Pulmonary and Allergy, Boston Medical Center, Boston, MA †Division of Respiratory Diseases, Boston Children’s Hospital, Boston, MA

Practice Gap

The primary cause of cardiopulmonary arrest in children is unrecognized respiratory failure. Clinicians must recognize respiratory failure in its early stage of presentation and know the appropriate clinical interventions.

Objectives After completing this article, readers should be able to:

1. Recognize the clinical parameters of respiratory failure. 2. Describe the respiratory developmental differences between children and adults. 3. List the clinical causes of respiratory failure. 4. Review the pathophysiologic mechanisms of respiratory failure. 5. Evaluate and diagnose respiratory failure. 6. Discuss the various clinical interventions for respiratory failure.

WHAT IS RESPIRATORY FAILURE?

Respiratory failure is a condition in which the fails in oxy- genation or carbon dioxide elimination or both. There are 2 types of impaired gas exchange: (1) hypoxemic respiratory failure, which is a result of failure, and (2) hypercapnic respiratory failure, which is a result of respiratory pump failure (Figure 1). (1)(2) In hypoxemic respiratory failure, ventilation-perfusion (V_ =Q)_ mismatch

results in the decrease of PaO2) to below 60 mm Hg with normal or low PaCO2. _ = _ (1) In hypercapnic respiratory failure, V Q mismatch results in the increase of AUTHOR DISCLOSURE Drs Vo and Kharasch fi PaCO2 to above 50 mm Hg. Either hypoxemic or hypercapnic respiratory failure have disclosed no nancial relationships can be acute or chronic. Acute respiratory failure develops in minutes to hours, relevant to this article. This commentary does not contain a discussion of an unapproved/ whereas chronic respiratory failure develops in several days or longer. In acute investigative use of a commercial product/ hypercapnic respiratory failure, the pH decreases below 7.35, and, for patients device.

with underlying chronic respiratory failure, the PaCO2 increases by 20 mm Hg ABBREVIATIONS from baseline. (2) Acute and chronic hypoxemic respiratory failure cannot be ECMO extracorporeal membrane readily distinguished from arterial blood gases. Clinical markers, such as oxygenation polycythemia, pulmonary hypertension, or cor pulmonale, indicate chronic VAP ventilator-associated . V_ =Q_ ventilation perfusion

476 Pediatrics in Review Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 Figure 1. Types of respiratory failure.

EPIDEMIOLOGY conditions, such as lung and airway disorders, respiratory pump failure, respiratory center failure, and failure to meet Infants and young children have a higher frequency of increased metabolic needs (Table 1). respiratory failure. (3)(4) Approximately half of respiratory The pathophysiologic mechanisms that lead to respira- failure cases are seen in the neonatal period, resulting from tory failure involve primarily either V_ =Q_ mismatch or im- complications of prematurity and transitioning to extrauter- pairment of oxygen transfer at the alveolar-capillary ine life. In addition, developmental differences between membrane. (1)(2)(5) V_ =Q_ mismatch most commonly con- children and adults also explain the higher incidence. (1) tributes to respiratory failure. During gas exchange, per- (3)(4) First, infants and young children have a smaller upper fusion and ventilation try to match each other (V_ =Q_ ¼1). (6) airway, with the subglottic area being the narrowest. Any However, both do not perfectly match, even in healthy inflammatory process can result in airway narrowing and . During alveolar ventilation, some capillary units are subsequently in increased work of . Second, underperfused, whereas others are overperfused. Simi- immature stages of lung growth and development present larly, during perfusion, some alveolar units are under- with fewer numbers of alveoli, smaller intrathoracic airway ventilated, whereas others are overventilated. A high V_ =Q_ caliber with little cartilaginous support, and underdeveloped ratio is when the alveoli are well ventilated but are not well collateral ventilation, predisposing infants to . perfused. High V_ =Q_ ratios act like dead space. A low V_ =Q_ Third, infant respiratory muscles have reduced type 1 mus- ratio is when the alveoli units are well perfused but are not cle fibers, specifically the diaphragm, resulting in lower well ventilated. Low V_ =Q_ ratios act like shunts. respiratory tract muscle bulk and reserve. Fourth, the chest Diffusion limitation is the impairment of transfer of oxygen wall is more compliant than in adults because of a less bony at the alveolar-capillary membrane. (1)(2)(6) This can result thorax, compromising thoracic expansion, and may result in from alveolar or interstitial inflammation and fibrosis. Diffu- accessory muscle use and paradoxical patterns of respiration. sion limitation usually coexists with V_ =Qmismatch._ Fifth, , , or commonly results from These 2 common pathophysiologic mechanisms of respi- the immaturity of the respiratory center. All these factors ratory failure are observed in a variety of diseases. Pulmonary result in a higher metabolic demand per kilogram of body conditions that involve the bronchi (eg, status asthmaticus weight, resulting in increased work of breathing and early and ) or inflammation or infection of the paren- fatigue. chyma (eg, pneumonia, aspiration, cystic fibrosis, and ciliary dysmotility) result in airway obstruction and/or parenchymal _ = _ PATHOPHYSIOLOGY loss, leading to V Q mismatch and impaired gas exchange. Specifically, status asthmaticus occurs because of progression Respiration involves the nervous, cardiovascular, musculo- of airway inflammation, bronchospasm, and mucous plug- skeletal, and respiratory systems. The causes of respiratory ging during days to weeks or sudden onset of from failure can come from any of these systems and are expan- bronchospasm. In either case, airway obstruction causes V_ =Q_ sive. Common causes can be grouped based on underlying mismatch, incomplete alveolar gas exchange, and lung

Vol. 35 No. 11 NOVEMBER 2014 477 Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 mismatch, impairment of gas exchange at the alveolar- TABLE 1. Causes of Respiratory Failure capillary membrane is observed in progressive cystic fibrosis disease with pulmonary fibrosis and destruction. (8) Obstruc- Lung and airway disorders tion from infectious causes, foreign-body aspiration, burn Lung parenchyma injuries, anaphylaxis, or decreased muscle tone from de- • Bronchiolitis pressed consciousness or neuromuscular disorders can • Severe result in complete or partial airway obstruction. Complete • Aspiration obstruction causes asphyxia, where the lungs are not venti- lated but well perfused. Adequate airflow is usually initially • Pneumonia observed in partial obstruction. As airflow obstruction in- • creases from either a valvelike effect in foreign-body aspi- • Cystic fibrosis ration or airway inflammation and mucous secretions, Airway respiratory failure can occur. (9) Central nervous system disorders include congenital malformations, such as absent • Laryngotracheobronchomalacia corpus callosum; abnormal central control of respiration, • such as periodic breathing; ; central • Tracheitis apnea; Ondine curse; acquired injuries, such as head trauma; • Vascular malformations (ring, sling, right-sided aortic arch) intracranial bleeding; hypoxic ischemic encephalopathy; and • Subglottic stenosis, complete tracheal ring cerebral palsy. In these conditions, respiratory efforts are inadequate and or apnea ensues, resulting in Respiratory pump failure carbon dioxide retention and respiratory failure. (10) • Restrictive lung disorders (kyphoscoliosis) • fl Chest wall abnormalities: congenital or traumatic ( ail chest) CLINICAL PRESENTATIONS • Neuromuscular disorders (phrenic nerve paralysis, myopathies, muscular dystrophies) The clinical presentations of respiratory failure depend on • Diaphragmatic disorders (paralysis, congenital diaphragmatic the underlying cause and the level of hypoxemia and hyper- hernia) capnia. Infants and children most commonly present with Respiratory center failure increased work of breathing: tachypnea, grunting, nasal fl • Brain injuries (traumatic) aring, and retractions. (3)(11) These signs of increased work of breathing are blunted in those with neuromuscular • Central nervous system infection (controlled mechanical ventilation) or hypoxic encephalopathies disorders. These patients instead present with tachypnea and without retractions. • Drug overdose or adverse effects Additional of respiratory failure • Congenital (leukomalacia) or genetic disorders (congenital hypoventilation syndrome) may be observed, depending on the level of hypoxemia and (Table 2). (4) Impending respiratory failure Failure to meet increased metabolic needs can present as dyspnea, mood changes, disorientation, • Septic shock pallor, or fatigue. With acute hypercapnia, flushing, agita- tion, restlessness, headache, and tachycardia can occur. Children with chronic respiratory failure often present with hyperinflation. End-expiratory alveolar pressure increases as worsening hypercapnia and hypoxemia. Reduced con- a result, creating an autopositive end-expiratory pressure sciousness or coma and depressed tendon reflexes occur state. Work of breathing is increased to overcome the auto- with severe chronic carbon dioxide retention. , positive end-expiratory pressure for inspiratory flow to occur, polycythemia, cor pulmonale, and pulmonary hypertension eventually leading to inspiratory muscle fatigue and respira- are complications of chronic hypoxemia. tory failure. (7) In cystic fibrosis, similarly, an acute pulmo- nary exacerbation can result in airway obstruction and HISTORY AND mucous plugging, leading to V_ =Q_ mismatch and reduced functional residual capacity. Increased work of breathing Determining whether there is any need for emergency results in respiratory muscle fatigue, leading to hypoventila- intervention is the first step in assessing a patient with tion, hypercarbia, and respiratory failure. In addition to V_ =Q_ respiratory failure. Vital signs, work of breathing, and level

478 Pediatrics in Review Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 muscular dystrophy) must be identified. (4) Additional fac- TABLE 2. Signs and Symptoms of Hypoxia and tors, such as history of fevers, symptoms of respiratory Hypercapnia infection (, rhinorrhea, or nasal congestion), history of seizures, head trauma, or possible exposures to sedatives, HYPOXIA HYPERCAPNIAa must be noted. (3)(4) Mild Mild For the physical examination, vital signs are very helpful • None or depressed • Flushed skin to indicate the severity of the respiratory failure. (3)(11) fi • ef ciency Headaches Tachypnea is a sensitive indicator of . Moderate Moderate Increased is one of the earliest compensa- • Dyspnea • Tachypnea tory mechanisms of respiratory failure. However, respira- tory rates can be elevated during infancy, sleeping, eating, • Headaches, dizziness • Tachycardia and increased activity in healthy children. rate also • Fatigue • Dyspnea increases to maintain adequate oxygen delivery. Blood pres- • Pallor • Muscle twitches, sure can be initially normal or high. When respiratory depressed tendon reflexes failure is in the decompensated phase, low blood pressure occurs. Pulse oximetry saturation estimates the oxygen • Tachycardia, cardiac • Drowsiness, confusion arrhythmias saturation of hemoglobin. A 90% oxygen saturation on • Hypertension • Hypertension pulse oximetry correlates with a PaO2 of 60 mm Hg based • Mood changes: euphoria, on the sigmoid shape of the oxyhemoglobin dissociation disorientation, or depression curve (Figure 2). (6) Pulse oximetry measures only satura- • Ataxia, tingling tion. It does not measure oxygen content or delivery. Thus, Severe Severe pulse oximetry has several limitations. The oxygen satura- • Cyanosis • Papilledema tion can be falsely high with an elevated carboxyhemoglobin • Hypotension • Coma level in a patient with carbon monoxide or methylene • Bradycardia chloride poisoning. (12) Carbon monoxide binds to hemo- • Visual impairment • Loss of consciousness, globin with much greater affinity than oxygen, leading to seizures, coma tissue hypoxia. It also causes a left shift of the oxyhemoglo- bin dissociation curve, thereby decreasing the release of the aIn chronic hypercapnia, signs and symptoms of hypercapnia are observed when PCO2 increases above baseline level. oxygen and causing further tissue hypoxia. In a patient with an elevated methemoglobin level, the pulse oximetry satu- ration tends to be overestimated. In patients with poor tissue of consciousness indicate which patients require immediate perfusion due to shock, hypovolemia, or hypothermia, the respiratory support. Respiratory support should be urgently pulse oximetry is unable to detect the oxygen saturation accu- provided for a patient with significant tachypnea, retrac- rately; these patients may have falsely low oxygen saturation. tions, grunting, nasal flaring, and head bobbing. (11) Delay The initial step of the physical examination of respiratory in respiratory support may lead to the patient becoming failure is assessing the work of breathing. (3)(11) One should increasingly fatigued, resulting in shallow breathing, reduced assess the respiratory rate and quality, keeping in mind age- consciousness, and cyanosis. Emergency intubation and specific norms. When tachypnea is accompanied by retrac- mechanical ventilation should be initiated when such im- tions, nasal flaring, or grunting, respiratory support with pending signs of respiratory failure are assessed. Airway either noninvasive or invasive positive pressure is needed. control and ventilatory support should also be initiated in Bradypnea is often observed in respiratory center failure, patients with impending or central nervous indicating the need for emergency respiratory intervention. system disorders with decreased responsiveness. (3)(11) Bradypnea or hypoventilation is also observed in patients After determining whether emergency respiratory inter- with neuromuscular disorders. These patients have shallow vention is necessary, the next step is to obtain a comprehen- and ineffective breathing and usually do not present with sive history to evaluate for likely causes of the respiratory retractions. In these patients, spirometric measurements failure. Risk factors, such as prematurity, immunodeficiency, with forced vital capacity less than 40% correlate with anatomical abnormalities, and chronic pulmonary, cardiac, or carbon dioxide retention and nocturnal hypoventilation. neuromuscular disorders (eg, cystic fibrosis, asthma, unre- When assessing the respiratory rate, the chest wall should paired congenital heart disease, myasthenia gravis, or spinal also be inspected. Asymmetric chest expansion indicates

Vol. 35 No. 11 NOVEMBER 2014 479 Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 Figure 2. Oxygen dissociation curve.

possible pneumothorax, moderate to severe empyema or mechanical ventilation are required. Aside from assessing pleural effusion, or chest trauma. Paradoxical movement of for mental status changes, the neurologic examination should the chest and abdomen during inspiration and expiration also include examination of muscle strength. Conditions signals respiratory distress. in which muscle strength are decreased, such as mito- of the chest provides information about the chondrial diseases, Guillain-Barre syndrome, spinal muscular symmetry and quality of air movement and the presence of atrophy, or Duchenne muscular dystrophy, lead to respiratory abnormal breath sounds. (3)(11) Wheezing can be heard on failure. (3)(4) inspiration or expiration. Typically, expiratory re- fl ects disease of the lower airways, such as asthma. In acute DIAGNOSIS moderate to severe asthma, inspiratory wheeze may accom- pany expiratory wheeze. A local or asymmetric wheeze can Laboratory and radiographic studies are helpful in the as- indicate possible airway obstruction due to a foreign body or sessment of respiratory failure and the monitoring of the a mass. is a high-pitched inspiratory wheeze usually response to therapeutic management. However, emergency caused by upper airway narrowing or obstruction in such respiratory support should be initiated when indicated and conditions as laryngomalacia, croup, tracheitis, subglottic not be delayed while awaiting results of diagnostic studies. stenosis, or vascular rings. or rales are heard when Laboratory studies, such as an arterial blood gas, end- alveoli open and imply small airway diseases, such as tidal carbon dioxide, oxygen saturation, a complete blood pneumonia, congestive , pulmonary fibrosis, cell count with differential, and renal and liver functions, or other interstitial pulmonary processes. should be performed. The arterial blood gas accurately mea- In addition to the , examination sures the extent of the gas exchange abnormality and con- of the heart for any abnormal heart sounds is important for firms the type and chronicity of respiratory failure. (4) assessing heart conditions that can lead to respiratory Normal arterial blood gas values are as follows: pH 7.4 – failure. (3)(11) Furthermore, a neurologic examination is (reference range, 7.38 7.42); PO2,80to100mmHg;PCO2,35 also pertinent by assessing for mental status changes with to 45 mm Hg; oxygen saturation, 95% on room air; bicar- the Glasgow Coma Scale. (4) Neurologic impairment is bonate, 22 to 26 mEq/L; and base excess, 2toþ2 mEq/L. In

observed when the Glasgow Coma Scale score is low. A acute respiratory failure, PaO2 is less than 60 mm Hg, pH is

score of 8 or below indicates severe neurologic compromise. below 7.35, PaCO2 is greater than 50 mm Hg, and serum At this level of altered mental status, the patient is not able bicarbonate concentration is low or normal. In chronic to control his or her airway and secretions. Intubation and carbon dioxide retention, carbon dioxide is increased, pH

480 Pediatrics in Review Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 is normal, and serum bicarbonate concentration and base Biopsies and bronchoalveolar lavage for microbiologic, excess are increased. The arterial blood gas of the patient cytologic, and histologic testing can be obtained with bron- with an opiate overdose differs based on the severity of the choscopy. When a patient is critically ill, it may not be safe to overdose. In mild to moderate opiate overdose, respiratory perform the bronchoscopy because manipulation of the acidosis is observed with a pH below 7.35, PaCO2 greater airway may induce bronchospasm or atelectasis. than 50 mm Hg, and a low or normal serum bicarbonate concentration. In severe opiate overdose, a mixed respiratory MANAGEMENT and metabolic acidosis is observed. End-tidal carbon dioxide is measured from expired air from the nose by a capnometer Early diagnosis, close monitoring, and timely intervention and is a common and reliable tool used in the emergency are of utmost importance in a patient presenting with department and critical care setting. respiratory distress. (3)(4) The primary cause of cardiopul- Thecompletebloodcellcounthelpstoassesssuch monary arrest in children is unrecognized respiratory fail- causes as infection, anemia, or polycythemia. In addition, ure. Interventions in a patient with respiratory failure range respiratory, blood, urine, and pleural cultures and polymerase from close monitoring and supplemental oxygen to full chain reaction can be performed when indicated to identify respiratory support with mechanical ventilation. The initial the specific bacterial cause. Renal and liver function tests step in the treatment of a patient with respiratory failure is provide clues to the cause of or identify complications asso- rapid assessment of airway, breathing, and circulation to ciated with respiratory failure. Electrolyte abnormalities, such determine whether the patient needs urgent intervention. as hypernatremia or hyponatremia, cause seizures, and hy- Indications for intubation and mechanical ventilation perkalemia causes cardiac arrhythmia. include the patient’s inability to maintain an adequate Chest radiography should be performed in patients who airway and protect the airway from aspiration, failure of present with respiratory failure to help identify or confirm oxygenation and ventilation, and deteriorating status that the cause of the respiratory failure. If a cardiac cause of acute will lead to inability to maintain airway patency and normal respiratory failure is suspected, electrocardiography and gas exchange. echocardiography should be performed. The initial step and most basic airway management for Pulmonary function testing evaluates the functional sta- a patient in respiratory failure is bag-mask ventilation, tus of the respiratory system by measuring the volume and which allows for oxygenation and ventilation until a more flow of air movement, gas exchange, and strength of the definitive airway can be established. Although the patient is respiratory muscles. Pulmonary function testing includes receiving bag-mask ventilation, necessary equipment (endo- a group of tests, such as spirometry, lung volumes, diffusion tracheal tube, large-bore suction, fiberoptic scope, laryngo- capacity, and maximal respiratory pressures, among others. scope, carbon dioxide detector, and intubation drugs) can be It helps to determine the characteristics of the respiratory prepared for intubation. (4) When possible, intubation disease and to guide management. Pulmonary function should be performed by the most experienced medical testing is not typically performed when the patient is crit- professional (emergency care personnel, critical care physi- ically ill. Flexible bronchoscopy can also be performed to aid cians, and anesthesiologists) to ensure successful intuba- in diagnosis and therapeutic management. tion and to avoid multiple unsuccessful attempts. Failure to

a TABLE 3. Interpretation of Blood Gas Results

CONDITION pH Paco2 BASE EXCESS

Acute respiratory acidosis or acute hypoventilation Y[4 Acute respiratory alkalosis or acute [Y4 Acute or chronic respiratory acidosis Y /[[ Acute metabolic acidosis with respiratory compensation YYY Chronic respiratory acidosis with metabolic compensation Normal/slightly Y[ [

Y¼decrease; [¼increase; 4¼no change.

Vol. 35 No. 11 NOVEMBER 2014 481 Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 quickly secure an adequate airway can lead to morbidity or patient breathes in, providing effective inspiratory volume death. expansion, whereas the expiratory positive airway pressure Sedative agents alone or in conjunction with paralytic is generated as the patient breathes out, maintaining pos- agents are used for intubation. When a difficult airway is itive end-expiratory pressure to prevent airway collapse and anticipated (eg, Pierre Robin syndrome or anterior medias- to keep the lungs expanded. Common complications of tinal mass), paralytic agents are avoided, and the patient is noninvasive ventilation include facial pressure skin injury intubated in a more awake state or with a fiberscope. If from prolonged use, dry mucous membranes, and thick- successful intubation is unlikely, the airway can be secured ened secretions. with a laryngeal mask airway. (3) The laryngeal mask airway is Positive pressure ventilation or mechanical ventilation is a supraglottic airway device used as an important alterna- most commonly used to manage acute respiratory failure. tive airway device in the emergency setting when a very (5) The goal of mechanical ventilation is to relieve respira- difficult airway is encountered. Placement of the laryngeal tory distress by decreasing the inspiratory work of breathing, mask airway does not require laryngoscopy or paralytic improving pulmonary gas exchange, allowing the lungs to agents. Although it is an easier device to secure an ade- heal, reversing respiratory muscle fatigue, and preventing quateairway,thelaryngealmaskairwaydoesnotprotect further complications due to abnormal gas exchange. There against aspiration. are several types of mechanical ventilators that offer differ- Once patients are evaluated and emergency intervention ent modes and features. Mechanical ventilators provide with intubation and mechanical ventilation is not indicated, positive pressure ventilation by pressure-limited ventilation mild cases of respiratory failure may require only close or volume-limited ventilation. In pressure-limited ventila- monitoring and supplemental oxygen as needed by low- tion, the gas is allowed to flow into the lungs until a preset or high-flow nasal canula or a nonrebreather mask. airway pressure limit is reached, at which time a valve A nonrebreather mask can deliver a higher amount of opens, allowing exhalation to ensue. In volume-limited oxygen (10–15 L/min) than a nasal cannula. (4) Respiratory ventilation, gas flows to the patient until a preset volume drive in patients with chronic respiratory failure is stim- is delivered to the ventilator circuit, even if this entails a very ulated primarily by hypoxia. Improving oxygenation in high airway pressure. One of the factors to consider when these patients can lead to blunting of the hypoxic drive deciding which ventilator to use is the mode of mechanical of the respiratory center, resulting in decreased alveolar ventilation or the method of inspiratory support. There is ventilation and increased carbon dioxide retention and limited evidence-based research to demonstrate that the leadingtoacuterespiratoryfailureontopofchronic mode affects clinical outcomes; therefore, the decision on respiratory failure. which mode to use is based on the capability of available Noninvasive ventilation is used to manage both acute and ventilators to manage small infant volumes and clinicians’ chronic respiratory failure. (10)(13) It is now commonly used experience with the mechanical ventilators. Common modes not only in the emergency department and critical care of mechanical ventilation include controlled mechanical ven- setting but also in the patients’ homes. It is indicated in tilation, assist control, synchronized intermittent mandatory patients who are cooperative and have increased work of ventilation, and pressure support ventilation. In the con- breathing or respiratory muscle fatigue. It is contraindicated trolled mechanical ventilation mode, the ventilator delivers in patients with altered mental status, cardiac instability, and a preset minute ventilation (preset tidal volume and respira- inability to protect the airway because of a weak cough or tory rate), and the patient cannot trigger additional breaths swallowing. Its use in the pediatric intensive care unit is above what is set. This mode is usually used for patients who associated with decreased intubation rates. (14) Modes of are paralyzed, heavily sedated, or comatose. In the assist noninvasive ventilation include continuous positive airway control mode, minimum minute ventilation is set, and the pressure or bilevel positive airway pressure. The positive patient can trigger additional breaths. If the patient fails to pressure can be delivered through a variety of interfaces trigger a breath within a selected time, the ventilator delivers (mouthpiece, oronasal face mask, nasal pillow, or helmet the breaths. The assist control mode is not appropriate when mask). Continuous positive airway pressure provides a con- the patient is ready to wean off the ventilator because it gives tinuous level of positive airway pressure during the entire a full breath each time. The synchronized intermittent man- respiratory cycle to keep the airways open. Bilevel positive datory ventilation mode allows the patient to increase minute airway pressure provides an inspiratory positive airway ventilation by preset breath rate synchronized with sponta- pressure and an expiratory positive airway pressure. The neous breathing, rather than patient-initiated ventilator inspiratory positive airway pressure is generated as the breathing as in the assist control mode. In the pressure

482 Pediatrics in Review Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 support ventilation mode, the ventilator delivers a preset atelectasis from high pulmonary pressure and oxygenation. pressure support level while the patient triggers each breath The most common risk factor for ventilator-induced lung because there is no preset minute ventilation. In addition to injury is acute respiratory distress syndrome. Strategies to these conventional modes of ventilation, high-frequency prevent ventilator-induced lung injury include using small ventilation is commonly used, especially in premature neo- tidal volumes that range from 6 to 8 mL/kg, applying nates. The high-frequency oscillatory ventilator delivers small positive-end expiratory pressure, and maintaining a low tidal volumes by oscillating air movements at an extremely plateau airway pressure of 30 cm H2O or less. (20)(21) rapid rate (300–1500 breaths per minute). A Cochrane review (22) These strategies are based on adult studies. concludes no difference in benefit between high-frequency In premature infants particularly, prolonged mechan- oscillatory ventilation compared with conventional ventila- ical ventilation not only leads to acute complications, such tion in preterm infants. (15) A previous study found that as infection and lung injury, but also results in long-term length of mechanical ventilation, intensive care unit length sequelae, such as chronic lung disease and neurodevelop- of stay, and mortality were significantly higher in high- mental delays. Strategies to minimize these complications frequency oscillatory ventilation patients compared with include preservation of spontaneous breathing by apply- the controlled mechanical ventilation patients ages 1 to 18 ing patient-triggered and volume target ventilation, years who were hospitalized in the pediatric intensive care administering respiratory stimulants (eg, caffeine), and unit of a diverse group of hospitals that care for children in using nasal continuous positive airway pressure or nasal the United States. (16) intermittent positive pressure ventilation after extubation. Newer modalities include neurally adjusted ventilatory (23) assist and proportional assist ventilation. These modalities Extracorporeal membrane oxygenation (ECMO) can be of assisted ventilation require that the patient spontane- considered when all other options have failed and the ously breathes and the delivered airway pressure changes, respiratory failure is a result of a reversible underlying depending on the patient’s breathing effort; thus, varying illness. (24)(25) ECMO provides cardiopulmonary support degrees of unloading of work by the respiratory muscles on extracorporeally to prevent further lung injury from high- inspiration on a breath by breath basis are delivered. In the pressure ventilation and allow the lungs to heal. ECMO was neurally adjusted ventilatory assist, an esophageal sensor initially used almost exclusively in neonates. Its use to represents neural output from the respiratory center, con- support older pediatric patients has increased throughout trolling the timing and magnitude of the delivered pressure. the years. In the past 5 years, there have been approximately (17) 300 to 500 cases annually. (25) Relative contraindications for Ventilator complications include infection and lung ECMO include patients who have irreversible respiratory or injury. Ventilator-associated pneumonia (VAP) has been cardiac failure, who cannot undergo anticoagulation, and described more in adult than children. The estimated inci- who undergo ventricular assist device implantation. Compli- dence of VAP in pediatrics is 3 per 1000 ventilator-days. (18) cations include bleeding, thromboembolism, and heparin- Objective diagnosis of VAP is not well defined, even in induced thrombocytopenia. (26) Prognosis depends primarily adults. In a prospective study of a sample of children in the on the underlying illness. Mortality remains approximately pediatric intensive care unit, Srinivasan et al (18) found that 43%. Risk factors associated with death include older patient VAP was more likely in patients who were female, had age, other nonpulmonary organ dysfunction, prolonged undergone surgery, were taking narcotics, and were fed use of mechanical ventilation (>2 weeks) before ECMO, enterally. In 2011, the Centers for Disease Control and prolonged ECMO support, and complications during Prevention formed a VAP Surveillance Definition Working ECMO. (25)(26) Group. Guidelines outline the identification of patients with A small group of severely compromised children may respiratory status deterioration (eg, increased need of require prolonged mechanical ventilation. Overall, their inspired oxygen or positive end-expiratory pressure) after prognosis is good compared with adults. Outcomes data having been stable while receiving ventilatory support; reveal that 65% of children who require a post–acute evidence of respiratory infection with abnormal white blood rehabilitation facility for prolonged weaning are eventually cell count, culture, or temperature; and initiation of antibi- discharged to home and that 45% of children discharged to otic therapy. (19) pulmonary rehabilitation were weaned on discharge. (27) Ventilator-induced lung injury is another potential com- (28) Weaning protocols have been established for the plication of mechanical ventilation. Ventilator-induced lung management of chronic respiratory failure in children. injury is a result of alveolar overdistension and cyclic (29)

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1. You are seeing 2 brothers ages 2 months and 6 years, respectively, for upper respiratory REQUIREMENTS: Learners tract infection. Rapid antigen testing suggests infection with respiratory syncytial virus. can take Pediatrics in Which of the following factors is most important in placing the younger sibling at greater Review quizzes and claim risk of developing respiratory decompensation compared with his older brother? credit online only at: A. Decreased accessory muscle use. http://pedsinreview.org. B. Decreased airway size. C. Decreased chest wall compliance. To successfully complete D. Decreased lung compliance. 2014 Pediatrics in Review E. Greater reliance on . articles for AMA PRA 2. Which of the following is a clinical marker of chronic hypoxemia? Category 1 CreditTM, A. Depressed tendon reflexes. learners must B. Flushed skin. demonstrate a minimum C. Papilledema. performance level of 60% D. Polycythemia. or higher on this E. Tachypnea. assessment, which measures achievement of 3. A 10-month-old girl presents with poor feeding, fever, cough, and respiratory difficulty for the educational purpose the last 2 days. Physical examination reveals axillary temperature of 38.9°C, respiratory rate and/or objectives of this of 65 breaths per minute, and heart rate of 170 beats per minute. Respirations are labored activity. If you score less with nasal flaring and intercostal retractions. Auscultation of chest reveals diffuse crackles than 60% on the (rales) and wheezing throughout the chest. There are alternating periods of drowsiness assessment, you will be and agitation. Use of 100% oxygen at 15 L/min via a nonrebreather face mask is initiated. given additional Pulse oximetry recording reveals 93% oxygen saturation. Which of the following will opportunities to answer prompt you to proceed with tracheal intubation and mechanical support of respiration? questions until an overall A. Arterial blood gas revealing PaO2 less than 60 mm Hg on currently administered 60% or greater score is oxygen. achieved. B. Arterial blood gas revealing pH less than 7.25 and PCO2 less than 60 mm Hg. C. Chest radiograph revealing diffuse alveolar interstitial infiltrates. D. Lack of improvement after a trial of nebulized albuterol inhalation. E. No new information is necessary, so the patient should undergo tracheal intu- bation and mechanical support of respiration now. 4. A 12-year-old boy presents with tingling, numbness, and weakness of his lower extremities for 1 day. The weakness has gradually progressed, and now he is unable to walk. Physical examination reveals a comfortable-appearing child with normal sensorium. He is afebrile, with a respiratory rate of 18 breaths per minute and a heart rate of 74 beats per minute. Respiratory pattern appears normal. He has sensory loss to pinprick up to the midabdomen. He has decreased muscle strength: grade II/V in the lower extremities and IV/V in the muscles of the hand. He appears to have normal strength in his shoulders and arms. He has good gag and cough reflexes. Deep tendon reflexes are absent in the lower extremities and diminished in the upper extremities. The rest of his physical examination findings are normal. Which of the following is the best method of determining need for assisted ventilation? A. Assessment of respiratory distress by frequent physical examinations. B. Capnography to measure end-tidal PCO2 in exhaled gas at the nose. C. Frequent assessment for mental status changes using the Glasgow Coma Scale. D. Pulse oximetry recording to measure oxygen-hemoglobin saturation. E. Serial arterial blood gas measurements. 5. A 16-year-old girl with cystic fibrosis is admitted for low-grade fever, productive cough, and . She is being followed up in the clinic for advancing lung disease. Her baseline vital capacity is 40% of normal. Vital signs on presentation are as follows: axillary temperature, 38.5°C; pulse, 100 beats per minute; and respirations, 24 breaths per minute. She has nasal flaring, intercostal retractions, and diffuse bilateral and crackles (rales) on chest auscultation. She is appropriately interactive. Her pulse oximetry oxygen hemoglobin saturation on 30% oxygen, which she receives at home, is 85%. Her

Vol. 35 No. 11 NOVEMBER 2014 485 Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 arterial blood gas reveals the following: pH, 7.28; PCO2, 62 mm Hg; and PO2, 55 mm Hg. High- flow nasal cannula (15 L/min) with 100% oxygen is initiated. Fifteen minutes later, the patient becomes unresponsive with shallow respirations at rate of 10 breaths per minute; lung examination findings are unchanged. A subsequent arterial blood gas determination reveals the following: pH, 7.08; PCO2, 110 mm Hg; and PO2, 102 mm Hg. Which of the following is the most likely explanation of the change in this child’s worsened clinical state? A. Bilateral pneumothoraces. B. Cerebral edema. C. Exacerbation of cor pulmonale. D. Respiratory muscle fatigue. E. Suppression of peripheral chemoreceptors.

486 Pediatrics in Review Downloaded from http://pedsinreview.aappublications.org/ by guest on November 14, 2018 Respiratory Failure Phuong Vo and Virginia S. Kharasch Pediatrics in Review 2014;35;476 DOI: 10.1542/pir.35-11-476

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Pediatrics in Review is the official journal of the American Academy of Pediatrics. A monthly publication, it has been published continuously since 1979. Pediatrics in Review is owned, published, and trademarked by the American Academy of Pediatrics, 345 Park Avenue, Itasca, Illinois, 60143. Copyright © 2014 by the American Academy of Pediatrics. All rights reserved. Print ISSN: 0191-9601.

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