e71CHAPTER 136 Board Review Questions Rationale Newborns of most mammalian species have developed physio logic strategies to maintain their FRC above the relaxation volume of the thorax These strategi[.]
CHAPTER 136 Board Review Questions Rationale Newborns of most mammalian species have developed physiologic strategies to maintain their FRC above the relaxation volume of the thorax These strategies are generally directed at interrupting expiratory flow before expiration is complete and include shortening of the expiratory time, contraction of adductor muscles of the glottis to retard exhalation, and persistence of the tonic activity of the inspiratory muscles during expiration Compared with adults and older children, premature infants and neonates are able to tolerate high lung volumes during mechanical ventilation without cardiovascular compromise, possibly because of which of the following conditions? A Their lower airway resistance B Their higher cardiac contractility C Their higher cardiac output D Their higher chest wall compliance Preferred response: D Rationale The pressure inside the pleural space is really determined by the elastic recoil of the chest wall and the volume of the thoracic contents As long as lung volume is not forced above its normal range and chest wall compliance is unaltered by disease, pleural pressure (and thus the pressure around the major vessels and the heart) remains low, regardless of the airway pressures Conversely, excessive lung distention (e.g., in asthma) is always associated with a high pleural pressure and, for that reason, is less well tolerated from a cardiovascular point of view The dependence of pleural pressure on chest wall compliance explains why premature infants and newborns, who have very large chest wall compliance, have limited changes in this pressure during positive pressure ventilation, even if physiologic lung volumes are exceeded Disease-induced reductions in chest wall compliance, on the other hand, always increase pleural pressure and reduce venous return to the heart This is one reason why patients with abdominal distention typically have low cardiac output and why relief of the distention (e.g., by paracentesis in patients with ascites) reduces pleural pressure and increases cardiac output Which one of the following areas is considered the zero reference during inspiration? A The alveoli B The extrathoracic airway C The intrapleural space D The mouth Preferred response: D Rationale Airway transmural pressure varies during breathing Its variations result from the fact that inspiration and expiration have very different effects on the pressures inside and outside the airways The pressure inside all airways undergoes qualitatively similar changes during each phase of the breathing cycle During inspiration, for instance, there is a gradient of increasingly negative pressures from the mouth, where pressure is atmospheric (or the zero reference), to the alveolar spaces, where the pressure must be negative (or subatmospheric) for gas to flow in This negative pressure is of course driven by the actions of the respiratory muscles and transmitted to the lungs via the link between the chest wall and lungs at the pleural space During expiration, alveolar pressure becomes positive and the gradient is inverted, with the pressures inside the airways being always positive but diminishing toward the mouth e71 10 What happens to the extrathoracic and intrathoracic portion of the airways during a normal respiratory cycle of inspiration and expiration with airflow? A During inspiration, the pressure surrounding the extrathoracic airway is more positive than the lumen, resulting in narrowing of the airway B During inspiration, the pressure surrounding the extrathoracic airway is more negative than the lumen, resulting in narrowing of the airway C During expiration, the pressure surrounding the intrathoracic airway is more negative than the lumen, resulting in narrowing of the airway D During expiration, the pressure surrounding the intrathoracic airway is more negative than the lumen, resulting in dilation of the airway Preferred response: A Rationale During inspiration, there is a gradient of increasingly negative pressures from the mouth (zero reference), where the pressure is atmospheric, distally to the airway The pressure at the alveolar spaces must be negative (or subatmospheric) for air to flow The pressure inside the airways is always negative, regardless of intraor extrathoracic location During expiration, for air to move from the alveolar spaces to the mouth, the pressures must be more positive distally and decrease toward the mouth Normal breathing changes in airway caliber depend on the location of the airway (intrathoracic versus extrathoracic) and the phase of the respiratory cycle (inspiration versus expiration) Extrathoracic airways include the pharynx, larynx, and extrathoracic portion of the trachea and are surrounded by neck tissue, maintaining constant atmospheric pressure around these areas During inspiration, the pressures distal to the extrathoracic airway become more negative, causing the extrathoracic portions of the airway to narrow The opposite holds true for the intrathoracic airway During inspiration, the pressure surrounding their walls (intrapleural pressure) becomes more negative compared with the pressure inside the lumen, which causes these portions of the airway to dilate To be correct, responses B through D should read as follows: B During inspiration, the pressure surrounding the extrathoracic airway is more positive than the lumen resulting in narrowing of the airway C During expiration, the pressure surrounding the extrathoracic airway is less positive than the lumen, resulting in dilation of the airway D During expiration, the pressure surrounding the intrathoracic airway is more positive than the lumen, resulting in narrowing of the airway 1 What is the equal pressure point? A During inspiration, the point at which transmural pressure is positive B During inspiration, the point at which transmural pressure is negative C During expiration, the point at which the pleural pressure equals alveolar pressure D The pressure midway in the airway, where the pressure distal to the mouth equals the pressure proximal to the alveoli Preferred response: C e72 S E C T I O N XV Pediatric Critical Care: Board Review Questions Rationale The narrowing of the intrathoracic airways during expiration is contingent on the existence of a pressure gradient from the alveoli to the mouth Alveolar pressure (Pa) must always exceed pleural pressure (Ppl) by a magnitude equivalent to the elastic recoil of the lungs As the gas progresses downstream during expiration, frictional pressure losses lower the pressure inside the airways Eventually the cumulative pressure losses can be as large as the pulmonary elastic recoil, and the pressure inside the airways becomes equal to Ppl Beyond this equal pressure point, airway transmural pressure becomes negative (i.e., the pressure outside exceeds the pressure inside the airway) and acts to collapse the airway Stridor in a child with croup occurs during which process? A Expiration due to a more positive pressure downstream from the obstruction B Expiration due to a more negative pressure downstream from the obstruction C Inspiration due to a more negative pressure downstream from the obstruction D Inspiration due to a more positive pressure downstream from the obstruction Preferred response: C Rationale When airway obstruction is extrathoracic (e.g., with croup, glossoptosis, or tonsil or adenoid hypertrophy), the person must create a more negative pressure inside the airway segment downstream from the obstruction to overcome the increased resistance during inspiration Therefore this segment of the airway tends to collapse, worsening the obstruction and producing a characteristic turbulent noise (inspiratory stridor) as gas accelerates through the narrowest point and induces vibrations in the airway mucosa, creating in the process a decrease in inside pressure that approximates the walls of the airway even further The obstruction is relieved during expiration because the pressure inside the airway segment, now upstream from the obstruction, must become more positive with respect to atmospheric pressure to force gas flow through the obstruction (see Figure 136.19, below) • Fig 136.19 13 When does wheezing in a child with tracheobronchial compression occur? A During inspiration and expiration due to a more positive pressure downstream from the obstruction B During expiration due to a less positive pressure downstream from the obstruction C During expiration due to a more positive pressure downstream from the obstruction D During inspiration due to a more positive pressure downstream from the obstruction Preferred response: C Rationale When airway obstruction is intrathoracic (e.g., with extrinsic compression of the trachea and bronchi, tracheobronchomalacia, and asthma), during inspiration, the pressure inside the airways downstream from the obstruction has to become more negative than that inside the airways upstream However, no matter how negative, the pressure inside the airways still must be less negative than the pleural pressure because otherwise the lung recoil (Pa – Ppl) would be negative, which is unimaginable Thus during inspiration the transmural pressure of intrathoracic airways remains positive In contrast, during expiration the pressure inside the airway segment located between the obstruction and the thoracic outlet may become lower than the pleural pressure at some point This situation, coupled with the convective acceleration of flow at the obstructed segments, causes these airways to collapse and produce high-pitched vibrations (wheezing), expiratory delay, and dynamic hyperinflation Chapter 47: Diseases of the Upper Respiratory Tract An 18-month-old boy arrives to the emergency department with sudden onset high fever, toxic appearance, stridor, and drooling His oxygen saturation on blow-by oxygen supplementation is 96% Lateral neck radiograph shows a “thumb sign.” What is the most appropriate next step in the treatment of his condition? A Bedside nasal fiberoptic examination of the pharynx to confirm the diagnosis B Conservative management with noninvasive ventilation and antibiotics C Endotracheal intubation in the emergency room D Transport to the operating room for intubation Preferred response: D Rationale This patient shows the classic signs and symptoms of epiglottitis It is now a rare disease among vaccinated young children, but the sudden onset of severe airway obstruction requires prompt recognition and treatment At the same time, care should be taken not to disturb the patient, as agitation can result in complete airway obstruction For this reason, fiberoptic examination of the epiglottis in the patient who is awake is usually not advisable Similarly, attempts to examine the oropharynx directly or to start an intravenous line should be discouraged If the patient will tolerate it, humidified oxygen should be administered, preferably through a plastic hose held by the parent If the suspicion for epiglottitis is high, the child should go to the operating room as quickly as possible In the operating room, the patient is anesthetized with an inhaled anesthetic (sevoflurane) and oxygen while the patient is spontaneously breathing CHAPTER 136 Board Review Questions Once the patient has been anesthetized, an intravenous catheter is inserted Laryngoscopy is then performed It may be exceedingly difficult to obtain a direct view of the glottis and trachea because of the large swollen epiglottis Nevertheless, it is almost always possible to pass an endotracheal tube through the edematous tissues and into the trachea Nasotracheal intubation is preferred to orotracheal intubation because the tube is more readily secured to the face, the patient cannot bite the tube, and salivation is decreased An otolaryngologist should be in the operating room and ready to an emergency tracheostomy if an airway cannot be secured by endotracheal intubation, although this is rarely necessary Endotracheal intubation is preferred to tracheostomy because it has been shown that complications are more common when a tracheostomy has been routinely used to treat epiglottitis After the airway is secured, blood cultures and cultures of the epiglottis are obtained, and antibiotic therapy is initiated with a penicillinase-resistant antibiotic because of the high incidence of H influenzae resistance to ampicillin Patients usually require endotracheal intubation for 24 to 72 hours while the swollen epiglottis returns to normal size The patient may be allowed to breathe spontaneously through the endotracheal tube or may undergo mechanical ventilation A 5-year-old child with newly diagnosed leukemia is admitted to the pediatric intensive care unit in severe respiratory distress Chest radiograph shows a widened mediastinum Which one of the following measures is to be avoided during airway management in this child? A Administration of muscle relaxants B Endotracheal intubation C Heliox administration D Left lateral decubitus position Preferred response: A Rationale This child likely has an anterior mediastinal mass compressing the intrathoracic trachea Because the symptoms produced by a malignant mass impinging on the trachea can worsen dramatically over several days, the child with respiratory compromise resulting from a mediastinal mass deserves rapid evaluation and aggressive medical therapy The child’s refusal of certain body positions (mostly the supine position) to avoid dyspnea often precedes other signs and symptoms (cough, tachypnea, respiratory distress) of an anterior mediastinal mass Forcing the child to lie down may result in airway obstruction or even cardiac arrest Conversely, airway obstruction by the mediastinal mass in the supine position is sometimes relieved by changing one’s body position (lateral decubitus, prone, sitting) Heliox (a mixture of 70% helium and 30% oxygen) administration may be beneficial in case there is severe narrowing of the trachea, because the characteristics of this mixture permit greater gas flow past areas of airway narrowing Endotracheal intubation is indicated only if respiratory function becomes severely compromised This measure, of course, is only of benefit if the tip of the endotracheal tube can be advanced distal to the site of tracheal compression, which often means that main stem intubation is necessary to bypass the lesion if it is at the level of the distal trachea or carina If intubation is necessary, sedation/anesthesia before laryngoscopy should be carried out while maintaining spontaneous ventilation, as positive pressure ventilation might be impossible Thus muscle relaxants in this situation should be avoided e73 Mechanical support with ECMO has been used to support patients with large mediastinal masses; however, the mass may distort the great vessels and pose unusual challenges for the ECMO team Unfortunately, if the airway is lost or if the degree of cardiac compression is grave, ECMO might be the only option left to provide tissue oxygenation until the compression is relieved Chapter 48: Pediatric Acute Respiratory Distress Syndrome and Ventilator-Associated Lung Injury You are called to the emergency department to assess a previously healthy 3-year-old male who presented with a 2-day history of fever and cough He had been started on high flow nasal cannula and was escalated to full face bilevel positive airway pressure (BiPAP) with the following settings: inspiratory pressure, 16 cm H2O; expiratory pressure cm H2O; fraction of inspired oxygen (Fio2), 0.8; oxygen saturation as measured by pulse oximetry (Spo2), 100% His chest radiograph (CXR) revealed a right-sided opacity You recall that mortality patients with pediatric acute respiratory distress syndrome (PARDS) treated with noninvasive ventilation is 15% Which of the following statements regarding diagnosing PARDS in this child is correct? A He has PARDS based on his timing, trigger, CXR, and Spo2/Fio2 of 125 B He is admitted to the inpatient unit since he cannot have PARDS with a unilateral opacity on chest imaging C In order to diagnose PARDS, Pao2/Fio2 should be used so an arterial blood gas should be performed D The Fio2 should be titrated down until his Spo2 is #97% so that you can calculate the Spo2/Fio2 Preferred response: D Rationale There is a strong linear association between Spo2 and Pao2 as long as the Spo2 is #97% The Pediatric Acute Lung Injury Consensus Conference (PALICC) definition of PARDS recommends use of the oxygenation index or oxygenation saturation index when a Pao2 is not available Although the PALICC definition of PARDS does not require new bilateral infiltrates, it recommends future studies investigate whether bilateral versus unilateral infiltrates improves discrimination of risk stratification The patient in question is admitted to the PICU since he required endotracheal intubation due to increased work of breathing and persistent hypoxemia He is currently medically paralyzed after intubation, and he is placed on the following ventilator settings: volume control mode with tidal volume mL/kg; inspiratory plateau pressure, 28 cm H2O; positive-end expiratory pressure (PEEP), 10 cm H2O; fraction of inspired oxygen (Fio2), 0.9; Spo2, 85% The respiratory therapist recommends increasing the PEEP and you: A Agree and recommend increasing PEEP to 14 cm H2O B Disagree because you are worried about raising his plateau pressure and causing barotrauma C Disagree because he is treated with low tidal volume, and moderate hypoxemia is probably okay in a previously healthy year old D Suggest that the extracorporeal life support team be consulted because he is failing maximal support Preferred response: A e74 S E C T I O N XV Pediatric Critical Care: Board Review Questions Rationale The optimal method to set PEEP for an individual patient remains a research question, and existing data not support a single PEEP level (high or low) that improves outcome for adults or children with ARDS However, multiple studies suggest high variability in use of PEEP by PICU providers, and a retrospective study suggest that mortality in children was lower when providers were adherent with the ARDSNet lower PEEP/higher Fio2 table Lower PEEP/Higher Fio2 Fio2 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 PEEP 5 8 10 10 10 12 Fio2 0.7 0.8 0.9 0.9 0.9 1.0 PEEP 14 14 14 16 18 18-24 These data suggest that this PEEP/Fio2 table is a reasonable starting point, but adherence requires attention to the effect on plateau pressure, driving pressure, markers of oxygenation, and hemodynamics The patient in question is now breathing spontaneously and is treated with pressure control synchronized intermittent mandatory ventilation on the following settings: pressure control, 28 cm H2O; positive-end expiratory pressure (PEEP), 12 cm H2O; pressure support, 20 cm H2O, ventilator rate, 20 per minute; fraction of inspired oxygen (Fio2), 0.7 His tidal volumes range from 5–6 mL/kg, and his oxygen saturation as measured by pulse oximetry (Spo2) is 94% The patient is breathing above the ventilator at a rate of 36 breaths/minute, he has high inspiratory work with retractions, his end-tidal CO2 is 45 mm Hg and his Paco2 is 55 mm Hg The nurse is concerned that the patient is uncomfortable and is asking if the patient can be sedated more deeply You: A Agree because most children who are intubated and mechanically ventilated need to be deeply sedated B Agree and you consider whether neuromuscular blockade is indicated because you are worried that the patient’s respiratory effort is contributing to lung injury C Disagree and raise the tidal volume because the patient’s effort and Paco2 suggest that he cannot be supported with low tidal volume ventilation D Disagree because you are worried about causing delirium with more sedation and you think he is adequately supported Preferred response: C Rationale Although a randomized controlled trial of protocolized sedation did not reduce the number of days of mechanical ventilation, there are substantial data suggesting multiple harmful effects of sustained deep sedation of critically ill children and adults, including delirium and prolonged duration of hospitalization The amount of patient effort required to identify patient self-inflicted lung injury (P-SILI) is difficult to determine without esophageal manometry Although prevention of P-SILI is likely one mechanism of benefit of early neuromuscular blockade, a recent randomized controlled trial did not show benefit of neuromuscular blockade in adults with ARDS 4 On the third day of the hospitalization, the patient in question develops progressively worse hypoxemia His oxygen saturation index (OSI) is now 22 Data suggest that pulmonary- specific ancillary therapies that are indicated in children include which of the following? A Exogenous surfactant B High-frequency oscillatory ventilation (HFOV) C Inhaled nitric oxide D There are no data in children supporting specific pulmonary ancillary therapies Preferred response: D Rationale There are no conclusive data supporting the specific pulmonary or pulmonary ancillary therapies in children The most conclusive data supporting pulmonary therapy address limiting tidal volume in adults Limiting the driving pressure and prone positioning seem to be beneficial in adults with ARDS, but there are no pediatric data There are no studies supporting the use of exogenous surfactant, HFOV, or inhaled nitric oxide to improve mortality in children or adults Chapter 49: Acute Viral Bronchiolitis A 9-month-old previously healthy infant is admitted to the pediatric intensive care unit with respiratory distress including nasal flaring, grunting, subcostal retractions, and bilateral scattered wheezing Current symptoms were preceded by days of rhinorrhea, cough, and fever Which of the following treatment options is most associated with improved outcomes in bronchiolitis and is suggested to have utility in some inpatients by both the American Academy of Pediatrics (AAP) and the Canadian Pediatric Society (CPS)? A Albuterol B Heliox C Inhaled epinephrine D Inhaled hypertonic saline Preferred response: D Rationale Hypertonic saline (HTS) may improve respiratory mechanics by increasing mucociliary clearance and reducing airway edema HTS was prescribed to 13% of critical bronchiolitis subjects in one recent multicenter report and one-third of surveyed intensivists report prescribing HTS In general, treatment guidelines not encourage its routine use in children hospitalized with bronchiolitis, though the AAP and Canadian Pediatric Society (CPS) suggest it may have some utility in inpatients Some data suggest that heliox may improve respiratory distress, but not necessarily clinical outcomes Recent studies show that albuterol improves respiratory resistance by 20% in ,40% of subjects, though clinicians’ ability to identify “responders” based on subjective clinical exams was generally no better than a coin flip Meta-analyzed data support that albuterol does not shorten hospital length of stay The AAP, the Australasian Guidelines, and the United Kingdom’s National Institute for Health and Care Excellence (NICE) Guidelines state that neither epinephrine nor albuterol should be used in inpatients, though the AAP points out that critically ill children are generally excluded from the trials supporting that recommendation Both the AAP and CPS suggest considering epinephrine specifically in select circumstances (e.g., “as a rescue agent in severe disease”) CHAPTER 136 Board Review Questions Which of the following is true about the spread of respiratory syncytial virus (RSV)? A Hand washing with soap and water is the only acceptable method of hand hygiene after examining a patient with RSV B Hospitalized children with RSV infection not require precautions to minimize spread of disease C Palivizumab prevents all cases of bronchiolitis, so hospitalized children receiving palivizumab prophylaxis may share a room with an RSV-infected child D RSV can remain infectious on counter tops for over hours Preferred response: D Rationale Viruses that cause bronchiolitis, like RSV and rhinovirus, are spread via multiple mechanisms including aerosols, direct contact with virus-containing secretions, and indirect contact (e.g., fomites) RSV can survive on surfaces for several hours Many patients in the PICU without bronchiolitis have risk factors for severe disease, so preventing spread to these susceptible children may help to improve their outcomes Hand disinfection, with either alcohol-based rubs or soap and water (if hands are visibly soiled), is recommended by the AAP before and after direct contact with patients, after contact with nearby inanimate objects, and after removing gloves Use of gowns, gloves, and face protection also reduces transmission Children at high-risk for severe and lifethreatening disease from RSV may be candidates for prophylactic passive immunization Palivizumab, a monoclonal antibody against the RSV F glycoprotein, reduces the rates of hospitalization and ICU admission by 50% in high-risk children Local guidelines vary by region, but prophylaxis may be warranted in children born extremely premature and those with chronic lung disease, hemodynamically significant congenital heart disease, immunodeficiency, and other comorbidities Palivizumab does not improve clinical outcomes when given during acute illness to lower risk children Vaccines against RSV are under development A 3-month-old infant is admitted to the pediatric intensive care unit with acute respiratory failure secondary to bronchiolitis, and high-flow nasal cannula (HFNC) at a flow rate of L/kg/minute is initiated What is the primary mechanism by which HFNC improves work of breathing? A Application of positive-end expiratory pressure at 5–10 cmH2O B Provision of oxygen to the anatomic dead space C Increased laminar flow in the bronchioles D Activation of alpha and beta adrenergic receptors Preferred response: B Rationale HFNC improves a patient’s respiratory status via several mechanisms, including reduced metabolic work of the nasopharyngeal tissues, improved mucociliary function, and reduced inspiratory resistance Substantial effects of HFNC are due to wash out of the nasopharyngeal anatomical dead space, replacing the CO2-rich and O2-poor air that remains in the nasopharynx at the end of exhalation with CO2-free and O2-rich gas, thereby improving CO2 removal and oxygenation This may be particularly beneficial in young children—such as those with bronchiolitis—given the e75 higher ratio of anatomic dead space to tidal volume in infants HFNC is intended to be an open system, with the nares 50% unobstructed by the cannula to enable wash out, thereby limiting the amount of positive airway pressure generated Nasopharyngeal pressures may reach 4–8 cm-H2O with flows up to ,2.5 L/ kg/min, but depend heavily on flow rate and whether the child’s mouth is open or closed, and vary widely between patients even if those factors are equivalent How much of this pressure is transmitted to the alveoli is unclear Regardless of the mechanisms, HFNC reduces work of breathing in children with bronchiolitis, with maximal effects seen at 1.5–2.0 L/kg/min, and its introduction into clinical practice has been associated with reduced rates of intubation for bronchiolitis In RSV bronchiolitis, what is the primary mechanism of respiratory pathophysiology? A Endothelial damage of small blood vessels with associated focal hemorrhagic necrosis, and mononuclear infiltration of alveolar walls and fibrinous exudates with macrophages in the alveoli B Viral particles replicating inside the type II pneumocytes initiate cellular apoptosis C Viral replication initiates a cascade of T and B cell infiltration into the peribronchiolar tissue, leading to edema, mucous secretion and cellular sloughing D Viral surface glycoproteins F and G inactivate surfactant leading to increased alveolar permeability, airway edema, and impaired gas exchange Preferred response: C Rationale In an autopsy study, children who died from RSV infection were found to have extensive RSV antigen in lung epithelium, sloughed epithelial cells blocking the small airways, significant apoptosis, low quantities of lymphocyte cytokines, and a near absence of CD81 lymphocytes and NK cells These findings suggest that the pathogenesis of fatal RSV infection may be secondary to the failure of the child to develop an appropriate adaptive cytotoxic T cell response to infection A larger autopsy study included 250 children who died from a variety of acute respiratory infections including RSV, adenovirus, influenza, and parainfluenza This study described RSV as causing the most profound damage and inflammation to the bronchiolar epithelial cells More recent studies have described a pattern of necrotic RSV infected epithelial cells contributing to small airway inflammation Furthermore, RSV likely destroys ciliated cells, contributing to impaired mechanical clearance of the distal airways Young children and infants are disproportionately burdened by viral lower respiratory tract disease In addition to functionally immature immune systems, infant respiratory anatomy and mechanics predispose to severe disease The viral induced inflammatory response occurring in proportionally smaller bronchioles leads to alveolar obstruction and collapse with edema, mucus, and cellular debris The increased resistance affects both inspiration and expiration in the small airways, ultimately leading to a “ballvalve” mechanism of air-trapping, hyperinflation, and resorption atelectasis The subsequent pulmonary ventilation and perfusion mismatch may lead to hypoxemia ... management in this child? A Administration of muscle relaxants B Endotracheal intubation C Heliox administration D Left lateral decubitus position Preferred response: A Rationale This child likely... characteristics of this mixture permit greater gas flow past areas of airway narrowing Endotracheal intubation is indicated only if respiratory function becomes severely compromised This measure,... those factors are equivalent How much of this pressure is transmitted to the alveoli is unclear Regardless of the mechanisms, HFNC reduces work of breathing in children with bronchiolitis, with