e61CHAPTER 136 Board Review Questions 2 A newborn intubation maybe challenging due to the anterior superior location of the larynx compared to a toddler What oropharyngeal changes with growth and deve[.]
CHAPTER 136 Board Review Questions A newborn intubation maybe challenging due to the anterior superior location of the larynx compared to a toddler What oropharyngeal changes with growth and development account for this? A Growth in the oropharynx is primarily in the anteroposterior direction B Lateral walls of the pharynx consist of a pair of constrictor muscles innervated by cranial nerves V, IX, and X C Oropharynx is the crossroads for the soft palate above and the hypopharynx below D The oropharynx is prominent in young infants E The oropharynx is first evident in children between ages and years Preferred response: E Rationale In young infants there is no defined oropharynx The nasopharynx and hypopharynx are contiguous Over the first 2–3 years, growth is primarily in the vertical direction such that a distinct oropharynx becomes evident, usually between and years of age Three pairs of constrictor muscles are seen in the lateral walls of the pharynx, not just one pair The innervation is via cranial nerves, V, IX, and X The oropharynx forms the crossroads for the nasopharynx above and the hypopharynx below The soft palate is the muscular extension of the bony hard palate and a critical structure for occlusion of the nasal cavity while eating and drinking, as well as retraction is important for speech production What is narrowest part of the upper airway in infants? A Larynx B Nasal valve C Nasopharynx D Subglottis Preferred response: B Rationale The structure of the upper airway differs in the infant, young child, and young adult Preferential nasal breathing is present in neonates and persists until months of age because of the highriding larynx in the neck with the soft palate and vallecula in close anatomic approximation The nasal tip—in particular, the nasal valve area—is the area of highest resistance in the upper airway of the infant A pediatric patient requires intubation Laryngoscopy shows an easy grade view; however, the age-appropriate endotracheal tube is difficult to pass Which is not a possible reason for this to happen? A Laryngeal web B Subglottic stenosis C Tracheal stenosis D Tracheomalacia Preferred response: D Rationale Tracheomalacia would not obstruct passing of the endotracheal tube because it is weakness or external compression of the trachea It may hinder ventilation but the endotracheal tube should be able to pass easily e61 What method can be used to reach a definitive diagnosis of a laryngeal cleft? A Fiberoptic endoscopic examination of swallowing (FEES) B Flexible nasopharyngoscopy C Operative endoscopy with palpation of the larynx D Videofluoroscopic swallow study (VFSS) Preferred response: C Rationale To assess for a laryngeal cleft, palpation of the interarytenoid area is the gold standard Chapter 41: Structure and Development of the Lower Respiratory System A baby is born at 24 weeks’ gestation and has a difficult respiratory course in the NICU She eventually gets a tracheostomy for chronic ventilation and is transferred to the PICU at months of age Her oxygen requirement has been decreasing, and she is discharged home on a ventilator Which of the following is a correct statement regarding the development of this child’s lower respiratory system? A Alveolarization is complete in this child B The acinus is the gas exchange area of the lung C The pulmonary veins course with the airways and the bronchioles throughout the lung D Type I alveolar epithelial cells produce and secrete surfactant Preferred response: B Rationale Surfactant is produced by type II cells, not type I cells Gas exchange occurs in the acinus Alveolarization appears to be nearly complete at about age years and so should continue to occur in this child The pulmonary veins not normally course with the airways and bronchioles When they do, this suggests alveolarcapillary dysplasia The primary role of the lung is gas exchange What structural feature of the lung supports this function? A Alveolar macrophages are scarce in the normal lung B The connective tissue space, or interstitium of the lung at the alveolar level, has abundant lymphatics C The internal surface area of the adult lung is 70 to 80 m2, of which 90% covers the pulmonary capillaries D When fully matured the pulmonary artery and its thickness is approximately 90% that of the aorta Preferred response: C Rationale The internal surface area of the adult lung is 70 to 80 m2, of which 90% covers the pulmonary capillaries; thus the air-blood surface available for gas exchange is 60 to 70 m2 When fully matured, the pulmonary artery and its thickness is only about 60% that of the aorta Alveolar macrophages are abundant and form an important arm of the defense mechanism of the lung The connective tissue space, or interstitium of the lung at the alveolar level, does not have lymphatics, but it can accumulate fluid that can be absorbed into the lymphatic system, which ends usually at the respiratory bronchiolar level e62 S E C T I O N XV Pediatric Critical Care: Board Review Questions Which of the following is the most predominant bronchial mucosal cell type? A Basal cells B Brush cells C Ciliated cells D Neuroendocrine cells Preferred response: C Rationale The bronchial mucosa contains several epithelial cell types: ciliated, mucus producing (goblet cells), basal, brush, and neuroendocrine Ciliated cells constitute more than 90% of the epithelial cell population in the conducting airways, but the proportion and number of cilia per cell decrease from the proximal to the distal airways In addition to its ciliary beating movement, the ciliated columnar cells regulate the depth of the composition of the periciliary fluid and transport ions across the epithelium The basal cell has a progenitor cell role and also functions to maintain adherence of columnar cells to the basement membrane The brush cell, thought to have a role in fluid absorption or chemoreceptor function, is found rarely in the tracheobronchial and alveolar epithelia Although mucous goblet cells secrete mucin, it is the submucosal glands that produce more than 90% of the mucus needed for mucociliary function Neuroendocrine cells can be solitary near the basal lamina between columnar cells or in collections called neuroepithelial bodies that occur near branch points of bronchi A number of neural markers are expressed (e.g., 5-hydroxytryptamine, chromogranin A, neuron-specific enolase, and synaptophysin), and a number of hormones are produced (e.g., endothelin, calcitonin, and bombesin [gastrin-releasing peptide]) They are more abundant in the fetus and likely have a role in lung growth or maturation It is not known with certainty when alveolar development is completed However, based on our current knowledge, we believe which of the following statements? A All alveoli are present at birth B All alveoli are present at 16 weeks’ gestation C Alveoli continue to develop until to years of age D Alveoli continue to develop into adulthood Preferred response: C Rationale At birth, primitive alveoli called saccules are evident, but approximately 50 million alveoli are already formed The number of alveoli in a normal adult can vary from 300 to 500 million, and they have a diameter of 150 to 200 µm The early work by Dunnell suggesting that new alveolar formation ceased at about age years has been challenged by Thurlbeck, who has shown that alveolarization appears to be nearly complete at about age years Lung volume correlates with body size, but alveolar surface area correlates with metabolic activity; thus alveoli become more complex in shape during maturation and as increasing O2 is required Chapter 42: Physiology of the Respiratory System Regarding respiratory physiology, which one of the following statements is least accurate? A Peripheral airway resistance in children ,5 years is fourfold higher than in older children and adults B Specific compliance is the same for adults and children, but specific conductance is higher in children C With laminar flow, resistance to flow is proportional to viscosity D With turbulent flow, resistance to flow is proportional to density Preferred response: B Rationale Compliance is a measure of the elastic nature of the chest wall and lungs In children, due to decreased development of the structure of the lungs and developing calcification of the ribs, the compliance of both the lungs and chest wall is decreased Which one of the following clinical conditions is not expected to be associated with sudden decline in end-tidal CO2 as it relates to the alveolar gas equation? A Air embolism B Cardiac standstill C Hypoventilation D Obstruction of the endotracheal tube Preferred response: C Rationale The volume of air entering the lungs each minute that actually participates in gas exchange is called the alveolar ventilation (A) It is therefore the difference between the total volume of air entering the lungs each minute (minute ventilation, E) and the volume of air entering the lungs that does not participate in gas exchange (dead space: D): A E D Anything decreasing the amount of CO2 seen by the end-tidal sensor will decrease the level displayed, but a sudden decrease represents a sudden change, whereas hypoventilation would demonstrate a gradual increase Lack of oxygen equilibration due to diffusion limitation (alveolarcapillary block) can be evaluated by measuring which of the following? A Diffusing capacity of CO (carbon monoxide) B Diffusing capacity of CO2 (carbon dioxide) C Distribution of an inhaled gas mixture containing a radioactive marker D FEV1/FVC when inhaling pure oxygen Preferred response: A Rationale DCO is a good index of the diffusion capacity of oxygen (Do2) Reduction of the pulmonary diffusing (D) capacity to onefourth of its normal value would be expected to have what effect on systemic arterial oxygen and carbon dioxide partial pressures (compared to normal)? A Decrease Pao2 and decrease Paco2 B Decrease Pao2 but no change in Paco2 C Increase Pao2 and decrease Paco2 D Increase Pao2 and increase Paco2 Preferred Response: B CHAPTER 136 Board Review Questions e63 Rationale Pao2 decreases when the diffusion capacity of oxygen (Do2) decreases to less than one-third its normal value But Do2 is so high normally that even a decrease to one-fourth will still permit carbon dioxide to equilibrate in the time that blood passes through pulmonary capillaries 3 A standard pulse oximeter is able to detect: A Carboxyhemoglobin B Methemoglobin C Oxygenated hemoglobin only D Oxygenated and deoxygenated hemoglobin Preferred response: D Chapter 43: Noninvasive Respiratory Monitoring and Assessment of Gas Exchange Pulse oximetry is based on the observation that the attenuation of light passing through blood-perfused tissue changes with pulsation of blood and that the alternating component of the light attenuation results from the composition of arterial blood Hemoglobin has characteristic light-absorbing properties that change with oxygen binding The deoxy form of hemoglobin (deoxyHb) has a single peak in the visible and near-infrared region Oxyhemoglobin (oxyHb) has two peaks in the visible region but no significant peak in the near-infrared region At any given wavelength, there is a difference in absorption between oxyHb and deoxyHb except where the spectra cross, at wavelengths called isosbestic wavelengths, where the absorption is the same for each state At nonisosbestic wavelengths, the difference in absorption can be used to determine the fraction of oxyhemoglobin Saturation of hemoglobin is defined as follows: Which of the following is least likely associated with a source of error when measuring oxygen saturation via pulse oximetry (Spo2)? A Increased proportion of the oxidized form of hemoglobin B Presence of fetal hemoglobin (HgbF) C Probe placement on a digit of a patient immediately status post–cold water submersion D Probe placement on the right second digit of a patient experiencing bilateral upper extremity tonic-clonic seizure activity Preferred response: B Rationale Fetal hemoglobin and adult hemoglobin have nearly identical absorption Studies have demonstrated that Spo2 measurements by pulse oximetry are unaffected by the presence of HgbF in neonates All other choices are associated with known sources of error for pulse oximetry readings Specifically, patient movement (such as seizure activity in answer D) can be associated with poor signal and inaccurate pulse oximetry readings Additionally, local perfusion and patient temperature may affect the probe’s ability to measure Spo2 due to alterations in the local pulsatile blood flow In patients with cold extremities and significant peripheral vasoconstriction (expected in a patient status post–cold water submersion in answer C), perfusion to the digits is likely significantly impaired and will affect the accuracy of pulse oximetry readings Which of the following is true regarding near-infrared spectroscopy (NIRS)? A NIRS measures only light absorbed by hemoglobin B NIRS measurement is not affected by skin temperature C Values from NIRS may be helpful for trending a patient’s oxygenation and hemodynamic status D When placed on the forehead, NIRS provides a measurement that is equivalent to the mixed venous saturation Preferred response: C Rationale Near-infrared spectroscopy (NIRS) is a noninvasive method utilized to measure the Hgb-oxygen saturation of a local region of interest This is achieved through the use of multiple (2–4) wavelengths of near-infrared light directed via a cutaneous probe into the underlying tissue, which are absorbed by pigments such as myoglobin, hemoglobin, and cytochrome Studies have reported varying degrees of accuracy for cerebral NIRS oximeters and have also found large variation in reading errors Extracranial tissue changes due to superficial vasoconstriction secondary to vasoactive medication (e.g., norepinephrine, phenylephrine) or sympathetic response to pain or hypothermia can be additional sources of error with cerebral NIRS oximetry Based on these findings, many authors recommend the use of cerebral oximetry as trend monitors and not absolute tissue oxygenation measures or injury threshold determinants Rationale Hbsat [OxyHb]/([OxyHb] [DeoxyHb]) where Hbsat fractional saturation of hemoglobin, [oxyHb] concentration of oxyhemoglobin, and [deoxyHb] concentration of deoxyhemoglobin Hemoglobin percent saturation, as commonly reported, is determined by multiplying Hbsat by 100 Which of the following are the most reliable sites for monitoring rapidly changing core temperature? A Distal esophagus, tympanic membrane, pulmonary artery, and nasopharynx B Distal esophagus, pulmonary artery, bladder, and rectum C Skin, bladder, and rectum D Skin, bladder, and nasopharynx Preferred response: A Rationale Commonly used core temperature monitoring sites include the distal esophagus, tympanic membrane, pulmonary artery, and nasopharynx These sites detect core temperature changes rapidly, in contrast to urinary bladder or rectal measurements, which are good reflections of core temperature during steady-state conditions Cutaneous temperature monitoring is the least reliable indicator of rapid core temperature changes However, monitoring peripheral temperatures can be useful in defining core peripheral gradients in temperature and assist in tracking vasoconstriction and vasodilation Oral probes are used as thermometers, and some have been attached to pacifiers A thermometer that scans the temporal artery is also available The ideal spot for continuous core temperature monitoring is a pulmonary artery catheter, but because of the invasive nature of this monitor, it would never be placed for temperature monitoring alone An esophageal temperature probe positioned in the lower third of the esophagus is a good alternative In this position, the temperature sensor is immediately behind the left atrium and accurately tracks core temperature without significant time lag in the majority of situations If a gastric tube with applied suction is present next to the temperature probe, it must be on the low intermittent setting or the temperature readings will be falsely S E C T I O N XV Pediatric Critical Care: Board Review Questions lowered Nasopharyngeal and tympanic membrane temperatures are good indicators of cerebral temperature but can be inaccurate as a result of sensor positioning Axillary and peripheral skin probably are the most convenient sites for monitoring temperatures, but they also are the most inaccurate because of skin perfusion You are leading resuscitation for a 2-year-old boy who suffers a bradycardic cardiac arrest requiring cardiopulmonary resuscitation (CPR) He receives approximately minutes of highquality CPR and then a code dose of epinephrine After approximately 30 seconds you noticed a change in his end-tidal CO2 waveform (Figure 136.16, below) What does this change in capnography most likely indicate? A Dislodgement of the endotracheal tube B Inadequate depth of chest compressions C Presence of lower airway obstruction D Restoration of pulmonary blood flow through return of spontaneous circulation (ROSC) Preferred response: D ETCO2 40 15 Time • Fig 136.16 CO2 (mm Hg) e64 50 37 Real-time Trend • Fig 136.17 Rationale Incorrect placement of the endotracheal tube in the esophagus results in initial detection of trace PETCO2, which is not sustained over time, and an uncharacteristic waveform that lacks a defined respiratory upstroke, plateau, or inspiratory downstroke Hypoventilation may be indicated by a gradual rise of PETCO2, while airway obstruction is demonstrated by a change in the shape of the capnography waveform (absence of expiratory or alveolar plateau) Sudden loss of PETCO2 with a waveform that transitions from normal to flat line is an indication of laryngospasm or apnea Chapter 44: Overview of Breathing Failure Compared with adults, neonates are more predisposed to respiratory failure because: A Airway resistance is lower in neonates B Neonates have a greater proportion of type fibers in the diaphragm C The neonatal diaphragm has a greater angle from the vertical than the adult D The neonatal chest wall is less compliant than the adult E The ribs are more vertical than the adult Preferred response: C Rationale Capnography has been shown to be a useful tool in many clinical situations Recent studies have demonstrated that use of end-tidal CO2 monitoring during CPR can help improve the quality of CPR and provide insight into the patient’s physiology Recent Advanced Cardiac Life Support (ACLS) and PALS guidelines recommend using capnography to monitor the effectiveness of chest compressions during CPR A sudden decrease in PETCO2 is seen with loss of pulmonary blood flow in cardiac arrest Increasing PETCO2 values generated during CPR are associated with chest compression depth and ventilation rate, and an acute rise in PETCO2 exceeding 10 mm Hg is seen with return of spontaneous circulation Patients with ROSC after CPR have statistically higher levels of PETCO2, suggesting better lung perfusion and cardiac output Current guidelines suggest achieving a threshold of 10 to 15 mm Hg to ensure adequate delivery of chest compressions, although an average PETCO2 level of 25 mm Hg was found in patients with ROSC in a recent systematic review and meta-analysis In the above waveform, we see initial PETCO2 values of approximately 15–20 mm Hg, suggesting adequate chest compression depth We then see an acute rise in PETCO2 up to levels of 40 mm Hg and above This acute rise is characteristic of increased pulmonary blood flow and is suggestive of achieving ROSC Rationale Neonates are at a number of mechanical disadvantages for breathing when compared with older children and adults Because the neonatal chest wall is more compliant than the adult, the ribs recoil more and are more horizontal This in turn promotes the diaphragm to be less apposed to the chest wall and a greater angle of the diaphragm to the chest well Both of these make the diaphragm less efficient These effects all act together to promote restrictive lung disease in the normal neonate Therefore, they are more tachypneic at baseline and susceptible to any further restrictive process In addition, neonates have smaller airways, which greatly increases resistance to airflow and predisposes to more severe obstructive airway disease (both inspiratory and expiratory) Airway resistance is inversely proportional to the fourth power of the radius of the airway (R5 where h is gas viscosity, L is airway length, and r is radius of the airways) Thus, small changes in the airway caliber due to edema or mucus can cause severe increase in the respiratory work a neonate must perform Because the neonatal diaphragm is composed of a greater proportion of type fibers, it tolerates prolonged loads less well and becomes fatigued more easily Type fibers, which are more prevalent in the adult and well-trained diaphragm, resist fatigue better than type 6 Which of the following clinical scenarios best explains this capnography waveform (Figure 136.17)? A Airway obstruction B Apnea C Esophageal intubation D Hypoventilation Preferred response: C Of the following, which is a cause of central hypoventilation? A Botulism B Cerebral palsy C Metabolic acidosis D Phox2B mutation E Tetrodotoxin Preferred response: D CHAPTER 136 Board Review Questions Rationale Central hypoventilation is caused by a decreased stimulus, or altered threshold, for respiratory rhythm generators in the central nervous system Patients with the congenital central hypoventilation syndrome lack normal automatic control of breathing due to mutations in Phox2B, which is expressed in the retrotrapezoid nucleus of the medulla, one of the major chemosensitive regions controlling ventilation Because chemosensitive regions in both the periphery and the brain sense pco2 through local changes in pH, metabolic acidosis increases the drive to breathe, as opposed to decreases it Patients with central hypoventilation lack effort despite increased CO2 tension Disorders of the peripheral nervous system and muscles may also have inadequate respiratory effort Tetrodotoxin, via inhibition of nerve impulses, suppresses breathing, though the central drive is intact Similarly, botulism inhibits neurotransmission at the motor endplate and prevents muscle response to central stimuli Patients with cerebral palsy have a number of factors that predispose to respiratory failure These include increased (and inappropriate) airway tone as well as scoliosis and other chest wall deformities that occur over time However, these patients nearly always have adequate respiratory drive at baseline A patient with cerebral palsy who lacks adequate respiratory drive should be evaluated for other causes (i.e., seizures, sepsis, drug overdose) What is the primary mechanism by which shock causes respiratory failure? A Cortical brain ischemia B Inadequate muscle blood flow C Metabolic acidosis D Overstimulation of medullary respiratory centers Preferred response: B Rationale In shock, blood flow to respiratory muscles becomes inadequate for aerobic muscle work Respiratory muscles first develop an oxygen debt and then lose their ability to contract Metabolic acidosis stimulates chemoreceptors and brainstem respiratory sites, causing tachypnea and dyspnea, but not preventing muscle work The high respiratory muscle workload of respiratory failure does increase muscle blood flow to the extent supportable by the circulation and is a strain on the heart, but it is not the cause of respiratory failure in shock Cortical brain ischemia might impair volitional responses to respiratory distress, but it is the brainstem that governs automatic responses to respiratory stimuli Overstimulation of medullary respiratory centers may drive tachypnea but is not the cause of respiratory muscle failure from shock A child fell while rock climbing and suffered injury to his thoracic spinal cord at the level of T6 He has lower extremity flaccidity and a sensory level at the lower sternum and at the level of T6 posteriorly What would be the greatest impact of this injury on breathing? A Dependence on accessory muscles of respiration B Diminished strength of cough C Loss of the cough reflex D Reduced inspiratory capacity Preferred response: B e65 Rationale The muscles of the abdomen are used for active expiration and are innervated by the lower thoracic spinal cord They are important for coughing, sneezing, and for forced expiration, but play little role in passive expiration The cough reflex involves abdominal muscles as well as deep intercostals, which are innervated by both upper and lower thoracic motor neurons The reflex would be intact despite a T6 injury, but the cough itself would be weak Inspiration is powered by the superficial and parasternal intercostal muscles and by the accessory muscles of respiration, so inspiratory capacity should be preserved Dependence on accessory muscles for normal inspiratory power should not be necessary Retractions reflect inspiratory effort, which should not be directly altered by this injury Which of the following is a true statement about control of breathing? A Aortic and carotid chemoreceptors directly modulate respiratory drive B Brainstem respiratory control is located in a single medullary nucleus C Volitional and automatic control of breathing may be independently impaired D Volitional control of breathing requires medullary modulation Preferred response: C Rationale Volitional control of respiration normally may be asserted in the awake state, but only up to a point One cannot consciously hold the breath beyond a certain level of medullary stimulation Supratentorial injury may impair volitional control of breathing but spare automatic control On the other hand, medullary stroke may impair automatic control of breathing but leave volitional control intact Brainstem respiratory control is widely distributed in the pons and medulla and involves numerous other brainstem nuclei All mechanoreceptor and chemoreceptor input that modulates respiratory drive must be processed in the brain before effector responses can occur Aortic and carotid chemoreceptors modulate breathing only after integration in the medulla Patients with loss of all cortical behavior may exhibit respiratory distress and use accessory muscles of breathing Which of the following is a true statement about respiratory muscle exhaustion? A Myoglobin provides adequate oxygen reserves to protect against respiratory muscle exhaustion from hypoxemia B Muscle training can prevent fatigue of respiratory muscles C Rapid shallow breathing is a sign of respiratory muscle exhaustion D Shock may precipitate respiratory muscle exhaustion and respiratory arrest Preferred response: D Rationale Shock can diminish oxygen supply to the respiratory muscles and precipitate muscle exhaustion Respiratory arrest is a final common pathway to death in all forms of untreated shock Hypoxemia also can cause respiratory muscle exhaustion Although myoglobin may provide a short-term buffer to transient oxygen deficits, it cannot prevent persistent hypoxia or blood flow limitation from progressing to respiratory muscle exhaustion ... nature of this monitor, it would never be placed for temperature monitoring alone An esophageal temperature probe positioned in the lower third of the esophagus is a good alternative In this position,... and above This acute rise is characteristic of increased pulmonary blood flow and is suggestive of achieving ROSC Rationale Neonates are at a number of mechanical disadvantages for breathing when... lower sternum and at the level of T6 posteriorly What would be the greatest impact of this injury on breathing? A Dependence on accessory muscles of respiration B Diminished strength of cough