e81CHAPTER 136 Board Review Questions 3 What is the least accurate statement regarding the manage ment of pulmonary arterial hypertension (PAH) in children? A Coadministration of sildenafil with ketoc[.]
CHAPTER 136 Board Review Questions What is the least accurate statement regarding the management of pulmonary arterial hypertension (PAH) in children? A Coadministration of sildenafil with ketoconazole or rifampin should be avoided B Due to the risk of hepatic toxicity, the FDA requires that liver function tests be performed at least once in months in patients on endothelial receptor antagonists such as bosentan C Nitric oxide is currently the first-line drug in the acute management of PAH or in cases of postoperative PAH arising from congenital heart disease (CHD) repair D There is a mutual pharmacokinetic interaction between bosentan and sildenafil that may influence the dosage of each drug in a combination treatment Preferred response: B Rationale As sildenafil is metabolized by hepatic CYP450, coadministration of sildenafil with CYP3A inducers or inhibitors such as ketoconazole or rifampin should be avoided There is a mutual pharmacokinetic interaction between bosentan and sildenafil that may influence the dosage of each drug in a combination treatment Bosentan decreases the maximum plasma concentration of sildenafil (Cmax) by 55.4% on day 16, whereas sildenafil increased bosentan Cmax by 42%, hence close monitoring is advisable with coadministration Nitric oxide (NO) is currently the first-line drug in the acute management of PAH or in cases of postoperative PAH arising from CHD repair or other causes Due to the risk of hepatic toxicity, the FDA requires that liver function tests be performed at least monthly and hematocrit every months on patients on endothelial receptor antagonists such as bosentan There is concern that the endothelin antagonists as a class may be capable of causing testicular atrophy and male infertility Which of the following statements most accurately reflects acute vasoreactivity testing in persons with pulmonary arterial hypertension (PAH)? A Acute response to vasodilator testing is defined as a decrease in mean pulmonary arterial pressure by at least 10 mm Hg to an absolute level of less than 40 mm Hg with a decrease in cardiac output B Acute vasodilator testing is indicated in patients with significantly elevated left ventricular filling pressures C Inhaled nitric oxide (iNO) is the most commonly used drug for acute vasoreactivity D Responders to acute vasodilator testing (AVT) are more likely to respond to any therapy specific to PAH than are nonresponders Preferred response: C Rationale Vasoreactivity testing is an essential component in the diagnostic evaluation of PAH because it has therapeutic implications Responders are more likely to respond to oral CCBs than are nonresponders and seem to have a better prognosis AVT is usually performed during the same procedure as the diagnostic right heart catheterization AVT is performed using iNO, intravenous PGI2, or intravenous adenosine The most commonly used drug for AVT is iNO at doses of 20 to 40 ppm for minutes Hemodynamic measurements are recorded prior to and after administration of iNO, and the drug is discontinued completely Based largely on data from Sitbon and colleagues, the European Society e81 of Cardiology and American College of Chest Physicians guidelines propose that the acute response to vasodilator testing be defined as a decrease in mean pulmonary arterial pressure by at least 10 mm Hg to an absolute level of less than 40 mm Hg without a decrease in cardiac output Patients with PAH due to conditions other than idiopathic PAH, such as BMPR2 genotype or anorexigen-induced PAH, have a very low rate of long-term responsiveness to oral CCB therapy Accordingly, the decision to proceed with AVT in such patients should be individualized AVT testing is not indicated, and may be harmful, in patients with significantly elevated left heart filling pressures Which of the following statements is true regarding vasoactive mediators and their effect on vascular smooth muscle cells? A Nitric oxide stimulates the formation of cyclic adenosine monophosphate (cAMP) B Phosphodiesterase (PDE-3) inhibitors such as milrinone increase cAMP levels C Phosphodiesterase (PDE-5) inhibitors such as sildenafil increase cAMP levels D Prostacyclin increases the formation of cyclic guanosine monophosphate (cGMP) Preferred response: B Rationale Vasodilators such as NO and prostacyclin relax vascular smooth muscle by increasing intracellular concentrations of the second messengers cGMP and cAMP, respectively Inhibition of the cGMP degrading phosphodiesterase (PDE-5) by sildenafil and inhibition of the cAMP degrading phosphodiesterase (PDE-3) by milrinone offer additional tools to achieve pulmonary vasodilation in patients with persistent pulmonary hypertension Type phosphodiesterase (PDE-5) is primarily responsible for degradation of cGMP to the inactive metabolite GMP One way of augmenting the concentration of cGMP in pulmonary vessels is by inhibiting the activity of PDE-5 PDE-5 inhibitors, such as sildenafil and tadalafil, might therefore be expected to prolong the vasodilating effects of cGMP Sildenafil is a potent and selective inhibitor of cGMP-specific PDE-5 Which of the following statements is true regarding fetal circulation and transition at birth? A All the blood draining into the right atrium from the inferior vena cava (IVC) enters the left atrium B Pulmonary vascular resistance falls and systemic vascular resistance increases soon after birth C The ductus arteriosus shunts blood from right to left (pulmonary artery to aorta) soon after birth D The highest Pao2 levels in the fetus are in the umbilical arteries Preferred response: B Rationale Oxygenated blood (Pao2 approximately 30–40 mm Hg) returning from the placenta in the umbilical vein splits in the liver, with slightly more than half passing through the ductus venosus to the IVC The oxygenated blood streams along the medial aspect of the IVC as it enters the right atrium Approximately two-thirds of the IVC flow is directed toward the foramen ovale by the eustachian valve and the septum primum and enters the left atrium The remaining third of IVC flow mixes with the blood from the superior vena cava and enters the right ventricle The majority of e82 S E C T I O N XV Pediatric Critical Care: Board Review Questions the right ventricular output enters the ductus arteriosus and the descending aorta A small portion enters the lungs via the pulmonary arteries The ratio of blood flow to the pulmonary arteries to the flow that traverses the ductus arteriosus is determined by the fetal pulmonary vascular resistance (PVR) The first stage of transitional circulation is essentially a fetal pulmonary circulation that is characterized by high pressure and low flow because of both passive and active elevation of PVR Thus PVR exceeds systemic vascular resistance, resulting in right atrial and ventricular pressures exceeding left atrial and ventricular pressures High PVR results in right-to-left shunting of blood across the foramen ovale, and most of the blood ejected by the right ventricle flows across the ductus arteriosus into the descending aorta The second stage of normal transition is accomplished when the fluid-filled fetal lungs are distended with air during the first breath A rapid decrease in PVR occurs with mechanical distention of the pulmonary vascular bed The entry of air into the alveoli improves oxygenation of the pulmonary vascular bed, further decreasing PVR At birth, PVR decreases dramatically As PVR becomes less than systemic, flow across the ductus reverses Within the first minutes after birth, oxygen-induced vasodilation and lung expansion decrease PVR to approximately half of systemic resistance During the first few hours after birth, the ductus arteriosus closes, largely in response to the increase in oxygen tension At this point the normal postnatal circulatory pattern is established Chapter 54: Mechanical Ventilation and Respiratory Care Which of the following is a described advantage of using a decelerating flow pattern for mechanically ventilated patients? A Decreased length of ventilation in children with asthma B Higher mean airway pressures C Higher peak inspiratory pressures D Improved triggering Preferred response: B Rationale Given that the majority of flow occurs early in a breath delivered with decelerating flow pattern, pressure rises faster, functionally raising mean airway pressure, along with a lower peak inspiratory pressure for the same delivered tidal volume While decelerating flow is a more natural breath and may improve synchrony, the flow pattern has no effect on triggering, nor has it been associated with improved outcomes Which of the following is most consistent with a lung protective ventilation strategy in a child with new bilateral infiltrates, oxygenation index of 23, Spo2 88%, and hemodynamic instability? A Paco2 36 mm Hg B PEEP 14 cm H2O C Pplat 34 cm H2O D Tidal volume (Vt) of 10 mL/kg ideal body weight (IBW) Preferred response: B Rationale Lung protective strategies avoid types of lung injury: barotrauma, volutrauma, atelectotrauma, and biotrauma The former two types are avoided by limiting Vt to ,8 mL/kg, keeping Pplat ,28 cm H2O, and allowing permissive hypercapnia Elevated PEEP helps avoid atelectotrauma 3 Restrictive lung disease may be associated with which of the following: A Decreased compliance B Elevated functional residual capacity (FRC) C Increased airways resistance D Prolonged time constant Preferred response: A Rationale Restrictive lung diseases are a state of reduced compliance, either due to parenchymal disease or reduced chest wall compliance Generally, frictional resistance may be increased, but airways resistance is not significantly affected Because of the marked reduction in compliance, time constant is shortened, and FRC is reduced A 6-month old child with is endotracheally intubated and begun on mechanical ventilation for bronchiolitis Ventilator settings are pressure control mode with positive end-expiratory pressure (PEEP) cm H2O; peak inspiratory pressure (PIP), 14 cm H2O; measured tidal volume (Vt) of mL/kg of ideal body weight (IBW); pressure support (PS) 12 cm H2O; fraction of inspired oxygen (Fio2), 0.6; ventilator rate, 28 per minute Inspiratory time (Ti) is 1.2 sec As neuromuscular blockade wears off, the patient becomes agitated and asynchronous with the ventilator Evaluation of the patient reveals that the patient is awake, agitated, and not breathing over the ventilator Based on this information, what would be a reasonable next step? A Decrease Ti B Increase trigger sensitivity C Increase inspiratory flow demand D Re-dose neuromuscular blocking agent Preferred response: A Rationale The patient likely has asynchrony due to delayed cycling, and wants to start exhalation before the ventilator will allow it The inspiratory time is set at more than half of the entire cycle time, and every breath in a controlled breath with a set inspiratory time The patient would also likely benefit from a decreased respiratory rate to allow longer expiratory times and more supported breaths, where he is allowed to set his own inspiratory time Which of the following is correct in describing pressure-regulated volume control mode of ventilation? A Patient-triggered, flow-controlled, flow-cycled ventilation B Patient-triggered, flow-controlled, time-cycled ventilation C Patient/machine-triggered, pressure-controlled, time-cycled ventilation D Patient/machine-triggered, pressure-controlled, flow-cycled ventilation Preferred response: C Rationale PRVC or pressure-regulated volume control mode of ventilation is a dual-control mandatory mode Each breath is either patienttriggered (SIMV or Assist-control) or machine-triggered The primary control is pressure Between breaths, volume is controlled primarily by adjusting the pressure control level Cycling is by time All the other modes are common misconceptions of this mode CHAPTER 136 Board Review Questions Which of the following is associated with a high risk (.25%) of extubation failure? A Dynamic compliance of 0.9 mL/kg/cm H2O B Fraction of inspired oxygen (Fio2) of 0.45 to maintain Spo2 of 95% C Fraction of minute ventilation provided by the ventilator of 20% D Spontaneous tidal volume without pressure-support of mL/kg Preferred response: B Rationale Answers A, C, and D are associated with ,10% risk of failure Only Answer B is associated with at least a 25% of failure Respiratory Parameter Low Risk (10%) High Risk (25%) Spontaneous tidal volume (mL/kg) 6.5 ,3.5 Fio2 ,0.3 0.4 Mean airway pressure (cm H2O) ,5 8.5 Peak inspiratory pressure (cm H2O) ,25 30 Dynamic compliance (mL/kg/cm H2O) 0.9