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ABP Pediatric Critical Care Medicine study materials
ABP Pediatric Critical Care Medicine study resources

ABP Pediatric Critical Care Medicine practice questions

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Question 1Respiratory physiology, respiratory failure, and mechanical ventilation

In arterial blood with a normal hemoglobin concentration, which factors account for most of the oxygen content?

  1. Mixed venous oxygen saturation
  2. Serum bicarbonate and base excess
  3. Hemoglobin concentration and arterial oxygen saturation Correct answer.
  4. Dissolved oxygen reflected by PaO2 alone

Explanation

Arterial oxygen content equals 1.34 × hemoglobin × SaO2 plus a small dissolved fraction (0.003 × PaO2). Because dissolved oxygen is minimal at sea level, hemoglobin and saturation account for nearly all carried oxygen. This is why anemia can produce inadequate oxygen delivery despite a normal PaO2.

Question 2Respiratory physiology, respiratory failure, and mechanical ventilation

Which initial tidal volume is recommended for lung-protective ventilation in pediatric ARDS?

  1. 15 mL/kg of predicted body weight
  2. 10 mL/kg of actual body weight titrated to peak pressure
  3. 12 mL/kg of actual body weight
  4. 6 mL/kg of predicted body weight Correct answer.

Explanation

Pediatric ARDS guidance recommends tidal volumes of roughly 3 to 6 mL/kg predicted body weight, often starting near 6, with plateau pressure kept at or below 28 cm H2O. Actual body weight overestimates lung size in edematous children, so predicted body weight is used. Larger tidal volumes increase volutrauma and mortality.

Question 3Respiratory physiology, respiratory failure, and mechanical ventilation

Which pressure best estimates alveolar distending pressure during volume-controlled ventilation?

  1. Plateau pressure Correct answer.
  2. Mean airway pressure
  3. Peak inspiratory pressure
  4. Intrinsic PEEP measured after an expiratory hold

Explanation

Plateau pressure is read during an inspiratory hold, when flow has ceased and the resistive pressure drop across the tube and airways has dissipated, so it reflects alveolar pressure. Peak pressure includes resistive losses and rises with bronchospasm or a small tube. Plateau pressure is therefore the value used to judge barotrauma risk.

Question 4Respiratory physiology, respiratory failure, and mechanical ventilation

The oxygenation index used to grade hypoxemic respiratory failure is calculated from which variables?

  1. FiO2 and SpO2 divided by mean airway pressure
  2. Mean airway pressure and PaCO2
  3. PaO2 divided by FiO2
  4. Mean airway pressure, FiO2, and PaO2 Correct answer.

Explanation

Oxygenation index = (mean airway pressure × FiO2 × 100) / PaO2, so it rises as support escalates and oxygenation worsens. Unlike the P/F ratio, it incorporates the airway pressure required to oxygenate. Values above roughly 40 often prompt discussion of extracorporeal support.

Question 5Respiratory physiology, respiratory failure, and mechanical ventilation

A ventilated child with severe asthma has marked hyperinflation. Which strategy best reduces air trapping?

  1. Increasing the respiratory rate to improve minute ventilation
  2. Prolonging expiratory time and accepting hypercapnia Correct answer.
  3. Adding 10 cm H2O of extrinsic PEEP to stent the small airways
  4. Raising tidal volume to 12 mL/kg to overcome resistance

Explanation

Air trapping worsens when expiratory time is shorter than the time needed for the lung to empty, so the key maneuvers are lowering the rate and shortening inspiratory time to lengthen expiration. Permissive hypercapnia is accepted to keep plateau pressures safe. High rates, large tidal volumes, and excessive PEEP all worsen hyperinflation in this setting.

Question 6Respiratory physiology, respiratory failure, and mechanical ventilation

What is the effect of a rightward shift of the oxyhemoglobin dissociation curve?

  1. Reduced release of oxygen to peripheral tissues
  2. Lower hemoglobin oxygen affinity with greater tissue unloading Correct answer.
  3. Higher hemoglobin oxygen affinity at the alveolus
  4. Greater total oxygen carrying capacity of blood

Explanation

A rightward shift, produced by acidosis, hypercapnia, fever, or raised 2,3-DPG, reduces hemoglobin's affinity for oxygen so more oxygen is unloaded in tissues at any given PO2. Saturation at a fixed PaO2 therefore falls slightly. Total carrying capacity depends on hemoglobin mass, not curve position.

Question 7Respiratory physiology, respiratory failure, and mechanical ventilation

Which finding most suggests that intrapulmonary shunt is causing hypoxemia?

  1. Hypoxemia that barely improves when FiO2 is raised to 1.0 Correct answer.
  2. A widened alveolar-arterial gradient that normalizes on 100% oxygen
  3. Low mixed venous saturation with normal lung parenchyma
  4. Hypoxemia that corrects fully with 40% oxygen

Explanation

Blood passing through a true shunt never contacts ventilated alveoli, so raising FiO2 adds little oxygen to it and hypoxemia persists. Hypoxemia from hypoventilation or mild V/Q mismatch improves readily with supplemental oxygen. Shunt fraction is the portion of cardiac output perfusing unventilated lung.

Question 8Respiratory physiology, respiratory failure, and mechanical ventilation

During volume-controlled ventilation, a rising gap between peak and plateau pressure indicates which change?

  1. Increasing airway resistance Correct answer.
  2. Declining delivered tidal volume
  3. Falling lung compliance
  4. Rising chest wall compliance

Explanation

The peak-to-plateau difference is the pressure spent overcoming resistance, so a widening gap means resistance has risen, as with secretions, bronchospasm, or a small or kinked tube. Plateau pressure reflects compliance and rises when compliance falls, but it does not create a peak-to-plateau gap.

Question 9Respiratory physiology, respiratory failure, and mechanical ventilation

A lung unit has a compliance of 0.05 L/cm H2O and a resistance of 10 cm H2O/L per second. What is its time constant?

  1. 0.5 seconds Correct answer.
  2. 2 seconds
  3. 0.05 seconds
  4. 5 seconds

Explanation

The time constant equals compliance times resistance: 0.05 L/cm H2O × 10 cm H2O/L per second = 0.5 seconds. About 95% of a unit empties within three time constants (1.5 seconds) and essentially all within five. Units with long time constants need long expiratory times to avoid gas trapping.

Question 10Respiratory physiology, respiratory failure, and mechanical ventilation

Permissive hypercapnia should be avoided in a child with which condition?

  1. Bronchiolitis requiring high-flow oxygen
  2. Status asthmaticus with air trapping
  3. Moderate ARDS with plateau pressure at goal
  4. Raised intracranial pressure from traumatic brain injury Correct answer.

Explanation

Hypercapnia increases cerebral blood volume and intracranial pressure, so normocapnia is preferred when intracranial pressure is a concern. In obstructive lung disease and ARDS, accepting a higher PaCO2 protects against volutrauma and barotrauma. Severe pulmonary hypertension is another setting where it is avoided.

Question 11Respiratory physiology, respiratory failure, and mechanical ventilation

Which statement best describes high-flow nasal cannula therapy in an infant with bronchiolitis?

  1. Heated humidified flow that lowers dead space and gives variable low pressure Correct answer.
  2. Mandatory breaths that are synchronized to each inspiratory effort of the infant
  3. A fixed positive end-expiratory pressure that is independent of any leak around the prongs
  4. A completely airtight seal around the nares for the system to work

Explanation

High-flow devices deliver heated, humidified gas at flows that exceed inspiratory demand, flushing nasopharyngeal dead space, reducing work of breathing, and providing a modest leak-dependent positive pressure. Because the interface is not sealed, the pressure delivered varies. It is supportive therapy rather than a guaranteed distending pressure.

Question 12Respiratory physiology, respiratory failure, and mechanical ventilation

An intubated child's end-tidal CO2 suddenly falls to near zero with no change in ventilator settings. What is the most likely cause?

  1. Disconnection or tube dislodgement Correct answer.
  2. A sudden increase in cardiac output
  3. Partial mucus plugging of the tube
  4. Malignant hyperthermia

Explanation

End-tidal CO2 falls abruptly when exhaled gas no longer reaches the sensor, as with extubation, disconnection, or loss of pulmonary blood flow. Partial obstruction usually distorts or raises the waveform rather than abolishing it. A near-zero reading in a child with a previously normal trace demands immediate airway and circuit assessment.

Question 13Respiratory physiology, respiratory failure, and mechanical ventilation

In pediatric ARDS, what plateau pressure is commonly used as the upper limit for lung-protective ventilation?

  1. 40 cm H2O
  2. 20 cm H2O
  3. 35 cm H2O
  4. 28 cm H2O Correct answer.

Explanation

Pediatric ARDS consensus guidance recommends keeping plateau pressure at or below 28 cm H2O while using small tidal volumes. Plateau pressure is used because it approximates alveolar pressure and reflects barotrauma risk. Pressures above this threshold are associated with worse outcomes and prompt reduction of tidal volume or consideration of extracorporeal support.

Question 14Respiratory physiology, respiratory failure, and mechanical ventilation

A child with Guillain-Barré syndrome develops respiratory failure. Which blood gas pattern is most typical?

  1. Metabolic alkalosis with compensatory hypoventilation
  2. Hypoxemia that resolves with modest supplemental oxygen
  3. Hypoxemia with a markedly widened alveolar-arterial oxygen gradient
  4. Hypercapnia with a preserved alveolar-arterial oxygen gradient Correct answer.

Explanation

Neuromuscular weakness causes pump failure: alveolar ventilation falls and PaCO2 rises while the lungs themselves are normal, so the alveolar-arterial gradient stays near normal. Any hypoxemia is mild and oxygen-responsive. A widened gradient would instead point to parenchymal lung disease.

Question 15Respiratory physiology, respiratory failure, and mechanical ventilation

Which finding best supports readiness for extubation in a ventilated child?

  1. An FiO2 of 0.6 with 8 cm H2O of positive end-expiratory pressure
  2. Absence of any cuff leak when the cuff is deflated
  3. Tolerance of a spontaneous breathing trial with a strong cough Correct answer.
  4. A peak inspiratory pressure of 30 cm H2O during mandatory breaths

Explanation

Extubation succeeds when the child can sustain ventilation, clear secretions, and protect the airway, which a passed spontaneous breathing trial plus strong cough and manageable secretions captures. Oxygen needs and PEEP should be low, and a cuff leak is reassuring but not mandatory. Strength and mental status also contribute.

Question 16Respiratory physiology, respiratory failure, and mechanical ventilation

During pressure-control ventilation with a fixed inspiratory pressure, what happens when lung compliance decreases?

  1. Delivered tidal volume increases
  2. Minute ventilation stays constant
  3. Delivered tidal volume decreases Correct answer.
  4. Peak airway pressure rises above the set value

Explanation

In pressure-control modes the ventilator holds a set pressure, so the volume generated depends on compliance and resistance; when compliance falls, the same pressure inflates the lung less and tidal volume drops. Tidal volume must therefore be monitored and the pressure retitrated. Volume-controlled modes instead preserve volume and allow pressure to rise.

Question 17Respiratory physiology, respiratory failure, and mechanical ventilation

Flattening of the expiratory limb of a flow-volume loop suggests which problem?

  1. Poor effort during the maneuver
  2. Restrictive lung disease
  3. Extrathoracic airway obstruction
  4. Intrathoracic airway obstruction Correct answer.

Explanation

During forced expiration, pleural pressure compresses intrathoracic airways, so a fixed or variable intrathoracic obstruction limits expiratory flow and truncates the expiratory limb. Extrathoracic obstruction instead flattens the inspiratory limb. Restrictive disease narrows the loop while preserving its shape.

Question 18Respiratory physiology, respiratory failure, and mechanical ventilation

Which cause most often produces auto-triggering with a pressure-triggered ventilator?

  1. Deep sedation with a low respiratory drive
  2. Circuit leak or condensation causing pressure swings in the tubing Correct answer.
  3. A set respiratory rate lower than the child's spontaneous rate
  4. A trigger threshold set so negative that effort is ignored

Explanation

Pressure triggering responds to small pressure drops, so leaks, water in the circuit, or cardiac oscillations can be misread as inspiratory effort and trigger unscheduled breaths. The remedy is to eliminate the leak or switch to flow triggering. An insensitive threshold causes missed efforts rather than extra breaths.

Question 19Respiratory physiology, respiratory failure, and mechanical ventilation

Systemic oxygen delivery is best calculated from which relationship?

  1. Arterial saturation multiplied by PaCO2
  2. Cardiac output divided by systemic vascular resistance
  3. PaO2 multiplied by respiratory rate
  4. Cardiac index multiplied by arterial oxygen content Correct answer.

Explanation

Oxygen delivery equals cardiac output times arterial oxygen content (DO2 = CO × CaO2), with content driven mainly by hemoglobin and saturation. Anemia, low output, and desaturation each compromise delivery even when PaO2 appears acceptable. Mixed venous saturation indirectly reflects the balance between delivery and consumption.

Question 20Respiratory physiology, respiratory failure, and mechanical ventilation

How does surfactant administration improve oxygenation in neonatal respiratory distress syndrome?

  1. It increases pulmonary vascular resistance
  2. It dilates bronchial smooth muscle
  3. It thickens the alveolar-capillary membrane
  4. It lowers alveolar surface tension and reduces atelectasis Correct answer.

Explanation

Surfactant reduces surface tension at the air-liquid interface, stabilizing alveoli at low volumes and increasing functional residual capacity and compliance. Better aeration reduces intrapulmonary shunt and raises PaO2. It is instilled into the trachea and acts within minutes.

Question 21Respiratory physiology, respiratory failure, and mechanical ventilation

A child breathing 100% oxygen at sea level has a PaCO2 of 40 mmHg and a PaO2 of 300 mmHg. What is the alveolar oxygen tension?

  1. 300 mmHg
  2. 663 mmHg Correct answer.
  3. 713 mmHg
  4. 563 mmHg

Explanation

PAO2 = FiO2 (Patm − 47) − PaCO2/R = 1.0 × (760 − 47) − 40/0.8 = 713 − 50 = 663 mmHg. The resulting alveolar-arterial gradient of about 363 mmHg indicates substantial shunt or V/Q mismatch. Water vapor pressure must be subtracted before multiplying by FiO2.

Question 22Respiratory physiology, respiratory failure, and mechanical ventilation

A child with tense ascites has a plateau pressure of 30 cm H2O and an esophageal pressure of 18 cm H2O. What is the transpulmonary pressure?

  1. 48 cm H2O
  2. 30 cm H2O
  3. 12 cm H2O Correct answer.
  4. 18 cm H2O

Explanation

Transpulmonary pressure is airway (plateau) pressure minus pleural pressure, the latter estimated by esophageal pressure: 30 − 18 = 12 cm H2O. A modest transpulmonary pressure despite a high plateau means much of the measured pressure is distending the chest wall and abdomen rather than the lung. This distinction helps avoid both under- and over-distension.

Question 23Respiratory physiology, respiratory failure, and mechanical ventilation

During high-frequency oscillatory ventilation, which setting most directly determines carbon dioxide elimination?

  1. Fraction of inspired oxygen
  2. Inspiratory time as a fraction of the cycle
  3. Mean airway pressure
  4. Amplitude of the pressure oscillation Correct answer.

Explanation

In high-frequency oscillatory ventilation, CO2 removal depends on the tidal volume generated by the oscillating pressure amplitude, modulated by frequency. Oxygenation is set mainly by mean airway pressure and FiO2. Amplitude is titrated against chest wall vibration and PaCO2.

Question 24Respiratory physiology, respiratory failure, and mechanical ventilation

If the internal radius of an endotracheal tube is halved, resistance to laminar flow through it increases by what factor?

  1. 4
  2. 2
  3. 16 Correct answer.
  4. 8

Explanation

Poiseuille's law makes resistance inversely proportional to the fourth power of radius, so halving the radius raises resistance 16-fold. This is why a tube just one or two sizes smaller can sharply increase work of breathing and peak pressures. Turbulent flow, common at high flows in small tubes, amplifies the effect further.

Question 25Respiratory physiology, respiratory failure, and mechanical ventilation

Dead space fraction rises from 0.3 to 0.6 while tidal volume and CO2 production stay constant. What change in minute ventilation is needed to keep PaCO2 unchanged?

  1. A 50% increase
  2. Doubling Correct answer.
  3. No change
  4. Halving

Explanation

PaCO2 is inversely proportional to alveolar ventilation, which equals minute ventilation times (1 − dead space fraction). The non-dead-space fraction falls from 0.70 to 0.40, so minute ventilation must roughly double to preserve alveolar ventilation. Rising dead space from embolism or overdistension therefore forces higher minute ventilation or permits hypercapnia.

Question 26Cardiovascular physiology, shock, and hemodynamic support

Cardiac output is the product of heart rate and which other variable?

  1. Systemic vascular resistance
  2. Mean arterial pressure
  3. Stroke volume Correct answer.
  4. Central venous pressure

Explanation

Cardiac output equals heart rate multiplied by stroke volume, so either determinant can raise or lower total flow. Stroke volume itself depends on preload, afterload, and contractility. Resistance and pressure are related to flow but are not multiplicands of it.

Question 27Cardiovascular physiology, shock, and hemodynamic support

A 6-year-old develops urticaria, stridor, and hypotension minutes after a bee sting. The extremities are warm and the pulse pressure is wide. Which shock category fits best?

  1. Hypovolemic
  2. Cardiogenic
  3. Distributive Correct answer.
  4. Obstructive

Explanation

Anaphylaxis produces pathologic vasodilation and capillary leak, so pressure falls while the skin stays warm and the pulse pressure widens. This is the classic distributive pattern. Loss of vascular tone, rather than pump failure or a mechanical obstruction, drives the hypotension.

Question 28Cardiovascular physiology, shock, and hemodynamic support

Which principle best explains why tachycardia is such an important early compensation in pediatric shock?

  1. Rate dependence reflects limited stroke volume reserve Correct answer.
  2. Tachycardia directly increases systemic vascular resistance
  3. Tachycardia reduces myocardial oxygen consumption
  4. Children have greater stroke volume reserve than adults

Explanation

The pediatric ventricle has limited ability to augment stroke volume, so output is maintained largely by increasing heart rate. This compensation preserves perfusion until stroke volume falls further. Extremely fast rates eventually shorten filling time and reduce output, which is why persistent tachycardia is a warning sign.

Question 29Cardiovascular physiology, shock, and hemodynamic support

Which statement about hypotension in pediatric shock is most accurate?

  1. Hypotension develops before lactate rises
  2. Hypotension is a late sign of decompensation Correct answer.
  3. Hypotension is an early, sensitive sign of compensated shock
  4. Hypotension excludes the diagnosis of septic shock

Explanation

Children sustain blood pressure through intense vasoconstriction and tachycardia, so pressure may appear normal while perfusion is already failing. Hypotension therefore appears late, after a period of compensated shock. Therapy must begin on the basis of perfusion findings rather than waiting for the pressure to fall.

Question 30Cardiovascular physiology, shock, and hemodynamic support

A child with blunt chest trauma suddenly becomes hypotensive with distended neck veins, tracheal deviation, and absent breath sounds on one side. Which shock category is this?

  1. Cardiogenic
  2. Obstructive Correct answer.
  3. Hypovolemic
  4. Distributive

Explanation

Tension pneumothorax raises intrathoracic pressure and impedes venous return, so output falls despite adequate circulating volume. This is obstructive shock and requires immediate decompression. Tracheal shift with unilateral absent breath sounds points to the mechanical cause.

Question 31Cardiovascular physiology, shock, and hemodynamic support

Worldwide, which category accounts for the largest share of pediatric shock, especially in low-resource settings?

  1. Cardiogenic
  2. Distributive
  3. Hypovolemic Correct answer.
  4. Obstructive

Explanation

Severe dehydrating gastroenteritis and hemorrhage remain leading causes of pediatric shock globally, and both are hypovolemic. Loss of circulating volume lowers preload and stroke volume. Distributive and cardiogenic causes are less frequent in that context.

Question 32Cardiovascular physiology, shock, and hemodynamic support

A 10-year-old has a blood pressure of 100/60 mmHg. What is the approximate mean arterial pressure?

  1. 70 mmHg
  2. 80 mmHg
  3. 73 mmHg Correct answer.
  4. 60 mmHg

Explanation

Mean arterial pressure is approximated as diastolic pressure plus one third of the pulse pressure, or (systolic + 2 x diastolic)/3. The pulse pressure here is 40 mmHg, so MAP is about 60 + 13, or 73 mmHg. MAP rather than systolic pressure alone reflects the driving pressure for organ perfusion.

Question 33Cardiovascular physiology, shock, and hemodynamic support

A child in cardiogenic shock has cool extremities and a blood pressure of 88/70 mmHg. How should the narrow pulse pressure be interpreted?

  1. It suggests reduced systemic vascular resistance
  2. It is a normal finding in children
  3. It reflects low stroke volume with high resistance Correct answer.
  4. It suggests an unusually large stroke volume for age

Explanation

Pulse pressure varies directly with stroke volume and inversely with vascular resistance. A narrow pulse pressure indicates a small stroke volume ejecting into a high-resistance circulation, the pattern seen in cold shock. A wide pulse pressure suggests vasodilation or a large stroke volume.

Question 34Cardiovascular physiology, shock, and hemodynamic support

Why is an infant's cardiac output more dependent on heart rate than an older child's?

  1. Lower resting vagal tone prevents infants from changing stroke volume at all
  2. Higher beta-receptor density allows infants to raise contractility more sharply
  3. A stiffer pericardium gives infants more preload reserve than older children
  4. Reduced contractile reserve limits stroke volume increases in infants Correct answer.

Explanation

The neonatal myocardium has fewer mature contractile elements and depends heavily on extracellular calcium for excitation-contraction coupling, so its ability to augment stroke volume is limited. Output therefore rises mainly through heart rate. This also explains why bradycardia is poorly tolerated in infants.

Question 35Cardiovascular physiology, shock, and hemodynamic support

A 15 kg child in septic shock shows no signs of fluid overload. What initial crystalloid bolus is recommended?

  1. 5 mL/kg over 30 minutes
  2. 40 to 60 mL/kg as a single bolus
  3. 60 mL/kg over 1 hour
  4. 10 to 20 mL/kg over 5-20 min Correct answer.

Explanation

Guidelines recommend 10-20 mL/kg aliquots of isotonic crystalloid given rapidly with reassessment after each bolus. Reassessing between boluses limits fluid overload, which is common in septic children with myocardial dysfunction. Total volumes may reach 40-60 mL/kg, but only with repeated clinical evaluation.

Question 36Cardiovascular physiology, shock, and hemodynamic support

A child in septic shock has received 40 mL/kg of crystalloid with no improvement in perfusion. What is the most appropriate next step?

  1. Continue boluses until 100 mL/kg is reached
  2. Administer furosemide to prevent pulmonary edema
  3. Start a vasoactive infusion Correct answer.
  4. Give a bolus of 5% albumin

Explanation

Shock that persists after adequate volume resuscitation is fluid-refractory, and vasoactive support should begin while additional fluid is given only if responsiveness persists. Delaying epinephrine or norepinephrine worsens outcomes. The choice of agent depends on whether the child has warm or cold shock.

Question 37Cardiovascular physiology, shock, and hemodynamic support

After cardiac surgery, a child has cool mottled limbs, a narrow pulse pressure, and low cardiac output. Which infusion is most appropriate?

  1. Epinephrine infusion Correct answer.
  2. A 40 mL/kg crystalloid bolus
  3. Sodium nitroprusside as a single agent
  4. Norepinephrine at vasoconstricting doses

Explanation

Cold shock with low output and high vascular resistance responds to an agent that increases contractility and heart rate while supporting perfusion pressure, and epinephrine fits that profile. It raises cardiac output and provides some vasoconstriction. Pure vasoconstrictors may worsen the already elevated afterload.

Question 38Cardiovascular physiology, shock, and hemodynamic support

Milrinone improves cardiac output through which mechanism?

  1. Phosphodiesterase-3 inhibition increasing cyclic AMP Correct answer.
  2. Beta-1 receptor blockade that lowers myocardial oxygen demand
  3. Alpha-1 receptor stimulation that raises vascular resistance
  4. Inhibition of the sodium-potassium ATPase pump

Explanation

Milrinone inhibits phosphodiesterase-3, so cyclic AMP accumulates in cardiac and vascular smooth muscle. The result is increased contractility along with arterial and venous dilation, which reduces afterload and preload. Because it is renally cleared and can cause hypotension, loading doses are often omitted in unstable children.

Question 39Cardiovascular physiology, shock, and hemodynamic support

Which statement correctly describes the dose-dependent effects of dopamine?

  1. Higher doses act through beta-1 then alpha-1 receptors Correct answer.
  2. It is a pure vasodilator with no inotropic action
  3. It lowers systemic vascular resistance at all doses
  4. It increases renal blood flow at low doses with proven clinical benefit

Explanation

Dopamine stimulates beta-1 receptors at moderate doses, increasing contractility and heart rate, and alpha-1 receptors at higher doses, raising vascular resistance. The proposed low-dose renal benefit has not been confirmed in trials. Tachyarrhythmia is a common adverse effect.

Question 40Cardiovascular physiology, shock, and hemodynamic support

A child in septic shock remains hypotensive despite epinephrine and adequate fluid resuscitation. Which additional therapy is most reasonable?

  1. Increasing the epinephrine dose indefinitely without reassessment
  2. Hydrocortisone for suspected adrenal insufficiency Correct answer.
  3. A loop diuretic to mobilize fluid
  4. A beta-blocker to reduce tachycardia

Explanation

Catecholamine-resistant shock should prompt consideration of adrenal insufficiency, and stress-dose hydrocortisone is recommended in that setting, especially with purpura fulminans or prior steroid exposure. Cortisol increases vascular responsiveness to catecholamines. It is an adjunct to, not a replacement for, source control and vasoactive titration.

Question 41Cardiovascular physiology, shock, and hemodynamic support

A cyanotic newborn is suspected of having a ductal-dependent congenital heart lesion. What is the most appropriate immediate therapy?

  1. Prostaglandin E1 infusion to maintain ductal patency Correct answer.
  2. Supplemental oxygen to 100% with hyperventilation
  3. Furosemide to reduce pulmonary blood flow
  4. Sodium bicarbonate to reverse acidosis before any other therapy

Explanation

Prostaglandin E1 keeps the ductus arteriosus open, preserving pulmonary or systemic blood flow in lesions such as pulmonary atresia or critical coarctation. It should be started as soon as the lesion is suspected. Apnea is a predictable adverse effect, so the airway must be prepared for intubation.

Question 42Cardiovascular physiology, shock, and hemodynamic support

A child with septic shock has a central venous oxygen saturation of 55% while receiving adequate supplemental oxygen. What does this suggest?

  1. Arterial oxygen saturation must be below 80%
  2. Cardiac output is supranormal
  3. Oxygen consumption is abnormally low
  4. Oxygen delivery is inadequate for demand Correct answer.

Explanation

Central venous oxygen saturation reflects the balance between oxygen delivery and consumption. A low value means tissues are extracting a larger fraction of delivered oxygen, usually because output is insufficient. Values below roughly 70% in children suggest inadequate delivery or increased demand.

Question 43Cardiovascular physiology, shock, and hemodynamic support

Oxygen delivery is calculated as cardiac output multiplied by which factor?

  1. Systemic vascular resistance divided by 80
  2. Arterial-venous oxygen difference
  3. Arterial oxygen content times 10 Correct answer.
  4. Hemoglobin concentration alone

Explanation

Oxygen delivery equals cardiac output multiplied by arterial oxygen content, with a factor of 10 to reconcile units. Arterial oxygen content itself depends on hemoglobin, saturation, and dissolved oxygen. Raising output or content increases delivery.

Question 44Cardiovascular physiology, shock, and hemodynamic support

A toddler with tetralogy of Fallot becomes deeply cyanotic and agitated while crying. Which immediate maneuver is most appropriate?

  1. Place the child in knee-chest position Correct answer.
  2. Administer a pure vasodilator
  3. Begin aggressive oxygen therapy while keeping the child supine
  4. Start high-dose furosemide

Explanation

Crying increases right ventricular outflow obstruction and lowers systemic vascular resistance, worsening the right-to-left shunt. Knee-chest position raises systemic resistance and improves pulmonary blood flow. Calming the child, oxygen, and volume are adjuncts, whereas vasodilators aggravate the spell.

Question 45Cardiovascular physiology, shock, and hemodynamic support

Which statement best describes the value of central venous pressure for guiding fluid therapy in children?

  1. CVP rises predictably with stroke volume in all children
  2. A single CVP value accurately predicts fluid responsiveness
  3. A single CVP value poorly predicts fluid responsiveness Correct answer.
  4. CVP is unaffected by ventilator settings

Explanation

CVP reflects right atrial pressure, which is influenced by venous return, ventricular compliance, intrathoracic pressure, and the pericardium. Because of these influences, a single value cannot reliably identify who will increase output with fluid. Trends combined with bedside perfusion assessment are more useful.

Question 46Cardiovascular physiology, shock, and hemodynamic support

A neonate with hypoplastic left heart syndrome is being managed before surgery. What is the central goal of therapy?

  1. Maximize pulmonary blood flow to achieve saturation above 90%
  2. Balance pulmonary and systemic blood flow Correct answer.
  3. Keep both pulmonary and systemic blood flow at maximal rates
  4. Minimize systemic blood flow to protect the pulmonary vasculature

Explanation

In a parallel circulation, excessive pulmonary flow raises saturation but steals systemic flow and produces metabolic acidosis, while excessive systemic flow causes hypoxemia. Therapy aims for a balanced pulmonary-to-systemic flow ratio, usually with saturations in the mid-70s to low 80s. Mild hypercarbia and oxygen restriction can raise pulmonary vascular resistance when pulmonary flow is excessive.

Question 47Cardiovascular physiology, shock, and hemodynamic support

A child develops a pulmonary hypertensive crisis after cardiac surgery, with a sudden rise in pulmonary artery pressure and severe hypoxemia. Which combination is most appropriate?

  1. Acidosis and a systemic vasoconstrictor to raise systemic pressure
  2. A pure systemic vasodilator to reduce afterload
  3. Oxygen, alkalosis, and inhaled nitric oxide Correct answer.
  4. Rapid fluid loading to increase right ventricular preload

Explanation

Pulmonary hypertensive crisis is managed by reversing triggers and lowering pulmonary vascular resistance with oxygen, alkalosis, and agents such as inhaled nitric oxide. Sedation and avoidance of acidosis, pain, and hypothermia are essential. Inhaled nitric oxide is selective and less likely to drop systemic pressure.

Question 48Cardiovascular physiology, shock, and hemodynamic support

Which child is most likely to require venoarterial rather than venovenous extracorporeal support?

  1. A child with pneumonia who remains hypoxemic on maximal ventilation
  2. A child with refractory cardiogenic shock after myocarditis Correct answer.
  3. A child with an air leak and normal hemodynamics
  4. A child with isolated respiratory failure and stable cardiac function

Explanation

Venoarterial extracorporeal support provides both gas exchange and circulatory support, so it is chosen when cardiac output is inadequate. Venovenous support addresses oxygenation and carbon dioxide removal only and depends on native cardiac function. The decision rests on hemodynamic status rather than on the severity of hypoxemia alone.

Question 49Cardiovascular physiology, shock, and hemodynamic support

Oxygen consumption is steady at 6 mL/kg/min and oxygen delivery falls to 8 mL/kg/min. What is the oxygen extraction ratio and its implication?

  1. About 75%, indicating delivery dependence Correct answer.
  2. About 25%, indicating adequate reserve
  3. About 50%, indicating compensated shock
  4. About 130%, indicating high delivery

Explanation

Extraction ratio equals oxygen consumption divided by oxygen delivery, so 6 divided by 8 gives 0.75, or 75%. Once extraction approaches its critical threshold, further falls in delivery reduce consumption and anaerobic metabolism begins. This state indicates that delivery has become the limiting factor.

Question 50Cardiovascular physiology, shock, and hemodynamic support

A child with severe left ventricular dysfunction is intubated and placed on positive-pressure ventilation. Which hemodynamic change is expected?

  1. Increased right ventricular preload and decreased pulmonary vascular resistance
  2. No change in ventricular loading conditions
  3. Reduced left ventricular afterload and improved ejection Correct answer.
  4. Increased left ventricular afterload from higher intrathoracic pressure

Explanation

Positive intrathoracic pressure lowers left ventricular transmural pressure, reducing afterload and potentially improving ejection in a failing ventricle. At the same time it reduces systemic venous return and right ventricular filling. The net hemodynamic effect depends on preload dependence and ventricular function.