Critical Care Medicine: Common ICU Conditions — Acute Respiratory Failure
Pulmonary and Critical Care Medicine · Critical Care Medicine · study mode — pick an answer, then reveal.
Question · easy
A 68-year-old woman with community-acquired pneumonia develops worsening hypoxemia over 3 days. The team is applying the 2012 Berlin definition to determine whether she has ARDS. Which of the following accurately states what the Berlin definition requires?
The Berlin definition requires ALL of the following: onset within 1 week of a known ARDS insult (most cases occur within 72 hours), bilateral opacities consistent with pulmonary edema, respiratory failure not fully explained by cardiac failure or volume overload, and PaO2/FiO2 <=300 mm Hg on at least 5 cm H2O of PEEP delivered by a noninvasive or invasive ventilator. Severity is then graded by PaO2/FiO2: mild >200-300, moderate 100-200, severe <100. Option B is wrong because the window is 1 week (not a rigid 72-hour admission window), infiltrates must be bilateral, and PEEP >=5 is required. Option C uses the wrong threshold and left atrial hypertension points toward cardiogenic edema, which ARDS criteria specifically require excluding. Option D is wrong because Berlin accepts noninvasively delivered PEEP and the timing window is 1 week, not 2 weeks.
MKSAP 19 B.5 Ch.10; Harrison's 22e Ch.312
Question · easy
A postoperative patient develops severe hypoxemia that does not correct despite high-flow supplemental oxygen, and the calculated A-a gradient is widened. What is the most common mechanism of hypoxemic respiratory failure in the ICU, as illustrated by this presentation?
Shunt is the most common cause of hypoxemic respiratory failure in the ICU. It is an extreme V/Q mismatch in which perfused lung units receive no ventilation (V/Q = 0), caused principally by alveolar collapse (atelectasis) or alveolar filling with blood, cells, protein, or water. Its signature is a widened A-a gradient that does NOT correct with supplemental oxygen, which is why management centers on oxygen PLUS PEEP to reopen collapsed or flooded alveoli. Hypoventilation and low inspired oxygen produce hypoxemia with a normal A-a gradient and respond readily to oxygen; diffusion limitation also typically corrects with supplemental oxygen, so none of these distractors fits a shunt-like picture.
MKSAP 19 B.5 Ch.10
Question · medium
A 34-year-old man with Guillain-Barre syndrome (ascending symmetric paralysis and areflexia evolving over 3 weeks) is monitored in the ICU. Serial pulmonary function testing is performed. Which finding most strongly signals impending neuromuscular respiratory failure and the need for intubation?
Danger signals of impending neuromuscular respiratory failure are a supine FVC drop of more than 20% compared with upright, an MIP weaker (less negative) than -60 cm H2O, or an MEP weaker (less positive) than +60 cm H2O. A 25% supine FVC decrement crosses the >20% threshold and indicates diaphragmatic weakness severe enough to warrant intubation planning; about 25% of Guillain-Barre patients ultimately require intubation. The distractors are reassuring, not dangerous: an MIP of -75 cm H2O and an MEP of +70 cm H2O are STRONGER than the danger thresholds (-60 and +60 respectively), and oxygen saturation often remains normal until very late in neuromuscular failure - which is exactly why respiratory muscle strength, not pulse oximetry, must be monitored.
MKSAP 19 B.5 Ch.10; Harrison's 22e Ch.307
Question · medium
Two patients present with acute respiratory failure from obstructive airway disease: one with a hypercapnic COPD exacerbation and one with severe asthma. Which statement correctly contrasts the recommended ventilatory support for these conditions?
This is a classic contrast: for hypercapnic respiratory failure from a COPD exacerbation, NPPV (most often bilevel positive airway pressure) is the preferred initial means of lowering PaCO2 - it reduces both mortality (odds ratio ~0.5) and the need for intubation, provided the patient can protect the airway and is hemodynamically stable. The opposite default applies in asthma: little evidence supports NPPV, and for most asthmatics with respiratory failure intubation and mechanical ventilation are recommended, with expiratory time maximized to limit auto-PEEP. Recall also that a normal or elevated PaCO2 in a tiring asthmatic (who should be hypocapnic from tachypnea) is an ominous sign of imminent collapse. Options B and C invert or overgeneralize these rules, and option D is plainly false since hemodynamic instability is actually a reason to AVOID NPPV and proceed to intubation.
MKSAP 19 B.5 Ch.10; NIV meta-analysis, BMC Pulm Med 2025
Question · hard
The 2024 global definition of ARDS, developed by an international expert panel, broadens ARDS entry criteria beyond the 2012 Berlin definition. Which of the following is part of that expansion?
The 2024 global ARDS definition keeps the Berlin severity structure but broadens entry in four ways: (1) SpO2/FiO2 <=315 (when SpO2 <=97%) is accepted in place of PaO2/FiO2; (2) patients on high-flow nasal oxygen >=30 L/min or NIV/CPAP with >=5 cm H2O of PEEP now qualify, formally recognizing non-intubated ARDS; (3) bilateral opacities may be identified by chest ultrasound as well as radiography or CT; and (4) a resource-variable modification removes PEEP and flow minimums for austere settings. Parallel SpO2/FiO2 cutoffs (<=315 / <=235 / <=148) mirror the mild/moderate/severe categories, with caveats that ultrasound interpretation varies between operators and pulse oximeters may overestimate saturation in darker skin tones. Option B is wrong because the PaO2/FiO2 threshold remains <=300 (PEEP minimums are waived only in austere settings). Options C and D are wrong because the new definition EXPANDS - rather than restricts - imaging modalities and non-intubated eligibility, and no bronchoalveolar lavage requirement exists.