Critical Care Medicine: Common ICU Conditions — Acute Respiratory Failure
Pulmonary and Critical Care Medicine · Critical Care Medicine 🎯 Practice these cards
The initial approach to acute respiratory failure asks three sequential questions: secure the ____, assess ____, and assess ____.
MKSAP organizes the initial approach to acute respiratory failure into three sequential questions: secure the airway (Is it patent? Can the patient protect it?), assess oxygenation (Is saturation falling? Is the A-a gradient widened?), and assess ventilation (Is respiratory drive and minute ventilation adequate? Does the ABG show hypercapnia?). Therapy is then matched to the dominant mechanism.
The most common cause of hypoxemic respiratory failure in the ICU is ____, an extreme V/Q mismatch that responds poorly to oxygen alone and is treated with supplemental oxygen plus ____ to reopen collapsed or flooded alveoli.
The most common cause of hypoxemic respiratory failure in the ICU is shunt — perfused alveoli that receive no ventilation (V/Q = 0), due to alveolar collapse (atelectasis) or alveolar filling with blood, cells, protein, or water. Shunt produces a widened A-a gradient that does not correct with supplemental oxygen alone; management is supplemental oxygen plus PEEP to reopen collapsed or flooded alveoli.
The Berlin definition of ARDS requires onset within ____ of a known insult, bilateral opacities not fully explained by cardiac failure or volume overload, and PaO2/FiO2 ≤____ mm Hg on at least ____ cm H2O of PEEP.
The 2012 Berlin definition requires all of: onset within 1 week of a known ARDS insult (most cases within 72 hours); bilateral opacities on chest imaging 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.
By Berlin criteria, ARDS severity is graded by PaO2/FiO2: mild is ____, moderate is ____, and severe is ____.
Once Berlin criteria are met, ARDS severity is graded by PaO2/FiO2: mild >200 to ≤300, moderate 100 to 200, severe <100. In the LUNG SAFE study, hospital mortality rose with severity: roughly 35% for mild, 40% for moderate, and 46% for severe ARDS.
The 2024 global ARDS definition accepts SpO2/FiO2 ≤____ (when SpO2 ≤97%) in place of PaO2/FiO2 and formally recognizes non-intubated ARDS on high-flow nasal oxygen ≥____ L/min or NIV/CPAP with PEEP ≥5 cm H2O.
The 2024 global ARDS definition, developed with input from 21 critical care societies, keeps the Berlin severity structure but broadens entry: SpO2/FiO2 ≤315 (when SpO2 ≤97%) is accepted in place of PaO2/FiO2; patients on high-flow nasal oxygen ≥30 L/min or NIV/CPAP with PEEP ≥5 cm H2O now qualify (non-intubated ARDS); bilateral opacities may be identified by chest ultrasound; and a resource-variable modification removes PEEP and flow minimums. Parallel SpO2/FiO2 cutoffs (≤315/≤235/≤148) mirror mild/moderate/severe categories.
The ARDS Network trial showed that low tidal volume ventilation — ____ mL/kg predicted body weight with plateau pressure ≤____ cm H2O — reduced mortality from about 40% to ____% versus conventional ventilation.
The landmark ARDS Network trial of low tidal volume ventilation — 6 mL/kg predicted body weight with plateau pressure ≤30 cm H2O — versus conventional ventilation (12 mL/kg) reduced absolute mortality by roughly 9 to 11 points (31% vs 40%). Guidelines recommend tidal volumes of 4 to 8 mL/kg predicted body weight with plateau pressure below 30 cm H2O.
In ARDS with PaO2/FiO2 <____, prone positioning started within the first ____ hours and continued for at least ____ hours per day delivers a mortality benefit alongside low tidal volume ventilation.
A large randomized trial showed a mortality benefit when patients with ARDS and PaO2/FiO2 <150 were proned early (<48 hours) alongside low tidal volume ventilation, for at least 12 to 16 hours per day. The 2023 ESICM ARDS guideline recommends prone positioning for at least 16 hours per day in moderate to severe ARDS. Proning requires an experienced team because of risks such as accidental extubation and lost lines.
The ROSE trial found no significant difference in ____-day mortality between early cisatracurium infusion and lighter sedation in moderate-to-severe ARDS, so early neuromuscular blockade is no longer ____ and is reserved for problems such as persistent patient-ventilator ____.
Early neuromuscular blockade in ARDS is no longer routine. Initial trials suggested a survival benefit from 48 hours of early cisatracurium, but the ROSE trial (Reevaluation of Systemic Early Neuromuscular Blockade), conducted with a high-PEEP strategy in moderate to severe ARDS, found no significant difference in 90-day mortality between cisatracurium infusion and a lighter-sedation strategy, with a non-statistically significant increase in ICU-acquired weakness. Reserve paralysis for selected patients, such as persistent patient-ventilator dyssynchrony despite optimized sedation.
After smoke inhalation, about ____ of patients develop airway edema or mucosal sloughing; the most frequent infectious complication is ____, particularly from Staphylococcus and ____ species.
After smoke inhalation, about one third of patients develop airway edema or mucosal sloughing from epithelial necrosis, often requiring chest physiotherapy with serial bronchoscopy. Secondary infection is common and a major driver of death — pneumonia is the most frequent complication, particularly from Staphylococcus and Pseudomonas species. Carbon monoxide and hydrogen cyanide toxicity should be suspected in every exposed patient.
EVALI is linked to ____ used to thicken illicit vaping products; a key diagnostic clue is vaping product use within the prior ____ days, and the mainstay of treatment is ____ care.
EVALI is linked to vitamin E acetate, used to thicken illicit (especially THC-containing) vaping products. Suspicion should be high in vapers with hypoxemia plus respiratory symptoms (cough, dyspnea) or GI symptoms (abdominal pain, vomiting, diarrhea). A history of vaping product use within the prior 90 days remains the key diagnostic clue; supportive care is the mainstay of treatment, with empiric corticosteroids commonly used in severe disease without a standardized protocol.
Obesity hypoventilation syndrome is defined by obesity, sleep-disordered breathing, and persistent daytime PaCO2 >____ mm Hg; about ____% of patients have coexisting obstructive sleep apnea, and an elevated serum ____ (≥27 mmol/L) is a screening clue.
OHS is defined by the triad of obesity, sleep-disordered breathing, and persistent daytime hypercapnia (PaCO2 >45 mm Hg). Roughly 90% of OHS patients have coexisting obstructive sleep apnea, and an elevated serum bicarbonate (≥27 mmol/L) with normal renal function is a sensitive screening clue worth confirming with an ABG. Hospitalized patients should be started on NIV, with ABGs rechecked within 2 hours; substantial weight loss (20% to 25% of body weight) can normalize PaCO2 long-term.
For hypercapnic failure from COPD exacerbation, the preferred initial ventilatory support is ____, with the most effective mode ____; oxygen is titrated to an SpO2 of ____% to avoid worsening hypercapnia.
For hypercapnic failure from COPD exacerbation, NPPV is the preferred initial means of lowering PaCO2, with bilevel positive airway pressure the most used and most effective mode; intubation is needed if the airway cannot be protected, the patient is unstable, or NPPV fails. Oxygen is titrated to SpO2 88% to 92% because excess oxygen worsens hypercapnia via increased V/Q mismatch, decreased respiratory drive, and the Haldane effect. A 2025 meta-analysis reaffirms that NIV reduces mortality (odds ratio ~0.5) and intubation need in acute hypercapnic COPD exacerbations.
For most asthmatics with respiratory failure, ____ is recommended over NPPV; a normal or elevated ____ in a tiring asthmatic signals imminent collapse, and ventilator management centers on maximizing ____ time to reduce auto-PEEP.
Little evidence supports NPPV in asthma; for most asthmatics with respiratory failure, intubation and mechanical ventilation are recommended. Blood gases typically show respiratory alkalosis, so a normal or elevated PaCO2 in a tiring asthmatic is an ominous sign of imminent collapse. The ventilator strategy centers on maximizing expiratory time to reduce auto-PEEP, often requiring sedation or paralysis with permissive hypercapnia.
Danger signals of impending respiratory failure in neuromuscular disease include a supine FVC drop >____% versus upright, MIP weaker than ____ cm H2O, or MEP weaker than ____ cm H2O; about 25% of patients with Guillain-Barré syndrome require intubation.
Guillain-Barré syndrome and myasthenic crisis are the most common causes of acute neurologic respiratory failure in the ICU. Serial effort-dependent PFTs track impending failure: a supine FVC drop >20% versus upright, MIP weaker than -60 cm H2O, or MEP weaker than +60 cm H2O are danger signals. About 25% of Guillain-Barré patients develop respiratory failure requiring intubation; in myasthenic crisis, early NPPV can prevent intubation if the airway can be protected.
The diaphragm is innervated by the phrenic nerves from nerve roots ____ and performs more than ____ of the work of inspiration; acute spinal cord injury at or above ____ invariably requires mechanical ventilation.
The diaphragm does more than two thirds of the work of inspiration and is innervated by the phrenic nerves from the C3-C5 nerve roots. Diaphragmatic weakness in the ICU typically follows postsurgical phrenic nerve injury or ICU-acquired weakness, producing orthopnea, shallow breathing, and paradoxical chest-abdomen movement. Acute spinal cord injury at or above C5 invariably requires mechanical ventilation.
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