Critical Care Medicine: Principles of Critical Care — Respiratory and Hemodynamic Support
Pulmonary and Critical Care Medicine · Critical Care Medicine · study mode — pick an answer, then reveal.
Question · easy
A 68-year-old man admitted for community-acquired pneumonia is receiving nasal cannula oxygen. His SpO2 has been 97-98% on 2 L/min for several hours, and he is hemodynamically stable. Which of the following is the most appropriate oxygen strategy?
Oxygen is a drug and should be titrated to a target. Higher saturation is not always desirable: supplementing oxygen to patients whose saturation is already 96% or higher may increase mortality, and there is no clinical benefit to a supraphysiologic PaO2 (>100 mm Hg). Patients on oxygen therapy should generally be kept at an SpO2 of 96% or lower, and oxygen should not even be started in acute MI or stroke when SpO2 is 93% or higher. Large trials (UK-ROX) and meta-analyses show conservative and liberal strategies produce similar mortality, so the surviving clear rule is to avoid sustained hyperoxia; a middle-range SpO2 of 92-96% is reasonable. Increasing flow to chase 99-100% or a PaO2 >100 mm Hg exposes the patient to potential harm without benefit, and continuing oxygen without titration ignores that oxygen requires a target.
MKSAP 19 B.5 Ch.10; UK-ROX trial (Martin DS et al, JAMA 2025); Nguyen N et al, Crit Care Med 2026
Question · easy
A 55-year-old woman with fever, hypotension, and altered mentation is diagnosed with septic shock. After initial fluid resuscitation her MAP remains 54 mm Hg, and a vasopressor is needed. What is the first-line agent and the usual MAP target?
Norepinephrine (alpha-1, alpha-2, beta-1 agonist) is the first-line vasopressor in distributive (septic), cardiogenic, and hypovolemic shock and has been shown to reduce mortality; the Surviving Sepsis Campaign 2026 guidelines reaffirm an initial MAP target of 65 mm Hg. A MAP of 65 is the perfusion threshold for most patients, and targeting higher pressures (80-85 mm Hg) in septic shock has not improved mortality. Dopamine is not first-line — it increases mortality versus norepinephrine in distributive shock and is reserved for severe bradycardia in septic shock. Phenylephrine is reserved for when norepinephrine is contraindicated (e.g., tachyarrhythmias) or first-line drugs fail, and it may depress cardiac output via reflex bradycardia. Vasopressin is an add-on to norepinephrine (added as doses escalate, for catecholamine sparing), not a first-line single agent.
MKSAP 19 B.5 Ch.10; Harrison's 22e Ch.314; Surviving Sepsis Campaign 2026 guidelines (Prescott HC et al, Crit Care Med 2026)
Question · medium
A 72-year-old man with a COPD exacerbation develops worsening dyspnea and a venous blood gas shows pH 7.31, PaCO2 62 mm Hg. Noninvasive positive pressure ventilation (NPPV) is being considered. Which of the following findings would be a contraindication to starting NPPV?
Contraindications to NPPV include persistent altered mental status, inability to protect the airway, copious airway secretions, emesis, gastric distention, airway obstruction, recent esophageal surgery, cardiac arrest, facial trauma or surgery, significant hemodynamic instability, and mask intolerance — an obtunded patient who cannot protect the airway needs invasive ventilation instead. Moderate respiratory acidosis (pH 7.25-7.35) in COPD is precisely the setting where NPPV benefit is greatest (reduced intubation rates and shorter hospital stay), so pH 7.31 is an indication, not a contraindication. BPAP is the appropriate NPPV mode for COPD exacerbation (it decreases work of breathing and augments tidal volume), and obesity hypoventilation syndrome is itself an indication for NPPV. Note that severe acidosis (pH <7.2) generally requires intubation, and every NPPV patient must be reevaluated within 2 hours.
MKSAP 19 B.5 Ch.10; Harrison's 22e Ch.313
Question · medium
A 45-year-old woman with severe ARDS is intubated and placed on volume-control ventilation. Which of the following ventilator strategies best reflects lung-protective ventilation?
When safety is the priority, lung-protective ventilation means delivering the lowest effective tidal volume (about 6 mL/kg of ideal — not actual — body weight) and keeping the end-inspiratory plateau pressure at or below 30 cm H2O, with PEEP set high enough to prevent cyclical end-expiratory alveolar collapse (atelectrauma). This prevents ventilator-induced lung injury from alveolar overdistension (volutrauma) and repetitive collapse, which can occur at any point in the ventilation course. Large tidal volumes based on actual body weight cause overdistension injury, and allowing plateau pressures of 40 cm H2O violates the <=30 cm H2O threshold. Minimizing PEEP invites atelectrauma; PEEP is used specifically to keep recruited alveoli open through exhalation. A subtle related hazard: in spontaneously breathing patients on pressure-control modes, the patient's own effort adds transalveolar pressure the ventilator does not display, so delivered tidal volumes must be watched closely.
MKSAP 19 B.5 Ch.10; Harrison's 22e Ch.313
Question · hard
A 70-year-old man with COPD and heart failure has been mechanically ventilated for 8 days. He passes a 45-minute spontaneous breathing trial on low pressure support without distress, SpO2 below 90% never occurs, respiratory rate stays under 35/min, and hemodynamics are stable. He is extubated. Which of the following is the most appropriate immediate post-extubation respiratory strategy?
This patient is high risk for extubation failure: older than 65, with COPD and heart failure, and ventilated more than 7 days. In high-risk patients, prophylactic NPPV applied immediately after extubation prevents post-extubation respiratory failure and reduces reintubation; in high-risk patients, high-flow oxygen alone is less effective than high flow combined with NIV. The governing principle is 'prevent, don't rescue': rescue NIV started after respiratory failure is already established is discouraged because it risks delaying reintubation without improving outcomes — so waiting for failure to appear is wrong. He is not low risk, making high flow alone insufficient, and observation alone forfeits the proven prophylactic benefit. SIMV is not a weaning mode and reintubation without a failed trial is inappropriate; liberation is driven by daily readiness assessment and SBTs, not gradual SIMV tapers.
MKSAP 19 B.5 Ch.10; Harrison's 22e Ch.313; Hernandez G et al, Intensive Care Med 2022