Bedside triage of acute desaturation: signal verification, immediate danger screening (DOPE / tension pneumothorax), oxygen escalation ladder, and mechanism-based differential.
Sudden arterial oxygen desaturation (SpO2 < 90% or acute drop > 4–5% from baseline) is an immediate critical care emergency. The priority is not contemplating a comprehensive differential diagnosis, but rapidly verifying the signal, screening for immediately fatal mechanical airway/ventilator crises, and escalating oxygenation while narrowing the physiological mechanism (shunt vs V/Q mismatch vs alveolar hypoventilation).
Caution
Dangerous Diagnosis Not to Miss: Tension Pneumothorax in a positive-pressure ventilated patient, or Acute Massive Pulmonary Embolism with obstructive shock. If breath sounds are absent unilaterally with hypotension, decompress the chest immediately without waiting for an X-ray.
Immediate Signal Check: Check the plethysmographic pulse oximeter waveform; motion artifact, severe peripheral vasoconstriction, hypothermia, and ambient light frequently cause false desaturations.
Clinical Assessment: Examine the patient directly: mental status, respiratory rate, sternocleidomastoid retractions, cyanosis, and sweating.
In Non-Intubated Patients: Look for upper airway obstruction (stridor, foreign body, tongue displacement, secretions), impending exhaustion, and severe hemodynamic collapse.
In Mechanically Ventilated Patients — The DOPE Framework:
Non-Intubated: Increase supplemental oxygen immediately (Non-Rebreather at 15 L/min + flush or High-Flow Nasal Cannula at 50–60 L/min and 100% FiO2).
Ventilated: Switch to 100% FiO2 immediately. If any question of equipment or ventilator failure arises, disconnect from the machine and ventilate manually with a self-inflating bag-valve-mask on 100% O2 to isolate the patient from the ventilator.
Caution
Common Diagnostic Trap: Reflexively giving fluid boluses for hypoxemia and borderline blood pressure when the underlying cause is acute right ventricular failure or cardiogenic pulmonary edema. Fluids worsen septal flattening and exacerbate pulmonary transudation.
Hypoxemic Respiratory Failure: Oxygen escalation ladder, ROX index trajectories, and P-SILI physiology.
ARDS: Lung-protective ventilation using low VT by PBW, plateau-pressure limitation, individualized PEEP, and prone positioning when indicated; track driving pressure as a physiologic risk marker rather than enforcing a universal <14 cmH2O cutoff.
Pneumothorax: Immediate needle decompression and chest tube thoracostomy.
Pulmonary Embolism & Obstructive Shock: Thrombolysis, anticoagulation, and RV resuscitation.
Cardiogenic Pulmonary Edema: SCAPE nitrates and noninvasive CPAP.
Evidence status
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From post-intubation verification and lung-protective settings to mechanics optimization.
From readiness screening and spontaneous breathing trials to extubation and post-extubation support.
From eligibility screening and team preparation to 16-hour proning cycles and response evaluation.
From initial noninvasive modality selection to ROX index tracking and timely intubation triggers.
Pathophysiologic mechanisms (shunt vs V/Q mismatch), dynamic ROX index trajectories, P-SILI prevention, and evidence-based oxygen escalation ladders.
Core taxonomy (Types I–IV), alveolar gas exchange physiology, work-of-breathing mechanics, and escalation thresholds in acute respiratory failure.
Acute, diffuse inflammatory lung injury causing hypoxemia and bilateral infiltrates not fully explained by cardiac failure or fluid overload.
Tension physiology, point-of-care ultrasound diagnosis, needle/finger/tube thoracostomy, and management of bronchopleural fistulas on mechanical ventilation.
Pulmonary vascular occlusion, acute RV pressure overload, ESC/AHA risk stratification, systemic thrombolysis, catheter-directed therapies, and hemodynamic support.
Hydrostatic pulmonary edema physiology, SCAPE vs decompensated HF vs cardiogenic shock, NIV, titrated vasodilators when hypertensive, diuresis, and sequential nephron blockade.
RV anatomy and ischemia spiral, ventricular interdependence (D-sign), echocardiographic metrics (TAPSE, S', PAPi, VExUS), and the 4-pillar resuscitation strategy.
IDSA/ATS severe CAP criteria, rapid microbiology, targeted empiric antimicrobial regimens, and landmark adjunctive hydrocortisone evidence (CAPE COD).
Complete clinical topic overview. For the full 10-level interactive course, visit Master MV. Covers core ventilator modes, respiratory mechanics (Cstat, Raw, driving pressure), waveform dyssynchrony analysis, VILI prevention, and liberation protocols.