1. Acute Respiratory Failure (Umbrella Syndrome)

Quick Recap

Entry point for undifferentiated respiratory distress. Once etiology is clear, continue into the nested disease protocol (ARDS, pneumonia, COPD, etc.).

1. Definition

• Type 1 (hypoxemic): PaO2 <60 mmHg / P:F <300
• Type 2 (hypercapnic): PaCO2 >45 mmHg, pH <7.35 (acute)
• Type 3: perioperative/atelectasis
• Type 4: shock-associated pump failure

2. Pathophysiology

• Hypercapnia = decreased minute ventilation, increased dead space, or increased CO2 production (rare). Acute delta-10 mmHg PaCO2 -> delta-0.08 pH; chronic (compensated) -> delta-0.03 pH.
• Hypoxemia: A-a gradient (normal 5-25 mmHg) separates hypoventilation (normal gradient) from V/Q mismatch/shunt/diffusion defect (widened gradient). Shunt responds poorly to supplemental O2; V/Q mismatch responds well.
• Hypoxia (tissue) is not the same as hypoxemia: hypoxemic, anemic, circulatory, cytopathic - often coexist.

3. Immediate Stabilization (ABCDE)

Airway: Patency, protective reflexes. Intubate if: GCS <=8, obstruction, apnea, refractory failure despite NIV, instability. Anticipate difficult airway (LEMON), have backup plan.

Breathing: Titrate O2 (SpO2 94-98%; 88-92% if hypercapnic risk). NIV for COPD/cardiogenic edema; HFNC for de novo hypoxemia. Define an intubation trigger in advance (e.g., ROX <4.88 at 2h). Default to lung-protective vent settings (Vt 6-8 mL/kg PBW, Pplat <30, driving pressure <15) even pre-diagnosis.

Circulation: Assess shock/perfusion, POCUS fluid responsiveness, vasopressor readiness before intubation drugs.

Disability: GCS, pupils, glucose, CO2 narcosis signs, RASS/CAM-ICU once stable.

Exposure: Cyanosis, accessory muscle use, paradoxical breathing, temperature, rash/trauma.

Checklist:

4. Focused History

Onset tempo; chest pain/fever/cough/hemoptysis; COPD/asthma/CHF/ILD/neuromuscular history; opioids/sedatives/new drugs; allergies; recent hospitalization/antibiotics; immunosuppression; baseline function/frailty; smoking/occupational/travel; home O2/NIV/trach; pregnancy; advance directives.

5. Examination + POCUS

Respiratory (rate, pattern, auscultation), CVS (JVP, S3, edema), neuro (mental status, asterixis), abdomen (distension limiting diaphragm), skin (cyanosis, urticaria).

POCUS (BLUE protocol): A-lines = normal aeration; diffuse B-lines = interstitial/edema/ARDS; focal consolidation = pneumonia; absent sliding + lung point = pneumothorax; effusion; RV strain/McConnell's sign = PE; IVC for volume status.

6. Syndrome Identification

Upper airway obstruction / bronchospasm / alveolar filling / interstitial / pleural / pulmonary vascular / neuromuscular pump failure / cardiogenic edema / shock-associated.

7. Differential Diagnosis

8. Severity Scores

NEWS2/qSOFA (bedside) -> SOFA/APACHE II (ICU) -> Berlin (if ARDS) -> CURB-65/PSI (if pneumonia) -> ROX/HACOR (NIV/HFNC failure prediction).

9. Investigations

• Bedside (mandatory): ABG, SpO2/EtCO2, ECG, portable CXR, POCUS, glucose
• Labs (mandatory): CBC, renal, electrolytes, LFTs, lactate, coagulation, troponin if cardiac suspected
• Biomarkers: BNP (CHF), procalcitonin, D-dimer (if low-moderate PE probability)
• Micro: blood/sputum cultures, viral panel, urinary antigens as indicated
• Imaging: CXR mandatory; CT chest/CTPA if diagnosis unclear
• Repeat: ABG 30-60 min post any vent change; labs daily; CXR only if clinically indicated

10. POCUS Findings -> Action

Bilateral B-lines -> treat as cardiogenic edema or ARDS (correlate echo). Focal consolidation -> pneumonia. Absent sliding+lung point -> decompress pneumothorax. Plethoric IVC -> diuresis-favoring; flat IVC -> fluid-responsive. RV strain -> treat as PE pending CTPA.

11. Management by Time

• 0-5 min: High-flow O2; treat immediate life threats (needle decompression, IM epinephrine, naloxone, airway maneuvers)
• First hour: Complete ABCDE + POCUS + ABG + CXR; NIV/HFNC/intubation decision; empiric therapy pending confirmation (e.g., antibiotics within 1h if septic)
• First 6h: Confirm diagnosis -> move to disease-specific protocol; optimize vent; reassess fluids; consults
• First 24h: Trend ABG/CXR; wean FiO2; start ICU bundle; nutrition; family update; goals of care
• Ongoing: Daily reassessment vs endpoints; SBTs; antibiotic de-escalation; mobilization

(Drug doses live in disease-specific nested protocols to avoid duplication/conflicting numbers.)

12. Organ Support

Ventilation (lung-protective default) - NIV/HFNC - vasopressors/inotropes if shock - CRRT if AKI/overload - blood products for DO2 - early enteral nutrition - glucose 140-180 - fever control - VV-ECMO for refractory hypoxemia (see ARDS protocol).

13. Disease-Specific Therapy

See nested protocols: ARDS, Pneumonia, COPD, Asthma, PE, Hemoptysis, Pneumothorax, Pleural Disease, DAH, ILD exacerbation, Airway Emergencies, Inhalational Injury.

14. Consultations

15. Monitoring

Clinical: RR/WOB hourly. Hemodynamic: continuous SpO2/ECG +/- art line. Labs: serial ABG, daily panels. Imaging: post-procedure or deterioration only. Device: vent alarms, cuff pressure, circuit checks/shift.

Escalate if: rising RR/WOB, falling SpO2 despite support, rising CO2 with falling pH, instability.

De-escalate if: stable gas exchange on less support, cause resolving.

16. Daily ICU Bundle

17. Complications

Early: post-intubation collapse, pneumothorax, aspiration, arrhythmia. Late: VAP, ICU-acquired weakness, delirium, tracheal stenosis, VILI. Prevention: lung-protective vent, VAP bundle, minimal sedation, early mobility. Rescue: recruitment maneuvers, proning, NMB, ECMO.

18. Escalation/De-escalation

Escalate: NIV/HFNC failure, refractory hypoxemia, instability -> intubate/prone/ECMO referral. Wean when: cause resolving, P:F >200 on low PEEP/FiO2, stable, passes SBT. Step down when: stable on low-flow O2, no pressors, resolving delirium.

19. ICU Discharge Criteria

RR <24, SpO2 >92% on <=4L (or baseline), stable ABG, off pressors, no escalating O2 need x24h, protecting airway, precipitant treated.

20. Documentation Checklist

21. Key Guidelines

Surviving Sepsis Campaign - ATS/ERS NIV/HFNC guidelines - ESICM/SCCM ventilation consensus - ARDS guidelines (ATS/ERS/ESICM/SCCM) - recommendation grades detailed in nested protocols.

22. Landmark Trials

Ashbaugh et al. 1967 (first ARDS description - foundational). Disease-specific trials (ARMA, PROSEVA, FLORALI, etc.) live in nested protocols.

23. Controversies

SpO2 targets (conservative vs liberal) in non-hypercapnic patients; HFNC vs NIV as first-line for de novo hypoxemia; intubation timing in "silent hypoxemia"; awake proning outside COVID context.

24. References

1. Grotberg JC, Kraft BD. An Approach to Respiratory Failure. Washington Manual of Critical Care, 4th ed, 2025.
2. Respiratory Acid-Base Disorders chapter, Washington Manual of Critical Care, 4th ed, 2025.
3. Chawla R, Todi S, eds. ICU Protocols: A Step-wise Approach, 2nd ed. Springer; 2020.
4. Lichtenstein DA. BLUE/FALLS-protocol. Chest. 2015;147(6):1659-1670.
5. Volpicelli G et al. International evidence-based recommendations for POCUS lung. Intensive Care Med. 2012;38:577-591.
6. Ashbaugh DG et al. Acute respiratory distress in adults. Lancet. 1967;2(7511):319-323.