Study guide
4.3 Severe Community-Acquired & Viral Pneumonia
ABIM Critical Care Medicine Study Guide Exam
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1 Chapter 1: Exam Orientation: Format, Blueprint & Study Strategy
1.1 ABIM Critical Care Medicine Exam: Format, Blueprint & Study Strategy
2 Chapter 2: Acute Respiratory Failure & ARDS
2.1 ARDS Definition, Pathophysiology & Phenotypes 2.2 Lung-Protective Mechanical Ventilation 2.3 Refractory ARDS: Prone Positioning, Neuromuscular Blockade & VV-ECMO
3 Chapter 3: Obstructive Airways, Pulmonary Vascular & Pleural Emergencies
3.1 Severe Asthma & COPD Exacerbations in the ICU 3.2 Massive & Submassive Pulmonary Embolism 3.3 Pulmonary Hypertension & Right Ventricular Failure in the ICU 3.4 Massive Hemoptysis, Complex Pleural Effusions & Thoracic Drainage
4 Chapter 4: Airway, Parenchymal & Nonthrombotic Pulmonary Emergencies
4.1 Airway Management, Upper-Airway Obstruction & Artificial-Airway Complications 4.2 Diffuse Alveolar Hemorrhage, Interstitial Lung Disease, Pulmonary Vasculitis & Noncardiogenic Edema 4.3 Severe Community-Acquired & Viral Pneumonia 4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome
5 Chapter 5: Mechanical Ventilation Modes, Dyssynchrony & Liberation
5.1 Mechanical Ventilator Modes & Advanced Breath Delivery 5.2 Patient-Ventilator Dyssynchrony & Waveform Analysis 5.3 Ventilator Liberation, Spontaneous Breathing Trials & Post-Extubation Support
6 Chapter 6: Shock Syndromes & Hemodynamic Principles
6.1 Shock Classification, Cellular Pathophysiology & Biomarkers 6.2 Hemodynamic Monitoring: Arterial Lines, CVP & Pulmonary Artery Catheter 6.3 Dynamic Assessment of Fluid Responsiveness & Resuscitation Targets
7 Chapter 7: Vasoactive Therapies & Mechanical Circulatory Support
7.1 Vasopressors & Inotropes: Pharmacology & Clinical Titration 7.2 Temporary Mechanical Circulatory Support: IABP, Impella & TandemHeart 7.3 Venoarterial ECMO (VA-ECMO) & Differential Hypoxemia 7.4 Post-Cardiac Arrest Care, Targeted Temperature Management & Neuroprognostication
8 Chapter 8: Acute Kidney Injury & Renal Replacement Therapy
8.1 KDIGO AKI Classification, Etiologies & Diagnostic Evaluation 8.2 Continuous Renal Replacement Therapy (CRRT) vs Intermittent Hemodialysis 8.3 Indications & Timing for RRT in Critical Illness: AKIKI & STARRT-AKI
9 Chapter 9: Electrolyte, Acid-Base & Endocrine Emergencies
9.1 Severe Dysnatremias: Hyponatremia, Hypernatremia & Osmotic Demyelination 9.2 Potassium, Calcium, Magnesium & Phosphate Disorders 9.3 Complex & Mixed Acid-Base Disorders: Boston vs Copenhagen vs Stewart 9.4 Endocrine Crises: DKA, HHS, Thyroid Storm, Myxedema Coma & Adrenal Crisis
10 Chapter 10: Glycemic Control, Hyperammonemia, Pituitary & Adrenal Disorders
10.1 ICU Glycemic Control & Severe Hypoglycemia 10.2 Non-Hepatic Hyperammonemia & Metabolic Encephalopathy 10.3 Pituitary Emergencies, Adrenal Excess & Critical Illness-Related Corticosteroid Insufficiency
11 Chapter 11: Acute Coronary Syndromes & Cardiac Arrhythmias
11.1 Acute Coronary Syndromes & Mechanical Complications of Myocardial Infarction 11.2 Critical Tachyarrhythmias: Atrial Fibrillation with RVR, VT & VF 11.3 Critical Bradyarrhythmias, Conduction Blocks & Temporary Cardiac Pacing
12 Chapter 12: Acute Heart Failure, Valvular & Pericardial Emergencies
12.1 Acute Decompensated Heart Failure & Cardiogenic Pulmonary Edema 12.2 Acute Valvular Regurgitation & Prosthetic Valve Emergencies 12.3 Pericardial Tamponade & Acute Aortic Syndromes
13 Chapter 13: Myocardial Disease, Hypertensive & Cardiac Device Emergencies
13.1 Fulminant Myocarditis, Stress & Peripartum Cardiomyopathy, and Hypertrophic Cardiomyopathy 13.2 Hypertensive Emergencies & Ruptured Abdominal Aortic Aneurysm 13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm
14 Chapter 14: Sepsis & Systemic Infectious Diseases
14.1 Sepsis-3 Definitions & Surviving Sepsis Campaign 2026 Guidelines 14.2 Refractory Septic Shock & Adjunctive Therapies 14.3 Multidrug-Resistant Pathogens & Antimicrobial Stewardship in the ICU
15 Chapter 15: ICU-Acquired & Severe Focal Infections
15.1 Hospital-Acquired & Ventilator-Associated Pneumonia 15.2 Central Line-Associated Bloodstream Infections & Catheter-Associated UTIs 15.3 Intra-Abdominal Sepsis, Necrotizing Soft Tissue Infections & CNS Infections
16 Chapter 16: Focal, Special-Host & Systemic Infections
16.1 CNS Infections Beyond Bacterial Meningitis: Encephalitis, Brain Abscess & Epidural Abscess 16.2 Infections in the Immunocompromised Host, Tropical & Bioterror Infections 16.3 Infective Endocarditis, Device Infections & Other Focal Cardiovascular Infections 16.4 Antimicrobial Pharmacokinetics, Allergy, Toxicity & Infection Prevention 16.5 Gastrointestinal & Hepatobiliary Infections: Fulminant C. difficile, Typhlitis, CMV Colitis & Abscesses
17 Chapter 17: Neurocritical Care & Coma
17.1 Coma, Altered Mental Status & Acute Delirium in the ICU 17.2 Status Epilepticus & Non-Convulsive Status Epilepticus 17.3 Acute Ischemic Stroke & Intracranial Hemorrhage
18 Chapter 18: Cerebrovascular Syndromes, Encephalopathy & Withdrawal States
18.1 Cerebral Venous Sinus Thrombosis, PRES & Reversible Cerebral Vasoconstriction Syndrome 18.2 Alcohol & Sedative Withdrawal, Wernicke Encephalopathy & Drug-Induced Encephalopathy
19 Chapter 19: Intracranial Hypertension & Neuromuscular Weakness
19.1 Intracranial Pressure Monitoring, Cerebral Perfusion & Tiered ICP Management 19.2 Acute Neuromuscular Respiratory Failure, ICU-Acquired Weakness & Brain Death Determination
20 Chapter 20: Traumatic Brain Injury, Spinal Cord Injury & Toxin-Mediated Paralysis
20.1 Traumatic Brain Injury Management & Paroxysmal Sympathetic Hyperactivity 20.2 Acute Spinal Cord Injury, Neurogenic Shock & Autonomic Dysreflexia 20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis
21 Chapter 21: Gastrointestinal, Hepatic & Abdominal Emergencies
21.1 Acute Upper & Lower Gastrointestinal Bleeding in the ICU 21.2 Acute Liver Failure & Severe Acute Pancreatitis 21.3 Abdominal Compartment Syndrome & Acute Mesenteric Ischemia
22 Chapter 22: Luminal GI Emergencies & Complications of Cirrhosis
22.1 Esophageal, Gastric & Bowel Emergencies: Perforation, Obstruction, Ogilvie Syndrome & Colonic Ischemia 22.2 Complications of Cirrhosis: Alcohol-Associated Hepatitis, Hepatorenal Syndrome & Pulmonary Vascular Syndromes
23 Chapter 23: Trauma, Burns & Perioperative Critical Care
23.1 Polytrauma Resuscitation, Damage Control & Massive Transfusion 23.2 Severe Burn Injury, Inhalation Injury & Environmental Emergencies 23.3 Perioperative Critical Care for High-Risk Surgical Patients
24 Chapter 24: Thoracic Trauma, Environmental Injury & Obstetric Critical Care
24.1 Thoracic Trauma: Flail Chest, Pulmonary Contusion, Great Vessel & Tracheobronchial Injury 24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation 24.3 Obstetric & Genitourinary Emergencies and the Physiology of Pregnancy
25 Chapter 25: Transplantation, Donor Management & Post-Cardiac Surgery Care
25.1 Solid Organ Transplant Recipients & Deceased Donor Management 25.2 Post-Cardiac Surgery Critical Care: Bleeding, Tamponade, Low Output & Vasoplegia
26 Chapter 26: Hematologic Emergencies, Toxicology, Critical Ultrasound & ICU Liberation
26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal 26.2 Critical Care Toxicology, Toxidromes & Specific Antidotes 26.3 Critical Care Point-of-Care Ultrasound (POCUS) 26.4 ICU Liberation, Analgosedation, Goals of Care & Critical Care Ethics
27 Chapter 27: Transfusion Medicine, Hematologic & Oncologic Disorders
27.1 Transfusion Medicine: Products, Thresholds, Reactions & Apheresis 27.2 Red and White Cell Disorders, Hemoglobinopathies, Factor Deficiencies & Hypercoagulable States 27.3 Oncologic Emergencies, Hematopoietic Cell Transplant Complications & Cellular Therapy Toxicity
28 Chapter 28: Clinical Pharmacology, Adverse Drug Reactions & Specific Poisonings
28.1 Pharmacokinetic Principles, Dose Adjustment & Drug Interactions in Critical Illness 28.2 Adverse Drug Reactions: Anaphylaxis, Severe Cutaneous Reactions & Hyperthermic Syndromes 28.3 Specific Poisonings: Sodium-Channel Blockers, Lithium, Valproate, Theophylline, Iron, Sulfonylureas & Methemoglobinemia
29 Chapter 29: Ethics, Research Methods, Administration & Abdominal Ultrasound
29.1 Advance Care Planning, Nonbeneficial Treatment, Informed Consent & Confidentiality 29.2 Critical Care Research Methods, Statistics, IRB Oversight & Quality Improvement 29.3 Abdominal, Vascular & Procedural Point-of-Care Ultrasound
4.3 Severe Community-Acquired & Viral Pneumonia
Key Takeaways Explain This Topic AI
ATS/IDSA 2019 defines severe CAP by one major criterion (septic shock needing vasopressors or respiratory failure needing mechanical ventilation) or at least three minor criteria.
Empiric therapy for severe CAP without MRSA or Pseudomonas risk factors is a beta-lactam plus a macrolide, or a beta-lactam plus a respiratory fluoroquinolone (ATS/IDSA 2019).
In the CAPE COD trial (2023), hydrocortisone lowered 28-day mortality in ICU patients with severe CAP from 11.9% to 6.2%; patients with septic shock or influenza were excluded.
Oseltamivir is recommended for every hospitalized patient with influenza as soon as possible, regardless of how long symptoms have been present (IDSA 2018).
A negative MRSA nasal PCR has a high negative predictive value for MRSA pneumonia and supports stopping empiric anti-MRSA therapy.
Last updated: October 2026
Defining Severe Community-Acquired Pneumonia
The 2019 ATS/IDSA guideline defines severe CAP by one major or three or more minor criteria.
- Major criteria Minor criteria
- Septic shock requiring vasopressors Respiratory rate of 30 breaths/min or more
- Respiratory failure requiring mechanical ventilation PaO2/FiO2 of 250 or less
- Multilobar infiltrates
- Confusion or disorientation
- BUN of 20 mg/dL or more
- White blood cell count below 4,000/µL (from infection)
- Platelets below 100,000/µL
- Core temperature below 36 °C
- Hypotension requiring aggressive fluid resuscitation
Leukopenia, hypothermia, and thrombocytopenia are ominous markers of overwhelming infection.
Microbiology and Testing
The leading organisms in severe CAP are:
Streptococcus pneumoniae .
Legionella .
Staphylococcus aureus (including post-influenza MRSA).
Haemophilus influenzae .
Enteric gram-negative bacilli.
Pseudomonas aeruginosa in patients with structural lung disease or recent antibiotics.
Respiratory viruses.
For severe CAP, obtain:
Blood cultures, and sputum or tracheal aspirate Gram stain and culture.
Pneumococcal and Legionella urinary antigens .
Influenza and SARS-CoV-2 testing, ideally a multiplex respiratory panel.
A MRSA nasal PCR .
A negative MRSA nasal PCR has a high negative predictive value for MRSA pneumonia and supports early de-escalation. Procalcitonin should not be used to withhold antibiotics at presentation.
Empiric Antibiotics for Severe CAP (ATS/IDSA 2019)
No MRSA or Pseudomonas risk factors : a beta-lactam (ceftriaxone, cefotaxime, ampicillin-sulbactam, or ceftaroline) plus a macrolide (azithromycin), or a beta-lactam plus a respiratory fluoroquinolone (levofloxacin or moxifloxacin). Observational data favor including a macrolide in severe disease.
Prior respiratory isolation of MRSA or Pseudomonas : add coverage empirically (vancomycin or linezolid for MRSA; piperacillin-tazobactam, cefepime, ceftazidime, meropenem, or imipenem for Pseudomonas ) and de-escalate with cultures.
Recent hospitalization with IV antibiotics in the past 90 days : add MRSA or Pseudomonas coverage pending cultures and rapid tests in severe CAP.
Aspiration : routine anaerobic coverage is not recommended unless there is lung abscess or empyema.
Duration : at least 5 days , continuing until the patient is clinically stable.
Corticosteroids in Severe CAP
In CAPE COD (NEJM 2023), ICU patients with severe CAP were randomized to hydrocortisone 200 mg/day for 4 or 8 days with a taper, or placebo. Hydrocortisone lowered 28-day mortality from 11.9% to 6.2% and reduced the need for intubation and vasopressors. Patients with septic shock or influenza were excluded . The 2024 SCCM corticosteroid guideline update suggests corticosteroids for hospitalized adults with severe bacterial CAP . Observational data link steroids to worse outcomes in influenza pneumonia, so avoid them there unless another indication, such as septic shock, exists.
Legionnaires' Disease
Suspect Legionella when severe pneumonia comes with:
High fever with relative bradycardia.
Diarrhea and confusion.
Hyponatremia .
Elevated liver enzymes and creatine kinase.
Failure to respond to beta-lactams.
Exposures include cooling towers, plumbing, and hot tubs. The urinary antigen detects only L. pneumophila serogroup 1, so a negative test does not exclude other strains; use respiratory PCR or culture on buffered charcoal yeast extract. Treat with azithromycin or levofloxacin .
Influenza
Oseltamivir (75 mg twice daily) is recommended for every hospitalized patient with influenza as early as possible, regardless of symptom duration (IDSA 2018). Longer courses are used for critically ill or immunocompromised patients, and IV peramivir is an alternative when enteral absorption is unreliable.
Secondary bacterial pneumonia is caused by S. aureus (including MRSA), S. pneumoniae , and Streptococcus pyogenes . Suspect it when the patient worsens after initial improvement, or with severe necrotizing disease.
Necrotizing staphylococcal pneumonia , often from Panton-Valentine leukocidin-producing strains, presents with:
Leukopenia.
Hemoptysis.
Rapid cavitation.
Septic shock.
Use linezolid , or vancomycin plus clindamycin , to suppress toxin production.
Influenza also causes myocarditis, rhabdomyolysis, and encephalopathy. Avian influenza (H5N1, H7N9) requires airborne precautions and early oseltamivir.
Critical COVID-19
Dexamethasone 6 mg daily for up to 10 days reduced mortality in patients requiring oxygen or ventilation (RECOVERY).
Add an IL-6 receptor antagonist (tocilizumab) or a JAK inhibitor (baricitinib) for patients with rising oxygen needs and systemic inflammation.
Remdesivir benefits are greatest in patients on low-flow oxygen who are not yet ventilated.
Anticoagulation : critically ill patients receive standard prophylactic doses, because therapeutic heparin helped only non-critically ill hospitalized patients in the multiplatform trials.
Awake prone positioning in patients on high-flow oxygen reduced intubation in a pooled meta-trial.
Other Viral and Atypical Causes
Agent ICU features Management
Respiratory syncytial virus Severe in older adults and immunocompromised hosts Supportive; ribavirin is considered in hematopoietic cell transplant recipients
Hantavirus (Sin Nombre) Rodent exposure; prodrome then rapid noncardiogenic edema, thrombocytopenia, hemoconcentration, cardiogenic shock Supportive; early transfer to an ECMO center
Adenovirus Severe pneumonia in transplant recipients and military recruits Supportive; cidofovir in severe immunocompromised disease
Mycoplasma and Chlamydophila Usually mild; Mycoplasma can cause cold agglutinin hemolysis and encephalitis Macrolide, doxycycline, or fluoroquinolone
Complications of severe pneumonia include parapneumonic effusion and empyema, lung abscess, ARDS, myocardial infarction, and arrhythmias. Reassess any patient who is not improving by 48 to 72 hours for resistant organisms, an undrained collection, or a noninfectious mimic.