Pulmonary Edema and ARDS Overview

Pulmonary Edema

• Pulmonary edema is fluid buildup in the alveoli, often due to left heart failure.
• Key factors include increased pulmonary capillary hydrostatic pressure.
• Non-cardiac causes include ARDS, TRALI.
• Symptoms include shortness of breath, crackles, and low oxygen saturation.
• Key diagnostic tools on USMLE are PCWP and LAP (increased).
• Conditions where bilateral, exudative chest infiltrates are present include pancreatitis, aspiration (vomitus, water), NG tube insertion, toxic shock, general trauma, and sepsis.
• Acute respiratory distress syndrome (ARDS) is a likely cause of death in toxic shock syndrome patients.

Acute Respiratory Distress Syndrome (ARDS)

• ARDS is a severe lung injury.
• PaO2/FiO2 ratio <300 is a technical definition, but not typically assessed on USMLE.
• Bilateral lung involvement is crucial.
• It's associated with near-drowning, toxic shock syndrome, and pancreatitis.
• Mechanical ventilation strategies include prone positioning, low tidal volume, and permissive hypercapnia.
• Increased surfactant protein D is a marker of lung injury and is elevated in ARDS patients.

Transfusion-Associated Lung Injury (TRALI)

• Non-cardiogenic pulmonary edema.
• It is a type of lung injury that can occur within 6 hours of a blood transfusion.
• The mechanism involves abnormal neutrophil activation in the lungs, reacting to cytokines within transfused blood products.

Transfusion-Associated Circulatory Overload (TACO)

• Cardiogenic pulmonary edema that arises from the left heart struggling to handle increased hydrostatic pressure from extra blood volume.
• It occurs after 6 hours of a transfusion and can affect patients with a history of heart failure or MI.
• Often a blood transfusion is combined with crystalloid solutions.

Pneumonia

• Lobar pneumonia (Strep pneumoniae): USMLE often links to right lower lobe consolidation, dullness to percussion.
• Bilateral Interstitial pneumonia (atypical pneumonia): Mycoplasma in immunocompetent patients.
• Mycoplasma may be indicated by interstitial markings and absence of strep pneumo, especially in bilateral cases.
• Pneumonia in AIDS patients: PCP (Pneumocystis jirovecii).
• Post-influenza bacterial pneumonia: S. aureus.
• Pneumonia with hyponatremia or diarrhea: Legionella.
• Neonatal pneumonia: Group B Strep (Strep agalactiae), or Listeria (if gram + rod), E. coli (if gram- rod)
• Pneumonia linked to certain exposures:
  • Chlamydia psittaci (bird-keepers).
  • Chlamydia trachomatis (infancy, conjunctivitis).
  • Coccidioides (southwest US, earthquake dust).
  • Francisella (rabbits).
  • Pseudomonas or S. aureus (CF).
  • S. epidermidis (central venous catheter, right upper lobe lesion).
• Key features for USMLE in pneumonia include adventitious or bronchial breath sounds, and increased tactile fremitus.
• Empiric treatment for community-acquired pneumonia (CAP) is often azithromycin.
• Severe pneumonia resulting in sepsis may lead to a ceftriaxone prescription.

Bronchiolitis

• Caused by respiratory syncytial virus (RSV) in children under 18 months
• Presents with bilateral wheezes and low-grade fever
• Treatment is supportive care.

Laryngotracheal Bronchitis (Croup)

• Caused by parainfluenza virus
• Characterized by a hoarse, barking, or seal-like cough in school-aged children
• Symptom relief may occur in cool air
• Diagnosis with neck x-ray showing a steeple sign (sub-glottic narrowing)
• Treatment is supportive, but racemic epinephrine may be indicated

Epiglottitis

• Caused by Haemophilus influenzae type B
• A medical emergency requiring prompt intubation.
• Key symptoms include difficulty breathing, drooling, and tripod positioning.
• Treatment involves antibiotics (third-generation cephalosporin), and possible supportive care.
• Close contacts should also receive rifampin prophylaxis.

Bacterial Tracheitis

• Typically caused by Staphylococcus aureus after a viral URTI.
• Key characteristics include stridor (suggesting upper airway narrowing), ability to fully open the mouth, lack of response to racemic epinephrine, and absence of a history of drooling.
• Treatment is broad-spectrum antibiotics.

Pertussis

• Whooping cough (succession of coughs followed by an inspiratory stridor).
• Diagnosis can include hypoglycemia or post-tussive emesis (vomiting after coughing).
• High WBC count with lymphocytosis is suggestive of pertussis.
• Vaccination is crucial for prevention.

Pleurodynia

• Viral infection (Coxsackie B).
• Characterised by chest pain, typically located laterally.
• It is not a lung condition.

Pulmonary Abscess

• Caused by aspiration of oropharyngeal flora (often anaerobes).
• Risk factors for aspiration should be present: alcoholism, dementia, stroke.
• Key feature on x-ray is foul-smelling sputum and an air-fluid level within the lesion.
• Treatment often involves clindamycin.

Acute Bronchopulmonary Aspergillosis (ABPA)

• Asthma-like presentation in a patient with heightened sensitivity to aspergillus skin antigen.
• Atypical pneumonia-like symptoms, resolving fever, may be triggered by exposure to organic dust/hay.

Hypersensitivity Pneumonitis

• An occupational or environmental exposure can trigger this reaction.
• Symptoms may appear hours to days following exposure.
• Characterised by fever and respiratory difficulties.

Cryptogenic Organizing Pneumonia (COP)

• A restrictive lung condition that is idiopathic (unknown cause) and does not respond to antibiotics.
• It is a restrictive lung condition (i.e. not actual pneumonia).

Otitis Media (OM)

• Inflammation of the middle ear space.
• Treatment involves amoxicillin, with Augmentin recommended for recurrent cases.
• Tympanostomy tube placement may be required for recurrent cases. Acute cases are often resolved with observation.
• Key feature is an immobile tympanic membrane.

Mastoiditis

• Infection of the mastoid bone, typically caused by untreated otitis media.
• Usually diagnosed radiographically (CT or MRI).
• If required, surgical care or oral antibiotics.

Myringitis

• Inflammation of the tympanic membrane.
• Possible causes: Strep pneumo, Mycoplasma.

Otitis Externa (OE)

• Infection of the external ear canal, often due to Pseudomonas.
• Risk factors include swimming, diabetes.
• Initial treatment can involve topical ciprofloxacin-hydrocortisone drops.
• Severe cases, especially in immunocompromised, may progress to nectirotizing OE.

Sinusitis

• Infection involving the sinuses.
• Diagnostic tools: X-rays, (CT if chronic).
• Symptoms include a prolonged recovery (over 10 days) from a URTI and potentially sore cheek.
• Treatment may involve antibiotics.

Tuberculosis (TB)

• Infection with Mycobacterium tuberculosis
• Presenting symptoms can include fever, night sweats, weight loss, and hemoptysis.
• Diagnosis starts with PPD skin test, followed by chest X-ray
• Treatment for latent TB is usually INH (isoniazid) for 9 months + vitamin B6 (important to note that INH can cause vitamin B6 deficiency- a key USMLE fact)
• Active TB treatment involves RIPE regimen for a period (rifampin, isoniazid, pyrazinamide, ethambutol)
• BCG vaccine is a live-attenuated vaccine - USMLE may avoid using the presence of this vaccine in the patient's history.

Hot Tub Lung

• Inhalation of mycobacterium avium complex (MAC) fumes.
• Usually in conjunction with hot tub use.
• Characterised by bilateral chest infection.

Influenza

• Viral infection
• Characterized by respiratory distress, fever, myalgias.
• Diagnosis is presumptive by symptoms and often involves amoxicillin/clavulanate (Augmentin).
• Distinction of influenza from other viral infections can be based on presentation (e.g. severe myalgias in flu, vs. milder symptoms in other infections/rhinovirus).
• Key structural components include two viral surface proteins, hemagglutinin and neuraminidase.

Coronavirus

• Refer to text in the chapter about SARS-CoV-2 (COVID-19).

Pediatric Respiratory Conditions

• Tracheoesophageal fistula (TEF): Proximal esophagus ends in blind pouch, distal esophagus connects to trachea. Presentation often involves initial feeding problems, with inability to completely insert a NG tube (as it will hit a pouch).
• Choanal atresia: A developmental blockage or narrowing of the nasal passages. Presenting symptom is obligate mouth-breathing by the neonate.

This quiz covers the essential concepts of pulmonary edema and acute respiratory distress syndrome (ARDS). It highlights causes, symptoms, and key diagnostic tools relevant for USMLE candidates, along with treatment strategies. Test your knowledge on these critical respiratory conditions and their implications.