Empyema

A parapneumonic effusion is a pleural effusion arising alongside bacterial pneumonia, ranging from a sterile uncomplicated collection to infected, loculated empyema. Diagnosis rests on thoracentesis with Light's criteria, pH, and glucose; complicated effusions and empyema require prompt chest tube drainage plus intravenous antibiotics, with intrapleural fibrinolytics or surgery for inadequate drainage.

Pleural effusion is fluid accumulation in the pleural space from an imbalance of hydrostatic/oncotic pressure or increased capillary permeability; Light's criteria separate exudates from transudates, and management treats the underlying cause, with therapeutic thoracentesis, chest tube drainage, or pleurodesis for symptomatic or complicated effusions.

Community-acquired pneumonia is a lower respiratory tract infection acquired outside the hospital that is diagnosed by a compatible clinical syndrome plus a new infiltrate on chest imaging, risk-stratified with CURB-65 or the Pneumonia Severity Index to guide site of care, and treated with empiric antibiotics chosen by site of care and comorbidity, escalating to cover MRSA or Pseudomonas aeruginosa when risk factors are present.

Hospital-acquired pneumonia is a new pulmonary infiltrate with clinical signs of infection developing 48 hours or more after admission in a nonintubated patient, driven by gram-negative bacilli and Staphylococcus aureus rather than typical community organisms; empiric therapy is broad-spectrum antipseudomonal coverage started without delay and narrowed at 48 to 72 hours.

Ventilator-associated pneumonia is a new pulmonary infiltrate with clinical signs of infection developing more than 48 hours after endotracheal intubation, driven by gram-negative bacilli and Staphylococcus aureus; empiric antipseudomonal therapy is started immediately from a semiquantitative respiratory culture and paired with ventilator-bundle prevention.

Lung abscess is a necrotic, pus-filled cavity in the lung parenchyma, most often from aspiration of oropharyngeal anaerobes in a patient with impaired airway protection, diagnosed by a cavity with an air-fluid level on imaging and treated with prolonged anaerobe-covering antibiotics plus postural drainage.

Tuberculosis, caused by Mycobacterium tuberculosis, remains a leading global cause of infectious death and presents as latent infection, primary/secondary pulmonary disease, or extrapulmonary and disseminated (miliary) disease. Diagnosis rests on AFB smear, NAAT, and mycobacterial culture (the gold standard), and drug-susceptible active disease is treated with a four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) for 2 months followed by isoniazid plus rifampin for 4 to 7 months.

Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, identified by an acute rise in SOFA score of 2 points or more in a patient with known or suspected infection. Survival depends on recognizing the pattern early and completing the hour-1 bundle: lactate, blood cultures before antibiotics, broad-spectrum antibiotics such as cefepime 2 g IV every 8 hours, and 30 mL/kg crystalloid for hypotension or a lactate of 4 mmol/L or higher.

Septic shock is the subset of sepsis with hypotension requiring vasopressors to maintain a mean arterial pressure above 65 mm Hg plus a serum lactate above 2 mmol/L despite adequate fluid resuscitation, carrying in-hospital mortality of 40% or higher. Management is a timed sequence: 30 mL/kg crystalloid bolus, blood cultures and broad-spectrum antibiotics within 1 hour, norepinephrine titrated to MAP >=65, and escalation to a second vasopressor and stress-dose hydrocortisone when hypotension persists.