Sepsis and septic shock (Sepsis-3 criteria) represent a life-threatening clinical syndrome defined by a dysregulated host response to infection, culminating in severe, acute organ dysfunction4,5. Under the international Sepsis-3 consensus definitions, sepsis is identified by a suspected or confirmed infection combined with an acute increase of 2 points or more in the Sequential Organ Failure Assessment (SOFA) score5. Septic shock denotes a profound circulatory, cellular, and metabolic sub-phenotype of sepsis characterized by persistent hypotension requiring vasopressor therapy to maintain a mean arterial pressure of 65 mmHg or greater, alongside a serum lactate concentration greater than 2.0 mmol/L despite adequate intravascular volume resuscitation5. Sepsis remains a leading cause of inpatient morbidity, critical care admission, and mortality worldwide, requiring immediate recognition, diagnostic workup, and protocol-driven therapeutic interventions4,7.

1. Etiology & Risk Factors

  • Common Bacterial Pathogens: Frequently precipitated by Gram-negative bacilli (such as Escherichia coli, Klebsiella species, and Pseudomonas aeruginosa) and Gram-positive cocci (including Staphylococcus aureus—both methicillin-susceptible and resistant strains—and Streptococcus pneumoniae)1,7.
  • Fungal and Viral Etiologies: Fungal sepsis (driven by Candida species) typically occurs in immunocompromised hosts, indwelling vascular catheter users, or patients receiving prolonged broad-spectrum antibiotics; viral pathogens (such as influenza and severe acute respiratory syndromes) can also trigger severe septic cascades4,7.
  • Primary Sites of Infection: Common anatomical sources include the respiratory tract (pneumonia), genitourinary tract (urosepsis, pyelonephritis), intra-abdominal cavity (peritonitis, cholangitis, diverticulitis), and skin or soft tissue structures (cellulitis, necrotizing fasciitis, infected intravascular devices)4,7.
  • Host Risk Factors: Advanced age (greater than 65 years), extremes of life, chronic comorbidities (diabetes mellitus, chronic kidney disease, cirrhosis, chronic heart failure, malignancy), immunosuppression (chemotherapy, solid organ transplantation, asplenia), and indwelling medical devices (central venous catheters, urinary catheters) significantly elevate susceptibility and mortality1,7.

2. Pathophysiology

The pathophysiology of sepsis originates from the interaction between invading microbial pathogen-associated molecular patterns (PAMPs)—such as lipopolysaccharides in Gram-negative bacteria or peptidoglycans in Gram-positive bacteria—and host pattern recognition receptors, including toll-like receptors on immune and endothelial cells5,7. This recognition triggers a massive, early pro-inflammatory cascade driven by the release of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1beta), and interleukin-6 (IL-6), which is subsequently counterbalanced by an anti-inflammatory response7. The concurrent activation of humoral systems, including the complement cascade, coagulation pathway, and kallikrein-kinin system, leads to widespread endothelial activation and injury7. Endothelial dysfunction causes profound systemic vasodilation, loss of vascular tone (attributable to inducible nitric oxide synthase upregulation), and increased capillary permeability, resulting in generalized third-spacing, tissue edema, and profound intravascular hypovolemia7. Simultaneously, microvascular thrombosis occurs due to tissue factor upregulation and impaired fibrinolysis (disseminated intravascular coagulation), causing localized tissue hypoxia, cellular metabolic dysfunction, anaerobic glycolysis, and subsequent accumulation of serum lactate7. This culminating cellular hypoxia and cytopathic injury drive multiple organ dysfunction syndrome (MODS) affecting the cardiovascular, pulmonary, renal, hepatic, and neurological systems5,7.

Sepsis and septic shock (Sepsis-3 criteria) — Pathophysiological Cascade & Clinical Flowchart 1 Trigger / Primary Insult Pathogen invasion and PAMPs/DAMPs activation 2 Cellular / Pathophysiological Cascade Dysregulated immune response and systemic cytokine storm 3 Target Organ / Structural Change Endothelial injury, vasodilation, and microvascular thrombosis 4 Hallmark Clinical & Diagnostic Manifestation Acute organ dysfunction, hypotension, and hyperlactatemia 5 Complications if Untreated & Therapeutic Target Refractory shock, multiorgan failure, and targeted resuscitation

3. Clinical Presentation & Classic Clinical Signs

  • History & Cardinal Symptoms: Patients frequently present with subjective fevers, shaking chills, rigors, malaise, generalized weakness, altered mental status, confusion, lethargy, oliguria or anuria, tachypnea, and localized symptoms corresponding to the primary site of infection (e.g., dysuria, cough, pleuritic chest pain, abdominal pain, or localized erythema)4,7.
  • Physical Examination & Named Clinical Signs: Examination reveals vital sign abnormalities including fever (temperature greater than 38.3 °C) or hypothermia (temperature less than 36.0 °C), tachycardia (heart rate greater than 90 beats per minute), tachypnea (respiratory rate greater than 20 breaths per minute), and hypotension (systolic blood pressure less than 90 mmHg or mean arterial pressure less than 65 mmHg)5,7. Skin findings may include warm, flushed extremities in early hyperdynamic septic shock, progressing to cool, pale, mottled extremities with delayed capillary refill (greater than 3 seconds) in uncompensated shock. Petechiae, purpura, or ecchymoses may indicate underlying disseminated intravascular coagulation (DIC) or specific pathogens such as Neisseria meningitidis7. Neurological assessment frequently demonstrates acute encephalopathy, disorientation, or a depressed Glasgow Coma Scale (GCS) score5,7.

4. Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)

Diagnostic Modality / Test Expected Clinical & Radiological / Laboratory Finding
Gold-Standard InvestigationTwo sets of blood cultures (one aerobic and one anaerobic bottle per set drawn from separate venipuncture sites, or one set from each newly placed vascular access device) obtained prior to antimicrobial administration, alongside serial arterial or venous serum lactate measurements5,7.
Laboratory PanelComplete blood count demonstrating leukocytosis (white blood cell count greater than 12,000/microL) or leukopenia (less than 4,000/microL) with a bandemia (left shift greater than 10% immature forms); thrombocytopenia (platelet count less than 100,000/microL); coagulopathy with an elevated international normalized ratio (INR) and prolonged activated partial thromboplastin time (aPTT); acute kidney injury marked by rising serum creatinine and blood urea nitrogen (BUN); elevated total bilirubin and transaminases indicating hepatic dysfunction; and hyperlactatemia (serum lactate greater than 2.0 mmol/L) reflecting tissue hypoperfusion and anaerobic metabolism5,7.
Imaging / Radiology (X-ray, US, CT, MRI)Chest radiography to evaluate for pulmonary infiltrates, consolidation, or pleural effusions suggestive of pneumonia or acute respiratory distress syndrome (ARDS); point-of-care ultrasound (POCUS) or formal abdominal/pelvic computed tomography (CT) to identify localized intra-abdominal fluid collections, abscesses, cholecystitis, or bowel perforation; renal ultrasound or CT urogram to assess for obstructive uropathy or pyelonephritis4,7.
ECG / Histopathology / Procedural12-lead electrocardiogram to rule out acute coronary syndromes, identify sepsis-induced myocardial injury or tachyarrhythmias (such as new-onset atrial fibrillation); arterial blood gas (ABG) analysis to evaluate oxygenation status (PaO2/FiO2 ratio) and metabolic acidosis; diagnostic thoracentesis, paracentesis, or lumbar puncture when empyema, spontaneous bacterial peritonitis, or meningitis is suspected5,7.

5. Staging, Classification & Clinical Scoring Systems

Criterion / Stage / Score Component Clinical Threshold, Points & Management Implication
Sepsis-3 Criteria (Infection + Organ Dysfunction)Suspected or documented infection accompanied by an acute increase of ≥2 points in the Sequential Organ Failure Assessment (SOFA) score. Signals high risk of inpatient mortality exceeding 10%5.
Sequential Organ Failure Assessment (SOFA) ScoreAssesses six organ systems (respiratory, coagulation, liver, cardiovascular, central nervous system, renal) scored from 0 to 4 each. A baseline score of 0 is assumed if no prior organ dysfunction is known. An acute increase of ≥2 defines sepsis5.
Quick SOFA (qSOFA) Clinical Screening ToolBedside screening tool utilizing three variables: respiratory rate ≥22 breaths/min, altered mental status (GCS <15), and systolic blood pressure ≤100 mmHg. Scoring ≥2 points prompts immediate full SOFA evaluation and consideration of ICU escalation5.
Septic Shock Definitive CriteriaPersistent hypotension requiring vasopressor therapy to maintain a mean arterial pressure (MAP) ≥65 mmHg AND a serum lactate level >2.0 mmol/L despite adequate fluid resuscitation (≥30 mL/kg crystalloids)5.

6. Differential Diagnosis

Differential Condition Distinguishing Clinical, Biochemical & Imaging Features
Cardiogenic ShockPrimary pump failure characterized by elevated jugular venous pressure, pulmonary edema on chest radiography, cold extremities, elevated cardiac biomarkers, and a low cardiac index without primary systemic vasodilation. Responds poorly to volume resuscitation and requires inotropic support.
Hypovolemic ShockResults from acute blood or fluid loss (hemorrhage, severe dehydration, burns). Manifests with flat neck veins, dry mucous membranes, history of fluid losses, and prompt hemodynamic improvement following aggressive crystalloid or blood product resuscitation.
Anaphylactic ShockAcute-onset distributive shock triggered by an allergen exposure. Characterized by prominent dermatologic manifestations (urticaria, angioedema), respiratory compromise (bronchospasm, laryngeal edema), and rapid response to intramuscular epinephrine.
Neurogenic / Spinal ShockDistributive shock resulting from acute spinal cord injury above T6. Characterized by hypotension accompanied by paradoxical bradycardia (loss of sympathetic tone) and warm, dry skin due to loss of vasomotor tone, without evidence of infection or elevated lactate.

7. Management & Treatment Protocol

  • Initial Stabilization & Resuscitation: Initiate the Surviving Sepsis Campaign 1-Hour Bundle immediately upon recognition. Measure serum lactate levels, obtain appropriate blood cultures prior to antimicrobial initiation, and administer broad-spectrum intravenous antimicrobials within 1 hour of recognition4,7.
  • Fluid Resuscitation Protocol: Administer a rapid intravenous fluid challenge of at least 30 mL/kg of balanced crystalloids (such as lactated Ringer's or Plasma-Lyte) within the first 3 hours for patients with hypotension (MAP less than 65 mmHg) or initial serum lactate levels equal to or greater than 4.0 mmol/L4,7. Utilize dynamic measures of fluid responsiveness (e.g., passive leg raise test, stroke volume variation, or bedside echocardiography) to guide subsequent fluid administration and prevent volume overload4,7.
  • First-Line Medical / Pharmacological Therapy:
    • Vasopressor Therapy: If fluid resuscitation fails to restore an adequate mean arterial pressure or during ongoing resuscitation, initiate Noradrenaline (Norepinephrine) as the first-line vasopressor via a central venous catheter, titrated at an initial infusion rate of 2 to 20 micrograms/min (or 0.05 to 0.5 mcg/kg/min) to target a mean arterial pressure (MAP) of ≥65 mmHg4,7. Add Vasopressin as a second-line agent at a fixed dose of 0.03 units/min to reduce norepinephrine requirements if needed4,7. Add Epinephrine (2 to 10 micrograms/min) if an inotropic agent is additionally required4,7.
    • Antimicrobial Therapy: Administer empiric intravenous broad-spectrum antimicrobials targeting all likely bacterial or fungal pathogens within 1 hour of recognition. For community-acquired sepsis of unknown source, standard adult regimens include IV Ceftriaxone (2 g IV every 24 hours) plus Vancomycin (15 to 20 mg/kg IV every 8 to 12 hours, targeting trough levels of 15 to 20 mg/L). For hospital-acquired or immunocompromised sepsis, use antipseudomonal agents such as Cefepime (2 g IV every 8 hours) or Piperacillin-Tazobactam (4.5 g IV every 6 hours) combined with Vancomycin4,7. Narrow antimicrobial therapy once culture and susceptibility results are finalized4,7.
    • Corticosteroids: Consider intravenous Hydrocortisone at a dose of 200 mg/day (administered as 50 mg IV every 6 hours or as a continuous infusion) only for patients with septic shock refractory to fluid resuscitation and moderate-to-high dose vasopressor therapy4,7.
  • Surgical / Interventional Indications: Urgent source control must be achieved as soon as anatomically and clinically feasible. This includes percutaneous or surgical drainage of infected fluid collections or abscesses, debridement of infected necrotic tissue, removal of infected indwelling vascular or urinary catheters, and definitive management of hollow viscus perforation or cholangitis within 6 to 12 hours of recognition4,7.

8. Complications & Prognosis

  • Acute Complications: Multiorgan dysfunction syndrome (MODS), acute respiratory distress syndrome (ARDS), acute kidney injury (AKI) requiring continuous renal replacement therapy, disseminated intravascular coagulation (DIC), stress-induced cardiomyopathy, septic encephalopathy, paralytic ileus, and critical illness myopathy/neuropathy4,7.
  • Long-Term Morbidity & Post-Sepsis Syndrome: Survivors frequently experience long-term physical debility, cognitive impairment, psychological distress (including post-traumatic stress disorder and depression), and reduced health-related quality of life4,7.
  • Prognosis & Mortality Data: In-hospital mortality for severe sepsis ranges between 15% and 25%, whereas septic shock carries an unacceptably high mortality rate exceeding 40% to 50% despite optimal evidence-based critical care management4,5,7. Advanced age, high baseline SOFA scores, delayed antimicrobial administration, persistent hyperlactatemia, and failure to achieve adequate source control are key independent predictors of mortality4,5,7.