Note on Sepsis

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I now have comprehensive content across definitions, pathophysiology, scoring, and management. I have enough to write a thorough clinical note on sepsis.

Sepsis: Clinical Overview

Definition & Nomenclature

Sepsis-3 (2016): Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Organ dysfunction is operationalized as an acute increase in SOFA score ≥2 from baseline, which correlates with an in-hospital mortality risk of ~10%. The older concept of "severe sepsis" (sepsis + organ dysfunction) is now considered redundant — all sepsis by definition involves organ dysfunction.

Septic shock (Sepsis-3): A subset of sepsis in which circulatory and cellular/metabolic derangements are severe enough to substantially increase mortality. Clinical criteria: sepsis + vasopressor requirement to maintain MAP ≥65 mmHg + serum lactate >2 mmol/L despite adequate fluid resuscitation. Mortality exceeds 40%.

Legacy SIRS-based Sepsis-1/2 (1992): SIRS = ≥2 of: temperature >38°C or <35°C; HR >90 bpm; RR >20 or PaCO₂ <32 mmHg; WBC >12,000/µL or <4,000/µL or >10% bands. Under this older framework, sepsis = SIRS + proven/suspected infection; septic shock = sepsis + hypotension unresponsive to fluids. SIRS alone proved overly sensitive and nonspecific (also triggered by non-infectious states such as pancreatitis, burns, trauma).

Epidemiology

Most common cause of death in non-coronary ICUs
11th most common cause of death overall in the United States (~10.3 per 100,000 in 2010)
Bacteremia is not obligatory — culture-negative and culture-positive sepsis have similar outcomes at equivalent illness severity
Common sources: pneumonia, intra-abdominal abscess/perforation, pyelonephritis
Causative organisms: Gram-positive 25–50%, Gram-negative 30–60%, fungi 2–10%
High-risk hosts: elderly, immunocompromised (neutropenia, HIV, steroids), indwelling devices (central lines, prostheses, ETT)

Pathophysiology

Innate Immune Activation

The pathogen is sensed by pattern recognition receptors — most notably Toll-like receptors (TLRs) — on neutrophils and macrophages. This triggers the release of cytokines and chemokines, including:

TNF-α — detected in serum ~90 min after endotoxin challenge
IL-1, IL-6, IL-8 — peak at ~120 min

Dysregulated Inflammatory Cascade

Under normal conditions the response is self-limited and clears the pathogen. In sepsis, the cascade is inadequately regulated:

Procoagulant state develops → activation of coagulation + fibrinolysis → DIC
Fibrin microthrombi obstruct the microvasculature
Protein C levels fall; D-dimer rises
Propagation leads to cellular hypoxia → organ dysfunction → shock → death

Haemodynamic Profile

Sepsis produces distributive shock — vasodilation with ↓SVR, ↓CVP, ↓PCWP, and initially ↑CO (warm shock). This distinguishes it from cardiogenic (↓CO, ↑SVR) and hypovolemic shock (↓CO, ↑SVR).

Hepatic Involvement

The liver is the primary organ of endotoxin detoxification. Kupffer cell activation recruits neutrophils → hepatocyte injury. Endothelial damage, sinusoidal flow reduction, and fibrin microthrombi cause hepatocellular necrosis. Sepsis-related jaundice is the most common cause of jaundice in ICU patients, with bilirubin typically 5–10 mg/dL (predominantly direct). A sepsis-specific lesion — "ductal cholestasis" (cholangitis lenta) — is associated with increased mortality.

Scoring Systems

SOFA Score

Six organ systems scored 0–4:

System	Parameter
Respiratory	PaO₂/FiO₂ ratio
Coagulation	Platelet count
Hepatic	Bilirubin
Cardiovascular	MAP / vasopressor dose
Neurological	Glasgow Coma Scale
Renal	Creatinine / urine output

SOFA ≥2 from baseline = sepsis (≥10% in-hospital mortality).

qSOFA (Quick SOFA)

Bedside screening tool — no labs needed. Score 1 point each for:

Respiratory rate ≥22 breaths/min
Altered mental status (any GCS <15)
Systolic BP ≤100 mmHg

qSOFA ≥2 = high risk for poor outcome; prompts urgent full assessment. Caveat: qSOFA is more specific but less sensitive than SIRS criteria — a negative qSOFA does not exclude sepsis. Clinical judgment remains essential.

Clinical Presentation & Differential

Common presentations: fever (or hypothermia), tachycardia, tachypnea, altered mental status, hypotension, mottled skin.

Differential diagnosis includes:

Sepsis mimics	Septic shock mimics
Dehydration, ARDS, CHF	Hypovolemic / haemorrhagic shock
DIC, anaphylaxis	Cardiogenic shock (PE, MI, tamponade)
Hyperthyroidism, DKA, adrenal crisis	Tension pneumothorax, anaphylaxis
Pancreatitis, NMS, burns	Neurogenic shock

Investigations

Haematology

WBC: leukocytosis or leukopenia (both can occur); bandemia ≥5–10%
Platelets: may be elevated (acute phase reactant) or low (DIC, severe sepsis)
Coagulation: ↑PT/aPTT, ↓fibrinogen, ↑fibrin split products → DIC

Chemistry

Lactate: elevated → tissue hypoperfusion; >2 mmol/L is a criterion for septic shock; >4 mmol/L warrants aggressive resuscitation even without hypotension
Bicarbonate: low → metabolic (lactic) acidosis
Creatinine: elevation → acute kidney injury (organ dysfunction)
Bilirubin: elevation → hepatic dysfunction

Microbiology

Blood cultures × 2 (before antibiotics, if possible without delay)
Cultures from suspected source (urine, sputum, wound, CSF, peritoneal fluid)
Cultures do not need to be positive to diagnose sepsis

Biomarkers

Procalcitonin (PCT): elevated (>2 SD above normal) → bacterial infection; useful for de-escalation of antibiotics
C-reactive protein: non-specific inflammatory marker

Management

The "Hour-1 Bundle" (Surviving Sepsis Campaign)

All actions to be initiated within 1 hour of recognition:

Measure lactate (if initial lactate >2 mmol/L, remeasure within 2–4 h to confirm clearance)
Blood cultures (×2 sets) before antibiotics
Broad-spectrum IV antibiotics — initiate within 1 hour
30 mL/kg IV crystalloid for hypotension (SBP <90) or lactate ≥4 mmol/L
Vasopressors — start during or after fluids to target MAP ≥65 mmHg

Antimicrobials

Broad-spectrum empirical coverage within 1 hour of diagnosis
Regimen tailored to suspected source, host immune status, local resistance patterns, and prior cultures
De-escalate to directed therapy once organism and sensitivities are known
Antibiotics excreted hepatically (e.g., ceftriaxone) should be dose-reduced in severe hepatic sepsis

Fluid Resuscitation

Initial bolus: 30 mL/kg isotonic crystalloid (normal saline or lactated Ringer's)
Subsequent fluid titrated to: HR, BP, mental status, capillary refill, skin temperature, urine output (target ≥0.5 mL/kg/h)
Ongoing capillary leak and venodilation drive intravascular hypovolemia
Avoid over-resuscitation — after initial resuscitation, reassess volume responsiveness before giving more

Vasopressors

Norepinephrine — first-line vasopressor
Target MAP ≥65 mmHg
Vasopressin may be added as second agent to reduce norepinephrine dose

Respiratory Support

Intubate for: altered mental status with airway compromise, refractory hypoxemia, hypercapnia, profound acidosis
Mechanical ventilation for ARDS: low tidal volumes 6 mL/kg ideal body weight, plateau pressure ≤30 cmH₂O (ARDSNet protocol), higher PEEP

Source Control

Identify and remove/drain the infectious source (abscess drainage, removal of infected catheter/device, debridement)
Should occur as early as feasible once the patient is stabilised

Adjuncts

Intervention	Note
Corticosteroids	Hydrocortisone 200 mg/day for refractory septic shock (requiring high-dose vasopressors); not routine for sepsis without shock
Glucose control	Target 140–180 mg/dL; avoid hypoglycaemia
DVT prophylaxis	Routine in all ICU patients
Stress ulcer prophylaxis	Indicated in mechanically ventilated patients
Renal replacement therapy	For AKI with metabolic/fluid complications

EGDT (Historical)

Early Goal-Directed Therapy (Rivers 2001) showed a 16% mortality reduction using a protocolised resuscitation targeting CVP, MAP, urine output, and ScvO₂. Subsequent multicentre RCTs (ProCESS, ProMISe, ARISE) failed to show superiority of formal EGDT over usual care — but all groups in those trials received early antibiotics and generous fluid resuscitation, reinforcing that early identification, early antibiotics, and careful titrated resuscitation remain the cornerstone.

Organ Complications of Sepsis

Organ	Complication
Lung	ARDS
Kidney	Acute kidney injury (AKI)
Liver	Cholestatic jaundice, hepatocellular necrosis
Brain	Sepsis-associated encephalopathy
Coagulation	DIC
Adrenal	Relative adrenal insufficiency
Gut	Ileus, bacterial translocation

Prognosis

Sepsis mortality: ~10% (SOFA-based)
Septic shock mortality: >40%
Prognosis worsens with number of organ failures, delay in antibiotics, immunocompromised state, and resistant organisms
Hepatic jaundice in sepsis does not independently worsen prognosis — outcome is driven by the underlying process

Recent Evidence (2024–2025)

β-lactam infusion strategy (JAMA 2024, PMID 38864162): Prolonged (extended/continuous) infusions of β-lactam antibiotics in sepsis/septic shock showed improved outcomes vs. intermittent dosing in a systematic review and meta-analysis — consistent with PK/PD rationale of maximising time above MIC.
Sepsis alert systems (JAMA Network Open 2024, PMID 39037814): ED sepsis alert systems were associated with reduced mortality and improved bundle adherence in a meta-analysis.
SEP-1 bundle compliance (Ann Intern Med 2025, PMID 39961104): Systematic review of CMS SEP-1 compliance showed variable mortality benefit — the debate over optimal bundle timing and composition continues.

Sources: Rosen's Emergency Medicine, 10e — Schwartz's Principles of Surgery, 11e — Harrison's Principles of Internal Medicine, 22e (2025) — Tintinalli's Emergency Medicine — Sleisenger & Fordtran's GI and Liver Disease

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