Sepsis & Septic Shock

The infection starts the fire, but the host’s own response does the damage. Under the Sepsis-3 definition (2016), sepsis is “life-threatening organ dysfunction caused by a dysregulated host response to infection,” operationalized as an acute rise in the SOFA score of ≥ 2 points. The pathogen triggers both pro- and anti-inflammatory immune activation at once: monocytes, macrophages, and neutrophils interact with the vessel lining through pathogen-recognition receptors and pour out cytokines, proteases, kinins, reactive oxygen species, and nitric oxide.

Two pieces of older vocabulary were retired in 2016 and still haunt test banks: “severe sepsis” no longer exists as a category, and “SIRS plus an infectious source” is no longer the definition of sepsis — SIRS survives only as a recognition aid. The scale of the problem explains the urgency: sepsis affects about 1.7 million US adults a year, contributes to 1 in 3 hospital deaths, and currently carries a mortality of roughly 20–25% — substantially higher once shock develops.

The dysregulated response injures tissue through three simultaneous arms. Vasodilation: nitric-oxide-driven dilation of both arteries and veins drops preload and afterload, while inflammatory mediators cause a marked increase in capillary permeability and a fall in peripheral vascular resistance — a distributive shock with relative hypovolemia, because volume is pooling and leaking rather than lost. Microthrombi: the injured, activated endothelium fires the coagulation and complement cascades, producing microvascular thrombosis with impaired fibrinolysis, while disrupted cell junctions leak fluid into the interstitium. Cellular failure: mitochondria stop running oxidative phosphorylation, so cells shift to anaerobic glycolysis and shunt pyruvate to lactate (a Type A lactic acidosis).

The result is the paradox that defines sepsis: tissues starve even while cardiac output is normal or high, because the microcirculation is dilated, leaking, and plugged with microthrombi all at once. Unchecked, the cascade advances to multiorgan dysfunction syndrome (MODS) and death — which is why every treatment priority is a race to interrupt it early.

Early septic shock looks deceptively good: the vasodilated, high-output phase produces warm flushed extremities, flash capillary refill (< 1 second), and bounding pulses — a patient who is “pink and warm” while their organs are already starving. As compensation fails, the picture inverts to the late “cold” phase: cool extremities, capillary refill > 3 seconds, thready pulses. The warm-to-cold transition is a deterioration alarm, not a curiosity. One caution: warm vs cold describes the assessment, not the treatment — norepinephrine is the first-line vasopressor regardless of phase.

The formal line into septic shock is crossed when hypotension persists despite adequate fluid resuscitation: the patient needs vasopressors to maintain a MAP ≥ 65 mmHg AND the lactate stays > 2 mmol/L. Both criteria together mark the circulatory, cellular, and metabolic failure that gives septic shock its far higher mortality.

Three scoring systems divide the labor. SIRS (≥ 2 of: temperature > 38 °C or < 36 °C; HR > 90; RR > 20 or PaCO₂ < 32 mmHg; WBC > 12,000/µL, < 4,000/µL, or > 10% bands) is met fastest — sensitive but not specific. qSOFA (SBP ≤ 100 mmHg, RR ≥ 22, GCS < 15 — one point each) flags risk at the bedside: a score ≥ 2 is associated with poor outcomes. But the Surviving Sepsis Campaign guidelines (2021 and again 2026) advise against relying on qSOFA alone as a screening tool — the 2026 edition recommends broader scores such as NEWS/NEWS2, MEWS or SIRS over qSOFA because qSOFA misses too many early cases. It is a risk-stratifier, not a stand-alone screen. The full SOFA score, tracking six organ systems, is what formally defines the organ dysfunction of sepsis.

Once sepsis is recognized, treatment is a sequence against the clock. The Surviving Sepsis Campaign Hour-1 bundle (2018 update, merging the old 3-hour and 6-hour bundles) has five elements, all initiated within the first hour of recognition — completing them may take longer. The 2026 guidelines keep the bundle as a practical framework but grade each element as its own recommendation, leaving more room for clinical judgment than a single one-hour clock. Resuscitation is most effective when achieved within the first six hours of diagnosis, and every hour of antibiotic delay raises mortality.

The numbers on this page — the Hour-1 bundle, MAP ≥ 65 mmHg, 30 mL/kg — are not free-floating conventions. They come from the Surviving Sepsis Campaign (SSC), the international guidelines for management of sepsis and septic shock (current adult edition 2026, published in Critical Care Medicine and Intensive Care Medicine; it replaced the 2021 edition). Hospitals translate these recommendations into the local sepsis protocols and screening tools nurses actually work from, so knowing the SSC playbook means understanding why the protocol orders arrive in the sequence they do.

The antimicrobial arm. For possible, probable or definite septic shock — and for probable or definite sepsis without shock — broad-spectrum antimicrobials go in immediately, ideally within 1 hour of recognition (a strong recommendation). When sepsis is only possible and there is no shock, a short, time-limited workup comes first, and antimicrobials follow within 3 hours of the first suspicion of sepsis if infection is still a concern. Empiric therapy should cover all likely pathogens and penetrate the suspected source tissue, and is narrowed once cultures and sensitivities return. Under SSC 2026, extra empiric coverage for a specific multidrug-resistant organism or for anaerobes is added only when the patient has risk factors for it, and routine empiric antifungal therapy is discouraged. The clock matters because every hour of antibiotic delay is associated with higher mortality.

The hemodynamic arm. Resuscitate with at least 30 mL/kg of IV crystalloid within the first 3 hours for sepsis-induced hypoperfusion or septic shock — kept in 2026 as a conditional suggestion on low-certainty evidence, with the volume calculated on adjusted or ideal body weight when BMI is over 30 kg/m² — using balanced solutions (e.g., lactated Ringer’s) in preference to 0.9% saline, and reassess frequently to avoid both under- and over-resuscitation. When pressure doesn’t hold: norepinephrine first-line (in unstable shock it may run alongside the first fluids; with coexisting cardiac dysfunction, norepinephrine or epinephrine may go first), targeting an initial MAP of 65 mmHg — or 60–65 mmHg for adults aged 65 or older (new in 2026); vasopressin is the preferred second agent when norepinephrine alone is inadequate, and vasopressors can be started through a peripheral line rather than delaying for central access.

When shock is refractory, and after the first hour. SSC 2026 suggests IV corticosteroids for adults with septic shock — typically hydrocortisone 200 mg/day (50 mg IV every 6 hours or a continuous infusion), started once norepinephrine or epinephrine has reached ≥ 0.25 µg/kg/min at least 4 hours after initiation. Source control — draining the abscess, debriding necrotic tissue, removing the infected line or device — should happen as soon as it is medically and logistically safe, ideally within 6 hours of diagnosis, because antibiotics cannot sterilize an undrained focus. StatPearls lists the supportive-care targets that round out the protocol: transfuse at Hgb 7 g/dL, keep glucose < 180 mg/dL, ventilate lung-protectively (plateau pressure < 30 cm H₂O), give DVT and stress-ulcer prophylaxis, and start enteral nutrition early.