How is septic shock defined under Sepsis-3?

It is sepsis with circulatory and cellular-metabolic abnormalities severe enough to substantially raise mortality, identified by persisting hypotension requiring vasopressors to maintain an adequate mean arterial pressure plus an elevated lactate despite adequate fluid resuscitation.

Why is septic shock called distributive shock?

Because the primary defect is loss of vascular tone with maldistribution of blood flow, so tissue perfusion is inadequate even though cardiac output is frequently normal or high.

Septic Shock

Septic shock is the most severe form of sepsis, in which a dysregulated host response to infection produces circulatory and cellular-metabolic abnormalities profound enough to substantially raise the risk of death. It is the prototypical distributive shock, marked by vasodilation, hypotension that persists despite volume, and tissue hypoperfusion reflected in elevated lactate.

Definition

Under the Sepsis-3 consensus, septic shock is a subset of sepsis in which underlying circulatory and cellular-metabolic abnormalities are profound enough to substantially increase mortality, identified clinically by sepsis with persisting hypotension requiring vasopressors to maintain an adequate mean arterial pressure together with an elevated serum lactate despite adequate volume resuscitation.

Scope

The entry covers the consensus definition of septic shock, its place within the sepsis spectrum, the distributive pathophysiology that distinguishes it, and the evolution of resuscitation evidence. It is a reference topic and does not provide thresholds for dosing, fluid volumes, or individualized management.

Key concepts

Dysregulated host response to infection
Distributive (vasodilatory) shock
Vasopressor-dependent hypotension
Hyperlactatemia as a perfusion marker
Sepsis-3 consensus definition
Mean arterial pressure target
Source control and the role of timely care

Mechanisms

Septic shock arises from a dysregulated response to infection in which inflammatory mediators cause widespread vasodilation, increased vascular permeability, and microcirculatory dysfunction. The result is a fall in systemic vascular resistance and maldistribution of blood flow, so that tissue oxygen delivery becomes inadequate despite a cardiac output that is often normal or elevated - the hallmark of distributive shock. Persisting hypotension and hyperlactatemia reflect this hypoperfusion. The Sepsis-3 consensus reframed septic shock around these circulatory and cellular-metabolic abnormalities rather than around the older systemic inflammatory response criteria.

Clinical relevance

Septic shock is a high-mortality emergency, and understanding its definition and physiology underlies how clinicians recognize the sickest patients with infection. This entry describes the concept and the evidence base, including how resuscitation strategies have been studied; it is reference material and does not constitute treatment instructions for any individual patient.

Epidemiology

Septic shock is the most common form of distributive shock seen in intensive care and carries a high mortality, historically reported in the range of roughly a third to over half of cases depending on population and era. Incidence estimates vary with the definition used and with case ascertainment, and the Sepsis-3 work was motivated in part by the need for more consistent identification.

Evidence & guidelines

The Surviving Sepsis Campaign guidelines synthesize the evidence on recognizing and supporting patients with sepsis and septic shock, and the Sepsis-3 statement provides the current consensus definition. Rivers' early goal-directed therapy trial shaped a generation of resuscitation practice, and later trials such as ProMISe (Mouncey et al., 2015) re-examined protocolized resuscitation against usual care. These works are cited here to describe the evidence landscape, not to recommend a protocol.

History

Definitions of sepsis and septic shock have shifted substantially over time. The 1990s consensus framed sepsis around systemic inflammatory response criteria; Rivers' 2001 early goal-directed therapy trial then focused attention on early hemodynamic resuscitation. In 2016 the Sepsis-3 consensus redefined sepsis as life-threatening organ dysfunction from a dysregulated host response and characterized septic shock by vasopressor-requiring hypotension and hyperlactatemia, and successive Surviving Sepsis Campaign guidelines have updated supportive-care recommendations.

Debates

Does protocolized early goal-directed therapy improve outcomes over usual care?: Rivers' single-center trial reported a mortality benefit from a protocolized resuscitation bundle, but later multicenter trials including ProMISe found no advantage of strict protocolized care over contemporary usual care, prompting a move toward early recognition and individualized resuscitation rather than a fixed algorithm.

Key figures

Mervyn Singer
Emanuel Rivers
Laura Evans
Derek Angus

Seminal works

singer-2016
rivers-2001
evans-2021

Frequently asked questions

How is septic shock defined under Sepsis-3?: It is sepsis with circulatory and cellular-metabolic abnormalities severe enough to substantially raise mortality, identified by persisting hypotension requiring vasopressors to maintain an adequate mean arterial pressure plus an elevated lactate despite adequate fluid resuscitation.
Why is septic shock called distributive shock?: Because the primary defect is loss of vascular tone with maldistribution of blood flow, so tissue perfusion is inadequate even though cardiac output is frequently normal or high.