Shock

Q: What hemodynamic parameters and criteria are used to determine the severity of hemorrhagic shock?

The Allgöwer shock index is used to assess the severity of shock and associated blood loss. It is based on the principle that during shock, heart rate increases while systolic blood pressure decreases. Formula: Index = Heart Rate (bpm) / Systolic BP (mmHg) Interpretation: Index ValueInterpretation0.5Normal1.0Transition from early stage to marked shock1.5Developed shock Blood Loss Estimation via Allgöwer Index: Index 1 ≈ blood loss of 20–30% of total blood volume (TBV);Index > 1 ≈ blood loss of 30–50% of TBV. The higher the index, the more severe the shock and the worse the prognosis.

For medical students2 min readUpdated 2026-10-10

Shock is an acute, critical, generalized condition resulting from the direct impact of an overwhelming extreme stressor. This pathology presents as a staged and steadily progressive life-threatening disorder. During the development of shock, there is a progressive impairment of major life-support systems, primarily the nervous, endocrine, and cardiovascular systems. Spontaneous recovery is virtually impossible: a favorable outcome is achieved only through prompt and effective medical intervention. Without treatment, the process inevitably progresses to a terminal state.

Primary criterionThe classification of shock types is based exclusively on the etiological factor (the underlying cause).

Blood transfusionTransfusion of incompatible blood is a classic cause of transfusion-related shock.

TerminologyThe name of the second stage derives from the Latin word torpidus, meaning "sluggish" or "numb".

Staged progressionRegardless of the severity of manifestations, the pathogenesis always includes two consecutive stages.

Etiology: Triggers of the Shock Response

Shock is triggered by a severe extreme factor. Typically, such an impact leads to massive destruction of structural elements in tissues and organs.

The main causes of this pathology include:

Massive trauma. This includes tissue tears and crushing injuries, extensive burns, and severe electrical injuries.
Massive blood loss. In most clinical cases, this is combined with severe trauma.
Transfusion complications. These occur when a patient receives a large volume of incompatible donor blood.
Allergic reactions. These develop when specific allergens enter the internal environment of a previously sensitized organism.
Acute organ damage. The condition can be triggered by significant ischemia or extensive necrosis of vital structures (heart, kidneys, liver, intestine).

Risk Factors (Predisposition)

Not every extreme stressor leads to shock. The likelihood of its development largely depends on the baseline state of the organism. Factors that increase risk (predisposing factors) include:

Extreme temperature exposure (severe hypothermia or hyperthermia).
Prolonged nutritional starvation.
Pronounced nervous or psychological overexcitation.
Significant physical fatigue and exhaustion.
Impairments in general reactivity (formation of hyperergic or hypoergic states).
Presence of concurrent severe chronic diseases.
High individual patient sensitivity to a specific extreme stressor.

Classification of Shock Types

In modern pathophysiology, there is no single universally accepted classification. The primary criterion for differentiating these conditions is the cause (etiology).

Clinically significant types of shock include:

Traumatic (wound) and hemorrhagic.
Burn and electrical.
Post-transfusion.
Allergic (anaphylactic).
Cardiogenic.
Toxic and septic.
Psychogenic (psychological).

In practical medicine, classification by severity is also used, divided into three grades:

Grade I shock (mild).
Grade II shock (moderate).
Grade III shock (severe).

Stages of the Pathological Process

Regardless of the inciting cause and the severity of clinical manifestations, the pathogenesis of shock always unfolds in two consecutive stages.

1. First Stage Historically called the erectile stage. Modern terms include: adaptive, compensatory, non-progressive, or early stage. Clinically and pathophysiologically, it is characterized by generalized excitation. During this period, both specific and non-specific adaptive reactions are urgently activated to maintain vital functions and combat the extreme factor.

2. Second Stage The key condition for its development is the failure of the body's adaptive processes. Previously called the stage of general inhibition or the torpid stage (from Latin torpidus — sluggish). Modern medical terminology designates it as the stage of maladaptation or decompensation.

This second stage is heterogeneous and includes two substages:

Progressive: complete exhaustion of the body's compensatory mechanisms occurs, leading to pronounced tissue hypoperfusion (reduced blood supply).
Irreversible: characterized by the development of critical structural and functional changes that are incompatible with life.

Mnemonic

To avoid confusing the stages, remember the rule of two "E"s and two "T"s. The first stage is Erectile (characterized by Extreme excitation and adaptation). The second stage is Torpid (manifested by Severe Torpor and decompensation).

Frequently asked questions

Which specific compensatory mechanisms are activated during the erectile stage of shock?

During the erectile stage of shock, mechanisms aimed at urgent compensation for hypoxia and centralization of blood circulation are activated. Key reactions include:

Neuroendocrine activation — a significant increase in the activity of the sympathoadrenal and adrenocortical systems.
Vascular response — compensatory vasoconstriction (primarily in skin and intestinal vessels), ensuring the preservation of blood volume in vital organs.
Hemodynamic shifts — elevated blood pressure, tachycardia, and increased blood flow velocity.

What is the detailed microcirculatory pathogenesis of the progressive substage of shock?

In the progressive substage of shock, literature points to:

Exhaustion of adaptive mechanisms / compensatory reactions.
Tissue hypoperfusion of all organs due to progressive arterial dilation.
Profound collapse and a pronounced clinical picture.
Development of metabolic and circulatory disorders.

Regulatory changes at this stage also include:

progressive reduction of neural and hormonal influences up to complete unresponsiveness;
the cause of this reduction is receptor hyposensitization;
contributing factors: mounting acidosis, intra- and extracellular ion imbalances, and altered cell membrane states, especially in neurons.

What hemodynamic parameters and criteria are used to determine the severity of hemorrhagic shock?

The Allgöwer shock index is used to assess the severity of shock and associated blood loss.

It is based on the principle that during shock, heart rate increases while systolic blood pressure decreases.

Formula:

Index = Heart Rate (bpm) / Systolic BP (mmHg)

Interpretation:

Index Value	Interpretation
0.5	Normal
1.0	Transition from early stage to marked shock
1.5	Developed shock

Blood Loss Estimation via Allgöwer Index:

Index 1 ≈ blood loss of 20–30% of total blood volume (TBV);
Index > 1 ≈ blood loss of 30–50% of TBV.

The higher the index, the more severe the shock and the worse the prognosis.

What pathomorphological changes occur in so-called "shock organs"?

Changes in "shock organs" result from the centralization of blood circulation, circulatory hypoxia, and disseminated intravascular coagulation (DIC). Key manifestations include:

Shock kidney — acute tubular necrosis (necrosis of convoluted tubule epithelium), sludging and microthrombi in vessels, and interstitial edema.
Shock lung — areas of atelectasis, serous-hemorrhagic edema, and fibrin strands (hyaline membranes).
Brain — ischemic encephalopathy (edema, petechial hemorrhages, foci of necrosis).
Heart — subendocardial hemorrhages, myocardial necrosis, fatty degeneration of cardiomyocytes, and hypercontraction.

Can the body recover from shock spontaneously?

As a rule, no. Recovery from this critical state is possible only with prompt and effective medical intervention. Without treatment, the process progresses to a terminal state.

What is the primary criterion in classifying types of shock?

Since there is no single universally accepted classification, the primary differentiating criterion is the etiological factor (the direct cause), such as trauma, burn, allergen, or incompatible blood.

Why does the erectile stage transition into the torpid stage?

The transition to the second stage (decompensation) occurs due to the failure of adaptive processes. When specific and non-specific compensatory reactions are exhausted, generalized excitation gives way to general inhibition and tissue hypoperfusion.

Go deeper

Mechanisms of tissue hypoperfusion development in the progressive substage.
Specific and non-specific adaptive reactions of the erectile stage.
Pathogenesis of transfusion-related shock during incompatible blood transfusion.
Criteria for the transition from the progressive substage to the irreversible stage.
The role of the nervous and endocrine systems in shaping compensatory reactions.