Definition and classification of shock

I thought there may be some utility in having shock in its own little category, as failure of the "circulatory" organ system. Yes, there is a specific treatment for shock which addresses the causes, but let us presume that you are in some sort of nightmarish environment where the resources are scarce and competent assistance is absent. What do you do? It is "undifferentiated shock". And what about those situations when a patient with sepsis has a simultaneous sepsis-related cardiomyopathy, epidural abscess, and iatrogenic tension pneumothorax?

In short, non-specific shock ought to have its own clinical classification category and this page is in tribute to this under-appreciated entity.

Physiological classifications

Hypoxic: there isn’t enough oxygen, duuh.

Anaemic the blood is exposed to enough oxygen, but there is not enough hemoglobin to carry the oxygen

Stagnant: the blood is well oxygenated, but the circulation is slow, and the oxygen isn’t getting to the tissues- eg. cardiogenic shock

Histotoxic: the cells receive plenty of oxygen, but are unable to utilize it, eg. in cyanide poisoning

The mnemonic acronym for these four categories is HASH.

Clinical classifications

Neurogenic: another form of “distributive” shock

Anaphylactic: also “distributive” shock

Cardiogenic: pump failure. No pumping = no blood flow

Hypovolemic: loss of blood or water

Obstructive: eg. tension pneumothorax or cardiac tamponade

Septic: “distributive” shock; stagnation of blood flow owing to vasodilation

The mnemonic is NACHOS.

Whether these mnemonics are helpful or not remains to be seen. I am merely delighted to have my shock classifications spontaneously organise themselves into HASH and NACHOS.

Differential diagnosis of shock

This table has been compiled out of a collection of boxes which can be found in Matthew J Maiden and Sandra L Peake's chapter for the 7th edition of Oh's Manual (Ch. 15, "Overview of Shock" - p. 115). Other little bits and pieces have been added by the author, which degrades the authenticity somewhat. The goal was to blend HASH with NACHOS in a productive manner.

Differential Diagnosis of Shock

Artifactual or spurious

  • Inaccurately measured blood pressure
  • Noradrenaline line is not connected

Mechanical support failure

  • IABP augmentation failure
  • VA ECMO malfunction


  • Inadequate fluid intake
  • Loss of fluid
    • Vomiting
    • Diarrhoea
    • Ileostomy losses
    • Sweating
    • Polyuria
    • Burns
    • Pancreatitis
    • Ascites
    • Post-operative "third spacing"
  • Loss of blood
    • Traumatic or surgical
    • Gastrointestinal
    • Uterine (postpartum)
    • Retroperitoneal or abdominal
    • Fractures
    • Pulmonary / intrathoracic

Non-mechanical failure of the circulation

  • Extreme anaemia
  • Extreme hypoxia
  • Mitochondrial toxicity (eg. cyanide poisoning)
  • Inappropriately high metabolic demand (eg. malignant hyperthermia)


  • Ischaemia
  • Sudden "valve failure", eg. infective endocarditis
  • Septal or ventricular rupture
  • Myocarditis
  • Cardiac contusion (contusio cordis)
  • Drug overdose (of negative inotropes)
  • Rate problem: too fast or too slow
  • AF (loss of atrial kick)
  • Severe acidosis (myocardial depression)


  • Septic shock
  • Toxic shock syndrome
  • Anaphylaxis
  • Angioedema
  • Neurogenic (i.e. loss of sympathetic tone)
  • Adrenal insufficiency
  • Thyroid insufficiency (myxoedema)
  • Drug overdose (of vasodilators)
  • CO2 excess
  • Reperfusion "post arrest" syndrome


  • Intracardiac obstruction:
    • Pulmonary embolism
    • Valve obstruction (thrombosis, myxoma)
    • LVOT or RVOT obstruction
    • Amniotic fluid embolism
  • Extracardiac obstruction
    • Cardiac tamponade
    • Tension pneumothorax
    • Dynamic hyperinflation
    • Excessive positive pressure ventilation
    • Restrictive pericarditis
    • Chest compression (traumatic asphyxia)