Question 13

Classify circulatory shock and provide examples (40% of marks). Outline the cardiovascular responses (60% of marks).

[Click here to toggle visibility of the answers]

College Answer

Answers should have included the various types of shock and provided clear examples. Cardiovascular responses including sensor, integrator, effector mechanisms were necessary to pass

Discussion

Definition of shock:
- Failure to deliver and/or utilize adequate amounts of oxygen, leading to tissue dysoxia
Classification of shock:
- Hypovolemic
  - Haemorrhage
  - Water loss (eg. dehydration)
  - Fluid shift (eg. burns, or following extensive trauma or surgery)
- Cardiogenic
  - Cardiomyopathy (eg. myocardial infarction)
  - Arrhythmia (eg. bradycardia, atrial fibrillation)
  - Mechanical failure (eg. valve failure or HOCM)
- Distributive
  - Septic/inflammatory vasoplegia (eg. following cardiopulmonary bypass)
  - Anaphylaxis
  - Neurogenic shock (eg. high transection of the spinal cord)
- Obstructive
  - Cardiac tamponade
  - Tension pneumothorax
  - Pulmonary embolism
- Cytotoxic
  - Mitochondrial toxicity (eg. cyanide toxicity)

Cardiovascular Responses to Shock
Stimulus	Sensor	Integrator	Effector mechanism
Hypotension	Baroreceptors	Nucleus of the solitary tract	Vagus (increased heart rate) Sympathetic nervous system (vasoconstriction and increased cardiac output; redistribution of blood flow away from splanchnic circulation and skin) RAAS activation (increased angiotensin levels; vasoconstriction)
Decreased VO₂	Aortic arch chemoreceptors	Nucleus of the solitary tract
Decreased circulatory volume	Atrium (atrial myocytes)		Decreased release of atrial natriuretic peptide
	Baroreceptors	Hypothalamus	Increased release of vasopressin; water retention
	Renal juxtaglomerular cells		Increased release of renin; RAAS activation; aldosterone release; salt retention
Inadequate tissue perfusion	Vascular smooth muscle and endothelium		Autoregulatory vasodilation (myogenic, metabolic, and mediated by endothelial vasoactive mediators such as nitric oxide)

References

Antonelli, Massimo, et al. "Hemodynamic monitoring in shock and implications for management." Intensive care medicine 33.4 (2007): 575-590.

Standl, Thomas, et al. "The nomenclature, definition and distinction of types of shock." Deutsches Ärzteblatt International 115.45 (2018): 757.

Thal, Alan P., and John M. Kinney. "On the definition and classification of shock." Progress in cardiovascular Diseases 9.6 (1967): 527-557.

[Submit a comment or correction]