Pathology
Haemodynamic Disorders
Haemodynamic disorders for MBBS and NEET-PG: oedema, congestion, haemorrhage, Virchow triad, thrombosis, embolism, infarction and shock, mapped to NMC codes PA6.1 to PA6.7.
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Haemodynamic Disorders
Haemodynamic disorders for MBBS and NEET-PG: oedema, congestion, haemorrhage, Virchow triad, thrombosis, embolism, infarction and shock, mapped to NMC codes PA6.1 to PA6.7.
This chapter deals with disturbances of blood and fluid balance. It covers oedema, hyperaemia and congestion, haemorrhage, thrombosis and its triggers, embolism and its varied forms, infarction, and shock with its types and stages, all high-yield for examinations.
High-yield: Haemodynamic Disorders
- Oedema is the accumulation of excess fluid in the interstitial space and is governed by hydrostatic and oncotic pressure and lymphatic drainage.
- A transudate is protein-poor fluid from altered haemodynamics; an exudate is protein-rich fluid from increased vascular permeability in inflammation.
- Left heart failure causes pulmonary oedema; right heart failure causes peripheral and dependent oedema.
- Hyperaemia is an active increase in blood flow; congestion is a passive engorgement due to impaired venous outflow.
- Chronic pulmonary congestion produces heart failure cells, which are haemosiderin-laden alveolar macrophages.
- Chronic hepatic congestion produces the nutmeg liver, with congested centrilobular zones alternating with paler periportal areas.
- Virchow triad for thrombosis comprises endothelial injury, abnormal blood flow (stasis or turbulence) and hypercoagulability.
- Lines of Zahn, alternating pale and dark laminations, indicate a thrombus formed in flowing blood before death.
- The most common source of a pulmonary embolus is a deep vein thrombosis of the lower limb.
- A saddle embolus lodges at the bifurcation of the main pulmonary artery and can cause sudden death.
- Fat embolism follows long bone fractures; amniotic fluid embolism complicates labour; air embolism follows neck trauma or surgery.
- A red (haemorrhagic) infarct occurs in organs with dual blood supply or loose tissue such as lung and intestine; a white infarct occurs in solid organs with end arteries such as heart, kidney and spleen.
- Shock is a state of inadequate tissue perfusion, classified as hypovolaemic, cardiogenic, septic, neurogenic or anaphylactic.
- Septic shock is typically warm and vasodilated early, most often caused by gram-negative endotoxaemia.
- The stages of shock are non-progressive (compensated), progressive and irreversible.
Thrombosis, embolism and infarction essentials
- **Virchow triad:** Endothelial injury, abnormal flow (stasis or turbulence), hypercoagulability.
- **Commonest embolus:** Pulmonary embolus from a lower limb deep vein thrombosis.
- **Red infarct:** Lung and intestine, dual supply or loose tissue.
- **White infarct:** Heart, kidney and spleen, solid organs with end arteries.
NMC competencies in this chapter
- **PA6.1:** Oedema: types, pathogenesis and clinical correlations
- **PA6.2:** Hyperaemia, congestion and haemorrhage
- **PA6.3:** Shock: pathogenesis and stages
- **PA6.4:** Normal haemostasis and the pathogenesis and consequences of thrombosis
- **PA6.5:** Embolism: causes and common types
- **PA6.6:** Ischaemia and infarction: types, aetiology and effects
- **PA6.7:** Identify gross and microscopic features of infarction in a specimen
Frequently Asked Questions
What is Virchow triad?
The three contributors to thrombosis: endothelial injury, abnormal blood flow such as stasis or turbulence, and a hypercoagulable state.
What is the difference between a transudate and an exudate?
A transudate is protein-poor fluid from altered pressures, while an exudate is protein-rich fluid from increased vascular permeability during inflammation.
When does a red infarct occur?
A red or haemorrhagic infarct occurs in organs with a dual blood supply or loose tissue, such as the lung and intestine, or when a previously infarcted area is reperfused.
What are lines of Zahn?
Alternating pale and dark laminations within a thrombus, indicating that it formed in flowing blood before death rather than as a post-mortem clot.
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