L63: Shock And Heart Failure

Question 1

Shock

Answer 1

Generalised hypoperfusion due to
1. Reduction in blood volume
2. Reduction in cardiac output
3. Redistribution of blood
Overall —> Inadequate effective circulating volume (circulatory collapse)

Shock state: preference circulation for heart and brain first, other organs sacrificed

Question 2

Types of shock

Answer 2

1. Hypovolemic (insufficient volume)
   - Haemorrhage (external / internal)
   - Fluid loss (dehydration)
   —> Asymptomatic
   —> Early stage: compensated hypotension:
   sympathetico-adrenal stimulation —> RAAS + Atrial receptor system —> vasoconstriction + salt / fluid retention
   —> Advance stage: continued impaired perfusion —> autoregulation mechanism breakdown —> irreversible hypoxic injury —> tissue necrosis + inflammation —> increase capillary permeability —> further decrease in volume
2. Anaphylactic: pooling of blood (insufficient back to heart)
   - Prior sensitisation by exposure to certain antigens
   - histamine, prostaglandin, complement
   - vasodilation —> pooling + fluid extravasation
3. Cardiogenic (insufficient pump)
   - Acute MI
   - Cardiac tamponade: blood leak into percardial sac —> press on myocardium —> ↓ venous return
   —> ruptured MI / ruptured dissecting aortic aneurysm / penetrating injury
4. Septic (volume + pump problem)
   - Gram -ve endotoxin (Peritonitis, Strep/Staph generalised skin infection, Gangrenous infection, disseminated UTI/kidney infection)
   —> inflammation —> vasodilation by histamine / complement
   —> intravascular coagulopathy —> activation + consumption of clothing factors —> subsequent bleeding tendency —> thrombosis etc.
   —> endothelial damage
   —> IL-1, TNF-alpha by macrophage
   Overall result: multiorgan failure

Question 3

Heart failure

Answer 3

• Acute (↓ end organ perfusion) / Chronic (adaptive changes in heart) (Cardiogenic shock: acute only)
• Volume / Pressure failure

1. Less able to pump (MI, myocarditis, cardiomyopathy)
2. Not coordinated pump (valvular problems, arrhythmia)
3. Physically prevented from pumping (External: landslides, Internal: tamponade)

Question 4

Ejection fraction

Answer 4

Measured by echocardiogram

Fraction of volume in left ventricle pumped out in each ejection:

(End-diastolic volume - End-systolic volume) / End-diastolic volume

Normal: 55-70%, Decreased < 40%

Question 5

Heart failure with decreased ejection fraction

Answer 5

Ischaemic heart disease —> damaged heart muscle —> weakened ventricular wall —> dilated heart —> ↑ end-diastolic volume + ↓ forward volume —> ↓ EF

Contract poorly —> ↓ forward volume —> backing up of blood into venous system

Question 6

Heart failure with normal ejection fraction

Answer 6

Chronic hypertension —> thickened ventricular wall —> ↓ ventricular volume —> ↓ filling of ventricle —> ↓ end diastolic volume + ↓ forward volume —> NO change in EF

↓ filling of ventricule —> backing up of blood into venous system

Question 7

Investigations of heart failure

Answer 7

1. Chest X-ray (heart size)
2. Echocardiogram (EF)
3. ECG
4. CT
5. MRI
6. Catheterisation

Question 8

Treatment of heart failure

Answer 8

Symptoms

• Diuretics
• Salt reduction

Cause:

• GTN
• Digitalis (anti-arrhythmics)
• ACE inhibitor / β blocker (hypertension)

Non-pharmacological:

• Catheterisation
• Stenting
• Valvular surgery
• Pacing
• Ablation