Shock Stages

Expansion

1. Compensated (non-progressive): baroreceptor reflexes, catecholamines, renin-angiotensin activation and fluid shift maintain perfusion of vital organs. Blood pressure may be normal, with tachycardia, cool peripheries, narrowed pulse pressure and rising lactate as the only clues
2. Decompensated (progressive): compensation fails. Tissue hypoperfusion causes lactic acidosis, which itself blunts vasomotor tone and myocardial contractility. Hypotension, oliguria and confusion appear
3. Irreversible: cellular and organ injury is established. Even restoring haemodynamics does not prevent death

Organ consequences

• Kidney: acute tubular necrosis, the outer medulla being most vulnerable
• Lung: acute respiratory distress syndrome, the “shock lung”
• Gut: mucosal necrosis and bacterial translocation
• Liver: centrilobular necrosis, giving ischaemic hepatitis
• Heart: subendocardial ischaemia
• Adrenal: haemorrhage, classically Waterhouse-Friderichsen syndrome in meningococcal sepsis

The key clinical lesson from the staging is that treating shock at the compensated stage is far more effective than waiting for hypotension, which is a late and ominous sign, particularly in the young.