Background Definition Circulatory failure leading to ↓perfusion and thus tissue dysfunction due to ↓O 2 . Due to pump failure – cardiogenic or obstructive shock – or peripheral circulation failure – hypovolaemic or distributive shock. Stages 1. Initial:↓O 2  and ↑lactate. 2. Compensatory: ↑RR Sympathetic response: ↑HR, fluid retention. ↑Renin, ↑ADH. 3. Progressive. If compensatory mechanisms and treatment are unsuccessful: Worsening hypotension due to vasodilation, blood pooling in capillaries, and fluid leak from vessels. Metabolic acidosis. Altered mental status. Electrolyte imbalances. 4. Refractory: irreversible. Types and causes Hypovolaemic shock Haemorrhage: Trauma Ruptured AAA. Aortic dissection. Upper GI bleed. Ruptured ectopic pregnancy. Gastrointestinal: Diarrhoea and vomiting. Fluid sequestration e.g. in acute pancreatitis. Others: Burns Heat exhaustion. Distributive shock Vasodilation leads to a relative (thoug...