Expansion
Preload, Afterload, Contractility
Expansion
Think PAC:
- P - Preload: the filling of the ventricle. Raised by fluids, lowered by haemorrhage, vasodilators and positive pressure ventilation
- A - Afterload: the resistance to ejection. Raised by vasoconstriction and aortic stenosis, lowered by vasodilators and sepsis
- C - Contractility: the intrinsic force of contraction. Raised by catecholamines, lowered by ischaemia, acidosis and beta blockade
Stroke volume is roughly 70 ml at rest.
Combined with heart rate, this gives a complete framework for hypotension. Ask in turn: is the tank empty (preload), is the pump weak (contractility), are the pipes too wide or too narrow (afterload), and is the rate or rhythm appropriate.