Physiologic variable | Preload | Pump function | Afterload | Tissue perfusion | Tissue perfusion |
Clinical measurement | Clinical signs* or central venous pressure (if measured) | Cardiac output or index¶ | Systemic vascular resistance | Capillary refill timeΔ | Mixed venous oxygen saturation◊ |
Hypovolemic | ↓ | ↓ | ↑ | ↑ | Low |
Cardiogenic | ↑ | ↓ | ↑ | ↑ | Low |
Distributive | ↓ or ↔ | ↑ | ↓ | ↓ (initial) | High |
Obstructive | ↑§ | ↓ | ↑ | ↑ | Low |
* Clinical signs of decreased preload include tachycardia, tachypnea, decreased or absent peripheral pulses; normal or weak central pulses; capillary refill time >2 seconds; skin that is pale, mottled, cold or diaphoretic; dusky or pale extremities, altered mental status, decreased urine output, and flat jugular veins.
Clinical signs of increased preload include jugular venous distension, pulmonary edema, and hepatomegaly. These patients are also typically tachycardic and poorly perfused. Refer to topics on evaluation of shock in children.
¶ Cardiac index (cardiac output per body surface area) is typically what is measured during clinical care.
Δ In patients with shock, capillary refill time >2 seconds is associated with low mixed venous oxygen saturation while flash capillary refill suggests increased mixed venous oxygen saturation.
◊ A low mixed oxygen saturation is <70% when measured through a triple lumen catheter and <65% when measured through a pulmonary artery catheter.
§ In patients with obstructive shock caused by tension pneumothorax, the patient typically displays clinical signs of increased preload. However, because blood return to the heart is obstructed by compression or occlusion of the superior and inferior vena cavae, physiologic preload is decreased.Do you want to add Medilib to your home screen?