13. Hypovolemic shock: Causes and hemodynamics

Hypovolemic shock occurs when there is loss of more than 20 % of intravascular fluid volume. It can be caused by hemorrhagic and non-hemorrhagic fluid loss.

Here are the most common causes:

• Haemorrhagic fluid loss
  • Trauma
  • Surgery
  • Variceal bleeding
  • Postpartum bleeding
• Non-haemorrhagic
  • Diarrhoea
  • Vomiting
  • Burns
  • Dehydration
  • Loss of fluid to “third spaces”
    • Fluid moving to peritoneal, pleural or pericardial cavity
    • Acute pancreatitis
    • Ileus
    • Ascites

Pathomechanism and compensation

The blood volume will decrease, leading to a decreased venous return. Due to this, every circulatory parameter that has something with the blood volume and pressure to do decreases, while heart rate, the resistance and the time of the circulation increases.

Blood volume	↓
Venous return	↓
Central venous pressure	↓
End-diastolic volume and pressure	↓
Stroke volume	↓
Cardiac output	↓
Arterial blood pressure	↓
Heart rate	↑
Total peripheral resistance	↑
Circulatory time	↑

To compensate this, as discussed in the previous topic, the sympathetic activation will lead to tachycardia and increased total peripheral resistance. It will also empty the blood stores and increase the retention of water and salt to try to regain the lost fluid.