63 Deficit of circulatory blood

Circulating blood volume deficit: ATLS classes of haemorrhage, causes of hypovolaemia and the body’s response.

The circulating blood volume deficit is the difference between the expected (normal) blood volume and the actual one, usually expressed as a percentage or in millilitres. It develops with bleeding and with loss of fluid (vomiting, diarrhoea, burns, excessive urination), or when fluid moves from the vessels into the tissues. Water and salt balance, and so blood volume, are regulated by antidiuretic hormone, the renin–angiotensin–aldosterone system, natriuretic peptides and thyroid hormones. A falling plasma oncotic pressure (low albumin) and a rising capillary hydrostatic pressure drive fluid out of the vessels. A large deficit leads to hypovolaemic shock.

HypovolaemiaShockBleeding

Class Iup to 15% (≈ 750 mL)

Class II15–30% (750–1500 mL)

Class III30–40% (1500–2000 mL)

Class IVover 40% (over 2000 mL)

Figure 1. ATLS classes of haemorrhage in a 70 kg adult. Pulse, blood pressure, breathing, urine output and mental state worsen as the deficit grows.

Main causes

Bleeding: external or internal (gastrointestinal bleeding, trauma, ruptured aneurysm or ectopic pregnancy, postpartum haemorrhage)
Fluid loss: persistent vomiting, severe diarrhoea (infections), extensive burns, excessive urination (diabetes, diabetes insipidus, diuretics)
Fluid shift into tissues: sepsis, pancreatitis, bowel obstruction, very low albumin
Haemolysis: destruction of red cells in some infections and inherited blood disorders

Body's response

In class I the body compensates fully. As the deficit grows, the heart rate rises, vessels in the skin, gut and kidneys constrict, urine output falls, and finally blood pressure drops and consciousness is impaired. Older people and those on beta-blockers may not develop a fast pulse. Treatment aims to stop the bleeding or fluid loss and restore volume with fluids and, in major bleeding, with blood products.

Seek emergency care

for heavy bleeding, vomiting blood or black stools, or fluid loss with dizziness, fainting, fast pulse, cold pale skin, confusion or little urine.

References

American College of Surgeons Committee on Trauma. Advanced Trauma Life Support (ATLS) Student Course Manual. 10th ed. Chicago: American College of Surgeons; 2018.
Rossaint R, Afshari A, Bouillon B, et al. The European guideline on management of major bleeding and coagulopathy following trauma: sixth edition. Crit Care. 2023;27(1):80. doi:10.1186/s13054-023-04327-7

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 28 April 2024