Inadequate oxygenation due to poor perfusion as a result of reduced circulatory fluid volume, caused by:

  • Blood loss (internal or external) e.g. trauma.
  • Burns.
  • Dehydration e.g. from vomiting / diarrhoea.
  • Uncontrolled diabetes, and / or inadequate fluid intake.
  • Aortic Aneurism.
  • Ruptured ectopic pregnancy.


  • Pulse rises 30 beats/min or systolic BP drops 15mmHg when moving from lying to sitting or standing = sign of low blood volume.

Haemorrhage classification:

ClassFluid lossSigns / Symptoms
Class 1 < 15%Few signs
Class 2
15 - 30%Increased pulse & respiration rate, decreased pulse pressure
Class 3
30 - 40%Pulse > 120/min, respiratory rate 30 - 40/min, decompensation (systolic BP < 90mmHg)
Class 4
> 40%
Pulse > 140/min, marked decrease in systolic BP, profound lethargy.


Page contributors:

DefaultDefault Author
St John WA
Want to help improve this article? Visit our Contribute page.

St John Ambulance Western Australia Ltd © Copyright 2020, All Rights Reserved

Privacy Policy | Copyright Statement & Disclaimer