Common causes of critical bleeding include trauma, gastrointestinal bleeding, ruptured aortic aneurysm, obstetric haemorrhage and surgical procedures.18 It can be difficult to recognise the early signs of blood loss. However, significant blood loss from any cause results in a sequence of physiological responses that help to maintain cardiac output and preserve blood flow to vital organs. Thus, changes in physiological and biochemical parameters can be used to recognise a critical haemorrhage.19 Reliance on systolic blood pressure alone may delay recognition of haemorrhagic shock.
The physiological response to haemorrhage may also vary with underlying conditions (e.g. cardiovascular disease), the presence of certain medications or drugs, the patient’s age and the presence of hypothermia.20
A useful classification of blood loss that may assist with the clinical assessment of the bleeding adult patient has been described by the American College of Surgeons (ACS) in their advanced trauma life support education program; this classification is shown in Table 3.1.
- history
- systolic blood pressure
- heart rate
- pulse pressure
- peripheral perfusion
- mental status
- respiratory rate
- urine output
- haemoglobin and haematocrit
- coagulation status
- acid–base status
- temperature
Source: Adapted from American College of Surgeons (ACS) Committee on Trauma (2008)19
Reproduced with permission from ACS
Note: Values are estimated for a 70 kg male