Clinical signs of hypovolaemic shock
Hypovolaemic shock is divided into four classes of severity, depending on blood loss and clinical signs. Classes 3 and 4 are associated with a mortality of approximately 30 per cent.
Shock is a clinical diagnosis. Clinical signs are often non-specific, varying according to the amount of blood lost, the age of the patient and any concurrent medical conditions. Classic clinical signs include the following:
● Poor peripheral perfusion
● Change in mental state.
The most important clinical signs are hypotension, oliguria and poor peripheral perfusion.
Systolic blood pressure is not a reliable indicator of shock. Blood loss in healthy adults is often underestimated as rapid vasoconstriction occurs, maintaining a relatively normal blood pressure until 30 per cent of the blood volume is lost. Diastolic pressure is a more sensitive indicator of hypovolaemia. Conversely, in patients with ischaemic heart disease, a relatively small loss of blood can cause a significant drop in blood pressure. Care should be taken when interpreting signs in patients taking beta-blockers, who will not develop tachycardia. It is important to realise that patients who are drowsy or unconscious secondary to hypovolaemic shock have lost at least 40 per cent of their blood volume. Clinically, haemorrhage occurs at a variable rather than a fixed rate, which usually slows as the blood pressure drops. In a surgical or trauma situation, the source of bleeding should be established promptly. Patients who need emergency surgery have a better outcome if the time between assessment and diagnosis and theatre is minimised.