Chapter 22. Shock
Shock is a clinical syndrome which is defined as ‘inadequate tissue perfusion resulting in hypoxia and ultimately in cell death’. Shock can be classified according to the mechanism by which it occurs:
Types of shock
• Hypovolaemic or haemorrhagic shock due to loss of circulating volume. Causes include: blood loss, burns and diarrhoea and vomiting
• Cardiogenic shock due to loss of normal cardiac function (‘pump failure’). Causes include: myocardial ischaemia, infarction, contusion, cardiac tamponade, massive pulmonary embolism
• Septic shock due to dilation of blood vessels by substances released in overwhelming infection. Causes include: bacterial viral or fungal infection
• Neurogenic shock due to dilation of blood vessels caused by spinal injury
• Anaphylactic shock due to dilation of blood vessels as part of a severe allergic reaction.
Hypovolaemic shock
The most common cause of shock in the prehospital environment is hypovolaemia (inadequate blood volume), usually related to blood or plasma loss from trauma, ruptured aortic aneurysm, ectopic pregnancy or gastrointestinal haemorrhage.
The priorities in the management of shock are:
• Identification of the patient at risk of significant bleeding
• Identification of shock
• Control of compressible haemorrhage
• Urgent transfer to hospital for surgical intervention.
• Tachycardia (arrhythmias may develop)
• Change in blood pressure (initially reduced pulse pressure, later lowered systolic and diastolic pressures)
• Altered mental state
• Tachypnoea
• Cool, clammy skin
• Cyanosis
• Oliguria
Compensatory mechanisms in hypovolaemic shock
• Tachycardia
• Peripheral vasoconstriction (with diversion of blood to vital organs)
• Increase in frequency and depth of respiration
• Diversion of blood within the lungs to areas of maximal gas exchange
• Increased release of oxygen from haemoglobin
• Reduced urine output.
Classification of haemorrhagic shock
Hypovolaemic shock can be divided into four grades depending on the extent of circulating volume lost.
Exact estimation of blood loss will almost never be possible and is usually overestimated. However, the following factors should be taken into consideration:
• Age (the elderly are less able to compensate for volume loss and have signs associated with a higher grade of shock but with lower blood loss)
• Fitness (athletes and fit individuals may compensate and hence have few signs or symptoms even with major losses): eventual decompensation may be very rapid
• Medications (drugs such as β-blockers, antihypertensives and antianginals may mask normal responses such as tachycardia)
• Pre-existing disease (patients with underlying conditions such as ischaemic heart disease, cerebrovascular disease and pregnancy are less able to cope with the effects of shock).
A pulse of 95 bpm may be normal in an elderly patient, but can represent severe vascular compromise in a marathon runner whose resting pulse is 40 bpm.
All grades of shock will progress if the bleeding is not stopped, the only endpoint of uncontrolled bleeding is death.
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