Problem Sets

Circulatory shock, commonly known simply as shock, is a serious, life-threatening medical condition characterized by a decrease in tissue perfusion to a point at which it is inadequate to meet cellular metabolic needs. (Collins, 35-41) As the blood carries oxygen and nutrients around the body, reduced flow hinders the delivery of these components to the tissues, and can stop the tissues from functioning properly. The process of blood entering the tissues is called perfusion, so when perfusion is not occurring properly this is called a hypoperfusional (hypo = below) state.

A circulatory shock should not be confused with the emotional state of shock, as the two are not related. Medical shock is a life-threatening medical emergency and one of the most common causes of death for critically-ill people. Shock can have a variety of effects (Ledingham, 169-189), all with similar outcomes, but all relate to a problem with the body's circulatory system. For example, shock may lead to hypoxemia (a lack of oxygen in arterial blood) or cardiac arrest (the heart stopping).

The essential signs of shock are seen as tachycardia/tachypnoea (compensatory mechanisms), hypotension, and signs of poor end-organ perfusion (such as low urine output, confusion or loss of consciousness) (failure to compensate). Other signs should be looked for to establish the underlying cause for the shock to guide effective treatment. (Ledingham, 169-189)

Signs of severity

The severity of shock can be graded 1-4 based on the physical signs. This approximates to the effective loss of blood volume. The blood volume does not have to actually be lost from the circulation as an expansion in the volume of the circulatory system (e.g. in septic shock) will render the patient proportionally hypovolaemic. (Collins, 35-41)

Grade 1

Up to about 15% loss of effective blood volume (~750ml in an average adult who is assumed to have a blood volume of 5 liters). This leads to a mild resting tachycardia and can be well tolerated in otherwise healthy individuals. In the elderly or those with underlying conditions such as ischaemic heart disease the additional myocardial oxygen demands may not be tolerated so well.

Grade 2

Between 15-30% loss of blood volume (750-1500ml) will provoke a moderate tachycardia and begin to narrow the pulse pressure. The time taken for the capillaries to refill after 5 seconds of pressure (capillary refill time) will be extended.

Grade 3

At 30 - 40% loss of effective blood volume (1500 - 2000 ml) the compensatory ...