Circulation (C)
 
In almost all medical and surgical emergencies, consider hypovolaemia to be the primary cause of shock, until proven otherwise. Unless there are obvious signs of a cardiac cause, give intravenous fluid to any patient with cool peripheries and a fast heart rate. In surgical patients, rapidly exclude haemorrhage (overt or hidden). Remember that respiratory pathology, such as a tension pneumothorax, can also compromise a patient’s circulatory state. This should have been treated earlier on in the assessment.

1. Look at the colour of the hands and digits: are they blue, pink, pale or mottled?
    
2. Assess the limb temperature by feeling the patient’s hands: are they cool or warm?
    
3. Measure the capillary refill time (CRT). It is assessed by applying cutaneous pressure for five seconds on a fingertip held at heart level (or just above) and counting the time it takes for capillary refill after the pressure has been released. The normal value for CRT is usually less than two seconds.
    
4. Assess the state of the veins: they may be under-filled or collapsed when hypovolaemia is present.
    
5. Count the patient’s pulse rate.
    
6. Palpate all the peripheral and central pulses, assessing for presence, rate, quality, regularity and equality. Barely palpable pulses suggest a poor cardiac output, whilst a bounding pulse may indicate sepsis.
    
7. Measure the patient’s blood pressure. Even in shock, the blood pressure may be entirely normal, as compensatory mechanisms increase peripheral resistance in response to reduced cardiac output. Where possible, the diastolic and systolic values should be noted. A low diastolic BP suggests arterial vasodilatation (as in anaphylaxis or sepsis). A narrowed pulse pressure (difference between systolic and diastolic pressures; normally ~ 35-45 mmHg) suggests arterial vasoconstriction (cardiogenic shock or hypovolaemia).
    
8. Auscultate the heart.
    
9. Look for other signs of a poor cardiac output, such as reduced level of consciousness and, if the patient has a urinary catheter, oliguria (urine volume < 0.5 ml kg^-1 hour^-1).
    
10. Examine the patient thoroughly for external haemorrhage from wounds or drains or evidence of concealed haemorrhage (e.g., thoracic, intraperitoneal or into gut). Remember that intrathoracic, intrabdominal or pelvis blood loss may be significant, even if drains are empty.
     
11. The specific treatment of cardiovascular collapse will be determined by the cause, but should be directed at fluid replacement, haemorrhage control and restoration of tissue perfusion. Seek out the signs of conditions that are immediately life threatening, e.g., cardiac tamponade, massive or continuing haemorrhage, septicaemic shock, and treat them urgently.
     
12. Insert one or more large (14 or 16 G) intravenous cannulae. Use short, wide-bore cannulae, as they have the highest flow rate.
     
13. Take blood from the cannula for routine haematological, biochemical, coagulation and microbiological investigations, and cross-matching, before infusing intravenous fluid.
     
14. Give a rapid fluid challenge (over 5-10 minutes) of 500 ml of warmed crystalloid solution if the patient is normotensive. Give 1 litre, if the patient is hypotensive. Use smaller volumes (e.g., 250 ml) for patients with known cardiac failure and use closer monitoring (listen to the chest for crepitations after each bolus, consider a CVP line).
     
15. Reassess the pulse rate and BP regularly (every 5 minutes), aiming for the patient's normal BP or, if this is unknown, a target > 100 mmHg systolic.
     
16. If the patient shows no signs of improvement, the fluid challenge can be repeated.
     
17. If symptoms and signs of cardiac failure (dyspnoea, increased heart rate, raised JVP, a third heart sound and pulmonary crepitations on auscultation) occur, decrease the fluid infusion rate or stop the fluids altogether. Seek alternative means of improving tissue perfusion (e.g., inotropes or vasopressors).