3.2 Clinical signs and stages of shock 

3.2.1 Clinical signs of shock 

• Hypotension, a mean arterial pressure less than60 mmHg or systolic blood pressure less than 90 mmHg in previously normotensive persons, is perhaps the hallmark of acute circulatory failure. In most types of shock, especially shock caused by severe blood loss, the arterial blood pressure decreases at the same time as the cardiac output decreases. However, the arterial pressure can often be seriously misleading. At times, a person may be in severe shock and still have an almost normal arterial pressure because of powerful nervous reflexes that keep the pressure from falling. At other times, the arterial pressure can fall to half of normal, but the person still has normal tissue perfusion and is not in shock. 
• Signs of tissue hypoperfusion: These are usually recognized at three levels: 
Cutaneous: The skin is usually vasoconstricted, cold, and clammy. 
Poor filling of peripheral veins and nail beds (decreased capillary refill) is a better sign than a falling blood pressure. 
Collapsed peripheral veins 
Renal: A reduction in renal perfusion is manifested in adults by a fall in urine output below 0.5 mL/kg/h and, in more severe cases, below 20 mL/h. 
Neurologic: This can, of course, be appreciated only in the unanesthetized, unsedated patient. 
Decreased cerebral perfusion is demonstrated by an altered intellect, with disorientation and confusion, and lack of collaboration; there is often obtundation, but coma develops only in advanced stages of multiple organ failure.
• Biologic signs of altered cellular oxygen availability: The development of anaerobic metabolism is manifest by the development of hyperlactatemia and metabolic acidosis. 
  

3.2.2: Stages of Shock: Look table 3:1