[Intensive care] Shock

Shock is a failure of the circulatory system to deliver sufficient oxygen to the tissues around the body. This is a medical emergency and there is a significant risk of imminent death.

As the tissues are not receiving sufficient oxygen, they begin to use anaerobic respiration to produce the energy which they need for cellular functions. Anaerobic respiration does not require oxygen but it produces lactate (lactic acid). This accumulates in the blood because it cannot be cleared sufficiently without oxygen. A high serum lactate correlates to a poor prognosis.

 

Types of shock

• Distributive : where the blood pressure falls, because the circulating volume is distributed throughout a larger space.
• Septic  
• Anaphylactic  
• Neurogenic 
• Hypovolaemic 
• Cardiogenic 
• Obstructive   
• Endocrine  

Hypovolaemic, anaphylactic and neurogenic shock are likely to respond to medical therapy. Septic shock has a relatively grave prognosis. Cardiogenic shock has an even larger mortality rate.

 

Management

In the setting of intensive care, patients are at very high risk of death and disability. The immediate priority in shock is to maintain the blood pressure to maintain adequate organ perfusion.

1. Give intravenous fluids to restore raise intravascular volume. This aims to increase cardiac filling until the preload is optimal. See the Frank-Starling law. Many recommend that treatment should raise central venous pressure (CVP) to a level greater than 8 mmHg. There is evidence that this may be too aggressive, since there is no benefit to adding fluid once the stroke volume is maximised. 
2. Give vasopressors to constrict the arterioles. This means that the force of the bloodstream is acting on a small cross-sectional area. This means the intravascular pressure is higher. The mean arterial pressure (MAP) should be raised to at least 65 mmHg. 
3. Give ionotropes to increase the heart rate and stroke volume of the heart. 
4. Correct the underlying cause as soon as possible. 

Vasopressors and inotropes are used mainly in an intensive care settings, because they can cause dangerous adverse effects. This includes:

• Necrosis and limb amputation. This occurs due to peripheral vasoconstriction, poor flow to the peripheries, and tissue hypoxia. 
• Ischaemia of the liver (hepatic), kidneys (renal), intestines (mesenteric) and heart (myocardial). This occurs due to vasoconstriction of the visceral arteries and organ hypoxia. 
• Angina and myocardial infarction. 
• Arrhythmias: bradycardia, tachycardia. 
• Life-threatening hypertension or hypotension.
• Other life threatening adverse effects unique to each medication. 

Psychological shock

In popular culture, characters who experience psychological trauma are described as "going into shock". This is a completely different phenomenon which is best described as acute stress reaction. There is no impact on the oxygen saturation of tissues. In the long-term this reaction may continue as post-traumatic stress disorder (PTSD). The term shock is probably used here because "feeling shocked" is an emotional response to unexpected psychological trauma.