Shock and Serum Lactate

Video Lecture:
youtu.be/Y8k3OGXY_Mg

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Shock and Serum Lactate

Shock is defined as a life-threatening condition characterized by inadequate oxygen delivery to tissues, which leads to cellular and tissue hypoxia. This state can result from various underlying mechanisms, including reduced blood flow, decreased circulating volume, impaired cardiac function, or vascular dysregulation.

Shock is commonly classified into four main types:
Hypovolemic Shock: Caused by significant loss of blood volume, such as from hemorrhage or severe dehydration.
Cardiogenic Shock: Results from the heart's inability to pump effectively, often due to conditions like myocardial infarction or heart failure.
Obstructive Shock: Occurs when blood flow is obstructed, for instance, by cardiac tamponade or pulmonary embolism.
Distributive Shock: Characterized by severe vasodilation, leading to inadequate blood flow despite normal or increased blood volume. This includes septic shock (due to infection), anaphylactic shock (due to allergic reactions), and neurogenic shock (due to spinal cord injury)

Serum lactate: 
Serum lactate is a useful marker to assess the adequacy of resuscitation by indirectly indicating the degree of tissue perfusion and oxygenation. 

Shock, by definition, involves inadequate organ perfusion and tissue oxygenation, leading to a reliance on anaerobic metabolism for energy production.  
A byproduct of this anaerobic metabolism is lactic acid. Therefore, elevated serum lactate levels indicate that the body has switched to anaerobic metabolism to produce energy, which suggests inadequate tissue perfusion.
Successful resuscitation aims to restore adequate blood flow, thus decreasing reliance on anaerobic metabolism and consequently, lowering serum lactate levels.  

Normal lactate levels are less than two millimoles per liter, with hyperlactatemia defined as lactate levels between 2 millimoles per liter and 4 millimoles per liter. Severe levels of lactate are 4 millimoles per liter or higher. A lactate level of 4.0 mmol/L or higher is considered significantly elevated and requires urgent medical evaluation due to increased risks of morbidity and mortality

Serial lactate measurements is helpful during resuscitation.
Trending lactate values over time helps clinicians understand:
The presence and severity of shock.
The patient's response to resuscitation efforts. 
A downward trend in lactate levels suggests improving tissue perfusion and successful resuscitation, while a static or upward trend warrants further investigation and more aggressive management.