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Module 3 : Prescribing

 

 

Intravascular Repletion

 

In emergency situations patients may become hypotensive (shocked). This may be through blood or plasma loss (hypovolemic shock), blood redistribution (distributive shock) or due to failure of the heart to adequately pressurise the blood (cardiogenic shock). The effect of this low pressure is poor tissue perfusion, leading to ischemia and organ failure, which may be fatal.

 

Therefore the aim of emergency fluid resuscitation is simply to provide extra volume to increase the blood pressure. Therefore, unlike in maintenance fluid prescribing, there is little interest in the water or electrolyte content of the fluid (except that it is never a good idea to give patients large volumes of potassium containing fluids quickly, due to the risk of hyperkalaemia).

 

 

  Test Yourself !  
   
  Which of the following fluids would be ideal for intravascular repletion in an emergency situation?

That's correct, well done!
 

Doesn't matter – Correct answer: Logically, as colloids are designed to stay mostly within the intravascular space, you might expect these to be best fluids in a resus situation. However, large multicentre international trails have shown that there is no difference in mortality in patients resuscitated with colloids over normal saline or other crystalloids. The key in a resus situation is to give whichever fluid is available, as quickly as possible. Initially, any fluid you give a patient will be in the intravascular space, if you gave it intravenously! It takes some time (aprox 20 min) for the fluid to redistribute across the body, by which time hopefully the patient is more stable and in experienced hands. It is also important to note that colloid fluids (especially gelatin based) have a significant rate of allergy and anaphylaxis associated with their use, which may be worth considering in a resus situation. However, the bottom line is to give the most readily available fluid, as quickly as possible (although try to avoid pre-added potassium!)

 

Colloid

 

Crystalloid

 

Sorry, that's incorrect!
 

Doesn't matter – Correct answer: Logically, as colloids are designed to stay mostly within the intravascular space, you might expect these to be best fluids in a resus situation. However, large multicentre international trails have shown that there is no difference in mortality in patients resuscitated with colloids over normal saline. The key in a resus situation is to give whichever fluid is available, as quickly as possible. Initially, any fluid you give a patient will be in the intravascular space, if you gave it intravenously! It takes some time (aprox 20 min) for the fluid to redistribute across the body, by which time hopefully the patient is more stable and in experienced hands. It is also important to note that colloid fluids (especially gelatin based) have a significant rate of allergy and anaphylaxis associated with their use, which may be worth considering in a resus situation. However, the bottom line is to give the most readily available fluid, as quickly as possible (although try to avoid pre-added potassium!)

 

Colloid

 

Crystalloid

 

 

 

 

Note that the speed at which you can infuse fluid into a patient depends on two important factors which are within your control:

 

1.The size of the cannula

2.The pressure under which the fluid is being squeezed into the patient

 

Therefore, it is important to ensure you use the largest cannula possible, in two places, and put pressure on the fluid bags (use pressure bags or get someone to squeeze them!)

 

 

  Test Yourself !  
   
  Which of the following would be the best cannula to use in a resus situation?

That's correct, well done!
 

Brown / Orange 14G - These are the biggest cannula. By the Hagen–Poiseuille law, the rate of infusion increases by the power of four for each unit increase of the cannula radius, and so a bigger cannula can infuse much much more fluid than a small one in a given unit of time. The exact colour of the 14G cannula varies slightly by trust, so check locally.

 

Blue 22G

Pink 20G

Green 18G

 

Sorry, that's incorrect!
 

Brown / Orange 14G - These are the biggest cannula. By the Hagen–Poiseuille law, the rate of infusion increases by the power of four for each unit increase of the cannula radius, and so a bigger cannula can infuse much much more fluid than a small one in a given unit of time. The exact colour of the 14G cannula varies slightly by trust, so check locally.

 

Blue 22G

Pink 20G

Green 18G

 

 

 

 

Once venous access has been established in these patients, it is useful to take a baseline blood sample for FBC, U+E and group/cross-match, before the fluid infusions start.

 

 

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