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Module 1 : Physiology

 

 

In Disease

 

In disease states, the body’s ability to maintain fluid homeostasis may be impaired. There are two main mechanisms for this:

 

1. Normal mechanisms of water loss/gain may be disturbed

2. Abnormal mechanisms of losses or gains may occur

 

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It is important to note that these losses and gains can be hugely variable, e.g. DKA may involve fluid losses of 10 litres or more (and as such would require equally high volumes of resuscitation fluids)!

 

The human body is very well adapted to maintain homeostasis even in fairly extreme fluctuations in fluid input/output. The kidneys play a vital role in this and can easily handle (and remove) huge volumes of extra fluid in health. However, in disease states (eg CKD), the kidneys are much less efficient and these patients are at high risk of fluid overload.

 

 

  Test Yourself !  
   
  A patient with normal renal and cardiac function has been nil by mouth (NBM) for 3 days. She has been receiving 3.0 L per day of IV fluids. She is currently well hydrated and the nurses have not reported any other fluid inputs or outputs. Assuming insensible losses of 1000 ml each day, what has her urine output been?

That's correct, well done!
 

~ 2000 ml per day - This is the correct answer. If she has an input of 3L per day and insensible losses of 1L per day, this leaves 2L of output remaining. As no other inputs or outputs have been recorded, we must assume the rest of the output has been in the form of urine as fluid cannot disappear – all that goes in must come out somewhere!

 

There are two exceptions to this rule:

 

1. (Most common) not all the inputs and outputs have been recorded on the fluid balance chart. This may happen in a patient who has been drinking freely and so it is difficult to determine input. It is also practically very difficult to measure urine output if the patient is not catheterised, so in these cases the fluid chart may be somewhat inaccurate.

 

2. The patient themselves is not in a fluid neutral state (ie, overall they are gaining or losing fluid). This is unlikely to be the case here as we are told in the question that she is 'well hydrated'. There's much more about fluid balance charts, clinical assessment and fluid retention in the upcoming modules. Stay tuned!

 

~ 500 ml per day

~ 1000 ml per day

~ 1500 ml per day

 

Sorry, that's incorrect!
 

~ 2000 ml per day - This is the correct answer. If she has an input of 3L per day and insensible losses of 1L per day, this leaves 2L of output remaining. As no other inputs or outputs have been recorded, we must assume the rest of the output has been in the form of urine as fluid cannot disappear – all that goes in must come out somewhere!

 

There are two exceptions to this rule:

 

1. (Most common) not all the inputs and outputs have been recorded on the fluid balance chart. This may happen in a patient who has been drinking freely and so it is difficult to determine input. It is also practically very difficult to measure urine output if the patient is not catheterised, so in these cases the fluid chart may be somewhat inaccurate.

 

2. The patient themselves is not in a fluid neutral state (ie, overall they are gaining or losing fluid). This is unlikely to be the case here as we are told in the question that she is 'well hydrated'. There's much more about fluid balance charts, clinical assessment and fluid retention in the upcoming modules. Stay tuned!

 

~ 500 ml per day

~ 1000 ml per day

~ 1500 ml per day

 

 

 

 

 

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