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Module 3 : Prescribing

 

 

Balancing benefits and risks

 

In general, relatively well patients are probably better given slightly more fluid, rather than less. Patients with well functioning kidneys are able to remove moderate amounts of excess fluid without difficulty, whereas dehydration can predispose to a number of problems including pre-renal failure and venous thromboembolism.

 

However, some groups of patients are at significant risk of ‘fluid overloading’, and you should always check for these things before prescribing fluids for a patient:

 

 

Heart failure

 

In these patients the heart has poor forward-pumping function. Fluid given intravenously is likely to collect in either the systemic or pulmonary venous system and so raise the hydrostatic pressure in these areas. This may cause transudative fluid loss leading to peripheral or pulmonary oedema, the latter of which may be fatal if uncorrected.

 

 

Liver failure

 

These patients may have low blood albumin and so low colloid oncotic pressure. This also may cause transudative peripheral or pulmonary oedema in susceptible patients if high volumes of fluid are administered.

 

 

Chronic kidney disease

 

These patients are at risk of fluid overload if large volumes of intravenous fluid are administered, as their ability to excrete excess fluid is impaired. Generally however, up to the point of needing dialysis, most patients with CKD remain in fluid balance, although some require diuretics to maintain this. Only those with established renal failure who are on dialysis produce little or no urine.

 

 

  Test Yourself !  
   
  What would you prescribe for a clinically stable patient with known heart failure who's blood pressure today has dropped to 70/45 (from a baseline of 120/80)?

That's correct, well done!
 

Administer 250ml of normal saline and reassess in 30 mins – Correct answer! Most stable patients who have dropped their blood pressure a bit have done so because they are dehydrated. A small volume of fluid (such as 250-500ml) given over a short period (eg 30 mins) is a safe and effective method to determine whether they are in need of more fluids. In this case it would be better to give the lower end of this (250ml) as the patient is at increased risk of fluid overload. This test is called a fluid challenge. If after 30 mins the patient has not developed any oedema (most importantly pulmonary oedema – always listen to the patient's chest!) and the blood pressure has improved slightly, it suggests they are in need of more fluids. If there is no change in their condition or they have worsened, escalate the problem to your seniors.

 

Fluid restrict the patient and reassess the patient in 6 hours –wrong answer! Patients very rarely need to be fluid restricted, and this is a decision to be made by a senior clinician. Patients with dropping blood pressure are potentially at serious risk and must be reassessed regularly (every 30 mins at least).

 

Administer 1L of normal saline and reassess in 30 mins – wrong answer. Regular reassessment is good, however 1L of fluid would be too much to give this patient quickly, as they are at risk of fluid overload.

 

Administer 1L of normal saline and reassess in 6 hours – wrong answer! See information above.

 

Sorry, that's incorrect!
 

Administer 250ml of normal saline and reassess in 30 mins – Correct answer! Most stable patients who have marginally dropped their blood pressure have done so because they are dehydrated. A small volume of fluid (such as 250-500ml) given over a short period (eg 30 mins) is a safe and effective method to determine whether they are in need of more fluids. In this case it would be better to give the lower end of this (250ml) as the patient is at increased risk of fluid overload. This test is called a fluid challenge. If after 30 mins the patient has not developed any oedema (most importantly pulmonary oedema – always listen to the patient's chest!) and the blood pressure has improved slightly, it suggests they are in need of more fluids. If there is no change in their condition or they have worsened, escalate the problem to your seniors.

 

Fluid restrict the patient and reassess the patient in 6 hours –wrong answer! Patients very rarely need to be fluid restricted, and this is a decision to be made by a senior clinician. Patients with dropping blood pressure are potentially at serious risk and must be reassessed regularly (every 30 mins at least).

 

Administer 1L of normal saline and reassess in 30 mins – wrong answer. Regular reassessment is good, however 1L of fluid would be too much to give this patient quickly, as they are at risk of fluid overload.

 

Administer 1L of normal saline and reassess in 6 hours – wrong answer! See information above.

 

 

 

 

Patients who are taking large amounts of fluid containing medicines

 

It is important to note that a significant proportion of drugs are administered by intravenous infusion. These may be made up in a collectively significant amount of fluid which may be less apparent on the prescription chart, or not appear on the fluid balance chart.

 

 

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