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Fluid Balance

Fluid balance can alter with disease and illness so it important to be aware of how much fluid is in the body, taking steps such as measuring urea and electrolytes levels


Gail P. Mooney, MSc, PG Social Research Methods, RGN, lecturer, School of Health Science, University of Wales, Swansea.


Body fluids are regulated by fluid intake, hormonal controls, and fluid output (Potter and Perry, 2001).

Normal/ideal values

Approximately 60% of body weight in males constitutes total body fluid, with 52% in females. A reduction in body fluids can have major effects on the body: a reduction of 5% will cause thirst, a reduction of 8% will cause illness and a 10% reduction in fluid can cause death (Carroll, 2000). Age, gender and body fat influence the proportion of body fluid.

Disturbance in fluid balance

Hypovalemia is the term used for loss of fluid and hypervalemia is the term used when a patient has fluid overload.

There are a number of factors that will cause fluid loss and gain:


  • Diarrhoea;
  • Vomiting;
  • Sweating/fever;
  • Haemorrhage;
  • Diuretics;
  • Excessive urination.


  • Congestive cardiac failure;
  • Renal failure;
  • High sodium intake;
  • Cirrhosis of the liver;
  • Over infusion of intravenous fluids.

All of the above can be symptoms of disease and illness.

Another factor in fluid loss to consider is the patient’s physical mobility/abilities. If a patient is physically disabled they may not be able to access fluid. A patient who has had a cerebral vascular accident may not be able to physically take and drink the fluid. Some patients with continence problems may restrict their fluid intake believing this will alleviate the problem.

Recording fluid balance

The nursing assessment of fluid balance should include: the patient’s history, physical examination, clinical observation and interpretation of laboratory results (Place and Field, 1997).

A detailed account of the patient’s history should be taken especially the fluid intake and output. The nurse may have to rely on relatives and carers to give this information if the patient is unable to.

A clinical assessment of the patient should be carried out including vital observations such as measuring the blood pressure, pulse, respiration and temperature. The patient’s physical appearance should be noted: attention should be paid to the skin, tongue and face. The general well being of the patient is also a good indication of fluid loss or gain.

Central venous pressure (CVP) is a measurement of pressure in the right atrium of the heart. The CVP recording is a good indication to determine the amount of fluid contained within the body.

Table 1 gives an indication of clinical assessment made possible through measuring fluid balance (Place and Field, 1997).

Table 1. Observations related to fluid balance






Fluid depletion



Fluid overload












Blood pressure



Lowered smaller pulse pressure



Normal or raised






Rapid, shallow



Rapid, moist cough






Rapid, weak, thready






Urine output



Reduced, concentrated



Increased or decreased if heart is failing






Dry, less elastic









Thick, viscous



Copious, frothy






Dry, coated












No disturbance






Sunken eyes (severe depletion)



Peri-orbital oedema






May be raised



No disturbance



Patients with an imbalance in body fluid, whether loss or gain, would present with more than one of the above symptoms.

Patients’ intake and output are recorded on fluid balance charts, and accurate recording is crucial for their wellbeing. Output is often recorded as passed urine ++ or up to toilet, which is far from accurate and does not give a clear indication of the amount of urine passed.

An imbalance of electrolytes in the blood can cause fluid imbalance. Laboratory blood tests such as urea and electrolytes, glucose, magnesium, calcium will determine discrepancies and govern the treatment required to resolve the problem (Table 2) (Sheppard, 2000).


Table 2. Laboratory results associated with fluid imbalance



Fluid loss



Fluid gain


  • Increased serum osmolality
  • High urine osmolality and specific gravity
  • Raised haematocrit
  • Increased plasma-urea concentration


  • Reduced plasma urea
  • Reduced haematocrit



When and how often should the fluid balance be recorded?

Fluid balance is continually monitored on those patients who have already shown signs and symptoms of fluid imbalance. Other patients at risk, such as those in critical care or who have just undergone surgery, should be closely monitored.


  • Accurate measurement in the recording of patients’ intake and output is crucial to the patient’s wellbeing;
  • Close monitoring and observation of the patient will provide early detection of fluid imbalance;
  • Close monitoring of patients who are administered diuretics is essential.