The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [254]
Cook et al. 2004 describe the importance of correct fluid balance monitoring and recording, not only volumes but the type of fluid administered. They explain that the accurate recording of fluid balance should have the same emphasis and importance as prescription charting.
Fluid overload/hypervolaemia
Underestimating the fluid balance may lead to continued or increased administration of IV fluids, which if monitored incorrectly could result in circulatory overload. Excess IV fluid administration is not the only cause of circulatory overload, which can also result from acute renal failure, heart failure and intake of excessive sodium.
In health, homoeostatic mechanisms exist to compensate and redistribute excess fluids but in ill health, these mechanisms are often inadequate, leading to increasing circulatory volumes. As the volume within the circulatory system rises, so does the hydrostatic pressure, which when excessive results in leaking of fluid from the vessels into the surrounding tissues. This is evident as oedema, initially apparent in the ankles and legs or buttocks and sacrum if the patient is in bed. This can progress to generalized oedema, where even the tissues surrounding the eyes become puffy and swollen.
A bounding pulse and an increased blood pressure are also signs of fluid overload, as is an increased cardiac output and raised central venous pressure (Edwards 2000).
One of the most dangerous symptoms of fluid overload is pulmonary oedema, which occurs when the hydrostatic pressure within the vessels causes congestion within the pulmonary circulation, increasing the hydrostatic pressure there and causing fluid to leak into the lungs and pulmonary tissues (Casey 2004). This presents with respiratory symptoms, including shortness of breath, increased respiratory rate, a cough, often associated with pink frothy sputum and finally reduced oxygen saturations due to inadequate gaseous exchange at the alveolar level (Casey 2004). Left untreated, this can be fatal as the lungs are failing to provide essential cells and organs with oxygen, which would eventually cause organ dysfunction and then failure.
Cardiac ischaemia can also result from fluid overload, not only from the reduced availability of oxygen to the cardiac cells due to the pulmonary oedema, but also from the increase in volume causing the cardiac muscle to stretch, leading to cell damage (Alexander et al. 2000).
Treatment of hypovolaemia would involve restricting fluid intake, monitoring electrolytes and using diuretics in an attempt to offload some of the excess fluid. Vasodilators may also be considered to reduce the pressure in the vessels. If these mechanisms fail, it may be necessary to use renal replacement therapy to drive the fluid out of the circulation.
In some cases fluid overload is part of the disease process. However, with effective monitoring and fluid balance recording and assessment, it may be possible to avoid the devastating complications.
Hypovolaemia/dehydration
Dehydration refers to a negative fluid balance, when the fluid output exceeds the fluid intake (Jevon 2010). Overestimation of the fluid balance may lead to inadequate replacement of lost fluids. Dehydration can, however, be caused by a loss of fluids to ‘third spaces’ such as ascites or lost due to a reduction in colloid osmotic pressure (hypoalbuminaemia) (Casey 2004), losses which are not easy to account for. Fluid balance charts should therefore always be used in association with physical assessment of the patient, weight measurement and laboratory results.
There are three categories of dehydration (Mentes 2006) – isotonic, hypertonic and hypotonic – each related to the type of fluid and solutes lost. Isotonic describes the loss of both water and sodium from the ECF; hypertonic is excessive loss of water only, which leads to a rise