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Dehydration is a particular concern in ill health as often fluid intake is reduced (poor appetite, nil by mouth, nausea) and often coincides with an increased output (vomiting, diarrhoea, haemorrhage, drains, fever). The elderly are at particular risk of dehydration as the effectiveness of the thirst response diminishes with age (Ainslie et al. 2002, Mentes 2006). When the osmolarity of the ECF increases, it encourages water out of the cell into the ECF, which eventually leads to cellular dehydration, impaired metabolism, disturbed cellular shape and impaired cellular function.

If the osmolarity of the ECF falls, water moves into the cell. If this continues, it will lead to water toxicity, causing cells to expand and eventually burst. Care should therefore be taken when administering intravenous fluids, as fluids that are of lower osmolarity than ECF (hypotonic) will cause a shift of water into the cells. Conversely, hypertonic solutions will cause a shift of fluid from the cells, causing dehydration. Maintenance fluids should usually be isotonic (have the same osmolarity as ECF) (Sheppard and Wright 2006).

Evidence-based approaches

Fluid and electrolyte balance monitoring and management are integral and vital to nursing care (Jevon and Ewens 2007). Alexander et al. 2000 suggest that nurses must have a good understanding of the concepts involved in fluid balance in order to recognize or anticipate imbalances and implement the correct interventions/care. Understanding of the physiological mechanisms will ensure that tasks such as fluid balance charting are carried out with understanding and thought.

Fluid balance charting allows healthcare professionals to carefully monitor the fluid input and output and calculate the fluid balance. This is usually measured over a 24-hour period (Jevon and Ewens 2007). A positive fluid balance indicates that the input has exceeded the output, and a negative result the reverse. Although fluid balance charts are a good indication of fluid balance, this is not an exact measurement, for several reasons. Some losses are insensible such as those from perspiration, respiratory secretions and immeasurable bowel losses. The calculation of fluid balance also relies heavily on the accurate measuring and charting of input and output, a skill documented in the literature as often being done poorly by nurses (Callum et al. 1999, Mooney 2007). For such measurements to be taken accurately may require additional interventions such as the need for catheterization. Current recommendations highlight that the benefits of accurate fluid balance measurements outweigh the risks associated with such procedures (Callum et al. 1999, NICE 2007). Table 8.2 shows the possible routes and sources of fluid intake and output.

Table 8.2 Fluid intake and output

Intake Output

Oral

Food and drinks

Normally 2000 mL/per day

Urine output

Normally approx 1500 mL/per day

Parenteral/intravenous

Maintenance fluids, IVI, intermittent drugs, flushes

Additional to or replaces oral intake

Faeces

Normally approx 100 mL/per day

Enteral

Nasal gastric/nasal jejostomy, percutaneous gastric jejostomy feed, flushes

Additional to or replaces oral intake

Perspiration

Normally approx 200 mL/day

Gastric secretions

Vomit, nasal gastric/gastrostomy drainage

Additional to normal output

Wounds and drains

Additional to normal output

Insensible losses

Perspiration, respiratory secretions

Additional to normal output

From Sheppard and Wright (2006).

The National Confidential Enquiry into Perioperative Deaths (Callum et al. 1999) highlights how important effective fluid balance management is and states that imbalance can lead to ‘serious postoperative morbidity and mortality’. Of the patients reviewed, 20% were found to have poorly kept fluid balance records, emphasizing the need for effective monitoring and record keeping; the report suggests that accurate fluid balance recording should be as important as the recording of prescriptions and medicine