Fluid and electrolyte balance monitoring and management are integral and vital to nursing care (Davies et al. [44], Jevon and Ewens [73]). The fluid balance chart serves as a non‐invasive tool for monitoring fluid status and guides the prescription and administration of intravenous fluids (Davies et al. [44]).

Fluid balance charting allows healthcare professionals to carefully monitor a patient's fluid input and output and calculate their fluid balance. This is usually measured over a 24‐hour period (Jevon and Ewens [73], Pinnington et al. [143]). A positive fluid balance indicates that the input has exceeded the output, and a negative fluid balance indicates the reverse – that is, that the output has exceeded the input. Although a fluid balance chart is a good indication of fluid balance, it 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, charting and calculating of input, output and overall balance. For such measurements to be taken accurately, additional interventions (such as catheterization) may be required. The benefit of accurate fluid balance measurement in critically or acutely unwell patients must be considered to outweigh the risks associated with such interventions (NICE [122]). Table 8.3 identifies routes and sources of fluid intake and output.

Although a very useful tool, fluid balance charting should not be used in isolation. When considering fluid and electrolyte balance, physical assessment and monitoring electrolyte levels in the plasma should be integral to the observation and care of a patient with actual or potential fluid and electrolyte imbalances (NICE [122]).

Nursing assessment is discussed in detail in Chapter c02: Admissions and assessment, and the assessment of a patient's fluid status should be an integral part of any admission. There should also be subsequent daily assessments, particularly if the patient is critically ill, if a fluid deficit has been identified, if the patient requires continuous intravenous fluid replacement or if the patient is at risk of acute kidney injury. See Table 8.4 for details of what should be included in a fluid status assessment.

A simple way to assess whether a patient will be responsive to fluid replacement is to perform a passive leg raise (Figure 8.7). Raising the legs to 45° while simultaneously lowering the patient from a semi‐recumbent position to supine can cause a fluid shift from the legs to the central vascular system, which mimics a fluid bolus (Pickett et al. [142]). This can increase blood pressure and indicate whether the patient is likely to respond to fluid resuscitation (Cooke et al. [40], Monnet et al. [104], Pickett et al. [142]). However, the existing evidence on the use of the passive leg raise focuses on critically ill patients and evaluating the response using invasive cardiac output monitoring (such as LiDCO) to assess change in stroke volume. Assessing changes in systolic blood pressure has been suggested (Pickett et al. [142]); however, the lack of quality evidence to support the accuracy of this method means its routine use in practice is not recommended.

Haemodynamic monitoring methods in critical care (such as LiDCO, PiCCO or oesophageal Dopplar) can help to assess fluid status and efficacy of fluid challenges through the analysis of stroke volume as well as cardiac output, central venous pressure and mean arterial pressure (Cecconi et al. [31], Michard [103], Polderman and Varon [144]). Changes in cardiac output should be assessed 1 minute after a fluid challenge (Aya et al. [7]).

Throughout the literature, it is recognized that fluid balance monitoring is often poorly performed by nurses. Many authors identify barriers to accurate monitoring of fluid status and suggest that nurses must have a good understanding of the concepts involved in fluid balance in order to recognize and anticipate imbalances (Alexander and Allen [3], Davies et al. [44], Nazli et al. [107], NICE [122], Pinnington et al. [143], Shepherd [168]). They suggest the use of a fluid management policy to guide both nursing and medical staff and to standardize practice. NICE ([122]) offers guidance on the management of adult patients in hospital receiving intravenous fluids; it suggests that history taking, full clinical assessment, review of current medications, fluid balance charts and laboratory investigations are all required in order to fully assess the need for intravenous fluid and/or electrolyte administration.

Understanding of the physiological mechanisms and potential implications will ensure fluid balance charting is carried out with knowledge and thought. Nazli et al. ([107]) suggest that it is vital for staff involved in patient care to understand why fluid balance recording is important in maintaining patient safety. NICE ([122]) guidance on intravenous fluid therapy in adults has highlighted detrimental effects of fluid overload, such as pulmonary oedema, cardiac failure, cerebral oedema, impaired bowel function, delayed wound healing and tissue breakdown (Cooke et al. [40], Gross et al. [63]), and therefore the importance of accurate fluid balance monitoring. Recommendations include the need for improved accuracy and the need for medical staff to review these charts regularly, particularly prior to prescribing any intravenous fluids. Nazli et al. ([107]) highlight the implications of incorrect fluid balance calculations (by nurses and doctors), which may lead to under‐ or overprescribing of intravenous fluids and ultimately affect patient outcome. Inaccurate fluid balance monitoring can accumulate over the length of a patient's stay due to underestimation of fluid gains and losses. Measuring patients’ weights on a daily basis, where able, can be a reliable method of assessing fluid overload (Alexander and Allen [3], Davies et al. [44], NICE [122]). The organization Kidney Disease: Improving Global Outcomes (KDIGO [75]) uses urine output to classify the stage of acute kidney injury, emphasizing the need for accurate fluid output monitoring for any patient at risk of acute kidney injury (see the section on acute kidney injury below).

NICE ([122]) recommends that all patients receiving intravenous fluids should have at least a daily assessment of their fluid status and that clinicians should be mindful of the electrolyte content of the intravenous fluids they prescribe. Over‐administration of normal saline 0.9% can lead to hyperchloraemia and metabolic acidosis, which are linked to increased mortality. This can be avoided by using a buffered salt solution such as compound sodium lactate (also called Hartmann's solution) (Finfer et al. [52], Gross et al. [63]). Recent studies have compared saline and buffered salt solutions in relation to adverse renal events (Self et al. [160], Semler et al. [161]). No difference was found in mortality rates, but buffered solutions were found to be less harmful to patients with poor renal function.

With regard to fluid resuscitation, the current recommended practice is to attempt to restore normovolaemia with crystalloids (Resuscitation Council [150], Rhodes et al. [152]) but avoid dextrose as this can rapidly dilute plasma sodium and lead to the redistribution of fluid from the intravascular space and because it may cause hyperglycaemia. Albumin administration is suggested as a supplement to crystalloids in sepsis (NICE [122], Rhodes et al. [152]) but is contraindicated in traumatic brain injury (Gross et al. [63]). The Resuscitation Council (UK) ([150]) and NICE ([123]) suggest a bolus of 500 mL of warmed crystalloid solution (e.g. Hartmann's solution or 0.9% sodium chloride) over less than 15 minutes if the patient is hypotensive. Use smaller volumes (e.g. 250 mL) for patients with known cardiac failure or trauma and use closer monitoring (listen to the chest for crackles after each bolus). Rhodes et al. ([152]) recommend 30 mL/kg within the first 3 hours for sepsis‐induced hypoperfusion.

A wide variation in practice can be evident across trusts and even individual departments. NICE ([122]) offers clear, standardized guidance with regard to intravenous fluid administration for adult patients in hospital (excluding patients with diabetes, severe liver or renal disease, pregnant women and patients under the age of 16 years). A summary and useful form of this guidance can be found in the section on algorithms for intravenous fluid therapy in adults in NICE ([122]). See also Figure 8.8.

Synthetic colloid fluids containing hydroxyethyl starch have previously been utilized in fluid replacement. However, the relative benefits and risks of these have come under scrutiny and it was decided by the European Medicines Agency ([51]) that production and use of these be suspended. If a colloid is deemed to be necessary, NICE ([123]) recommends human albumin 4.5% for use only in patients with sepsis and shock.