Keywords: Fluid balance/Input/Output/ Nursing Practice /Overhydration Review ●This article has been double-blind Fluid balance peer reviewed

Assessing hydration status and measuring fluid balance can ensure optimal hydration Measuring and managing fluid balance headaches, fatigue In this article... 5 key and dry skin. What fluid balance is and how fluid moves around the body points Severe dehydra- Fluid balance is tion can lead to Causes and signs and symptoms of dehydration and 1the balance of hypovolaemic overhydration the input and shock, organ How to assess fluid balance, including clinical assessment output of fluids in failure and death the body to allow The three How to keep an accurate fluid balance chart metabolic pro- 4elements to cesses to function assessing fluid To assess fluid balance and Author Alison Shepherd is tutor in nursing, balance, including what fluid balance is, 2balance, hydration status department of primary care and child health, and how and why it is measured. It also dis- nurses need to are: clinical Florence Nightingale School of Nursing and cusses the importance of measuring fluid know about fluid assessment, body Midwifery, King’s College London. balance accurately, and the health implica- compartments in weight and Abstract Shepherd A (2011) Measuring and tions of dehydration and overhydration. the body and how output; review of managing fluid balance. Nursing Times; fluid moves fluid balance 107: 28, 12-16. What is fluid balance? between these charts; and review Ensuring patients are adequately hydrated Fluid balance is a term used to describe the compartments of blood chemistry is an essential part of nursing care, yet a balance of the input and output of fluids in Dehydration is Fluid balance recent report from the Care Quality the body to allow metabolic processes to 3defined as a 5recording is Commission found “appalling” levels of care function correctly (Welch, 2010). 1% or greater loss often inadequate in some NHS hospitals, with health Around 52% of total body weight in of body mass as a or inaccurate often professionals failing to manage dehydration. women and 60% in men is fluid. This con- result of fluid loss. because of staff This article discusses the importance of sists of and molecules containing, Symptoms include shortages, lack of hydration, and the health implications of for example, , and potas- impaired cognitive training or lack of dehydration and overhydration. It also sium (Mooney, 2007). These compounds function, time provides an overview of fluid balance, disassociate into particles which carry including how and why it should be an electrical charge; these particles in solu- measured, and discusses the importance tions are called . For example, of accurate fluid balance measurements. sodium chloride (NaCl) dissolves in solu- tion to form an equal number of positively ater is essential for life, charged sodium (Na+) ions, and negatively and maintaining the cor- charged chlorine (Cl-) ions (Waugh, 2007). rect balance of fluid in the Plasma electrolytes are balanced as it is Wbody is crucial to health important to have the correct concentration (Welch, 2010). of ions in the blood, especially sodium, However, according to a recent report and magnesium. Too much or from the Care Quality Commission (2011), too little of these electrolytes can cause car- some hospital patients are not being given diac arrhythmias (Docherty, 2006). enough water to drink. The report sug- To make a competent assessment of gests fluids are being left out of reach, or fluid balance, nurses need to understand are not being given at all for long periods. the within the body This article provides an overview of fluid and how fluid moves between these Dehydration affects brain function

12 Nursing Times 19.07.11 / Vol 107 No 28 / www.nursingtimes.net For more articles on fluid balance, go to Nursing nursingtimes.net/fluidbalance Times.net

fig 1. types of fluids

48% 40% Fluids comprise an solids solids average of 52% to Tissue cells 60% body weight

52% 60% 2/3 fluids fluids intracellular fluid (icf) TOTAL BODY WEIGHT FEMALE BODY TOTAL WEIGHT MALE BODY TOTAL

1/3 80% extracellular interstitial fluid (ecf) fluid

20% plasma Blood capillary compartments (Davies, 2010). Two-thirds spaces is determined by hydrostatic and disorders, such as glomerulo-nephritis, of total body fluid is intracellular, and the osmotic pressures (Day et al, 2009): and liver failure remaining third is , » Hydrostatic pressure is created by the (Schrier, 2007; Waugh, 2007). which is divided into plasma and intersti- pumping action of the heart, and the tial fluid (Docherty and McIntyre, 2002) effect of gravity on the blood within the Maintaining fluid balance (Fig 1). There is also a third space, known as blood vessels (Scales and Pilsworth, Total fluid volume fluctuates by less than “transcellular fluid”, which is contained in 2008); 1%, and fluid intake should be balanced by body cavities, such as cerebral spinal fluid » Osmotic pressure is generated by the fluid loss (Scales and Pilsworth, 2008; and synovial, peritoneal and pleural fluids molecules in a (Day et al, Thomas and Bishop, 2007). (Day et al, 2009). 2009). When generated by the presence Water intake is obtained from fluid and It is important to remember that, of molecules in solution it is in the diet, and is mostly lost through although these fluid compartments are called colloid oncotic pressure. urine output. It is also lost through the classed as separate areas, water and elec- Osmotic pressure created by dissolved skin as sweat, through the respiratory trolytes continually circulate between electrolytes in solution is called tract, and in faecal matter (Waugh 2007). them (Timby, 2008). crystalloid oncotic pressure (Scales and Fig 2 shows the normal balance of water Pilsworth, 2008). intake and output. Movement of fluids In healthy people, protein molecules Fluid intake is mainly regulated by Fluid circulates between compartments by are normally too large to pass out of the , a natural response to fluid deple- diffusion. This is “the random movement of capillaries into the interstitial fluid. This tion, and is accompanied by decreased particles from regions where they are highly is because of the tight intracellular junc- secretion of saliva and dryness of the oral concentrated to areas of low concentration. tions between adjacent endothelial cells in mucosa (Waugh, 2007). Movement continues until the concentra- the capillary wall (Rassam and Counsell, As the osmotic concentration of the tion is equally distributed” (Casey, 2004). 2005). Compromising the integrity of blood increases, this draws water from the This is normally a passive process but it these tight intracellular junctions allows cells into the blood. This dehydrates spe- can be facilitated by a carrier molecule, protein molecules to pass to the interstitial cific brain cells called , usually a specialist protein (Davies, 2010). spaces. The subsequent accumulation of which stimulate and the release Fluid also moves by osmosis, defined by tissue fluid is known as oedema (Ganong, of antidiuretic hormone (ADH). ADH Montague et al (2005) as “the flow of water 2000). reduces water loss by lowering urine across a semipermeable membrane from a Oedema can be caused by a number of volume, producing urine that is more con- dilute solution to a more concentrated pathological mechanisms, such as venous centrated (Thornton, 2010). When water solution until stability is reached”. congestion. This increases venous hydro- intake is high, less ADH is produced, so static pressure, common in disorders such the kidneys produce large quantities of Formation of tissue fluid as cardiac failure (Paulus et al, 2008). A dilute urine (Scales and Pilsworth, 2008). Distribution and movement of water decrease in plasma oncotic pressure causes During times of fluid insufficiency, the between the intracellular and interstitial the oedema associated with common renal adrenal glands produce the hormone Fotolia

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, which stimulates the reab- sorption of sodium from the distal renal fig 2. fluid intake and loss tubules and collecting ducts. This reab- Sources: McMillen and Pitcher (2010); Scales and Pilsworth (2008); Waugh (2007) sorption of sodium causes the water in the collecting ducts to be reabsorbed, main- Oral fluids and food (2,300ml) Urine output (1,500ml) taining . Water lost through faeces, sweat and evaporation cannot be regulated in the same way by the body, and is influenced by dietary intake, illness and the environ- ment (Scales and Pilsworth, 2008). A fluctuation in fluid volume of just 5-10% can have an adverse effect on health (Large, 2005). A deficit in fluid volume is known as a negative fluid balance and, if 2,500 ml : total fluid intake is greater than output, the body is in positive fluid balance (Scales Faeces (200ml) and Pilsworth, 2008). Skin (350ml) Dehydration 2,500 ml : total u id intake u id o tp t Dehydration is defined as a 1% or greater F l F l loss of body mass as a result of fluid loss, Sweat (100ml) where the body has less water than it needs Evaporation of fluid via the lungs to function properly (Madden, 2000). Metabolic water produced from (350ml) The physical symptoms of mild dehy- nutrient (200ml) dration include: » Impaired cognitive function; { { » Reduced physical performance; loss include haemorrhage, sweating, fever such as renal impairment and liver disease » Headaches, fatigue, sunken eyes and and severe burns (Mooney, 2007). (Large, 2005). dry, less elastic skin (Welch, 2010). In patients with , the If dehydration persists, the circulating Fluid overload reduced cardiac output fails to maintain volume of blood can drop. This leads to: Excessive fluid volume arises when there is adequate systemic , causing » ; retention of both electrolytes and water in reduced renal perfusion. This stimulates » Tachycardia; proportion to the levels in the extracellular thirst, which acts as a short-term compen- » Weak, thready pulse; fluid. This may be caused, for example, by satory mechanism to increase consump- » Cold hands and feet; sodium retention that leads to the reten- tion of fluid. The fluid is then retained in » Oliguria (reduced urine output) (Large, tion of water. As a result, excess fluid leaks an attempt to increase systemic blood 2005). into the interstitial spaces and forms pressure, leading to oedema (Scales and These symptoms of dehydration are the oedema (Waugh, 2007). This normally hap- Pilsworth, 2008; Faris et al, 2006). beginnings of hypovolaemic shock which, pens in people with long-term conditions, Symptoms vary, depending on the if not corrected, can lead to organ failure severity of fluid overload; patients with and death. Allowing moderate dehydra- acute fluid overload may present with a tion to become chronic can cause a general Box 1. inadequate sudden onset of acute dyspnoea secondary deterioration in health (Mulryan, 2009; fluid intake causes to pulmonary oedema (accumulation of Thomas et al, 2008; Bennett et al, 2004). fluid in the lungs). ● Refusal to drink for fear of The main symptoms exhibited by Causes of dehydration: incontinence; patients with a history of chronic fluid According to McMillen and Pitcher (2010), ● Dementia, Alzheimer’s disease or overload, such as those with heart failure, the main causes of dehydration are inade- cognitive impairment; are fatigue, dyspnoea and pitting oedema quate fluid intake, excessive fluid loss or ● Reliance on health professionals to (Khan and Heywood, 2010). both. provide adequate fluids; Inadequate fluid intake can be caused by ● Physical weakness or increased frailty; Assessing fluid balance a refusal to drink due to fear of inconti- ● Pre-operative fasting; Scales and Pilsworth (2008) identified nence, dementia or Alzheimer’s disease, ● Medication, such as laxatives or three elements to assessing fluid balance fluid restriction for conditions such as heart ; and hydration status: failure, and increased frailty (see Box 1). ● Illness causing physical and mental » Clinical assessment; Diarrhoea and are major stress; » Review of fluid balance charts; causes of excessive fluid loss. Polyuria can ● Nausea; » Review of blood chemistry. also cause dehydration unless fluid intake ● Reduced sensation of thirst in older is increased to compensate for such. Poly- people; Clinical assessment uria is usually caused by hyperglycaemia, ● Fluid restriction for conditions such as Patients should be asked if they are thirsty, diabetes or overuse of therapy heart failure or renal disorders although this is only effective for patients (Large, 2005). Other causes of excess fluid who are able to control their fluid intake.

14 Nursing Times 19.07.11 / Vol 107 No 28 / www.nursingtimes.net “We need to think of new ways to construct courses and support students’ learning” Ieuan Ellis p24

Patients with impaired ability to con- but a person with depleted fluids will have recording is notorious for being inade- trol fluid intake include those with speech additional furrows (Metheny, 2000). quately or inaccurately completed (Ben- difficulties, confusion or depression nett, 2010). (McMillen and Pitcher, 2010). Thirst per- Body weight A study by Reid (2004), which audited ception can also be impaired in older Acute changes in body weight, after the completion of fluid balance charts on people (Cannella et al, 2009). imposed fluid restrictions or exercise, is a different wards, found the major reasons Dehydration will cause the mouth and good indicator of hydration status. How- fluid balance charts were not completed mucous membranes to become dry, and ever, this can be affected by bowel move- appropriately were staff shortages, lack of the lips to become cracked so an assess- ments, as well as food and fluid, and would training, and lack of time. ment of the mouth and oral mucosa can be be difficult and unethical to measure in According to the Nursing and Mid- useful at this stage (McMillen and Pitcher, sick, immobile stroke patients (Vivanti et wifery Council (2007), record keeping is an 2010; Scales and Pilsworth, 2008). al, 2010). McMillen and Pitcher (2010) integral part of nursing care, not some- argued that to maximise the accuracy of thing to be “fitted in” where circumstances Observations weight assessment in fluid balance, the allow. It is the responsibility of the nurse Vital signs, such as pulse, blood pressure measurement should be performed at the caring for a patient to ensure observations and respiratory rate, will change when a same time of day using the same scales, and fluid balance are recorded in a timely patient becomes dehydrated. which should be calibrated regularly. manner, with any abnormal findings docu- Dehydrated patients may become tachy- mented and reported to the nurse in charge cardic and, when a lying and standing blood Urine output (Scales and Pilsworth, 2008). pressure is recorded, they will show a pos- In healthy people, urine should be a pale Smith and Roberts (2011) said that all tural drop, known as postural hypotension, straw colour. It should be clear, with no fluid intake and output, whatever the which often accompanies a fluid deficit debris or odour (Smith and Roberts, 2011). source, must be documented using quan- (Waugh, 2007). The respiratory rate may In dehydrated patients the kidneys con- tifiable amounts. This means it is impor- become rapid but only if fluid loss is severe. serve water, producing urine that is dark, tant to know how many millilitres of fluid These observations should be measured concentrated and reduced in volume are in an intravenous medication, a glass as part of the clinical assessment (Mooney, (Scales and Pilsworth, 2008). Normal urine of water or a cup of tea. How frequently the 2007; Large, 2005). output is around 1ml/kg of body weight per fluid balance chart data should be recorded hour, in a range of 0.5-2ml/kg per hour. The – such as hourly or two hourly – should be Capillary refill time clearly documented. It is not acceptable Capillary refill time (CRT) is a good || ||| practice to use shorthand. || | | | | 5% measure of the fluid present in the intra- | | Fig 3 shows best practice when com-

| The fluctuation in |

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| QUICK

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vascular fluid volume (Large, 2005). It is | fluid volume that pleting a fluid balance chart and Fig 4 |

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FACT | |

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| | can damage health measured by holding the patient’s hand at | shows an example of unacceptable prac- | |

heart level and pressing on the pad of their | tice (Smith and Roberts, 2011). middle finger for five seconds. The pres- The use of fluid balance charts that sure is released and the time measured in minimum acceptable urine output for a show cumulative input and output is now seconds until normal colour returns. patient with normal renal function is being debated in the literature (Bennett, Normal filling time is usually less than two 0.5ml/kg per hour. Anything less should be 2010). A recent study by Perren et al (2011) seconds (Resuscitation Council UK, 2006). reported (McMillen and Pitcher, 2010; suggested that for a large proportion It should be noted that CRT assessment Scales and Pilsworth, 2008). of patients, especially those in critical can sometimes be misleading, particularly When recording urine output on a fluid care, cumulative fluid balance charts are in patients with sepsis (Scales and balance chart, it is not acceptable practice not accurate and their use should be ques- Pilsworth, 2008). to record it as “passed urine +++” or “up to tioned. the toilet”. Notes such as these are unin- Skin elasticity formative and do not give a clear indica- Blood chemistry and hydration status The elasticity of skin, or turgor, is an indi- tion of the amount of urine passed While Scales and Pilsworth (2008) suggest cator of fluid status in most patients (Mooney, 2007). that the analysis of blood chemistry may (Scales and Pilsworth, 2008). The colour of the urine should not be be useful in the assessment of hydration Assessing skin turgor is a quick and relied on as a marker of fluid balance as status, the evidence surrounding this is simple test performed by pinching a fold some drugs, such as tuberculosis medica- equivocal. According to Wolfson (2009) of skin. In a well-hydrated person, the skin tion, can alter urine colour and give a false sodium, potassium, chloride, bicarbonate, will immediately fall back to its normal indication of urine concentration (Scales blood urea nitrogen (BUN) are helpful position when released. It is best practice and Pilsworth, 2008). blood electrolytes to measure when deter- to pinch the skin over the sternum or the If a patient has a urinary catheter and mining hydration status. Wolfson pro- inner thigh (Davies, 2010). the output is low, it is sensible to check poses that if any of these electrolytes are However, this assessment can be an whether the catheter or tubing is blocked found to be outside normal parameters, unreliable indicator of dehydration in or occluded in any way (McMillen and their levels should be used to guide the older people as skin elasticity reduces with Pitcher, 2010). prescription of intravenous fluids required age (Large, 2005). to restore homeostatic fluid balance. A good alternative to skin turgor is Fluid balance chart In contrast, Vivanti et al (2008) argue tongue turgor, as this is not age- Monitoring a patient’s fluid balance to pre- that there is limited value in the analysis of dependent. In a well-hydrated individual, vent dehydration or overhydration is a rel- biochemical indicators such as these for the tongue has one longitudinal furrow, atively simple task, but fluid balance less severe dehydration, particularly in

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balance. Nursing Times; 102: 17, 22. Fig 3. Accurate fluid balance chart Docherty B, McIntyre L (2002) Nursing considerations for fluid management in Time Oral input IVI input Cumulative Urine output Bowels output Vomit output Cumulative hypovolaemia. Professional Nurse; 17: 9, 545-549. input output Faris RF et al (2006) Diuretics for heart failure. Cochrane Database for Systematic Reviews. The 08.00 Water 150ml Normal 250ml 550ml 550ml Cochrane Collaboration: Wiley. tinyurl.com/ 0.9% Cochrane-diuretics 100ml Ganong WF (2000) Review of Medical Physiology. 09.00 100ml 350ml Stamford; Appleton and Lange. Khan T, Heywood JT (2010) Fluid Overload. 10.00 Coffee 150ml 100ml 600ml 250ml 800ml Patient.co.uk. tinyurl.com/fluid-overload Large W (2005) Fluid and electrolytes. In: 11.00 Water 300ml IVI tissued 900ml 150ml 950ml Sheppard M, Wright M (eds) Principles and Practice of High Dependency Nursing. Edinburgh: 12.00 Venflon 350ml 1,300 Elsevier. sited Madden V (2000) Nutritional benefits of drinks. 13.00 100ml 1,000ml Nursing Standard; 15: 13, 47-52. McMillen R, Pitcher B (2010) The balancing act: 14.00 Tea 150ml 1,150ml 100ml 1,400ml Body fluids and protecting patient health. British Journal of Healthcare Assistants; 5: 3, 117-121. 15.00 100ml 1,250ml Metheny NM (2000) Fluid and Balance: Nursing Considerations. Philadelphia: Lippincott Water 75ml 100ml 1,425ml 16.00 Williams and Wilkins. 17.00 100ml 1,525ml 200ml 1,600ml Montague SE et al (2005) Physiology for Nursing Practice. London: Elsevier. 18.00 Tea 150ml 100ml 1,775ml 100 1,700ml Mooney G (2007) Fluid balance. Nursingtimes.net. tinyurl.com/NT-fluid-balance Mulryan C (2009) An introduction to shock. British Journal of Healthcare Assistants; 3: 1, 21-24. Nursing and Midwifery Council (2007) Record Fig 4. inAccurate fluid balance chart Keeping. Guidance for Nurses and Midwives. London: NMC. tinyurl.com/NMC-record-keeping Time Oral input IVI input Cumulative Urine output Bowels output Vomit output Cumulative Paulus BM et al (2008) Causes and consequences input output of systemic venous hypertension. The American Journal of the Medical Sciences; 336: 6, 489-497. 08.00 Tea 100ml?? PU+++ Diarrhoea ? Perren A et al (2011) Fluid balance in critically ill 09.00 patients. Should we rely on it? Minerva Anestesiologica. tinyurl.com/fluid-balance-rely 10.00 H20 50ml Rassam SS, Counsell DJ (2005) Perioperative electrolyte and fluid balance. Continuing Education 11.00 Tissued +++ in Anaesthesia Critical Care and Pain; 5: 5, 157-160. (2004) Improving the monitoring and 12.00 Bed wet Soiled bed Reid J et al assessment of fluid balance. Nursing Times; 100: linen 20, 36-39. 13.00 Venflon sited Resuscitation Council UK (2006) Adult Advanced Life Support. London: RCUK. tinyurl.com/ 14.00 RCUK-ALS Scales K, Pilsworth J (2008) The importance of 15.00 Tea 200ml?? BO+++ fluid balance in clinical practice. Nursing Standard; Pump not 22: 47, 50-57. working Schrier RW (2007) Diseases of the and Urinary Tract. Philadelphia, PA: Lippincott Williams 16.00 and Wilkins Smith J, Roberts R (2011) Vital Signs for Nurses. An Juice 17.00 Introduction to Clinical Observations. Oxford: Wiley-Blackwell. References Thomas B, Bishop J (2007) Manual of Dietetic older people, and suggest that physical Practice. London: Blackwell Publishing. signs may be more promising indicators. Bennett C (2010) ‘At A Glance’ Fluid Balance Bar Thomas DR et al (2008) Understanding clinical Chart. London: NHS Institute for Innovation and dehydration and its treatment. Journal of the Conclusion Improvement. tinyurl.com/fluid-balance American Dietetic Association; 9: 5, 292-301. 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