The pathophysiology of fluid and electrolyte balance in the older adult surgical patient

  • Ahmed M. El-Sharkawy
    Affiliations
    Division of Gastrointestinal Surgery, Nottingham Digestive Diseases Centre National Institute for Health Research Biomedical Research Unit, Nottingham University Hospitals, Queen's Medical Centre, Nottingham, UK
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  • Opinder Sahota
    Affiliations
    Department of Elderly Medicine, Nottingham University Hospitals, Queen's Medical Centre, Nottingham, UK
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  • Ron J. Maughan
    Affiliations
    School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
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  • Dileep N. Lobo
    Correspondence
    Corresponding author. Division of Gastrointestinal Surgery, E Floor, West Block, Queen's Medical Centre, Nottingham NG7 2UH, UK. Tel.: +44 115 8231149; fax: +44 115 8231160.
    Affiliations
    Division of Gastrointestinal Surgery, Nottingham Digestive Diseases Centre National Institute for Health Research Biomedical Research Unit, Nottingham University Hospitals, Queen's Medical Centre, Nottingham, UK
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Open AccessPublished:November 25, 2013DOI:https://doi.org/10.1016/j.clnu.2013.11.010

      Summary

      Background & aims

      Age-related physiological changes predispose even the healthy older adult to fluid and electrolyte abnormalities which can cause morbidity and mortality. The aim of this narrative review is to highlight key aspects of age-related pathophysiological changes that affect fluid and electrolyte balance in older adults and underpin their importance in the perioperative period.

      Methods

      The Web of Science, MEDLINE, PubMed and Google Scholar databases were searched using key terms for relevant studies published in English on fluid balance in older adults during the 15 years preceding June 2013. Randomised controlled trials and large cohort studies were sought; other studies were used when these were not available. The bibliographies of extracted papers were also searched for relevant articles.

      Results

      Older adults are susceptible to dehydration and electrolyte abnormalities, with causes ranging from physical disability restricting access to fluid intake to iatrogenic causes including polypharmacy and unmonitored diuretic usage. Renal senescence, as well as physical and mental decline, increase this susceptibility. Older adults are also predisposed to water retention and related electrolyte abnormalities, exacerbated at times of physiological stress. Positive fluid balance has been shown to be an independent risk factor for morbidity and mortality in critically ill patients with acute kidney injury.

      Conclusions

      Age-related pathophysiological changes in the handling of fluid and electrolytes make older adults undergoing surgery a high-risk group and an understanding of these changes will enable better management of fluid and electrolyte therapy in the older adult.

      Keywords

      1. Introduction

      The number of people aged 65 years and over has increased significantly across the developed world, a likely result of advances in medical care. Between 1999 to 2000 and 2009 to 2010, there was a 66% rise across England in hospitalization of persons over the age of 75 years. The UK government estimates that the number of people aged 65 years and over will double by the year 2050, with an associated increase in public cost burden.
      Older adults are susceptible to dehydration and electrolyte abnormalities, causes of which are multifactorial, ranging from physical disability restricting access to adequate fluid intake to iatrogenic causes including polypharmacy and the unmonitored use of diuretics and other drugs.
      • Allison S.P.
      • Lobo D.N.
      Fluid and electrolytes in the elderly.
      Physical disability in older adults can limit access to water,
      • Gaspar P.M.
      Water intake of nursing home residents.
      whilst incontinence-associated embarrassment may lead older adults to restrict their oral fluid intake. Furthermore, those from lower socioeconomic backgrounds, living alone, with pre-existing comorbidities, or on multiple drugs are more susceptible to dehydration and electrolyte disturbances, and are at increased risk of associated morbidity and mortality.
      • Foroni M.
      • Salvioli G.
      • Rielli R.
      • Goldoni C.A.
      • Orlandi G.
      • Zauli Sajani S.
      • et al.
      A retrospective study on heat-related mortality in an elderly population during the 2003 heat wave in Modena, Italy: the Argento Project.
      Poor patient education has also been reported to lead to high rates of dehydration-related hospital readmissions after discharge, particularly in surgical patients.
      • Hari M.
      • Rosenzweig M.
      Incidence of preventable postoperative readmissions following pancreaticoduodenectomy: implications for patient education.
      • Khan M.A.
      • Hossain F.S.
      • Dashti Z.
      • Muthukumar N.
      Causes and predictors of early re-admission after surgery for a fracture of the hip.
      • Messaris E.
      • Sehgal R.
      • Deiling S.
      • Koltun W.A.
      • Stewart D.
      • McKenna K.
      • et al.
      Dehydration is the most common indication for readmission after diverting ileostomy creation.
      Dehydration has been shown to be the main reason for readmission following formation of a defunctioning ileostomy, with those on diuretics being at increased risk.
      • Messaris E.
      • Sehgal R.
      • Deiling S.
      • Koltun W.A.
      • Stewart D.
      • McKenna K.
      • et al.
      Dehydration is the most common indication for readmission after diverting ileostomy creation.
      Higher mortality rates at one year have been noted in those readmitted to hospital after surgery for hip fracture, a significant proportion of which were related to dehydration.
      • Khan M.A.
      • Hossain F.S.
      • Dashti Z.
      • Muthukumar N.
      Causes and predictors of early re-admission after surgery for a fracture of the hip.
      Age-related physiological changes, including renal senescence also increase the susceptibility of the older adult population to dehydration. Dehydration of as little as 2% of total body water can result in a significant impairment in physical, visuomotor, psychomotor and cognitive performances.
      • Grandjean A.C.
      • Grandjean N.R.
      Dehydration and cognitive performance.
      Furthermore, a study reported a 17%, 30-day mortality in older adults with the principal diagnosis of dehydration as per the ICD classification, with the one-year mortality being close to 50%.
      • Warren J.L.
      • Bacon W.E.
      • Harris T.
      • McBean A.M.
      • Foley D.J.
      • Phillips C.
      The burden and outcomes associated with dehydration among US elderly, 1991.
      Older adults are also susceptible to water retention and related electrolyte abnormalities. These are exacerbated at times of physiological stress, such as in the perioperative period
      • Desborough J.P.
      The stress response to trauma and surgery.
      and a positive fluid balance has been shown to be an independent risk factor for mortality in critically ill patients with acute kidney injury.
      • Bagshaw S.M.
      • Brophy P.D.
      • Cruz D.
      • Ronco C.
      Fluid balance as a biomarker: impact of fluid overload on outcome in critically ill patients with acute kidney injury.
      • Payen D.
      • de Pont A.C.
      • Sakr Y.
      • Spies C.
      • Reinhart K.
      • Vincent J.L.
      A positive fluid balance is associated with a worse outcome in patients with acute renal failure.
      The aim of this narrative review of the current literature is to highlight the key aspects of age-related pathophysiological changes that affect fluid and electrolyte balance in older adults and underpin their importance in the perioperative period.

      2. Search strategy

      The Web of Science, MEDLINE, PubMed and Google Scholar databases were searched using the terms elderly, older adults, ageing, fluids, electrolytes, hydration, dehydration, hypohydration, dysnatraemia, sodium, hypernatraemia, hyponatraemia, magnesium, hypomagnesaemia, hypermagnesaemia, potassium, hyperkalaemia, hypokalaemia and thirst, using the Boolean operators AND/OR for relevant studies from the 15 years preceding June 2013. Randomised controlled trials and large cohort studies were sought; other studies were used when these were not available. The bibliographies of extracted papers were also searched for relevant articles. Older papers were included if the topic was not covered by more recent work. Papers published in languages other than English, small case series and case reports were excluded.

      3. Physiological changes in older adults

      The ageing process is associated with physiological changes in water balance. Total body water is reduced by 10–15% in older adults, owing to reduced lean body mass, leading to an increased extracellular to intracellular water ratio.
      • Allison S.P.
      • Lobo D.N.
      Fluid and electrolytes in the elderly.
      This, coupled with reduced glomerular filtration rate and a reduced ability to concentrate urine, can predispose older adults to fluid retention and iatrogenic overload.
      • Allison S.P.
      • Lobo D.N.
      Fluid and electrolytes in the elderly.
      • Lindeman R.D.
      • Tobin J.
      • Shock N.W.
      Longitudinal studies on the rate of decline in renal function with age.
      Physiological changes associated with ageing also make older adults more susceptible to organ dysfunction, including acute and chronic kidney injury, which can result in electrolyte abnormities. Electrolyte abnormalities can also occur without any obvious kidney disease as a result of structural and functional changes associated with ageing.
      • Schlanger L.E.
      • Bailey J.L.
      • Sands J.M.
      Electrolytes in the aging.
      • Melk A.
      Senescence of renal cells: molecular basis and clinical implications.
      Fluid intake is primarily through oral ingestion of fluid: this is stimulated by the thirst mechanism which may be impaired in older adults, as a consequence of hormonal changes.
      • Kenney W.L.
      • Chiu P.
      Influence of age on thirst and fluid intake.
      • Phillips P.A.
      • Bretherton M.
      • Risvanis J.
      • Casley D.
      • Johnston C.
      • Gray L.
      Effects of drinking on thirst and vasopressin in dehydrated elderly men.
      • Phillips P.A.
      • Johnston C.I.
      • Gray L.
      Disturbed fluid and electrolyte homoeostasis following dehydration in elderly people.
      The daily fluid turnover in older subjects was found to be at the lower limits of normal when assessed using deuterium oxide.
      • Leiper J.B.
      • Seonaid Primrose C.
      • Primrose W.R.
      • Phillimore J.
      • Maughan R.J.
      A comparison of water turnover in older people in community and institutional settings.
      Furthermore, the daily water turnover was on average, 27% less in dependent older patients living in institutional care compared with those living in their own homes.
      • Leiper J.B.
      • Seonaid Primrose C.
      • Primrose W.R.
      • Phillimore J.
      • Maughan R.J.
      A comparison of water turnover in older people in community and institutional settings.
      Fluid loss occurs mostly through the urinary system, but variable amounts are attributed to insensible losses which can be up to 800 ml in 24 h, via the skin, gastrointestinal tract and lungs. Age-related skin changes make older adults vulnerable to extreme changes in environmental temperature. There is a decrease in the water content of the stratum corneum
      • Berardesca E.
      • Maibach H.I.
      Transepidermal water loss and skin surface hydration in the non invasive assessment of stratum corneum function.
      and a significantly higher transepidermal water loss from most anatomical regions compared with younger patients.
      • Wilhelm K.P.
      • Cua A.B.
      • Maibach H.I.
      Skin aging. Effect on transepidermal water loss, stratum corneum hydration, skin surface pH, and casual sebum content.
      Furthermore, decreased elasticity and skin turgor as well as the dry appearance of the aged skin make it harder to diagnose dehydration in older adults. The magnitude and distribution of fluid losses are influenced by the environment, disease and the physiological changes occurring with ageing.
      • Flynn A.
      • McGreevy C.
      • Mulkerrin E.C.
      Why do older patients die in a heatwave?.

      4. Renal senescence

      Renal senescence reflects irreversible structural and functional changes associated with the ageing kidney.
      • Melk A.
      Senescence of renal cells: molecular basis and clinical implications.
      Amongst other changes, there is a loss of renal mass due to glomerular sclerosis and glomerular loss.
      • Lindeman R.D.
      • Tobin J.
      • Shock N.W.
      Longitudinal studies on the rate of decline in renal function with age.
      • Nyengaard J.R.
      • Bendtsen T.F.
      Glomerular number and size in relation to age, kidney weight, and body surface in normal man.
      • Epstein M.
      Aging and the kidney.
      This impairs the ability to retain sodium and, therefore, water, thus predisposing the patient to dysnatraemia and hypovolaemia.
      • Hawkins R.C.
      Age and gender as risk factors for hyponatremia and hypernatremia.
      In addition, the ability to secrete potassium and excrete hydrogen is also impaired.
      • Musso C.
      • Liakopoulos V.
      • De Miguel R.
      • Imperiali N.
      • Algranati L.
      Transtubular potassium concentration gradient: comparison between healthy old people and chronic renal failure patients.
      • Frassetto L.
      • Sebastian A.
      Age and systemic acid-base equilibrium: analysis of published data.
      • Berkemeyer S.
      • Vormann J.
      • Gunther A.L.
      • Rylander R.
      • Frassetto L.A.
      • Remer T.
      Renal net acid excretion capacity is comparable in prepubescence, adolescence, and young adulthood but falls with aging.
      The creatinine clearance in the aged kidney is also reduced. Reduction in the mean creatinine clearance was reported in two-thirds of the population studied in the Baltimore Longitudinal Study of Ageing, with an estimated reduction in eGFR by 50–63% from the age of 30–80 years.
      • Lindeman R.D.
      • Tobin J.
      • Shock N.W.
      Longitudinal studies on the rate of decline in renal function with age.
      Furthermore, reduced tubular function and the medullary concentration gradient are also impaired in an aged kidney, diminishing the ability of the kidney to concentrate urine. Age-related reduction in renal blood flow has also been reported; this contributes to loss of nephrons as a result of ischaemia.
      • Lindeman R.D.
      • Tobin J.
      • Shock N.W.
      Longitudinal studies on the rate of decline in renal function with age.
      • Messerli F.H.
      • Sundgaard-Riise K.
      • Ventura H.O.
      • Dunn F.G.
      • Glade L.B.
      • Frohlich E.D.
      Essential hypertension in the elderly: haemodynamics, intravascular volume, plasma renin activity, and circulating catecholamine levels.
      • Hollenberg N.K.
      • Adams D.F.
      • Solomon H.S.
      • Rashid A.
      • Abrams H.L.
      • Merrill J.P.
      Senescence and the renal vasculature in normal man.
      • Beck L.H.
      The aging kidney. Defending a delicate balance of fluid and electrolytes.
      These changes impair the ability of the kidney to control water and electrolyte balance, predisposing to dehydration and electrolyte abnormalities, particularly in situations of physiological stress.

      5. Hormonal changes and ageing

      Hormonal changes that affect fluid and electrolyte homeostasis have been reported in older adults. There is an age-related reduction in the serum concentrations of renin and aldosterone as a result of increased atrial natriuretic peptide (ANP) activity, usually released in response to increased blood pressure and right atrial filling.
      • Lobo D.N.
      • Stanga Z.
      • Aloysius M.M.
      • Wicks C.
      • Nunes Q.M.
      • Ingram K.L.
      • et al.
      Effect of volume loading with 1 liter intravenous infusions of 0.9% saline, 4% succinylated gelatine (Gelofusine) and 6% hydroxyethyl starch (Voluven) on blood volume and endocrine responses: a randomized, three-way crossover study in healthy volunteers.
      This, coupled with age-related reduction in tubular response to aldosterone, predisposes to dehydration and electrolyte abnormalities.
      • Beck L.H.
      The aging kidney. Defending a delicate balance of fluid and electrolytes.
      • Kenny R.A.
      • Lyon C.C.
      • Bayliss J.
      • Lightman S.L.
      • Sutton R.
      Reduced plasma renin activity in elderly subjects in response to vasovagal hypotension and head-up tilt.
      Serum ANP concentrations were shown to be nearly five-times higher in older adults than in the young.
      • Ohashi M.
      • Fujio N.
      • Nawata H.
      • Kato K.
      • Ibayashi H.
      • Kangawa K.
      • et al.
      High plasma concentrations of human atrial natriuretic polypeptide in aged men.
      ANP inhibits renin secretion from the juxtaglomerular cells, therefore, limiting the conversion of angiotensinogen to angiotensin I, and reducing the activity of the renin–angiotensin–aldosterone system (RAAS) (Fig. 1).
      • Kurtz A.
      • Della Bruna R.
      • Pfeilschifter J.
      • Taugner R.
      • Bauer C.
      Atrial natriuretic peptide inhibits renin release from juxtaglomerular cells by a cGMP-mediated process.
      These changes result in a decreased ability to retain sodium in a hypovolaemic state and a reduced ability to excrete potassium,
      • Musso C.
      • Liakopoulos V.
      • De Miguel R.
      • Imperiali N.
      • Algranati L.
      Transtubular potassium concentration gradient: comparison between healthy old people and chronic renal failure patients.
      • Ling B.N.
      • Kemendy A.E.
      • Kokko K.E.
      • Hinton C.F.
      • Marunaka Y.
      • Eaton D.C.
      Regulation of the amiloride-blockable sodium channel from epithelial tissue.
      making it difficult to adapt to extracellular fluid depletion and sodium loss.
      Figure thumbnail gr1
      Fig. 1Age-related changes in the hormonal control of fluid and electrolyte homeostasis. There is an age-related reduction in the serum concentrations of renin and aldosterone as a result of increased atrial natriuretic peptide (ANP) activity. ANP inhibits renin secretion from the juxtaglomerular cells, therefore, limiting the conversion of angiotensinogen to angiotensin I, ultimately resulting in reduced angiotensin II, therefore inhibiting the renin–angiotensin–aldosterone system (RAAS). Consequences of this include; reduced aldosterone, impaired thirst response, reduced antidiuretic hormone. These changes result in a decreased ability to retain sodium and water making it difficult to adapt to extracellular fluid depletion and sodium loss.
      It is also important to consider the role of antidiuretic hormone (ADH) in older adults, where there is conflicting evidence suggesting increased as well as decreased serum concentrations. ADH acts to stimulate aquaporin, a group of proteins that allow the passage of water across cell membranes and thus conserve the body water. The normal diurnal variation results in increased plasma concentrations of ADH at night, but in older adults there is loss of the nocturnal rise in ADH concentrations which contributes to the high prevalence of nocturia.
      • Asplund R.
      • Aberg H.
      Diurnal variation in the levels of antidiuretic hormone in the elderly.
      This, along with reduced renal sensitivity to ADH, limits the ability to respond to extracellular fluid depletion.
      • Beck L.H.
      The aging kidney. Defending a delicate balance of fluid and electrolytes.
      • Stachenfeld N.S.
      • Mack G.W.
      • Takamata A.
      • DiPietro L.
      • Nadel E.R.
      Thirst and fluid regulatory responses to hypertonicity in older adults.
      • Phillips P.A.
      • Rolls B.J.
      • Ledingham J.G.
      • Forsling M.L.
      • Morton J.J.
      • Crowe M.J.
      • et al.
      Reduced thirst after water deprivation in healthy elderly men.
      Furthermore, decreased plasma ADH concentrations have been reported in patients with Alzheimer's disease, limiting the ability to conserve water.
      • Albert S.G.
      • Nakra B.R.S.
      • Grossberg G.T.
      • Caminal E.R.
      Vasopressin response to dehydration in Alzheimers-disease.

      6. Thirst response

      The thirst response is blunted in older adults resulting in a persistent hyperosmolar state,
      • McAloon Dyke M.
      • Davis K.M.
      • Clark B.A.
      • Fish L.C.
      • Elahi D.
      • Minaker K.L.
      Effects of hypertonicity on water intake in the elderly: an age-related failure.
      • Phillips P.A.
      • Bretherton M.
      • Johnston C.I.
      • Gray L.
      Reduced osmotic thirst in healthy elderly men.
      • Phillips P.A.
      • Rolls B.J.
      • Ledingham J.G.G.
      • Forsling M.L.
      • Morton J.J.
      • Crowe M.J.
      • et al.
      Reduced thirst after water-deprivation in healthy elderly men.
      • Silver A.J.
      • Morley J.E.
      Role of the opioid system in the hypodipsia associated with aging.
      • Stachenfeld N.S.
      • DiPietro L.
      • Nadel E.R.
      • Mack G.W.
      Mechanism of attenuated thirst in aging: role of central volume receptors.
      • Mack G.W.
      • Weseman C.A.
      • Langhans G.W.
      • Scherzer H.
      • Gillen C.M.
      • Nadel E.R.
      Body fluid balance in dehydrated healthy older men: thirst and renal osmoregulation.
      which is exacerbated by the reduced concentrating ability of the kidney. In a double-blinded crossover study investigating the thirst response in older men, healthy men aged 65–78 and 25–32 years were infused with isotonic, 0.154 M (0.9%) saline or hypertonic, 0.855 M (5% saline) two weeks apart.
      • Phillips P.A.
      • Bretherton M.
      • Johnston C.I.
      • Gray L.
      Reduced osmotic thirst in healthy elderly men.
      The authors reported less volume expansion in older adult subjects following hypertonic saline than in the younger subjects. Moreover, older adults felt less thirsty and consumed less water than the younger subjects during the hypertonic state, thus demonstrating the increased thirst threshold in older adults.
      • Phillips P.A.
      • Bretherton M.
      • Johnston C.I.
      • Gray L.
      Reduced osmotic thirst in healthy elderly men.
      Another study showed that older men had a blunted thirst response following 24 h without fluids when compared with younger men.
      • Phillips P.A.
      • Bretherton M.
      • Risvanis J.
      • Casley D.
      • Johnston C.
      • Gray L.
      Effects of drinking on thirst and vasopressin in dehydrated elderly men.
      The mechanism responsible for this is yet to be defined, but may be a result of blunted osmotic and baroreceptor sensitivity, particularly in the left atrium
      • Kenney W.L.
      • Chiu P.
      Influence of age on thirst and fluid intake.
      • Stachenfeld N.S.
      • DiPietro L.
      • Nadel E.R.
      • Mack G.W.
      Mechanism of attenuated thirst in aging: role of central volume receptors.
      or possibly inhibition of the RAAS as a result of the raised concentrations of ANP.
      • Burrell L.M.
      • Lambert H.J.
      • Baylis P.H.
      Effect of atrial natriuretic peptide on thirst and arginine vasopressin release in humans.
      It is important to note, however, that the amount of fluid consumed on a daily basis is not entirely physiologically driven, but is dependent on consumption that is driven by social factors, habit and other influences, such as the fluid intake with meals.
      • Kenney W.L.
      • Chiu P.
      Influence of age on thirst and fluid intake.
      • Phillips P.A.
      • Rolls B.J.
      • Ledingham J.G.
      • Morton J.J.
      Body fluid changes, thirst and drinking in man during free access to water.
      Therefore, the healthy independent older person is generally able to maintain adequate fluid balance through spontaneous consumption of fluids but may become vulnerable to dehydration in a state of physiological stress.

      7. Electrolyte abnormalities in older adults

      Electrolyte abnormalities, particularly dysnatraemia, should be considered in the context of water balance. Hypertonic dehydration occurs when proportionally more water than sodium is lost from the extracellular fluid compartment. This may occur as a result of age-related thirst impairment and would manifest as serum sodium concentration of greater than 145 mmol/l in the context of dehydration. Hypotonic dehydration on the other hand occurs when the proportion of sodium lost is greater than water, resulting in a serum sodium concentration of less than 135 mmol/l. This may occur with the use of diuretics. Isotonic dehydration results from proportionate loss of water and sodium and results in normal serum sodium concentrations. Isotonic dehydration may occur, for example, as a result of diarrhoea, where there is salt and water loss in similar proportions.

      7.1 Dysnatraemia in older adults

      The hyperosmolar state of the older person predisposes to dysnatraemia, the most common electrolyte abnormality in older adults, with age being an independent risk factor for dysnatraemia.
      • Hawkins R.C.
      Age and gender as risk factors for hyponatremia and hypernatremia.
      Clinical manifestations of dysnatraemia vary depending on the severity, with fatigue, seizure and coma being recognised complications. Dysnatraemia, particularly hypernatraemia, is also associated with an increased mortality rate of up to 70% in severe cases.
      • Alshayeb H.M.
      • Showkat A.
      • Babar F.
      • Mangold T.
      • Wall B.M.
      Severe hypernatremia correction rate and mortality in hospitalized patients.
      • Snyder N.A.
      • Feigal D.W.
      • Arieff A.I.
      Hypernatremia in elderly patients. A heterogeneous, morbid, and iatrogenic entity.
      A seven fold increase in mortality was also reported in patients with hypernatraemia compared with age-matched hospitalised patients.
      • Snyder N.A.
      • Feigal D.W.
      • Arieff A.I.
      Hypernatremia in elderly patients. A heterogeneous, morbid, and iatrogenic entity.
      In an audit of 1383 surgical inpatients, it was found that patients with dysnatraemias had a significantly higher mortality than those with normal serum sodium concentrations (12.7 vs. 2.3%, p < 0.001).
      • Herrod P.J.
      • Awad S.
      • Redfern A.
      • Morgan L.
      • Lobo D.N.
      Hypo- and hypernatraemia in surgical patients: is there room for improvement?.
      Hyponatraemia, on the other hand, is much more common in older adults than hypernatraemia and is an independent risk factor for bone fractures.
      • Gankam Kengne F.
      • Andres C.
      • Sattar L.
      • Melot C.
      • Decaux G.
      Mild hyponatremia and risk of fracture in the ambulatory elderly.
      • Zilberberg M.D.
      • Exuzides A.
      • Spalding J.
      • Foreman A.
      • Jones A.G.
      • Colby C.
      • et al.
      Epidemiology, clinical and economic outcomes of admission hyponatremia among hospitalized patients.
      • Kinsella S.
      • Moran S.
      • Sullivan M.O.
      • Molloy M.G.
      • Eustace J.A.
      Hyponatremia independent of osteoporosis is associated with fracture occurrence.
      This, may be a result of reduced bone mineral density and increased risk of osteoporosis.
      • Barsony J.
      • Manigrasso M.
      • Tam H.
      • Xu Q.
      • Sugimura Y.
      • Tian Y.
      • et al.
      Hyponatremia-induced osteoporosis.
      Moreover, hyponatraemia was associated with a 2.1-fold increase in mortality in mild cases and 4.6-fold increase in severe cases in patients admitted for orthopaedic surgery.
      • Zilberberg M.D.
      • Exuzides A.
      • Spalding J.
      • Foreman A.
      • Jones A.G.
      • Colby C.
      • et al.
      Epidemiology, clinical and economic outcomes of admission hyponatremia among hospitalized patients.
      • Waikar S.S.
      • Mount D.B.
      • Curhan G.C.
      Mortality after hospitalization with mild, moderate, and severe hyponatremia.
      It is important to note that a significant proportion of dysnatraemia in older adults occurs as a result of concurrent disease such as the syndrome of inappropriate ADH secretion (SIADH) and hyperglycaemia.
      • Anderson R.J.
      • Chung H.M.
      • Kluge R.
      • Schrier R.W.
      Hyponatremia: a prospective analysis of its epidemiology and the pathogenetic role of vasopressin.
      Iatrogenic causes of dysnatraemia, such as diuretic use as well as excessive administration of intravenous hypotonic fluids, must also be considered. Increased dietary salt content of processed foods on which many older adults are now dependent, and excess iatrogenic salt administration result in hypernatraemia as older adults require longer to excrete salt loads due to the age-related reduction in eGFR and they are more likely to become salt and water overloaded when challenged with a sodium load. The kidney is also unable to cope with the excess chloride load even in physiologically normal younger subjects.
      • Chowdhury A.H.
      • Cox E.F.
      • Francis S.T.
      • Lobo D.N.
      A randomized, controlled, double-blind crossover study on the effects of 2-L infusions of 0.9% saline and Plasma-Lyte(R) 148 on renal blood flow velocity and renal cortical tissue perfusion in healthy volunteers.

      7.2 Other electrolyte abnormalities in older adults

      Age-related renal changes make older adults vulnerable to other electrolyte abnormalities, in particular hyperkalaemia, resulting from impaired ability to secrete potassium and excrete acid, a consequence of age-related decline in distal renal tubular function.
      • Musso C.
      • Liakopoulos V.
      • De Miguel R.
      • Imperiali N.
      • Algranati L.
      Transtubular potassium concentration gradient: comparison between healthy old people and chronic renal failure patients.
      • Frassetto L.
      • Sebastian A.
      Age and systemic acid-base equilibrium: analysis of published data.
      • Berkemeyer S.
      • Vormann J.
      • Gunther A.L.
      • Rylander R.
      • Frassetto L.A.
      • Remer T.
      Renal net acid excretion capacity is comparable in prepubescence, adolescence, and young adulthood but falls with aging.
      • Biswas K.
      • Mulkerrin E.C.
      Potassium homoeostasis in the elderly.
      This is further exacerbated by a blunted renin and aldosterone response. It has been shown that there was a reduced aldosterone response to potassium infusion in healthy older adult volunteers when compared with younger controls.
      • Mulkerrin E.
      • Epstein F.H.
      • Clark B.A.
      Aldosterone responses to hyperkalemia in healthy elderly humans.
      Furthermore, the age-related blunting of the renin-aldosterone response to an acute rise in serum potassium further increases the susceptibility to hyperkalaemia.
      • Clark B.A.
      • Brown R.S.
      • Epstein F.H.
      Effect of atrial natriuretic peptide on potassium-stimulated aldosterone secretion: potential relevance to hypoaldosteronism in man.
      Other mechanisms have also been suggested to contribute to hyperkalaemia. Transtubular potassium concentration gradient, an index of potassium secretory activity in the distal tubule, was shown to be lower in healthy older adult subjects than in the young.
      • Musso C.
      • Liakopoulos V.
      • De Miguel R.
      • Imperiali N.
      • Algranati L.
      Transtubular potassium concentration gradient: comparison between healthy old people and chronic renal failure patients.
      This highlights the need to monitor for hyperkalaemia in older adults when prescribing medication, particularly in those who are physiologically stressed.
      Hypomagnesaemia has also been reported to be associated with normal ageing, often as a result of low dietary intake, but it is also known to be linked to acid-base status, with renal magnesium loss exacerbated by an acid load.
      • Gullestad L.
      • Nes M.
      • Ronneberg R.
      • Midtvedt K.
      • Falch D.
      • Kjekshus J.
      Magnesium status in healthy free-living elderly Norwegians.
      • Rude R.K.
      Magnesium deficiency: a cause of heterogeneous disease in humans.
      • Rylander R.
      • Remer T.
      • Berkemeyer S.
      • Vormann J.
      Acid-base status affects renal magnesium losses in healthy, elderly persons.
      Hypomagnesaemia is associated with a variety of heterogeneous disease processes and is known to reduce renal calcium reabsorption. If untreated, it can cause osteoporosis, arrhythmias and myocardial infarction. Slow progress, morbidity and even mortality have also been reported in the intensive care setting in association with hypomagnesaemia.
      • Rude R.K.
      Magnesium deficiency: a cause of heterogeneous disease in humans.
      • Safavi M.
      • Honarmand A.
      Admission hypomagnesemia–impact on mortality or morbidity in critically ill patients.

      8. Prescribing in older adults

      The predisposition of older adults to electrolyte abnormalities is further increased by the underlying co-morbidities that often coexist and can often be precipitated by polypharmacy. Some drugs also interfere with thermoregulation and predispose to dehydration (Table 1).
      • Cuddy M.L.
      The effects of drugs on thermoregulation.
      Medications such as angiotensin-converting enzyme inhibitors (ACE-I), potassium-sparing diuretics and non-steroidal anti-inflammatory drugs (NSAIDs) also interfere with potassium homeostasis. ACE-I prevent the conversion of angiotensin I to angiotensin II, thereby reduce aldosterone secretion. NSAIDs inhibit prostaglandin synthesis, associated with reduced renin and aldosterone, thus predisposing to hyperkalaemia.
      • Biswas K.
      • Mulkerrin E.C.
      Potassium homoeostasis in the elderly.
      • Nadler J.L.
      • Lee F.O.
      • Hsueh W.
      • Horton R.
      Evidence of prostacyclin deficiency in the syndrome of hyporeninemic hypoaldosteronism.
      Table 1Commonly prescribed drugs that affect thermoregulation and increase body temperature.
      • Levothyroxine
      • Selective serotonin reuptake inhibitors (SSRI)
      • Atypical antipsychotics e.g. olanzapine
      • Tricyclic antidepressants
      • Carbamazepine
      • Anticholinergics
      • Antihistamines
      NSAID prescribing in older adults is limited due to significant gastrointestinal side effects. However, older adult patients are susceptible to dehydration and significant electrolyte abnormalities with widespread unmonitored diuretic prescriptions.
      Complications associated with diuretic use are reported widely.
      • Gurwitz J.H.
      • Field T.S.
      • Harrold L.R.
      • Rothschild J.
      • Debellis K.
      • Seger A.C.
      • et al.
      Incidence and preventability of adverse drug events among older persons in the ambulatory setting.
      • Chapman M.D.
      • Hanrahan R.
      • McEwen J.
      • Marley J.E.
      Hyponatraemia and hypokalaemia due to indapamide.
      • Sandhofer A.
      • Kahler C.
      • Heininger D.
      • Bellmann R.
      • Wiedermann C.J.
      • Joannidis M.
      Severe electrolyte disturbances and renal failure in elderly patients with combined diuretic therapy including xipamid.
      Various studies have concluded that adverse events related to diuretics are amongst the most commonly reported.
      • Wierenga P.C.
      • Buurman B.M.
      • Parlevliet J.L.
      • van Munster B.C.
      • Smorenburg S.M.
      • Inouye S.K.
      • et al.
      Association between acute geriatric syndromes and medication-related hospital admissions.
      • Klopotowska J.E.
      • Wierenga P.C.
      • Smorenburg S.M.
      • Stuijt C.C.
      • Arisz L.
      • Kuks P.F.
      • et al.
      Recognition of adverse drug events in older hospitalized medical patients.
      A study showed that 25% of the adverse drug reactions reported in an older adult population were related to diuretic therapy, and all those admitted to hospital with medication-related falls were on diuretics.
      • Wierenga P.C.
      • Buurman B.M.
      • Parlevliet J.L.
      • van Munster B.C.
      • Smorenburg S.M.
      • Inouye S.K.
      • et al.
      Association between acute geriatric syndromes and medication-related hospital admissions.
      Various theories have been suggested for this. A systematic review into adverse drug reactions in ambulatory care that lack of monitoring of diuretic use caused over- or under-diuresis and potentially preventable hospitalisation.
      • Thomsen L.A.
      • Winterstein A.G.
      • Sondergaard B.
      • Haugbolle L.S.
      • Melander A.
      Systematic review of the incidence and characteristics of preventable adverse drug events in ambulatory care.
      The lack of patient education on the effective use of diuretics may also play a role in this, with a clear role for patient-led regulation of personal diuretic use based on regular weight measurement, empowering them with sufficient knowledge to decide on the daily doses.
      • Allison S.P.
      • Lobo D.N.
      Fluid and electrolytes in the elderly.
      Furthermore, sufficient information needs to be conveyed to allow the patients to recognise dehydration and to omit diuretics when they are at increased risk of fluid and electrolyte loss.
      • Allison S.P.
      • Lobo D.N.
      Fluid and electrolytes in the elderly.
      The use of diuretics should be monitored closely, particularly in older adults who are at increased risk or dehydration and potentially significant electrolyte abnormalities in the same way that glycaemic control is monitored.
      • Thomsen L.A.
      • Winterstein A.G.
      • Sondergaard B.
      • Haugbolle L.S.
      • Melander A.
      Systematic review of the incidence and characteristics of preventable adverse drug events in ambulatory care.

      9. Dehydration and the environment

      During ill health or periods of hot weather older adults are at particular risk of dehydration.
      • Schols J.M.
      • De Groot C.P.
      • van der Cammen T.J.
      • Olde Rikkert M.G.
      Preventing and treating dehydration in the elderly during periods of illness and warm weather.
      • Fouillet A.
      • Rey G.
      • Laurent F.
      • Pavillon G.
      • Bellec S.
      • Guihenneuc-Jouyaux C.
      • et al.
      Excess mortality related to the August 2003 heat wave in France.
      A heat wave in France in 2003 was associated with a 160–200% increase in mortality, mostly associated with dehydration and electrolyte abnormalities,
      • Fouillet A.
      • Rey G.
      • Laurent F.
      • Pavillon G.
      • Bellec S.
      • Guihenneuc-Jouyaux C.
      • et al.
      Excess mortality related to the August 2003 heat wave in France.
      owing to the diminished ability of older adults to thermoregulate as a result of reduced total intra and extracellular fluid. This results in reduced sweat production and is exacerbated by dehydrated and dry skin which reduces heat loss and acts to insulate.
      • Warren J.L.
      • Bacon W.E.
      • Harris T.
      • McBean A.M.
      • Foley D.J.
      • Phillips C.
      The burden and outcomes associated with dehydration among US elderly, 1991.
      This reduction in total body water worsens the severity of dehydration which is more dependent on the relative loss of total body water rather than the absolute loss.
      • Warren J.L.
      • Bacon W.E.
      • Harris T.
      • McBean A.M.
      • Foley D.J.
      • Phillips C.
      The burden and outcomes associated with dehydration among US elderly, 1991.
      • Olde Rikkert M.G.
      • Deurenberg P.
      • Jansen R.W.
      • van't Hof M.A.
      • Hoefnagels W.H.
      Validation of multi-frequency bioelectrical impedance analysis in detecting changes in fluid balance of geriatric patients.

      10. Dehydration and cognitive impairment

      Cognitive impairment is a risk factor for dehydration, particularly in older adults.
      • Mentes J.
      Oral hydration in older adults: greater awareness is needed in preventing, recognizing, and treating dehydration.
      However, there are few clinical studies that investigate dehydration in the cognitively impaired despite this increased risk. People with dementia often forget to drink, increasing the risk of dehydration, which may lead to further cognitive decline and further dehydration. Dehydration of as little as 2% may cause impaired cognitive function.
      • Grandjean A.C.
      • Grandjean N.R.
      Dehydration and cognitive performance.
      • Adan A.
      Cognitive performance and dehydration.
      Most agree, however, that further work is needed in this field to further clarify the extent of cognitive impairment in dehydrated older adult patients.

      11. Diagnosing dehydration

      Electrolyte abnormalities and dehydration, although common in older adults, are relatively simple to treat. However, recognising dehydration can be difficult in nursing home subjects and hospital patients partly due to poor monitoring and the challenges in recording accurate fluid balance that accounts for actual input and output as well as insensible fluid loss which is influenced by the disease process.
      • Cox P.
      Insensible water loss and its assessment in adult patients: a review.
      The limited knowledge of frontline staff surrounding hydration is also a contributing factor.
      • Woodrow P.
      Assessing fluid balance in older people: fluid needs.
      This, coupled with the difficulty in recognising the symptoms and signs of dehydration in older adult patients, can result in morbidity and even mortality.
      Clinical manifestations of dehydration include dry skin, reduced skin turgor and dry mucous membranes (Table 2). However, reduced skin turgor can occur with age and the commonest cause of dry mouth in older adults is mouth breathing. Other features of dehydration include dizziness weakness and apathy, all of which my erroneously be attributed to other causes or simply ascribed to the ageing process making dehydration difficult to diagnose.
      • Schols J.M.
      • De Groot C.P.
      • van der Cammen T.J.
      • Olde Rikkert M.G.
      Preventing and treating dehydration in the elderly during periods of illness and warm weather.
      • Shimizu M.
      • Kinoshita K.
      • Hattori K.
      • Ota Y.
      • Kanai T.
      • Kobayashi H.
      • et al.
      Physical signs of dehydration in the elderly.
      A prospective observational study was performed to identify accurate indicators of dehydration in older adults.
      • Shimizu M.
      • Kinoshita K.
      • Hattori K.
      • Ota Y.
      • Kanai T.
      • Kobayashi H.
      • et al.
      Physical signs of dehydration in the elderly.
      The authors reported various symptoms and signs as markers of dehydration, including dry axilla which was shown to have a sensitivity of 44% and a specificity of 89% in those with a urinary osmolality greater than 295 mOsm/L, but concluded that clinical assessment coupled with appropriate laboratory investigations were key to diagnosing dehydration in older adults accurately.
      • Shimizu M.
      • Kinoshita K.
      • Hattori K.
      • Ota Y.
      • Kanai T.
      • Kobayashi H.
      • et al.
      Physical signs of dehydration in the elderly.
      Table 2Clinical and biochemical features of dehydration.
      • Clinical features
        • Dry mucus membrane
        • Dry skin
        • Reduced skin turgor
        • Reduced axillary sweating
        • Orthostatic hypotension
        • Tachycardia and hypotension (indicates shock)
        • Cognitive impairment
        • Reduced urinary output [<0.5 ml/kg/h is suggestive of acute kidney injury
        • (AKI)]
        • Concentrated urine and high osmolality
      • Biochemical changes
        • Raised serum urea
        • Raised creatinine (>26 μmol/L within 48 h or >1.5 × upper limit within one week indicate AKI)
        • Reduced estimated glomerular filtration rate (eGFR)
        • Increased urea:creatinine ratio (>80)
        • Hypernatraemia (loss of water greater than salt loss)
        • Raised serum or urine osmolality
        • Raised urine specific gravity

      12. Physiological changes during the perioperative period

      The older adult population makes up a significant proportion of the surgical population. This is largely due to advances in medical care allowing the provision of more effective and less traumatic surgery. In combination with significant improvement in preoperative optimisation and more intensive postoperative monitoring and treatment, this has led to improved outcomes in the older adult surgical patient. Surgery, however, is associated with a stress response similar to that following trauma and results in a systemic response mediated by neurological, hormonal, immunological and haematological responses.
      • Desborough J.P.
      The stress response to trauma and surgery.
      This multisystem response to surgery, although essential to recovery, can be associated with poor outcome if not managed effectively, particularly given the physiological changes that occur with age. Amongst the physiological changes that occur during the acute phase of the stress response to surgery is an increased secretion of ADH from the posterior pituitary, resulting in increased water retention. Increased sympathetic efferent activity results in increased renin secretion and therefore increased aldosterone resulting in further water and sodium absorption. These changes make the older adult more vulnerable to salt and water retention.
      • Desborough J.P.
      The stress response to trauma and surgery.
      Although designed to maintain adequate cardiac output and renal perfusion, salt and water retention can be associated with delayed postoperative recovery and poor outcome.
      • Arieff A.I.
      Fatal postoperative pulmonary edema: pathogenesis and literature review.
      Perioperative fluid therapy has a direct bearing on outcome.
      • Lobo D.N.
      • Macafee D.A.
      • Allison S.P.
      How perioperative fluid balance influences postoperative outcomes.
      Morbidity caused by salt and water retention includes cardiorespiratory complications, increased infection risk and impaired wound healing.
      • Holte K.
      • Sharrock N.E.
      • Kehlet H.
      Pathophysiology and clinical implications of perioperative fluid excess.
      Impaired gastrointestinal function has also been reported in association with postoperative salt and water retention.
      • Lobo D.N.
      • Macafee D.A.
      • Allison S.P.
      How perioperative fluid balance influences postoperative outcomes.
      • Michell A.R.
      Diuresis and diarrhea: is the gut a misunderstood nephron?.
      • Lobo D.N.
      • Bostock K.A.
      • Neal K.R.
      • Perkins A.C.
      • Rowlands B.J.
      • Allison S.P.
      Effect of salt and water balance on recovery of gastrointestinal function after elective colonic resection: a randomised controlled trial.
      • Chowdhury A.H.
      • Lobo D.N.
      Fluids and gastrointestinal function.
      A randomised controlled trial investigating the effects of salt and water balance on recovery of gastrointestinal function after elective colonic resection, reported that positive salt and water balance delays return of gastrointestinal function and prolongs hospital stay.
      • Lobo D.N.
      • Bostock K.A.
      • Neal K.R.
      • Perkins A.C.
      • Rowlands B.J.
      • Allison S.P.
      Effect of salt and water balance on recovery of gastrointestinal function after elective colonic resection: a randomised controlled trial.
      This delayed recovery could result from mesenteric oedema that compromises blood flow to the bowel.
      • Shandall A.
      • Lowndes R.
      • Young H.L.
      Colonic anastomotic healing and oxygen tension.
      • Wilkes N.J.
      • Woolf R.
      • Mutch M.
      • Mallett S.V.
      • Peachey T.
      • Stephens R.
      • et al.
      The effects of balanced versus saline-based hetastarch and crystalloid solutions on acid-base and electrolyte status and gastric mucosal perfusion in elderly surgical patients.
      The same mechanisms contribute to prolonged postoperative ileus and intestinal failure and may inhibit anastomotic healing following bowel surgery.
      • Chowdhury A.H.
      • Lobo D.N.
      Fluids and gastrointestinal function.
      • Wilkes N.J.
      • Woolf R.
      • Mutch M.
      • Mallett S.V.
      • Peachey T.
      • Stephens R.
      • et al.
      The effects of balanced versus saline-based hetastarch and crystalloid solutions on acid-base and electrolyte status and gastric mucosal perfusion in elderly surgical patients.
      • Schnuriger B.
      • Inaba K.
      • Wu T.
      • Eberle B.M.
      • Belzberg H.
      • Demetriades D.
      Crystalloids after primary colon resection and anastomosis at initial trauma laparotomy: excessive volumes are associated with anastomotic leakage.
      Other studies have shown better outcome if intraoperative and postoperative fluids were restricted to maintain constant body mass and zero fluid balance.
      • Brandstrup B.
      • Tonnesen H.
      • Beier-Holgersen R.
      • Hjortso E.
      • Ording H.
      • Lindorff-Larsen K.
      • et al.
      Effects of intravenous fluid restriction on postoperative complications: comparison of two perioperative fluid regimens: a randomized assessor-blinded multicenter trial.
      • McArdle G.T.
      • McAuley D.F.
      • McKinley A.
      • Blair P.
      • Hoper M.
      • Harkin D.W.
      Preliminary results of a prospective randomized trial of restrictive versus standard fluid regime in elective open abdominal aortic aneurysm repair.
      • Neal J.M.
      • Wilcox R.T.
      • Allen H.W.
      • Low D.E.
      Near-total esophagectomy: the influence of standardized multimodal management and intraoperative fluid restriction.
      • Varadhan K.K.
      • Lobo D.N.
      A meta-analysis of randomised controlled trials of intravenous fluid therapy in major elective open abdominal surgery: getting the balance right.
      The Sepsis Occurrence in Acutely Ill Patients study conducted across 24 European countries showed that a positive fluid balance was an independent risk factor for 60-day mortality in critically ill patients.
      • Payen D.
      • de Pont A.C.
      • Sakr Y.
      • Spies C.
      • Reinhart K.
      • Vincent J.L.
      A positive fluid balance is associated with a worse outcome in patients with acute renal failure.

      13. Perioperative fluid management in older adults

      Fluid and electrolyte therapy form an essential part of perioperative care and have a direct bearing on outcome.
      • Lobo D.N.
      • Macafee D.A.
      • Allison S.P.
      How perioperative fluid balance influences postoperative outcomes.
      • Schnuriger B.
      • Inaba K.
      • Wu T.
      • Eberle B.M.
      • Belzberg H.
      • Demetriades D.
      Crystalloids after primary colon resection and anastomosis at initial trauma laparotomy: excessive volumes are associated with anastomotic leakage.
      The UK national confidential enquiry into perioperative deaths in 1999 found that at the extremes of age errors in fluid management, usually fluid excess, were the most common cause of avoidable postoperative morbidity and mortality, further highlighting the importance of accurate fluid prescription in older adults.
      • Callum K.G.
      • Gray A.J.
      • Hoile R.W.
      • Ingram G.S.
      • Martin I.C.
      • Sherry K.M.
      • et al.
      Extremes of age: the 1999 report of the national confidential enquiry into perioperative deaths.
      The perioperative fluid regimen is dependent on the quantity of fluid prescription as well as amount of electrolytes administered. 0.9% sodium chloride (saline) is one the most commonly used intravenous crystalloids in the world.
      • Awad S.
      • Allison S.P.
      • Lobo D.N.
      The history of 0.9% saline.
      It is commonly prescribed in surgical patients and has been shown to cause hyperchloraemic acidosis in large volumes, even in healthy subjects.
      • Lobo D.N.
      • Stanga Z.
      • Aloysius M.M.
      • Wicks C.
      • Nunes Q.M.
      • Ingram K.L.
      • et al.
      Effect of volume loading with 1 liter intravenous infusions of 0.9% saline, 4% succinylated gelatine (Gelofusine) and 6% hydroxyethyl starch (Voluven) on blood volume and endocrine responses: a randomized, three-way crossover study in healthy volunteers.
      • Reid F.
      • Lobo D.N.
      • Williams R.N.
      • Rowlands B.J.
      • Allison S.P.
      (Ab)normal saline and physiological Hartmann's solution: a randomized double-blind crossover study.
      • Williams E.L.
      • Hildebrand K.L.
      • McCormick S.A.
      • Bedel M.J.
      The effect of intravenous lactated Ringer's solution versus 0.9% sodium chloride solution on serum osmolality in human volunteers.
      Human studies have also shown sodium balance remains abnormal for up to two days post infusion of normal saline with associated suppression of the RAAS.
      • Drummer C.
      • Gerzer R.
      • Heer M.
      • Molz B.
      • Bie P.
      • Schlossberger M.
      • et al.
      Effects of an acute saline infusion on fluid and electrolyte metabolism in humans.
      Moreover, studies have reported higher complication rates and the need for renal replacement therapy in patients who had received 0.9% saline than in those who received balanced crystalloid solutions following major open abdominal surgery (Fig. 2).
      • Shaw A.D.
      • Bagshaw S.M.
      • Goldstein S.L.
      • Scherer L.A.
      • Duan M.
      • Schermer C.R.
      • et al.
      Major complications, mortality, and resource utilization after open abdominal surgery: 0.9% saline compared to plasma-lyte.
      Furthermore, chloride-restrictive intravenous fluid therapy has been shown to reduce the incidence of acute kidney injury and the need for renal replacement therapy in ICU patients.
      • Yunos N.M.
      • Bellomo R.
      • Hegarty C.
      • Story D.
      • Ho L.
      • Bailey M.
      Association between a chloride-liberal vs chloride-restrictive intravenous fluid administration strategy and kidney injury in critically ill adults.
      A randomised controlled double-blinded crossover study where two litres of saline or Plasma-Lyte (a balanced solution) were administered intravenously to healthy volunteers reported for the first time in humans that saline resulted in reduced renal blood flow velocity and cortical tissue perfusion.
      • Chowdhury A.H.
      • Cox E.F.
      • Francis S.T.
      • Lobo D.N.
      A randomized, controlled, double-blind crossover study on the effects of 2-L infusions of 0.9% saline and Plasma-Lyte(R) 148 on renal blood flow velocity and renal cortical tissue perfusion in healthy volunteers.
      This is likely to further increase salt and water retention, with older adults at increased risk because of the age-related physiological changes and the high incidence of renal failure and heart failure in this group. Saline-induced hyperchloraemic acidosis was also suggested to prolong postoperative recovery through reduced gastric blood flow and intramucosal pH in older adult patients.
      • Wilkes N.J.
      • Woolf R.
      • Mutch M.
      • Mallett S.V.
      • Peachey T.
      • Stephens R.
      • et al.
      The effects of balanced versus saline-based hetastarch and crystalloid solutions on acid-base and electrolyte status and gastric mucosal perfusion in elderly surgical patients.
      • Varadhan K.K.
      • Lobo D.N.
      A meta-analysis of randomised controlled trials of intravenous fluid therapy in major elective open abdominal surgery: getting the balance right.
      In contrast, balanced crystalloids induce less of a sodium and chloride load compared with saline and do not induce hyperchloraemic acidosis, leading to more rapid sodium excretion.
      • Reid F.
      • Lobo D.N.
      • Williams R.N.
      • Rowlands B.J.
      • Allison S.P.
      (Ab)normal saline and physiological Hartmann's solution: a randomized double-blind crossover study.
      • Williams E.L.
      • Hildebrand K.L.
      • McCormick S.A.
      • Bedel M.J.
      The effect of intravenous lactated Ringer's solution versus 0.9% sodium chloride solution on serum osmolality in human volunteers.
      A very recent study demonstrated a 22% incidence of acute postoperative hyperchloremia (serum chloride >110 mmol/l).
      • McCluskey S.A.
      • Karkouti K.
      • Wijeysundera D.
      • Minkovich L.
      • Tait G.
      • Beattie W.S.
      Hyperchloremia after noncardiac surgery is independently associated with increased morbidity and mortality: a propensity-matched cohort study.
      Patients with hyperchloremia were at increased risk of 30-day postoperative mortality [3.0% vs. 1.9%; odds ratio (95% CI): 1.58 (1.25–1.98)] and had a longer median hospital stay [7.0 days (IQR 4.1–12.3) vs. 6.3 days (IQR 4.0–11.3), p < 0.01] than those with normal postoperative serum chloride concentrations.
      • McCluskey S.A.
      • Karkouti K.
      • Wijeysundera D.
      • Minkovich L.
      • Tait G.
      • Beattie W.S.
      Hyperchloremia after noncardiac surgery is independently associated with increased morbidity and mortality: a propensity-matched cohort study.
      Patients with postoperative hyperchloremia were also more likely to have postoperative renal dysfunction as defined by a > 25% decrease in GFR (12.9% vs. 9.2%, p < 0.01).
      Figure thumbnail gr2
      Fig. 2Complications that are increased with 0.9% saline relative to balanced crystalloids.
      Monitoring of fluid input and output in all surgical patients is of great importance as a knowledge of fluid balance can help direct adequate fluid replacement where needed. This is usually poorly recorded on fluid balance charts and there are difficulties in accurately accounting for insensible fluid losses because these vary depending on the environment and on the disease process. Monitoring of perioperative fluid balance after liver transplant with controlled, appropriate negative fluid balance in the first three perioperative days has been shown to decrease the incidence of postoperative pulmonary oedema and lead to better postoperative recovery.
      • Jiang G.Q.
      • Peng M.H.
      • Yang D.H.
      Effect of perioperative fluid therapy on early phase prognosis after liver transplantation.
      • Walsh S.R.
      • Tang T.Y.
      • Farooq N.
      • Coveney E.C.
      • Gaunt M.E.
      Perioperative fluid restriction reduces complications after major gastrointestinal surgery.
      Furthermore, a meta-analysis of randomised clinical trials of intravenous fluid therapy in major elective open abdominal surgery reported a reduction in postoperative complications by 41% and length of hospital stay by 3.4 days in patients managed with appropriate (near zero) fluid balance as opposed to states of fluid imbalance.
      • Varadhan K.K.
      • Lobo D.N.
      A meta-analysis of randomised controlled trials of intravenous fluid therapy in major elective open abdominal surgery: getting the balance right.
      Moreover, various studies have shown that in high risk patients flow guided intraoperative fluid therapy and provision of small (200–250 ml) boluses of colloid to optimise stroke volume, results in a significant improvement in outcome.
      • Sinclair S.
      • James S.
      • Singer M.
      Intraoperative intravascular volume optimisation and length of hospital stay after repair of proximal femoral fracture: randomised controlled trial.
      • Venn R.
      • Steele A.
      • Richardson P.
      • Poloniecki J.
      • Grounds M.
      • Newman P.
      Randomized controlled trial to investigate influence of the fluid challenge on duration of hospital stay and perioperative morbidity in patients with hip fractures.
      • Abbas S.M.
      • Hill A.G.
      Systematic review of the literature for the use of oesophageal Doppler monitor for fluid replacement in major abdominal surgery.
      • Noblett S.E.
      • Snowden C.P.
      • Shenton B.K.
      • Horgan A.F.
      Randomized clinical trial assessing the effect of Doppler-optimized fluid management on outcome after elective colorectal resection.
      • Conway D.H.
      • Mayall R.
      • Abdul-Latif M.S.
      • Gilligan S.
      • Tackaberry C.
      Randomised controlled trial investigating the influence of intravenous fluid titration using oesophageal Doppler monitoring during bowel surgery.
      • Gan T.J.
      • Soppitt A.
      • Maroof M.
      • el-Moalem H.
      • Robertson K.M.
      • Moretti E.
      • et al.
      Goal-directed intraoperative fluid administration reduces length of hospital stay after major surgery.
      • Mythen M.G.
      • Webb A.R.
      Intra-operative gut mucosal hypoperfusion is associated with increased post-operative complications and cost.
      • Wakeling H.G.
      • McFall M.R.
      • Jenkins C.S.
      • Woods W.G.
      • Miles W.F.
      • Barclay G.R.
      • et al.
      Intraoperative oesophageal Doppler guided fluid management shortens postoperative hospital stay after major bowel surgery.
      • Walsh S.R.
      • Tang T.
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      However, such invasive means of monitoring patients may not be of additional benefit where patients receive accurate postoperative fluid management.
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      14. Fluid prescribing in the older adult surgical patient

      Salt and water retention is of great importance, but fluid prescription is often left to the most junior members of the medical team. Numerous studies have shown that inaccurate prescription of fluid results in fluid overload: some patients were reported to receive up to 5 L of excess water and 500 mmol of excess sodium (and chloride) per day.
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      If perioperative optimisation of fluid and electrolyte balance is to be achieved, doctors need to be well informed and, therefore, empowered to make accurate decisions on fluid prescription. This was shown to be achievable through the provision of a dedicated fluid and electrolyte physiology interactive workshop and maybe useful in tackling current gaps in knowledge and training.
      • Awad S.
      • Allison S.P.
      • Lobo D.N.
      Fluid and electrolyte balance: the impact of goal directed teaching.

      15. Conclusion

      The ageing population has increased in recent years due to advances in medical care. Work published in the 21st century has highlighted significant morbidity and mortality related to fluid and electrolytes abnormalities in older adults. Despite this, there is still major need for improvements in the way these key issues are assessed and managed. Age-related pathophysiological changes coupled with polypharmacy and poor physiological reserves predispose older adults to significant fluid and electrolyte abnormalities, particularly in the face of physiological stress. Improved awareness and monitoring together with better patient education is key. This together with knowledge of age-related pathophysiological changes, including renal senescence and age-related hormonal changes which directly effect fluid and electrolyte balance in older adult surgical patients are essential to diagnose and manage this common, yet potentially fatal, problem.

      Author contributions

      AMEl-S: Study design, literature search, selection of studies, data interpretation, writing of the manuscript and final approval.
      OS: Study design, data interpretation, critical revision of the manuscript and final approval.
      RM: Study design, data interpretation, critical revision of the manuscript and final approval.
      DNL: Study design, literature search, selection of studies, data interpretation, writing of the manuscript, critical revision and final approval.

      Funding

      Mr Ahmed M El-Sharkawy is funded by a research fellowship from the European Hydration Institute .

      Conflict of interest

      DNL has received unrestricted research funding and speaker's honoraria from BBraun , Fresenius Kabi and Baxter Healthcare for unrelated work. None of the other authors has a conflict of interest to declare.

      Acknowledgements

      None.

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