3. INTRODUCTION
• body is ~2/3rds water (males=63%; women=52%)
• This water occupies three “compartments”:
• Intracellular - 63% (or 40% of body wt)
25L
facilitates chemical reactions, solvent.
• Extracellular -37% (or 20% of body wt)
[15L] provides internal environment for cells
and transport, protection, etc(transcellular
(CSF, eye, synovial
• joints, bursae) 30% 12L
Interstitial
• lymph
• plasma (=intravascular) 7% 3L
• Total: 40L(25 + 15+12+3)
• based on 70kg(154lb) person
4. • Electrolyte and fluid balance means balancing input and output.
• The most important output organ is the kidney.
• Urine volume is controlled by glomerular filtration rate and reabsorption by the tubules .
• The output is controlled by the two major hormones
• ADH-increase water reabsorption and decrease urine volume(distal and collecting
duct)
• ALDOSTERONE- increase tubular reabsorption of sodium and other ion
5. • In most individuals between the ages of 30 and 85 years, there is a 20% to 25% loss of renal mass,
most of which is cortex?
• The aging kidney also exhibits hyalinization of blood vessel walls and a decrease in the number of
glomeruli.
• This process progresses to hyalinizing arteriosclerosis and scattered arteriolar obliteration with a
resultant loss of nephrons secondary to ischemia.
• A well-known comorbidity is that elevated blood pressure will advance the decline of renal
function.
• The kidneys exhibit an impaired concentrating capacity over time and a 10% decline in renal blood
flow per decade after young adulthood.
6. Physiological changes in renal function and fluid-
electrolytes balance associated with aging.
• Decrease in total body water
• Decrease in GFR
• Decrease in urinary concentrating ability
• Increase in ADH
• Increase in atrial natriuretic peptide (ANP)
• Decrease in thirst mechanism
• Decrease in aldosterone
• Decrease in free water clearance
7. Sodium balance and hypertension
• The most common electrolyte abnormalities in elderly is dysnatreamia.
• Age has been found to be an independent risk factor for developing both hyponatremia
and hypernatremia.
• With aging, muscle mass is replaced by fat, total body water is reduced and intracellular
volume is changed, which play a role in increasing prevalence of hyponatremia and
hypernatremia.
8. • Aging is associated with impaired excretion of a salt load and defective
conservation in the setting of sodium restriction.
• Proximal sodium reabsorption is increased in aging, whereas distal sodium reabsorption
may be reduced.
• The diet of most individuals in wealthier countries contains excess sodium (8–10 g of salt
daily), there is a tendency for total body sodium excess among elderly people.
9. • This relative defect in sodium excretion and increased total body sodium may be
predisposing factors for the development of hypertension.
• After the age of 60 years, most people are hypertensive.
• Salt sensitivity occurs in more than 85% of aging people, and sodium restriction will
result in a Signiant fall (>10 mm Hg) in mean arterial pressure.
• Populations that ingest low sodium diets, such as the Yanomami Indians of southern
Venezuela, do not show an increase in blood pressure (BP) with age.
10. • Treatment of hypertension in the elderly (>75 years) should be similar to that in the
younger population because treating to a systolic BP (SBP) target of less than 120 mm
Hg (compared with an SBP target of <140 mm Hg) resulted in significantly lower rates
of fatal and nonfatal major cardiovascular events. SPRINT trial
• But reaching these lower BP goals in the elderly may be more difficult, require more
medications, and have risk for orthostatic and diastolic hypotension. Hypotension in the
frail elderly patient may be associated with an increased risk of falls and morbidity.
11. Osmoregulation and Water Handling
• The most common electrolyte abnormalities in the elderly are the consequence of impaired
water handling with aging.
• Prevalence of hyponatremia is 11% among ambulatory geriatric population and 5.3% of
hospitalized elderly patients.
• Hypernatremia is found in about 1% of patients older than 60 years and admitted to the
hospital.
• Dysnatremia is cased by inability to concentrate and dilute urine with aging
Schlanger LE, Bailey JL, Sands JM. Electrolytes in the aging. Adv Chronic Kidney Dis. 2010 Jul;17(4):308-19. doi: 10.1053/j.ackd.2010.03.008. PMID: 20610358;
PMCID: PMC2901254.
12. • Total body water decreases with age. In a younger man near his ideal body weight, total
body water composes 60% to 65% of his body mass.
• By age 80 years, this contribution is reduced to 50%.
• With < 1% decrease in osmolality, hypothalamus-posterior pituitary axis respond by
inhibiting ADH release hence failure to concentrate urine
13. • In the elderly, the maximal urinary osmolality and thirst response to
hyperosmolality are reduced, which may predispose to dehydration and
hypernatremia.
• The impairment in urine concentrating ability results from a defect in the
concentrating gradient in the medullary region and can lead to nocturia.
• Hypernatremia can occur in ill elderly patient not having access to water.
14. • The elderly also have an impaired ability to dilute the urine and thus have a decreased
ability to excrete a water load, leading to an increased predisposition to hyponatremia
that is often compounded by the use of medications such as thiazide diuretics and
selective serotonin reuptake inhibitors.
• Whether age per se is an independent risk factor for the development of hyponatremia
has been questioned, because after adjustment for frailty, the relationship between age
and sodium disorders is no longer significant.
Vajdic CM, McDonald SP, McCredie MR, van Leeuwen MT, Stewart JH, Law M, Chapman JR, Webster AC, Kaldor JM, Grulich AE. Cancer incidence before and after kidney transplantation. JAMA. 2006 Dec
15. Other tubular defect and electrolyte abnormality
• Potassium excretion is impaired in the elderly, and the trans tubular potassium gradient is
decreased.
• Hyperkalemia occurs more frequently in elderly patients treated with drugs that interfere
with potassium excretion (such as potassium-sparing diuretics or agents that block the
renin-angiotensin-aldosterone system).
• Hypokalemia is also common because of kidney (especially with thiazide diuretics) or
extrarenal losses.
16. Calcium
• Hypercalcemia occurs in 1% to 3% of elderly patients.
• Causes include malignancy, hyperparathyroidism, immobilization, and use of thiazide
diuretics.
• Many patients with thiazide-associated hypercalcemia have underlying primary
hyperparathyroidism.
• Hypocalcemia is less common and is observed mainly in patients with advanced CKD (in
association with vitamin D deficiency and hyperphosphatemia), chronic malabsorption,
and severe malnutrition.
17. Magnesium
• Hypomagnesemia is reported in 7% to 10% of elderly patients admitted to the hospital,
most commonly because of malnutrition or laxative or diuretic use.
• Hypermagnesemia is less common and is found primarily in patients with CKD or who
are taking large doses of magnesium-containing antacids. Gout (as well as asymptomatic
elevations in serum uric acid levels) is also more common in older people.
18. Acid base balance
• Most elderly individuals can maintain acid-base balance under normal conditions.
• However, during conditions of stress when acid production is increased (sepsis or acute
kidney injury [AKI]), an inability to excrete an additional acid load may be uncovered.
• This is supported by a study demonstrating that elderly patients could not increase net
acid excretion to the same level as younger adults in response to a protein meal.48
• This tendency to metabolic acidosis becomes more manifest in the presence of CKD,
particularly in concomitant pulmonary disease limit compensatory hyperventilation.
• Evangelidis N, Craig JC, Tong A. Song Executive Committee and Investigators. Standardised Outcomes in Nephrology-Haemodialysis (Song-HD):
using the Delphi method to gain consensus on core outcomes for haemodialysis trials. J Ren Care. 2015;41
19. Conclusion
• Normal physiological changes of aging increase the likelihood of fluid-electrolyte disorders in the elderly
surgical patient.
• The aged kidney undergoes interstitial fibrosis as well as widespread sclerosis of glomeruli and of afferent
arterioles.
• The most crucial functional changes are a decrease in GFR, decreased urinary concentrating abil-ity, and
narrowed limits for the excretion of water, so-dium, potassium, and hydrogen ion.
• Despite these changes, body fluid homeostasis is effectively maintained under normal day-to-day
circumstances.
• Problems may arise when the older patient is placed in a state of fluid deprivation or iatrogenic insult.
• Attention to age-related limitations of fluid homeostasis can help the physician prevent clinical complications
such as hypotonicity and hypertonicity, hy-perkalemia, and volume depletion.
• Meticulous detail must be paid to salt and water balance and to drug dosing and choices.
20. References
• Comprehensive clinical nephrology 7th ED
• United States Renal Data System. International comparisons. USRDS 2016
• annual data report. Atlas of End-Stage Renal Disease in the United States.
• Vol. 2. Bethesda, MD: National Institutes of Health, National Institute of
• Diabetes and Digestive and Kidney Diseases; 2016.
• Vajdic CM, McDonald SP, McCredie MRE, et al. Cancer incidence before and after kidney
transplantation. JAMA. 2006;296:2823–2831.
• Investigators. Standardised Outcomes in Nephrology-Haemodialysis (Song-HD): using the Delphi
method to gain consensus on core outcomes for haemodialysis trials. J Ren Care. 2015;41(4):211–
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