© Borgis - Postępy Nauk Medycznych 10/2015, s. 744-748
*Ryszard Gellert
Odwodnienie u osób w wieku podeszłym – objawy przedmiotowe i podmiotowe
Signs and symptoms of dehydration in the elderly
Department of Nephrology and Internal Medicine, Medical Centre of Postgraduate Education, P. Jerzy Popiełuszko Bielański Hospital, Warszawa
Head of Department: prof. Ryszard Gellert, MD, PhD
Streszczenie
Ocena stanu nawodnienia jest prawdopodobnie najtrudniejszą częścią badania klinicznego. Wyniki obiektywnej oceny nawodnienia często się różnią od klinicznej. Objętość wody wewnątrzkomórkowej nie zmienia się, jeśli tylko jej ostry deficyt nie przekracza 2% ciężaru ciała, ale w pozycji leżącej odwodnienie rzędu 5% ciężaru ciała może być klinicznie niewykrywalne. Hipowolemia towarzyszy zwykle odwodnieniu co najmniej łagodnemu, ale objawy odwodnienia i hipowolemii są bardzo często kompletnie mylone przez lekarzy. Oznaki odwodnienia wyprzedzają jego niespecyficzne objawy, z wyjątkiem pragnienia, które osiąga maksimum przy ubytku wody powodującym utratę 1% ciężaru ciała, ale które może być znacznie zmniejszone z powodu starzenia się, przyjmowania leków lub obu. Wczesne rozpoznanie odwodnienia u osób w wieku podeszłym jest dla nich życiowo ważne, bo pomaga zapobiec hipowolemii i pogorszeniu stanu zdrowia. Powinno to być dokonane przez opiekunów, członków rodziny lub personel medyczny. Objawy podmiotowe i przedmiotowe odwodnienia mogą być pomocne przy określaniu deficytu wody i wspomagać decyzję co do właściwego postępowania. Autor podaje szczegółowe podstawy patofizjologiczne i sposoby oceny stopnia odwodnienia mogące służyć temu celowi.
Summary
Evaluation of the hydration status is probably the most difficult task in clinical examination. The clinical and objective determinations of hydration status frequently differ. The intracellular water volume remains stable when the acute water deficit is less than 2% of body weight (BW), and in the supine position dehydration of less than 5% may by clinically undetectable. Hypovolaemia ensues only from the mild-to-lethal dehydration, and the signs and symptoms of each are frequently wildly mixed up by the doctors. Signs of dehydration in the elderly precede the nonspecific symptoms, with the exception of thirst, which reaches maximum at water deficit of 1%, and is often suppressed by ageing, medication or both. The early detection of dehydration in the elderly is vital to prevent hypovolaemia and health deterioration and should be made by the caregivers, family members or medical professionals. The signs and symptoms can also help in water deficit quantitative evaluation which may support taking decision as to the proper intervention. The author details the pathophysiological background and the dehydration staging, to serve this purpose.
INTRODUCTION
Evaluation of the hydration status is probably the most difficult task in clinical examination. Clinical judgment of water content is based mainly on the results of skin, oral mucosa and jugular veins examination. This is why the clinical and objective determinations of hydration status frequently differ (1). The aged skin is thinner, stiffer, less tense, and flexible than the young one (2). The surface of such a skin appears dry and rough due to the reduced epidermal proliferation accompanied by slower desquamation of the stratum corneum (SC), which makes it thicker and deficient in water binding substances (3). This partly explains why the transepidermal water loss (TEWL) in individuals aged 65 years and above is lower than in younger adults – lowest for the breast skin, and highest for the axilla (4). Up to 60% of population aged 70+ may show some laboratory or clinical signs of dehydration (5).
INTRACELLULAR VOLUME STABILITY
The volume and mineral content of both the ICW and ECW is controlled both by the cells and by numerous body regulatory mechanisms, which stabilize the TBW in a healthy person within 0.22% (± 165 mL) of body weight (BW) (6).
Each of the 1014 cells of the body precisely regulates its own volume by controlling water exchange with the surrounding extracellular fluid. The ICW remains stable when the acute water deficit is less than 2% of BW (1-2 L) (7).
The marked and rapid “pure” water loss from the extracellular compartment, exceeding 2% BW, causes intracellular dehydration, which results in folding and denaturation of intracellular proteins and eventually cellular death – by necrosis or apoptosis. Similar acute isotonic changes in the ECW initially do not affect it, at least in haemodialysed patients with chronic renal insufficiency (8). However, the acute isotonic decrease of plasma or blood volume may cause water shift into the cells and increase the ICW (9, 10).
EXTRACELLULAR VOLUME CHANGES
Almost all extracellular fluid is distributed between the blood plasma (16-17%) and the interstitium – the extracellular space located extravascularly (83-84%). The equilibrium between plasma and interstitium volumes can be affected by many factors, which result in volume shift, either direction.
The hypohydrated interstitium shrinks and becomes hyperoncotic, whereas the hyperhydrated one expands. The first adsorbs water from the cells, which takes time, the second makes cell breathing, nutrition and detoxication more difficult.
The excessive interstitial water may form visible oedema – usually when fluid retention exceeds 4% BW. The loose connective tissues, lungs, gastrointestinal mesentery and mucosa can accumulate even more water – e.g. in pulmonary oedema the interstitial fluid expands fivefold from the normal 500 ml (11).
Due to the resulting adaptive morphological changes in the intracellular space in chronic overhydration, the chronic expansion of up to 8% of the ECW (1.6% of body weight, or 1.2 L in the “average” man) cannot be clinically diagnosed (12).
TISSUE HYDRATION EVALUATION
It is convenient, and correct, to assume for practical purposes, that the daily changes in hydration are limited to the ECW and do not affect the ICW. Thus, the changes in hydration status (ΔHS) can be calculated from the difference between the measured ECW and the normal ECW expected. The Relative Change in Tissue Hydration (RΔTH = AΔTH/ECW) greater than -7% of the ECW (reduction) is a cut off for the moderate-to-lethal dehydration. The RΔTH of +7% (expansion), can be classified as “fluid overload” (13). Because the ECW forms 25% of body weight, the aforementioned 7% of ECW makes 1.75% of BW. This is why the BW changes of less than 1.5% from the individual’s optimal weight (only 1 kg in a person of 70 kg BW), should not be, from the clinical point of view, alarming to the medical and social staff.
OSMOTICALLY DRIVEN INTRACOMPARTMENTAL FLUID SHIFTS
Intrinsic mechanisms keep plasma osmolality within a narrow range of 275-295 mOsm/kg; sodium is the principal osmolality determinant, at 135 to 145 mEq/L. Regulation of the extracellular volume prevails over the regulation of its composition, as it can be clearly seen in SIADH – when slight hyperhydration, mainly intracellular, accompanies severe hypotonicity second to hyponatraemia (14).
HYDRATION AND BLOOD VOLUME
Mild to severe dehydration (lack of water), acute or chronic, is accompanied by hypovolaemia (lack of blood), and so the diagnostic criteria for each of them are usually and incorrectly mixed up and presented together. Blood in the venous part of the vascular system is of lesser importance to hydration regulation as compared to that inside big arteries (“effective blood volume”). Blood volume insufficient to fill the big arteries and perfuse the body organs is called hypovolaemia. It results either from severe hypohydration, from decreased left heart contractitlity (heart failure), or from relaxation of small arteries (e.g. septic shock).
DEHYDRATION IDENTIFICATION
There is no single sign or symptom that would be pathognomonic to dehydration. Thus, the diagnosis of dehydration has to relay mainly on signs actively sought for.
Loss of “pure” water causes hyperosmolar dehydration – it affects exclusively the ECW when less than 2% of body weight is lost, and both, ICW and ECW at more advanced water loss stages.
Loss of water and sodium e.g. in sweat, after diuretics, in hyperglycaemia, results in hypohydration and concomitant hypovolaemia.
Dehydration may be isotonic, hypertonic or hypotonic, depending on the proportion of water and sodium lost.
Depending on the pure water deficit the dehydration can be divided, into:
– imminent: 0.22-1% of body weight,
– mild: 1-2% of body weight,
– moderate: 2-5% of body weight,
– severe: 5-10% of body weight,
– extreme: > 10% of body weight,
– fatal: > 15% of body weight.
Mild to moderate dehydration could be treated at home or in the nursing home (15).
CLINICAL SYMPTOMS BY STAGE OF DEHYDRATION
Hypohydration initially leads to increased urine concentration, which normally results in the output of lower than normal amounts of dark-yellow urine. The volume, osmolality, specific gravity, and colour of the urine are all very sensitive indicators of the extent of the imminent water deficit (16) provided the renal function is normal and the water deficit does not exceed 1% of body weight. The darkening of urine from straw-yellow to yellow, and less frequent visits to the toilet can be usually noticed as early as the water deficit reaches 0.5% of body weight (300-400 ml), and adults attain the maximum urine concentration when the body water deficit arrives at 1% (600-900 ml). In the elderly, the ability of the kidneys to excrete concentrated urine deteriorates, thus the pale urine colour can be deceiving in assuming euhydration, because the urine can remain yellow, even in mild and severe hypohydration, when the dark yellow urine would be expected.
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Piśmiennictwo
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