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Ubersicht / Review

Disorders of water and sodium metabolism in older patients

I. FUSGEN

Department of Geriatrics, University of Witten-Herdecke, Gemany

S u m m a r y : . , . :

Disorders of water and sodiurn metabolism can result in serious problems for older patients. Ilyponatraernia isof special significance in geriatric patients. In addition to the iatrogenic depletion of sodium, causes of hyponatraemiainclude comorbidity and changes associated with ageing that result in a more unstable homeostasis. Adequate fluidintake, but also the availability of needed ele'ctrolytes must be assured. A general recommendation for older, poly-pathic, patients to restrict their sofium intake must be viewed critically.

Keywords

Dehydration - hyponatraemia - geriatric patient

Z u s a m m e n f a s s u q g : . . . ' ' . . . . ' . , . . . . ' � � � � � � � � �

Stiirwngen d.es Wasser- and. Natriarnbaushaltes bei iilteren Patienten:Stcirungen des Wasser- und Natriumhaushaltes kcinnen bei dlteren Patienten zu einer ernsthaften Bedrohung wer-

den. Dabei kommt der Hyponatriiimie beim geriatrischen Patienten besondere Bedeutung zu. Grund dafiir sindneben der iatrogenen Natriumverarmung, u.a. die Komorbiditdt und alternsphysiologische Verdnderungen, die zueiner labileren Homiiostase fiihren. Eine ausreichende Fliissigkeitszufuhr, aber auch eine ausgleichende Elektroly"t-deckung ist zu beachten. Eine generelle Empfehlung zur Natriumrestriktion bei dlteren multirnorbiden Patientenist kritisch zu sehen.

Sdrliisselwrirter ' , "'

Dehydratation - Hyponatridmie - geriatrischer Patient

Disorders of fluid and electrollte metabolism are not un-

usual at an advanced age. Since merely slight disturbances can

lead to catastrophic decompensation and life-threatening sit-

uations, they require speciai attention [17]. Normally, the

older organism is able to maintain the correct osmolarity of

fluid volume as well as the electrolyte composition and con-

centration of the body fluids through the available regulato-

ry systems. llowever, it is necessary to consider some special

age-related factors that can el-icit changed reactions: The exis-

ting age-related physiological changes, the frequendy present

pollpathia with use of several med.ications, the effect of envi-

rorunental conditions, ancl an iatrogenic depletion of sodium.

In this context hyponatraemias with serum values beiow

130 mval/L have a special significance since they are en-

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countered more frequendy at an advanced age than highsodium leveis [21]. As many as 7 % of heaJthy elderly indi-

viduals exhibit a significant decrease in serum sodium values

[4]. Studies conducted in inpatient facilities have found that

7-I2 % of the geriatric patients suffer from hyponatraemia

[ l3 , t9 ] .If hyponatraemia develops slowly, the clinical symptoms

(tiredness, difEculty concentrating, uncertain gait) are fie-quendy ascribed to the ageing process- In the presence ofre-duced osmotic pressure with outflow of fluid from the vas-cular system it is the peripheral oedemas, effusions in theserous cavities, and ascites tiat are the main clinical symp-toms. With sodium values below I25 mvil/L cerebralswelling a.lso occurs and is accompanied by the clinical symp-

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toms of lethargy, confusion and even coma. Therefore, hy-ponatraemia has always been one of the great clinical prob-lems in geriatric patients [, 14].

PHYSIOLOGICAI CHANGES ASSOCIATED\4rITH AGEING

The proportion of fluids in an organism stands in a neg-ative relationship to age and the proportion of fat, but in apositive relationship to the proportion of muscle tissue.Total body water decreases due to the observed loss ofmuscle tissue with increasing age. A neonate's body weightconsists ofapproximately 82 % fluids, while that ofan adultis 60 %, and that of an individual in old age is approximately52 %. Obesity can displace the water content of the bodyto the tireshold ofwhat is pathophysiological. A total bodywater content of only approximately 40 % is more likely therule than the exception [8]. This decline in total body wa-ter content is partially the result of the reduced water bind-ing capacity of the connective tissues with increasing age,but is mainly due to a decrease of the intracellular fluid.The decreased intracellular fluid is a consequence ofa re-duced muscular mass and a simultaneous increase of thewater-poor fatty tissue. In other words, the distribution ofthe body water is displaced to the detriment of the intra-cellular space. This means that the safety mechanism forhomeostasis of the water/electrollte metabolism is im-paired.

On the one hand, fluid and electrolyte homeostasis ismaintained via the control offluid intake, the plasma volumeand fluid excretion and, on the other hand, via the (hor-monal) regulation of the electrolyte metabolism. The latteris likewise affected by the physiological changes of ageingsuch as reduced thirst, decline in renal function and changesin hormone secretion (Table 1). The loss of concentratingability is a characteristic symptom of ageing kidneys. Fur-thermore, increasing age is associated with salt loss becausethe capability of the kidneys to reabsorb sodium slowly de-clines. The reduction of intracellular fluid and electrolytescreates a "status quo" in fluid metabolism that falls quicklyout of balance when subiected to stress.

EFFECT OF POLYPATHIAWith regard to the frequendy occurring pollpathia ofold-

er individuals, the impaired homeostasis of the fluid and elec-trolyte balance is a special problem. On the other hand, myown studies indicate that increasing polypathia is frequendyassociated with an inadequate supply of sodium [6] Ac-cording to the available medical literature lI,I2,2I], it isthe following diseases that are especially responsible for thispolypathia: diabetes mellitus, heart failure, cfuonic obstruc-tive pulmonary disease, renal failure, carcer) myxoedema,chronic infections and febrile conditions as well as vomitins

2

1. Reduced thirst

2. Decline in renal function- Decline in glomerular filtration- Decline in tubular concentrating ability- Decline in sodium conservationw*- uecilne In Tne enect oT vasooresstn

3. Changes in hormone secretion- Decline of plasma renin activity with a decline of

aldosterone secretion- Increased secretion of the atrial natriuretic peptide- lncreased vasopressin secretion durinq osmotic stress

or volume loading

4. Loss of muscle tissue and increased fattv tissue

Tab. 1: Endogenous regulation of the fluid and salt balance in oldage.

or chronic diarrhoea. Even extensive sweating can be thecause of hyponatraemia in the elderly, as has been shown inSwiss studies [3]. Smoking also can cause hlponauaemia

[2]. These electrolyte disturbances often decisively influencethe course of any existing underlying illnesses.

As far as acute diseases are concerned, diarrhoea is mostdirecdy responsible for hyponatraemia. The cause of diar-rhoea can be iatrogenic (e.g., antibiotics), but it also occursfrequendy when the elderly travel. 80 7o of patients who areolder than 80 exhibit a reduced production of stomach acid,because of atrophic gastritis that is usually not associatedwith any therapeutic consequences. Flowever, the absentprotection that was provided by the acid can facilitate the de-velopment of infections, especially since electrolyte lossesthrough sweating decrease the production of stomach acideven further. The loss of sodium is unavoidably associatedwith the loss of water, and it is the extracellular component(i.e., the plasma) that is especially affected.

Osmotic,diuresis during hyperglycaemia ( diabetes melli-tus), severe sweating associated with febrile conditions (in-fections), as well as chronic vomiting are the most frequentcauses of fluid loss in association with diseases.

Fluid retention with hyponatraemia is frequendy causedby the inadequate ADH syndrome (SIADH) in older pa-tients [I8]. SIADH (Syndrome of Inappropriate Antidi-uretic Hormone Secretion) can be caused by a cerebral dis-ease with irritation ofthe posteriorpituitary gland [9], by tu-mour-associated substances or by medications 1241. How-ever, old age itself can be a risk factor for SIADH [13].

I{yponatraemia due to the dilution effect of oedemas as-sociated with heart failure is also common in old age. This"low sodium syndrome" is a complicated therapeutic situ-ation (e.g., frequendy after long-term administration of adiuretic agent). In this stage the effect of the diuretics con-tinuously decreases while the serum sodium concentrationpresents severely reduced values. This results in heart fail-

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ure with peripheral oedemas and venous hepatic conges-tion that no longer responds to medication.

CONSEQUENCES OF POLYMEDICATIONIatrogenic causes ofdisorders offluid and electrolyte bal-

ance within the scope of polymedication in older individualsare by no means rare [2I]. Drugs t]rat are the most likelycandidates include those that have a direct effect on diuresisor the electrolyte metabolism. The uncontrolled intake ofdi-uretic drugs is associated with excessive fluid loss until exsic-cosis, but also with the loss of sodium and/or potassium.

Additionally, the baroceptors in the elderly no longer re-spond adequately to a decrease in blood pressure. Therefore,any pharmacotherapy that even slighdy reduces the amount

Diuretics

ACE inhibitors

Beta blockers

SSRIs

Tricyclic antidepressants

Neuroleptics

NSAIDS

Oral antidiabetics

and others

Tab, 2: Medications possibly associ-ated with hyponatraemia [16].

A connection with respect to SIADH is suspected for thefollowing drugs: propafenone, SSRfs, ACE inhibitors, MAOinhibitors, neuroleptics, carbamazepine and sulfonylurea. In'ris context it should not be forgotten that a series of over-

vthe-counter drugs can cause hyponatraemia (e.g. laxatives).

I{TPOTONIC AND FITPERTONIC DEHT1DRATIONDehydration (inadequate levels of fluid and salt or of flu-

id alone) is rhe mosr frequent disorder of fluid and elec_trolyte balance in older individuals [23] The concomiranrloss of salt distinguishes hyponatraemic (hypotonic) dehy-dration from the isotonic and the hypernarraemic (hyper-tonic) forms of dehydrarion with little or no salt loss.

Hyponatraemic dehydration has special significance be_cause it occurs very frequendy and is often the cause ofatendency to fall in the elderly. The clinical presentation isthat of disturbed orthostatic blood pressure regulation,tachycard.ia and reduced skin rurgor. It is relatively difficultto treat because correcting ttre lack ofsalt cannot be un-dertaken quickly and completely, but requires that theserum sodium be increased gradually in increments ofl0-15 mvall l.

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INADEQUATE INTAIGThe changed cfucumstances of life (all forms of isolation)

accompanying old age can result in unbalanced nutritionthat can lead to deficiencies ranging from dehydration [23]to hyponatraemia If 3] and all the way to severe protein de-ficienry or vitamin and trace element deficiencies. The fur_ther context of the circumstances of life must also includeIaxative abuse that can lead to fluid loss, but especially to hy_ponatraemia and hypokalaemia. More than 60 % of the eld-erly feel consripated.

of body water quicklycan exceed the capacityof compensated regula-tory mechanisms thatare stretched to theirlimit, and can have seri-ous consequences forthe water or electrolltebalance and for the cir-culation.

The medical litera-ture describes a con-nection between hypo-natraemia and an entireseries of medications(Table 2).

IMPROVINGFLUID INTAKEIn many elderly individuals it may - for different reasons

- prove necessary to follow a ,,drinking schedule" to main_tain an adequare fluid intake. Apart from the quantity offluid ingested, its quality is important with regard ro anyexisting illnesses. For example, in tfre case of a catheterisedindividual the intake of acidic juices (e.g. currant juice) ormedicinal acidification through the oral administration ofL-methionine [7] is important. The manner in which thefluid is offered is also important: Who enjoys drinking froma "feeding cup", even if the person in question requiresnursing care|

- i.tf* AVorD RESTRTcTTNG soDruM **--Because of the physiological changes associated witli

ageing and the frequendy existing polypathia, many elder-ly individuals suffer from a latent deficit in their fluid andalso their mineral salt balances (including sodium chlo_ride). Therefore, the most frequent cause of sodium de_pletion in the elderly is very likely iatrogenic in nature (i.e.it can be traced to a restriction of sodium chloride). Manvof the elderly avoid consuming any salr, because salt sup-posedly increases the arterial blood pressure. Additional(the reabsorption of sodium through the kidneys is less ef_ficient in old age.

The medical literature has for some time repeatedly in_dicated rhe minimal importance of salt consumption forhypertensionlI5]. A mera-analysis published in f 99g If 0]summarised the results from a total of l14 studies on saltreduction conducted during the last 3 decacles. The resultwas a moderate reduction of the blood pressure values(SBP/DBP -3.9/7.9 mmHg) in hypertensive individuals;the results for normotensive individuals were marginal(-I.2/0.26 mmHg). An add.itional meta-analysis thar waspublished during t}le past year in the renowned BritishMedical /ournal I t I ] documents that the lons-re rm effects(13-60 monttrs) of switching to a low-salt di., "r. margi-nal: a de crease of l.l in the systolic blood pressure, and of0.6 mmHg in the diastolic blood pressure. Apparently,there was no connection between the extent of salt restric-tion and the resulting decrease in biood pressure.

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Most recendy, therefore, the recommendation given to

elderly hypertensive individuals to follow a low-salt d.iet has

clearly lost its credibility. The effects are minimal; even in cas-

es of massive salt reduction the blood pressure in the major-

ity of patients only decreases by a few mmHg 1221.-S_twrnpef20l even shows that a low-salt d.iet can lead to aei6l-t?Uta

iogrrti.,. deficitj when .o*prr.d *ith a higtr-sa1t diet.'

It appears that weight reducti<in, iriifdised physical activ-

ity, and reduced cilniumpi6n of atc;ffit are-riioie-ffipoitant '

ihnn u reduction of sodium chloride [22].

SODIUM CHLORIDE SUBSTITUTION

The average consumption of table salt in Western indus-

trialised nations is indicated as being 12 g(4-8 g sodium) per

day. However, these numbers are mainly based on surveys

and sales data. In contrast) some experimentai investigations

concerning salt intake partially at significandy lower values

that lie in the range of 7-8 g/d. The nutritional associations

of Switzerland, Austria and Germany recommend a daily

table salt intake of6 g [5]. Therefore, neither a general sait

restriction nor sodium chloride substitution is necessary in

most elderly patients.

CONCLUSIONSBecause of the physiological changes associated with age-

ing, the elderly person is increasingly susceptible to disorders

of electrollte and water balance. Dehydration and sodium

depletion play a special role in this regard. Illnesses tlat oc-

cur in old age, medications and changed circumstances oflife

frequendy have a special effect on this.In this context, an-adpqu^te fluid-ufaKg*Tq a balanced

supplyof ef ggl-olyrgyg:q|lP::14 j.-"Pgf an:g.TEeiide"dfor'electrohtis deoends on the individual circumstances of life.

How.,r.r, the available studies clearly ind.icate that a certain

daily reqtLirement of eleitroly'tes'is ir',dirpens"ble ' In this

io.rt.xt a gineral sodium restriction in elderly patients gives

cause for concern. This changes nothing about the fact that

;i restrittia iniake'of electrolytes must be accepted in certain

diseases. However, *ris must be seen in context with other

dietary measures.

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Pnor. Dn. MED. INGO FUSCSN.

UNngnsnv oF WITrEN-HERDECIc,

KrrNrrcN Sr. ANToNIUS.CanNnlgnsrnassn 60,42283 Wupplnr,q.r.E-MATT-: PROF,FUESGEN@ANTONTUS.NE

received/ eitgegangen: 28.09 .2003accepted/angenommen I 5. I 0.2003

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