Therapeutic Notes

DEHYDRATION and its treatment Part II

% R. N. CHAUDHUM, m.b., m.rc.p., t.d.d.

Professor of Tropical Medicine, School of Tropical Medicine, Calcutta

Sait Deficiency

;vjTHis occurs when water and salt are lost 1 e the patient is taking water freely or being

Foe0n Parenteral glucose but no salt. Such

wh'ef COmi?only come from digestive juices . i1 c.ontain a large volume of water and have

?minant sodium and chloride ions (total of pSe?re^i?ns approximate 2 gallons with 2 oz. , c!1\0rides) and hence are seen in diarrhoea or

fo^tmg. The latter is usually of a protracted

1 m as in pyloric stenosis or toxemia of

so i^nanc^ *n which water intake goes on while 'l MUm and chloride are being continually

donV S? effects ?f salt deficiency tend to

are ln,a^e ^'ie picture. Other digestive causes

, Pr?longed gastric or intestinal suction and fistula. Salt deficiency may also

bv Uf thro^h excessive sweating, accompanied exa T ̂ r*nking ?f unsalted water. Familiar o niPles are seen in firemen and stokers,

rln, .ltself is a hypotonic fluid, still quite an

GY?le.cljble amount of sodium chloride may be defi

when sweating is profuse. But salt

acUtC16nCy is.n?t necessarily an acute or sub- ove

? ,con^i?nJ smaller losses prolonged denll i-

or weeks can also cause severe P etion, particularly if salt intake is lowered.

evf1-! Deficiency the burden falls on the

ah>lUC r which becomes hypotonic from

the ?Iraa^ loss sdts. As this is liable to upset

rem jSm?^c equilibrium, the kidneys try to

deh ^ ^ excreting water. This causes

am ^ a^on' because the excretion of water may

0f ?Un^ to a large volume; a 70 kg. man depleted Htr ??" body salt, for example, needs 3-| no

88 Pints) of isotonic saline to restore the th m

. balance. Owing to the renal activity, mn

U-nne v?lume is not decreased at first and iy indeed be increased; it is more dilute and

chloride is absent except in Addison's disease. As there is no cellular dehydration, thirst is

absent; indeed water is often repellent as it tastes insipid. Cramps develop when depletion of salt continues. The patient suffers from

lassitude, weakness, headache and tendency to

fainting on standing up. Appetite becomes poor and there may be nausea and vomiting, thus starting a vicious circle. The plasma sodium and chloride fall. Rise of blood urea, mental

apathy and general exhaustion are greater than in water deficiency. There may be marked mental

changes, e.g. confusion and delusion. In severe cases water by mouth is very slowly excreted, which, as Marriott (1947) suggests, may be due to atony of the stomach and delayed absorption, a condition which may lead to the wrong diag- nosis of acute dilatation of stomach. Usually there is some disturbance of acid-base equilibrium caused by disproportionate loss of sodium and chloride ions from the digestive secretions. Vomiting causes a relatively greater depletion of chlorides and tendency to alkalosis.

Diarrhoea, on the other hand, has the reverse

effect with disproportionate loss of sodium and a tendency to acidosis. With the progressive loss of fluid, the

plasma volume is reduced, but tends to main- tain itself at the expense of the tissue fluid, and when this source fails, circulatory disturb- ance becomes manifest. A systolic blood pressure below 90 mm. Hg. probably indicates at least a 25 per cent reduction of plasma volume, but in some cases as much as two-thirds of it may be lost (normal plasma volume is about 3 litres). As a rough rule, plasma loss multiplied by 6 gives the total extracellular fluid loss (Marriott). Reduction of plasma volume is accompanied by haemo-concentration, increased viscosity of blood and diminished urine, and the patient passes into a state of circulatory collapse or

shock. He is pallid with sunken eyes, cold extremities and collapsed veins. Anuria occurs

when the blood pressure falls to about 70 to 80 mm. Hg. and finally there is stupor and coma. Unless the true nature of the condition is recog- nized, deaths are ascribed to unemia, toxsemia or circulatory failure.

A form of chronic salt deficiency must be mentioned which is more common among unacclimatized Europeans in the hot weather of the tropics who excrete increased amount of sodium chloride in their sweat. Its effects are more insidious; lassitude, apathy, undue fatigue and poor appetite. Such persons are benefited

by taking extra salt.

Mixed water and salt deficiency

This occurs from abnormal losses of secre-

tions, but the patient is not taking water freely. It is common in any condition with acute

vomiting. Most patients have a mixture of the symptoms of pure water and of pure salt

depletion. The extracellular fluid volume is

350 THE INDIAN MEDICAL GAZETTE [Aug., 1949

reduced and tends to be hypertonic owing to the disproportionate water loss, and this tendency causes some withdrawal of water from the cells.

The clinical picture is that of salt deficiency as described above; patients are also thirsty and have dry mouth and early oliguria. Thus we see that the body may become fluid-

deficit from lack of water, salt or both. In the

first case the loss is distributed over the whole

volume of body water, including the intracellular fluid; this accounts for the great thirst. In salt

deficiency, only the extracellular fluid is affected, the blood volume is early reduced and hence the

great weakness. ' For any given amount of fluid

loss, the effect on plasma volume and so on cir- culatory efficiency will be about three times

as great when the fluid loss is due to salt as

when it is due to water deficiency (Black). In

ordinary practice clear-cut deficiencies as des-

cribed above are not common and patients often show a fluid imbalance somewhere between

water and salt deficiency, its degree depending on the nature and amount of fluid lost and on

the food and water taken by the patient. The most frequent causes are diarrhoea and vomiting.

Fluids used in dehydration 1. Water.

2. Sodium chloride solution?

(a) Isotonic (normal)?0.85 per cent or

lesser strength. (b) Hypertonic?1.1 per cent.

3. Glucose solution?5 per cent.

4. Plasma.

Water.?This is indispensable in dehydration. Fluid by mouth is easily absorbed, more satis- factory and better retained than any fluid given parenterally. Moreover, there is no risk of overloading the circulation. In severe salt deficiency, however, when the patient is collapsed, water given by mouth tends to collect and over- fill the stomach from which it may be regurgitated or vomited with risk of being aspirated and infecting the lungs, owing to depression of the cough reflex. It is also dangerous to give much water either orally or intravenously when the blood pressure is low and anuria develops. For then the water, being unable to pass out, enters the cells and may cause symptoms of water

intoxication?vomiting, epigastric distress, dis- orientation and convulsions leading on to coma and death.

Sodium chloride solution.?This is most valu- able in dehydration secondary to salt deficiency, as it supplies at one and the same time the water and the lost electrolytes. Saline is also of help in correcting states of acidosis and alkalosis. Though it is usually given parenterally, half normal saline or an equal mixture of normal saline and glucose solution is often tolerated orally. A normal saline contains 9 gm. of salt per litre, while most body fluids contain 6 gm.

per litre; the excess is excreted by the kidney. But even in health, the power of the kidney to excrete salt has definite limits (not more than 2 per cent in urinej and the use of excessive

amounts adds to the work of the kidneys and may lead to its retention and cedema of the body. So as soon as the symptoms are relieved, isotonic saline should be discontinued in favour of 5

per cent glucose or hypotonic saline, if intra- venous infusion needs still to be continued. Infants have far less power than adults of excreting salt. Normal saline is a danger- ous drug to them and suitable concentrations are 1/4 or 1/5 isotonic, which is prepared by mixing one part of normal saline with three or four parts of 5 per cent glucose. Hypertonic saline is used only in severe forms of salt

deficiency, such as cholera, when several litres of saline fluid are lost in a few hours.

Glucose solution (5 per cent).?It serves the following purposes : (1) It is a good vehicle for supplying water when this is to be given parenterally. (2) It supplies some calories, since often the patient is starving. (3) It promotes the oxidation of any ketones that may be

present. (4) It promotes diuresis (probably in stronger solutions). Glucose is given for water deficiency and has in itself no value in salt

deficiency unless combined with salt.

Plasma.?It is used in circulatory collapse in which saline and glucose are only of temporary benefit because they rapidly leave the blood vessels. Plasma increases the lowered volume of circulating blood and raises the intravascular osmotic pressure owing to its protein and salt con- tent, the latter being approximately the same as in normal saline.

Routes of administration

In relatively minor degrees of dehydration or as a prophylactic measure, the oral route is sufficient. If the patient has difficulty in drink- ing or is comatose, a valuable method is continu- ous drip method through a Ryle's tube passed via the nose into the stomach. Another way is

through the rectum. Intravenous route is the method of choice when the fluid must be given as speedily as possible or when gastro-intestinal irritation is present. To prevent reactions, the solution should be free from pyrogenic sub- stances. Subcutaneous injection may be used, but in many instances the circulation is so defec- tive that there may be considerable delay in absorption of the fluid. In infants and young children, the intraperitoneal administration of fluid may be satisfactory at times. Glucose (except perhaps in 5 per cent solution) is inadvisable for subcutaneous or intraperitoneal injection as it may be irritating to the tissues. There is also the risk of collapse in cases of severe salt depletion, because the sodium and chloride ions from the already depleted plasma rapidly diffuse into the tissue depot of injected glucose solution.