fluid intake

8/4/2019 Fluid Intake

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Fluid intake

Two sources:

(1) exogenous

(2) endogenous.



Exogenous water:

average 23 litres per 24 hours

± Drunk or

± Ingested in solid food (nearly half).



� The water requirements of infants andchildren are relatively greater than those of adults because of:

(1) the larger surface area per unit of body weight;

(2) the greater metabolic activity due to growth; and

(3) the comparatively poor concentrating ability of the immature kidney.



� Endogenous water is released during the

oxidation of ingested food;

± Normally < 500 ml/ 24 hours.

± However, during starvation, this amount is

supplemented by water released from the

breakdown of body tissues.



� Fluid output: Water is lost from the body by

four routes.

1: By the lungs. About 400 ml / day.� the loss is correspondingly greater in:

± a dry atmosphere

±

when the respiratory rate is increased, ± trachea intubated or tracheostomy



2: By the skin.

� By visible perspiration and through invisibleperspiration.

� The cutaneous fluid loss varies with ± atmospheric temperature

± humidity

± muscular activity

±

body temperature.� In a temperate climate the average loss is

between 600 and 1000 ml/24 hours.



3: Faeces:

� Loss is between 60 and 150 ml/ daily.

� In diarrhoea this amount is greatly multiplied.



� Urine.

� The normal urinary output is approximately 1500ml/24 hours,

�

A minimum urinary output of approximately 400m1/24 hours is required to excrete the end products of protein metabolism

� Output of urine is under control of blood volume,hormonal and nervous influences.

�Antidiuretic hormone: stimulates the reabsorption of water from the renal tubules, thus varying the amountexcreted after the requirements of the first threeroutes have been met.



� Water depletion

Pure water depletion is usually due to diminishedintake.

± due to lack of availability, ± difficulty or inability to swallow because of painful

conditions of the mouth and pharynx,

± Obstruction in the oesophagus.

� As much as 500 ml in of water in excess of thenormal insensible loss may be seen intracheostomy.



Clinical features

� Weakness and intense thirst.

� The urinary output is diminished and its specific

gravity increased.

± The increased serum osmotic pressure causes water

to leave the cells (intracellular dehydration), and thus

delays the onset of overt compensated hypovolaemia.



Water intoxication

� when excessive amounts of water with low sodium orhypotonic solutions are taken or given by any route. ± The commonest cause in surgical wards is the overprescribing of

intravenous 5% cent glucose solutions to postoperative patients.

±

Colorectal washouts with plain water, instead of saline. ± TURP (transurethral resection of the prostate) syndrome is the

water intoxication caused by excessive uptake of water fromirrigation fluid.

� Similarly, water intoxication can occur if the body retainswater in excess to plasma solutes. ± Like: SIADH seen in lung conditions such as lobar pneumonia,

empyema and oat-cell carcinoma of bronchus, as well as headinjury.



Clinical features

� drowsiness,

� weakness,

� sometimes convulsions and coma.� Nausea and vomiting of clear fluid.

� patient passes a considerable amount of dilute urine(except in SIADH).

Laboratory investigations may show: falling haematocrit,serum sodium and other electrolyte concentrations.



T reatment: Best course is water restriction.

�Administration of diuretics or hypertonicsaline in severe cases.

� Rapid changes in serum sodium concentration

may result in neuronal demyelination and afatal outcome.

fluid intake

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