Fluid & Electrolyte

Balance

Dr. Deepaka Weerasekara

Objectives

Understand the physiology of fluid

distribution throughout the body.

Assessment of hypovolaemia

Managing fluid balance

Managing electrolyte balance

Basic Physiology

TOTAL BODY WATER

B.W X 0.6 600 ml/Kg(42 L)

ICF ECF

BW X 0.4 BW X 0.2

400ml/Kg 200 ml/Kg (14L)

(28 L )

Interstitial Fluid Plasma

BW X 0.15 BW X 0.05

150 ml/kg(11L) 50 ml/kg (3L)

Water Balance

Input ( Thirst )

Total Body water 600 ml/Kg

Output

Faeces

100ml/24hr

Insensible Loss

15ml/Kg/24Hr

(Skin, Respiration)

Urine Output

1ml/Kg/hr

1500ml/24hrs

OSMOLALITY

Normal plasma osmolality -290 mOsm/kg

Osmolality = 2( Na+ +k+ ) + glucose +

(mOsm/kg) urea (mmol/l)

Compartments from which fluids are lost

depends on the cause of fluid loss.

In which compartments fluid will end up

when administered to the patient depends

on the type of fluid administered.

Fluid replacement

Maintenance - basic needs

Prior deficits - Fasting , vomiting ,diarrhoea,

NG suction etc.

Continuing abnormal losses - Blood loss,

NG suction, Third space loss, fever etc.

Maintenance

Normal water requirement-30/35ml/kg/day

Sodium-2mmol/kg/day

Potassium-1mmol/kg/day

Continuing loss

Eg- Bowel obstruction

- By normal saline with added [k+]

- Keep a fluid balance chart

- Monitor input and output

- Replace 24 hour all fluid out + insensible (urine, drainage, vomitus) loss.

Any patient on IV fluids should have a daily

fluid balance, daily electrolyte measurement,

new regimen prescribed.

Repeat should NOT be used.

Pre existing losses

To identify which compartment / compartments

the fluid has been lost from.

To assess the extent of dehydration.

Which compartment?

Bowel losses - ECF

Pure water losses - total body water

Protein loss - plasma

Water and electrolyte

replacement

ECF losses - normal saline , Hartmanns with added (K+)

Acute hypovolaemia - Gelofusin

Plasma losses

Continuing losses- Hetastarch Dextran

Assessment of fluid loss

Clinical

Thirst

Reduced urine output

Loss of skin turgor

Rapid low volume pulse

Low BP

Low CVP

MILD MODERATE SEVERE

Thirst + + ++

Tongue ( Buccal sulcus) + ++

Skin and sunken eyes + ++

Urine output (kg/hr) <1 <0.5 <0.5

Pulse ( beats/min) Normal Normal 100-200

Blood pressure (mmHg) Normal Normal 80-100

Respiratory rate Normal Normal Normal

Clinical Assessment of Dehydration

Investigations

Blood urea

Serum electrolytes

Urine specific gravity & osmolality

Haematocrit - Unreliable in acute blood loss

Quantification of plasma and

ECF loss

Using changes in haematocrit and serum Albumin levels

In ECF depletion P1 - Initial Albumin [ ]

P2 - [ ] after dehydration

% fall in ECF volume=(1-p1/p2)x100

Also % fall in plasma volume=100[1-Hct1/100-Hct1 x100- Hct2

/Hct2]

Three questions???

WHAT to give?

HOW MUCH to give?

HOW fast?

What Fluids?

Depends on the compartment affected.

Gastric loss-N saline

Intestinal loss- Hartmanns

NG aspirate- N.S. + Hartmanns

Third space-(5-15 ml/kg/hr)-N.S.

HOW MUCH OF FLUID?

Calculated in litres as a percentage of

body weight in kg.

mild moderate severe

Adults 4% 6% 8%

(40ml/kg) (60ml/kg) (80ml/kg)

Children 5% 10% 15%

(this is a guide only .Should be tailored to individual needs.)

HOW FAST?

Give half the requirement in 12 hours and

other half in the next 48 hours.

In severe depletion 20 ml/kg for the 1st

hour. (caution-elderly)

MONITORING

Pulse ,blood pressure ,JVP ,Lung bases

Urine output/hour, serial PCV

Adequacy-urine output of 1ml/kg/hr

Over hydration-jugular venous engorgement ,

lung crepitations ,hypertension

Post-op Fluid Management

Normal maintenance fluid

If blood or serum is lost

If GI loss continued

* Normally K is not given during 1st 24Hr.

* After major surgery assessment of fluid should

be according to ;

Fluid balance , Clinical signs / symptoms , CVP monitoring

Replace

Potassium Balance

Adult Requirement -- 0.6 – 1mg / kg / day

Normal serum potassium – 3.5 - 5.3 meq / l

90% total body potassium is in the ICF

K+ < 3.5 mmol/l

How would you correct it?

Hypokalaemia

Hyperkalaemia

K+ > 5.5mmol/l

K+ >7 mmol/l symptomatic

Treatment of hyperkalaemia

10 ml of 10% calcium gluconate i.v. over 10 min.(why ?)

10 U of Insulin in 50ml of 50% dextrose i.v. over 30min.

NaHCO3 50 mmol

Beta 2 agonist

What is the purpose of dextrose infusion?

What is the best guide to adequate fluid

replacement?

What do you understand by the term

“Third space loss”?

Questions ?????

Following are True or False

Excessive sweating increases the haematocrit.

Infusion of normal saline increases the serum Na+

Infusion of 5% Glucose decreases the haematocrit

Diarrhoea causes decrease in the intracellular fluid

Hypertonic saline infusion causes no change

F

F

F

F

F

In the intracellular fluid

Thank You !