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FLUIDS AND ELECTROLYTES

Dr. Tanuj Paul BhatiaMBBS,MS

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Fluid compartments

Total body fluid (60% of TBW)

ECF(40% of body fluid)

Interstitial fluid

(25% of TBW)

Plasma(5-8%of

TBW)

Transcellular fluid (2%

of TBW)

ICF(60% of body fluid)

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Total body water varies with…

a) Ageb) Genderc) Body fat (Fat contains less water)

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Intracellular fluid

60% of body fluid Rich in :

Potassium Magnesium proteins

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Extracellular fluid

40 % of body fluid Rich in :

Sodium Chloride Bicarbonate

Interstitial fluid : between cells, low in protein

Intravascular fluid(Plasma) : High in protein Transcellular fluids – CSF, intraocular fluids,

serous membranes (third space)

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Spacing

First space: normal Second Space: interstitial -

edema; Third Space: in places not

normally found

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Fluid compartments are separated by membranes that are freely permeable to water.

Movement of fluids due to: Hydrostatic pressure Osmotic pressure

Examples: Capillary filtration (hydrostatic) pressure Capillary colloid osmotic pressure Interstitial hydrostatic pressure Tissue colloid osmotic pressure

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Fluid balance

Average intake Average output

Fluid: 1300 ml Urine: 1500 ml

Water in food: 1000 ml Feces: 150 ml

Water metabolism: 250 ml Lungs: 500 ml

Skin: 400 ml

Total for both is 2550ml

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Balance

Fluid and electrolyte homeostasis is maintained in the body

Neutral balance: input = output Positive balance: input > output Negative balance: input < output

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Regulators: organs & hormones

Kidneys: regulates fluid volume, electrolytes, pH, waste; influenced by ADH & aldosterone

Lungs: remove 500 cc fluid. Heart & blood vessels:

regulate pressure.

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Aldosterone: REGULATES SODIUM and potassium balance. INCREASED ALDOSTERONE TO RETAIN SODIUM & excrete potassium in kidneys.

ADH - CONTROLS WATER. ADH release causes kidney tubules to retain water

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Solutes – dissolved particles Electrolytes – charged particles

Cations – positively charged ionsNa+, K+ , Ca++, H+

Anions – negatively charged ionsCl-, HCO3

- , PO43-

Non-electrolytes - Uncharged Proteins, urea, glucose, O2, CO2

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MW (Molecular Weight) = sum of the weights of atoms in a molecule

mEq (milliequivalents) = MW (in mg)/ valence

mOsm (milliosmoles) = number of particles in a solution

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Solutes determine the tonicity of a solution

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tonicity

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Cell in a hypertonic solution

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Cell in a hypotonic solution

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Movement of body fluids “ Where sodium goes, water follows.”

Diffusion – movement of particles down a concentration gradient.

Osmosis – diffusion of water across a selectively permeable membrane

Active transport – movement of particles up a concentration gradient ; requires energy

Regulation of body water ADH – antidiuretic hormone + thirst

Decreased amount of water in body Increased amount of Na+ in the body Increased blood osmolality Decreased circulating blood volume

Stimulate osmoreceptors in hypothalamusADH released from posterior pituitaryIncreased thirst

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Result:increased water consumptionincreased water conservation

Increased water in body, increased volume and decreased Na+ concentration

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Different components of renal function occur along thenephron.

A normal glomerular filtration rate of 125 mL/minwould generate 180 L/day of filtrate containing 27,000 mmol ofsodium.

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Approximately two thirds of the filtered sodium is absorbed in the PCT,

20% in the LOH, 7% in the DCT, and 3%in the CD; the net excretion of urinary

sodium per day, as a fraction of the total sodium filtered load, is less than 1%.

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Disturbances of fluid and electrolyte balance

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Volume depletion

Pure volume deficits – RARE Causes : 1. Comatosed patients with

increased insensible loss (e.g. fever) 2. Diabetes insipdus Reflected biochemicaly by

hypernatremia.

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Clinical features

Due to depressed nervous system Lethargy Muscle rigidity Seizures Coma

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Treatment

Replacement of adequate water by 5% Dextrose

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Volume and electrolyte depletion Due to extrarenal loss of body fluid Causes :

Vomiting Diarrohoea Nasogastric suction Intestinal fistulae Intestinal obstruction Peritonitis

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Effects

Sodium loss

↓ ECF osmotic pressure

Water moves into cells

ICF becomes hypotonic

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Effects Concentrated urine(sp gravity >1020)

Prerenal azotemia : ↑Blood urea and serum creatinine.

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Clinical features

1. Sunken eyes2. Tongue – Dry and Coated3. Low urinary output

Lab: 1. Normal or Slightly reduced Serum

Sodium2. Low urinary sodium

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Treatment

Replacement of sodium deficit in addition to volume deficit by infusion of

Isotonic saline, or Ringer’s lactateDepending on the severity of hyponatremia

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Volume overload

Conservation of sodium and water following stress like surgery

If fluid intake is excessive in immediate post op fluid overload may occur.

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Tendency of fluid overload increases in patients with : Heart disease Liver disease Kidney disease

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Clinical features

Peripheral edema Jugular venous distension Tachypnoea ( due to pulmonary

edema)

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Treatment

Mild overload: Restriction of sodium and water

Severe overload : Diuretics

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Specific electrolyte disorders

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Hyponatremia

Always associated with volume depletion

Clinical features and treatment as discussed before

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Hypernatremia

Serum Na levels > 150Mmol/l Causes:

Renal dysfunction Cardiac failure Drug induced (NSAIDS, corticosteroids)

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Types of hypernatremia

1. Euvolemic (pure water loss)2. Hypovolemic (more water lost than

sodium)3. Hypervolemic (both gained but

more sodium gained)

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Clinical features

Pitting edema Puffiness of face Increased urination Dilated jugular veins Features of pulmonary edema

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Treatment

Restriction of sodium and saline. Treatment of pulmonary edema.

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Hypokalemia

Serum potassium levels <3.5 mEq/L Causes :

Diarrhoea Villous tumor of rectum After trauma or surgery Gastric outlet obstruction Duodenal fistula

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Clinical features

Slurred speech Muscular hypotonia Depressed reflexes Paralytic ileus Weakness of respiratory muscles Cardiac arrhythmiasECG shows prolonged QT interval ,

depessed ST segment and inversion of T waves

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Treatment

Oral potassium 2g 6th hourly Intravenous KCl 40 mmol/litre given

in 5% dextrose of normal saline, under ECG monitoring

Max dose per hour = 20 mmol

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Hyperkalemia

Normal range of K = 3.5-5 mEq/L Hyperkalemia >6 mEq/L Causes

Renal failure Rapid infusion of potassium Massive blood transfusion Diabetic ketoacidosis Potassium sparing diuretics

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Dangerous condition, can cause sudden cardiac arrest.

High serum potassium levels Peaked ‘T’ waves in ECG

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Treatment

IV admin. Of 50 ml of 50% glucose with 10 units of soluble insulin, slowly.

Hemodialysis if life threatening. Correction of acidosis.

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Hypermagnesimia

It is rare Occurs because of renal failure or

during treatment of pre eclampsia for which magnesium sulfate is given.

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Hypomagnesimia

Causes : Malnutrition Large GI fluid loss Patients on Total Parenteral Nutrition

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Clinical features

Hyperreflexia Muscle spasm Paraesthesia Tetany

It mimics hypocalcemia Often associated with hypokalemia

and hypocalcemia IV/Oral magnesium is needed.

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Hypocalcemia

Causes Hypoparathyroidism Severe pancreatitis Severe trauma Crush injuries

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Clinical features Circumoral parasthesia Hyperactive DTRs Carpopedal spasm Adbdominal cramps Rarely, convulsions

ECG shows prolonged Q-T interval

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Treatment

Treatment of alkalosis, if present Intravenous calcium gluconate Vitamin D Oral calcium suplements

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Hypercalcemia

Causes : Hyperparathyroidism Cancer with bony metastasis Sarcoidosis Prolonged immobilization

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Clinical features

Fatigue Muscle weakness Depression Anorexia Constipation

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Treatment

Expand ECF by IV normal saline Also increases urinary output and

thus increasing calcium excretion. Hemodialysis in case of renal failure.

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THANK YOU