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04/11/2023 1
FLUIDS AND ELECTROLYTES
Dr. Tanuj Paul BhatiaMBBS,MS
04/11/2023 2
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
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