Electrolyte and Water Balance PDF/PPT

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Electrolyte and Water
Balance

Dr Sarama Saha

 

Case Report

• A 55-year-old man was brought to the emergency with severe
multiple injuries in a road traffic accident and crush injuries, fractures
of the legs and scalp lacerations. He was conscious and breathing
spontaneously. Pulse 130/min, BP 60/40 mm Hg, serum sodium 142
mmol/L, potassium 7.9 mmol/L, chloride 110 mmol/L, Blood urea 40
mg/dL, and serum creatinine 1.2 mg/dL.

• Interpret the laboratory data?
• What is the basis of the changes?

 

The body water compartments

 

• During oxidation of foodstuffs,
• 1 g carbohydrate produces

• 0.6 mL of water,
• 1 g protein releases

• 0.4 mL water and
• 1 g fat generates

• 1.1 mL of water.

• major factors controlling the intake :
• thirst and
• the rate of metabolism.

 

Water balance in the body

 

• Osmolarity means osmotic pressure exerted by the
• number of moles per liter of solution.

• Osmolality is the osmotic pressure exerted by the
• number of moles per kg of solvent.

• osmotic balance is mainly maintained by

• Albumin

• the major determinant factor of osmolality is

• the sodium

• The osmolality of plasma varies from
• 285 to 295 mosm/kg

 

 

Gamblegrams showing composition of fluid
compartments

 

Electrolyte and Water Composition of Body Fluid Compartments
Components Plasma Interstitial fluid Intracellular fluid

Volume, H2O (TBW 3.5 L 10.5 L 28 L
= 42 L)

Na+ 142 145 12

K+ 4 4 156

Ca+2 2.4 2-3 2.3

Mg2+ 2 1-2 26

Trace elements 1 – –

Total cations 155

Cl− 103 114 4

HCO− 27 31 12

Protein− 16 – 55

Organic acids− 5

HPO2 − 2

SO2 − 1

Total anions 154

 

 

Regulation of Sodium and Water balance

• ADH

• Renin-Angiotensin system

• Autoregulation

 

Disturbances in Fluid and Electrolyte balance

• Isotonic contraction- Loss of fluid that is isotonic with plasma–Loss of
GI fluid

• Hypotonic contraction—Predominant Na loss– Infusion of fluids with
low sodium content like dextrose

• Hypertonic contraction —Predominantly water depletion—Diarrhoea

 

• Isotonic expansion—Secondary to hypertension

• Hypotonic expansion—ADH excess

• Hypertonic expansion—Conns syndrome & Cushings syndrome_
Excess mineralocorticoid- sodium retention

 

Reference interval of Sodium:
136-145 mmol/L (Adult)

128-148 mmol/L (New born at 48 h)

Approx 127 mmol/L (From Umbilical cord)
Urinary sodium excretion = 120-240 mmol/day with large diurnal variation

At night = 20% of the peak

Hyponatremia typically manifests clinically as
(1) nausea,
(2) generalize weakness, and
(3) mental confusion.

<120 mmol/L: mental confusion
<110 mmol/L : Ocular palsy
90-105 mmol/L: Severe mental impairment

 

Algorithm for the differential diagnosis of hyponatremia.

 

 

Hypernatremia Plasma sodium > 150 mmol/L

Symptoms are primarily neurologic
(because of neuronal cell loss of H2O into the ECF)

1.Tremors
2.Irritability
3.Ataxia
4.Confusion
5.coma

 

Hypernatremia

 

HYPOKALEMIA Reference interval of K+:
1.Muscle weakness Serum=3.5-5.0 mmol/L (Adult)
2.Irritability
3.Paralysis Plasma= 3.4-4.8 mmol/L (Adult)

4.Tachycardia
3.7-5.9 mmol/L ( Newborn)

5.Cardiac conduction defect
CSF= 70% that of plasma

6.Flattened T wave
7.Cardiac arrest

 

Hypokalemia

 

Hypokalemia (continued)

Metabolic Alkalosis

 

HYPERKALEMIA

1. Mental confusion
2. Weakness
3. Tingling
4. Flaccid paralysis of the extremities
5. Weakness of the respiratory muscles
6. Bradicardia
7. Conduction defects
8. Peripheral vascular collapse : Prolonged severe hyperkalemia >7 mmol/L
9. Cardiac arrest

 

Hyperkalemia

 

MCQ 1

• A patient with diarrhoea may have all the following abnormalities
except:
• A. Metabolic acidosis
• B. Hypertonic contraction of ECF
• C. Urine with a high specific gravity
• D. Isotonic contraction of ECF

 

MCQ 2

• Which of the following is the major intracellular cation?
• A. Magnesium
• B. Sodium
• C. Calcium
• D. Potassium

 

 

MCQ 3

• All 5the following hormones affect fluid and electrolyte balance
except:

• A. Aldosterone
• B. ADH
• C. Cortisone
• D. Thyroxine

 

References

• DM Vasudevan, textbook of medical biochemistry, 7th Edition,
• Tietz fundamentals of clinical chemistry and molecular diagnostics, 7th

edition