Serum electrolytes for MBBS

1. SERUM ELECTROLYTES
SODIUM & POTASSIUM
ESTIMATION

2. What are electrolytes?
• Electrolytes are minerals that are present in our blood & body tissue
• Electrolytes are important for
1. Maintaining fluid and pH balance
2. Nerve and muscle functioning

3. SODIUM
• Major cation of ECF
• RDA <2gm/day
• Normal range : 135-145 mmol/L
• Na levels are regulated by the kidneys
• Maintain the normal distribution of water and the osmotic pressure in ECF
• Maintain membrane potential of cells

5. HYPERNATREMIA
ECF
Increased Decreased
TBW ↑ TBW ↓↓
Total body sodium↑↑ Total body sodium↓
Hypertonic NaCl Insensible water loss
GI water loss

6. HYPONATREMIA
Volume Status
Hypovolemia Euvolemia Hypervolemia
TBW ↓
Total body sodium↓↓
UNa > 20
Renal losses
UNa < 10
Extra renal losses
Vomiting
Diarrhea
trauma
TBW ↑
Total body Sodium ↔
UNa>20
Polydipsia
TBW ↑↑
Total body sodium ↑
UNa < 10 UNa > 20
Renal
failure
Cirrhosis
CCF

7. HYPERNATREMIA >145 mmol/L HYPONATREMIA <135 mmol/L
Dehydration Vomiting
Elderly with poor water intake Diarrhea
Excessive salt intake Excess non-electrolyte iv infusion
Hyperglycemia and Ketoacidosis

8. POTASSIUM
• Major cation of ICF
• High cellular concentration maintained by Active transport mechanism via
Na+/K+ ATPase pump
• RDA : 3.5 g/day
• Normal range : 3.5-5 mmol/L
• Major determinant of cell volume and osmolality of Intracellular compartment

9. HYPERKALEMIA
Pseudohyperkalemia Intra to Extracellular Shift Inadequate Excretion
Hemolysis Acidosis CKD
Increase in blood cells Tumor lysis

10. HYPOKALEMIA
Decreased Intake Extra to Intracellular Shift Increased Loss
Starvation Insulin Diarrhea
sweating

11. HYPERKALEMIA >5.5 mmol/L HYPOKALEMIA <3mmol/L
Renal failure Diarrhea, Vomiting
Burns Hyperaldosteronism
Increased haemolysis Thyrotoxic periodic paralysis (ab N Na-K-
ATPase)
Tumor lysis syndrome Alkalosis
Insulin deficiency (DM) Malabsorption
Drug induced: ACE inhibitors Drug Induced: Bronchodialators
Rhabdomyolysis, Crush injury

12. Estimation of Na+ & K+
1. Ion selective electrodes
2. Atomic absorption spectroscopy
3. Flame emmision photometry

13. ION SELECTIVE METHOD
• Ion selective membrane:
1. Na+ : Glass
2. K+ : PVC impregnated with Valinomycin
• I.S.E. consists of a thin membrane across which only the intended ion
can be transported.
• The transport of ions from a high concentration to a low one through
selective binding with some sites within the membrane creates a
potential difference

14. • An ISE with its own internal
reference electrode is immersed in
an aqueous solution containing the
ions to be measured, together with
a separate, external reference
electrode.
• The electrochemical circuit is
completed by connecting the
electrodes to a sensitive milli-volt
meter.
• A potential difference is developed
across the ISE membrane when the
target ions diffuse through from
the high concentration side to the
lower concentration.

15. ISE : Principle
• The electrode produces a difference in potential between itself and a
reference electrode.
• This difference in potential is proportional to the concentration of the
selected ion in solution and is described by the Nernst equation
• The ISE system is calibrated with solution containing known
concentration of analytes
• the concentration of an unknown solution is derived by comparing its
potential with that of a solution of known concentration.

16. E = Eo – 2.3 (RT/nF) log (C + Co)
• E = measured potential (mV) between the ion-selective and the reference
electrode
• Eo = measured potential (mV) at the lower concentration standard
• R = universal gas constant (R = 8.314 J mol–1 K–1)
• T = temperature in K (Kelvin), with T (K) = 273.15 + t °C where t is the
temperature of the measured solution in °C
• F = Faraday constant (96485 C·mol–1)
• n = valency of the ion
• C = concentration of ion to be measured
• Co= detection limit

17. COMPONENTS OF ELECTROLYTE ANALYZER
• Reagents Calibrator, Slope standards and the wash solution.
• Electrode Module houses the air/fluid detector,
measuring electrodes and reference electrode
• Peristaltic Pump pushes the reagent fluids and patient sample
through the tubing to the sample probe and electrode module out to
the waste bottle.
• Sample Probe aspirates fluids into the analyzer via the peristaltic
pump. The probe automatically accepts samples from a test tube
• Waste Chamber

18. components inside an
electrolyte analyser
components inside electrode
module

19. THANK YOU