Serum Electrolytes

Target Group: MBBS and MD Students
Slides prepared in April 2017

1. Estimation of Sodium & Potassium Ashikh Seethy Senior Resident Department of Biochemistry

2. Objectives: At the end of this briefing, you should be able to describe: The distribution of Na + , K + and water in the body. The role of Na + and K + in maintenance of homeostasis. The different pathological conditions in which Na + and K + balance is disturbed. Various techniques utilized for estimation of serum Na + and K + .

3. The Body as Organized “Solutions” In the body of a young adult male: P roteins:18 % Minerals: 7% Fat: 15% Water: 60%

4. Fluids Compartments:

5. Fluids Compartments: Total Body Water: 42 L Intra-cellular Fluid 28 L 66% Extra-cellular Fluid 14 L 34% Interstitial Fluid 10.5 L Plasma 3.5 L

6. Electrolytes and Proteins are Unequally Distributed Among the Body Fl u ids

7. Osmolality: Measure of the number of osmotically active particles in serum. Calculated serum osmolality = ( 2 x serum Na + ) + Glucose + Urea (in mmol /L ). Estimated in lab by Osmometer (based on colligative properties). Reference interval: 275–295 mOsmol /kg of water. What are the other molecules that can affect osmolality?

8. Water Balance is Regulated by the Hypothalamus, the Neurohypophysis and the Kidneys

9. Action of Vasopressin in Renal Tubules:

10. Water and electrolytes can be lost through Gastrointestinal tract Skin B ronchial tree etc. But kidneys are the only organs able to conserve or excrete electrolytes and water under tight regulatory control.

11. Osmolality: Carbonic Anhydrase Inhibitors Loop Diuretics Bartter Syndrome Thiazide Diuretics Gitelman Syndrome Minerallocorticoid -R Antagonists Liddle Syndrome ENaC Na +

12. Nephron is the Target of Many Hormones

13. Renin-Angiotensin-Aldosterone System

14. Sodium: Principle cation of ECF Reference interval (Plasma): 136 to 145 mmol /L Recommended daily dietary intake : < 2 g (<5 g salt) Na + levels are regulated by the kidneys Functions: Maintains normal water distribution and osmolality Maintenance of membrane potential Absorption of chloride, amino acids , and glucose

15. Abnormality in Sodium Levels Affects Neuronal Function: Normal Hyponatremia Hypernatremia Plasma sodium:136 to 145 mmol /L Hyponatremia: Plasma sodium <135 mmol /L Hypernatremia: Plasma sodium >145 mmol /L

16. Hypernatremia ECF Volume Increased Total body water↑ Total body sodium↑↑ Not Increased Total body water ↓↓ Total body sodium↓ Hypertonic NaCl NaHCO 3 Insensible water loss GI water loss Central Diabetes Insipidus Nephrogenic Diabetes Insipidus Osmotic Diuresis

17. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water↑ Total body sodium ↔ Hypervolemia Total body water ↑↑ Total body sodium ↑ U Na > 20 U Na < 20

18. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water↑ Total body sodium ↔ Hypervolemia Total body water ↑↑ Total body sodium ↑ U Na > 20 U N a < 20 Renal losses Diuretics ↓↓ Minerallocorticoids Osmotic diuresis Metabolic alkalosis

19. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water↑ Total body sodium ↔ Hypervolemia Total body water ↑↑ Total body sodium ↑ U Na > 20 U Na < 20 Renal losses Diuretics ↓↓ Minerallocorticoids Osmotic diuresis Metabolic alkalosis Extra-renal losses Vomiting Diarrhea Trauma Pancreatitis

20. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water↑ Total body sodium ↔ Hypervolemia Total body water ↑↑ Total body sodium ↑ U Na > 20 U na < 20 U na > 20 U Na > 20 U na < 20 Renal losses Diuretics ↓↓ Minerallocorticoids Osmotic diuresis Cerebral salt wasting

21. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water ↓ Total body sodium ↔ Hypervolemia Total body water ↑↑ Total body sodium ↑ U Na > 20 U Na < 20 Nephrotic syndrome Cirrhosis Cardiac failure Acute Renal Failure Chronic Renal Failure

22. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water ↑ Total body sodium ↔ Hypervolemia Total body water ↑↑ Total body sodium ↑ U na > 20 Glucocorticoid deficiency Polydipsia SIAD- Syndrome of Inappropiate Antidiuresis

23. Hyponatremia Volume Status Hypovolemia Total body water ↓ Total body sodium ↓↓ Euvolemia Total body water ↑ Total body sodium ↔ Hypervolemia Total body water↑↑ Total body sodium ↑ Total body water ↔ Sodium intake↓ Beer potomania Nutrient restricted diet

24. Potassium: Principle intracellular cation ( 140 mmol /L ) High cellular concentrations maintained by active transport mechanism via Na + /K + ATPase pump Reference interval (Plasma): 3.5 – 5.0 mmol /L Normal daily dietary intake : at least 90 mmol /day (3510 mg/day) Functions: Maintenance of ionic gradients which is required for: Nerve impulse transmission Muscle contractility Activation of enzymes

25. Abnormality in Potassium Levels Adversely Affects Cardiac Function : Plasma Potassium:3.5 to 5.0 mmol /L Hypokalemia : Plasma potassium <3.5 mmol /L Hyperkalemia : Plasma potassium >5.5 mmol /L Cardiac muscles- Arrhythmias; Cardiac arrest Skeletal muscles Intestinal muscles

26. Hyperkalemia Pseudohyperkalemia: Hemolysis Increase in blood cells Intra- to Extracellular Shift Acidosis Digoxin Trauma Tumor lysis Drugs Inadequate Excretion Inhibition of RAAS Chronic kidney disease Adrenal insufficiency ↓ Renin production

27. Hypokalemia Decreased Intake: Starvation Clay ingestion Extra- to Intracellular Shift Alkalosis Insulin Anabolic states Drugs Thyrotoxicosis Increased Loss Diarrhea , sweating Diuretics other than potassium sparing diuretics Conn syndrome Cushing syndrome Bartter’s syndrome Gitelman’s syndrome Liddle’s syndrome Diabetic ketoacidosis

28. Sample Considerations: Serum, heparinized plasma or whole blood may be used for Na + estimation Whole blood or heparinized plasma preferred for K + Samples should be maintained near 25 °C Preferably plasma to be separated by high speed centrifugation without cooling Hemolysis to be avoided Avoid prolonged tourniquet use and fist clenching

29. Techniques for Estimation of Na + and K + Ion selective electrode (ISE) Atomic absorption spectroscopy Flame emission photometry

30. Ion Selective Electrode Ion selective membrane: Na + : Glass K + : Valinomycin

31. Flame Emission Photometry The intensity of emission is proportional to the number of excited atoms, which is indeed proportional to the concentration of the element in the solution.

32. Flame Emission Photometry Ion selective electrode (ISE) Atomic absorption spectroscopy