Metabolism of water, sodium, potassium, chloride, and ABB M. Srbová, R. Průša

Water Total body water 60% of body weight in adults (70 kg – 42 l) Women have lower percentage of BW than men Older people have a lower percentage of BW than younger people TBW: 20% of body weight is ECF ( IVF 5% + 15% ISF), 40% of body weight is ICF The electrolytes are unevenly distributed between ECF or ICF, it is maintained by: Gibbs-Donnan equilibrium Ions pumps (ex. Na + - K + -ATPase)

Gibbs-Donnan equilibrium: Distribution of kations and anions between plasma and ISF Biological membranes are impermeable to macromolecular protein anions which have far higher concentration in the plasma than in interstial fluids. Plasma (contains protein anions) has  Na + and  K +, Interstitial fluids (no protein anions) have  Cl - and  HCO 3-

Body water balance Disease state: Water gain: hyperhydratation – infusion, SIADH, CSWS Water loss: dehydratation - bleeding, burns, vomiting, diarrhea… Inner balance: fluids distribution between compartments - water leak from plasma to the interstitial fluid during hypoproteinemia Water gain ml/dWater loss ml/d Fluids 1500Urine 1500 Solid food 600Feces 50 Fuel metabolism 400Evaporation 500 Expired air 450 Total 2500

Plasma osmolality Proportionate to the total concentration of all dissolved molecules ( ions, proteins, organic molecules) mmol/kg, 1.8x [Na + ] + urea + glucose Systems that control water balance, control provides constant volume of TBW and also provides constant osmolality. Osmolal gap is the difference between measured plasma osmolality (freezing point depression)and calculated plasma osmolality higher than 10 mmol/kg – substances dissolved in plasma 1g ethanol in 1l plasma increases osmolality by 23 mmol/l/kg

Metabolic disorders Acidosis  HCO 3-  some anions (Cl -, lactate, albumin) replace ↓ HCO 3- Loss of HCO 3- (diarhhea, kidney) Dilution acidosis ◦ (ratio ↓ Na + : H 2 O) Alkalosis   HCO 3- ↓ anions ( Cl -, proteins)  kations (Na + )  aldosteron. Cushing´s s. Concentration alkalosis ◦ (ratio ↑ Na + : H 2 O)

Na + main kation of ECF mmol/l, ICT 3-10 mmol/l All of the ions sodium binds the highest amount of water (sodium retention results in water retention) Daily nedd: 70 mmol/d Actual intake: 260 mmol/d High salt intake – the risk of hypertension Na + - K + -ATPase

Na + Hyponatremia Na + lower than132 mmol/l Hyponatremia with hypoosmolality  loss of water and ions (CSWS, diuretics, sweating, burns, GIT)  Excess of clean water (SIADH, hypocorticalism, polydipsia) Hyponatremic encefphalopathy – cerebral edema Hypernatremia Na + higher than 145 mmol/l With hyperosmolality  Water loss (diabetes insipidus)  Inadequate supply of water (thirsting in the desert)  Increased salt intake Dehydration of the brain

Na + - Cl - The difference between plasma concentration of Na + and Cl - is 37 Changes in the differences are accompanied by changes in HCO 3- Increased difference– metabolic alkalosis Decreased difference – metabolic acidosis – retention of Cl -

K+K+K+K+ Main intracellular kation– bound to proteins and polysaccharides mmol/l in ICF 3,8-5,2 mmol/l in ECF K + ratio in ECF and ICF– membrane polarization, neuromuscular excitability K + concentration in blood is dependent on pH: cK + = 33,05 -3,87xpH  pH – blood potassium increases ↑ pH – blood potassium decreases Relation between potassium concentration in blood and pH. The space between lines includes 95% of cases.

Main aniont of ECF mmol/l ICF 3-10 mmol/l Together with Na + is involved in osmotic pressure of ECF Important for maintainig of ABB: ◦ Cl -   HCO 3- ◦ Cl -   HCO 3- Cl -

Normal stateHypochloremic alkalosis SO 4 2-, HPO 4 2-, lactate, ketoacids

Development of the combined ABB disturbances in vomiting and starvation.

Blood gases analysis and ABB Temperature – 37 st. C Hemoglobin – 150 g/l FiO2 (21 %) Cooxymetry: metHb, sulfHb, karbonylHb

pH dependent changes S- K – 0.6 mmol/l, change of pH 0,1 (from ICT to ECT) S-Ca mmol/l, change of albumin by 10 g/l, change of Ca2+ according pH HCO3 – decrease of protein anion will cause increase of HCO 3 - ; decrease of S- albuminu by 10 g/l represents increase of P-HCO 3 - by 3.4 mmol/l

AG, RA, BBs, Protein anion BBs = [HCO 3 - ] + [protein anion] Norm.: 41.7 mmol/l AG (anion gap): [Na + + K + ] - [Cl - + HCO 3 - ] Norm.: 15.2 ± 1.6 mmol/l More than 18 mmol/l: anions of lactate, acetacetate, hydroxybutyrate, phosphate, sulphate RA (rezidual anions): [Na + + K + + Ca + Mg] - [Cl - + HCO protein anion] Norm.: 7.08 ± 2.41 (3.2 – 10.9) mmol/l Proteinátový anion = [S-protein] : (pH – 5.08) Norm.: ~ 17.1 mmol/l