FLUIDS AND ELECTROLYTES

FLUIDS AND ELECTROLYTES

Terms to KNOW • Total Body Water (TBW) • Intracellular fluid • Extracellular fluid • Intravascular fluid • Interstitial fluid • Solvent

Electrolyte • Dissociate • ion • cation • Anion • Buffer • Isotonic

Hypotonic • Osmotic gradient • Diffusion • Osmosis • Active transport • Facilitated diffusion • Osmolality

Osmolarity • Osmotic pressure • pH

PaO2 • PaCO2 • HCO3- • Acidosis • Alkalosis • Metabolic Acidosis • Respiratory Acidosis • Respiratory Alkalosis

WATER • Most abundant substance in the body • Aprox. 60% of TBW • 70 kg adult (154 lbs) TBW aprox. 42L (11 gallons) Water distribution

Various compartments all separated by a cell membrane • Intracellular fluid (ICF) Fluid inside body cells Largest compartment Contains 75% of TBW

Extracellular Fluid (ECF) • All of the fluid found outside the body’s cells • Contains the 25% of TBW • Two divisions intravascular fluid interstitial fluid

Intravascular Fluid • Outside the cells, within the circulatory system • Pretty much the same as blood plasma Interstitial Fluid • Outside the cell membranes but outside the circulatory system

Examples of Interstitial Fluid • Synovial fluid • Aqueous humor of the eye • Secretions Water is a universal solvent • Solvent dissolves other substances yeilding a solution

ELECTROLYTES • when placed in water dissociates into electrically charged particles or IONS Cation • Positively charged ion Anion • Negatively charged ion Cations in our body

Sodium • Na+ • Common in extracellular fluid • Regulates the distribution of water WATER FOLLOWS SALT • Transmission of nervous impulses

Potassium • K+ • Prevelent in extracellular fluid • Transmission of electrical impulses Calcium • Ca++ • Muscle contraction • Nervous impulse transmission

Magnesium • Mg++ • Several biochemical processes enzymes require magnesium to function ATP, DNA and RNA also need Magnesium

Anions in our body Chloride • Cl- • Balances cations • Renal function • Closely associated with sodium

Bicarbonate • HCO3- • Primary buffer Phosphate • HPO4- • Energy stores • Buffer primarily in the intracellular space

OSMOSIS AND DIFFUSION • Cells have semipermeable membranes • When the concentration of fluid is equal on both sides of the membrane this is ISOTONIC • When the concentration of fluid is less on one side of the membrane this is HYPOTONIC

When the concentration of fluid is greater on one side of the membrane this is HYPERTONIC • The difference in concentration is the OSMOTIC GRADIENT • There is a shift to maintain homeostasis or a state of equilibrium

Molecules will normally move to an area of higher concentration to that of lower concentration which is DIFFUSION • Diffusion does not require E • Water, which moves faster than electrolytes moves across the membrane to dilute the higher concentration of electrolytes

Osmosis The movement of any solvent across the membrane Active Transport {requires E} • Movement against the osmotic gradient less concentrated to more concentrated area i.e.

The inside of a myocardium cell must be negatively charged. Sodium being positively charged diffuses passively into the cell. Sodium ions are pumped out of the cell while potassium is pumped into the cell More sodium than potassium is moved achieving equillibrium

Facilitated diffusion Requires the assistance of a helper protein to move into the cell An example is Glucose

Osmolality • The concentration of solute per Kg • The movement of water and solutes across the cell membrane maintains a state of equilibrium of osmolality Osmolarity • The concentration of solute per L of water

Sodium maintains osmolality in the extracellular space • Potassium maintains omolality in the intracellular space

ACID-BASE BALANCE

Acid-Base Balance • The regulation of H+ in the body • H+ Is acidic • A deviation has an adverse affects on all biochemical functions of the body pH • Potential of Hydrogen

Through metabolism and other biochemical processes, H+ is constantly produced Normal pH is 7.35 to 7.45 <7.35 = Acidosis >7.45 = Alkalosis THREE FORMS OF REGULATION

Bicarbonate Buffer System • The fastest • The players [in equilibrium with H+ ] Bicarbonate {HCO3-} Carbonic Acid {H2CO3-} • Either H+ will combine with bicarbonate ion to produce carbonic acid or

Carbonic acid will dissociate into bicarbonate ion and hydrogen ion • Erythrocytes contain have an enzyme called carbonic anhydrase which converts carbonic acid into CO2 and H2O and this occurs very rapidly • Most buffering occurs in the erythrocytes

Respiration | two other mechanisms Kidney function| of regulation Respiration • An increase blows off CO2 thus decreases H+ thus decreases pH Kidneys • Modifies the concentration of HCO3- in the blood

Increased elimination of HCO3- lowers pH • Decreased elimination of HCO3- raises pH The kidneys achieve acid-base balance by removing or retaining certain chemicals So what is the significance of all this?

The bottom line is to determine: • If a patient is in a state of acidosis • If a patient is in a state of alkalosis • If the disturbance is respiratory in nature • If the disturbance is metabolic in nature In order to make this determination we must know the norms

pH 7.35 to 7.45 • PaCO2 35 to 45 mm Hg • HCO3- 22 to 26 mEq/L • PaCO2 75 to 100 mm Hg

The first determination is if the patient is in a state of acidosis or alkalosis • <7.35 Acidosis • >7.45 Alkalosis Next is to determine if the disturbance is respiratory or metabolic in nature

Assess the PaCO2 level • If respiratory the PaCO2 should rise as the pH falls {acidosis} conversely the PaCO2 should fall as the pH rises SO……. If the pH and PaCO2 are moving in opposite directions then the disturbance is respiratory

To determine if the disturbance is metabolic in nature the HCO3- is considered • As pH increases, so should the HCO3- • The opposite is true Thus If the pH and HCO3- is moving in the same direction then the disturbance is metabolic in nature

COMPENSATION • Remember with the buffering systems the body attempts to regulate hence a state of compensation uncompensated partially compensated fully compensated

In a state of uncompensated or partially compensated the ph is still abnormal • In full compensation the pH is normal but other values may not be

Partial Compensation • Assess the pH this step is unchanged • Assess the PaCO2 remember the pH and PaCO2 should be moving opposite If however they are moving in the same direction would indicate a metabolic disturbance

If as an example the PaCO2 was decreasing it would mean the body was blowing off CO2 in order to return pH to normal limits. Meaning the respiratory system is acting as a buffer system As evidenced that this is actually metabolic in nature then plugging in the PaCO2 moving in the same direction………

The determination then would be a metabolic disturbance with partial respiratory compensation • Assess the HCO3- which moves in the same direction as the pH If they move in the opposite direction, the disturbance would actually be respiratory in nature with the kidneys acting as the buffer system by retaining HCO3- .

TO SUMMARIZE

FLUIDS AND ELECTROLYTES