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• SecretionsWater is a universal solvent• Solvent

dissolves other substances yeilding a solution

ELECTROLYTES• when placed in water dissociates into

electrically charged particles or IONSCation• Positively charged ionAnion• 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 impulsesCalcium• 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

• pH7.35 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

Ph7.35-7.45

PaCO2

35-45

HCO3-

22-26Respiratory

AcidosisFall Rise Normal

Respiratory

AlkalosisRise Fall Normal

Metabolic

AcidosisFall Normal Fall

Metabolic

AlkalosisRise Normal Rise

Ph

7.22

PaCO2

55

HCO3-

25

Respiratory

Acidosis

Respiratory

Alkalosis

Metabolic

Acidosis

Metabolic

Alkalosis

Ph

7.22

PaCO2

55

HCO3-

25

Respiratory

Acidosisdecreased increased normal

Respiratory

Alkalosis

Metabolic

Acidosis

Metabolic

Alkalosis

pH

7.50

PaCO2

42

HCO3-

33

Respiratory

Acidosis

Respiratory

Alkalosis

Metabolic

Acidosis

Metabolic

Alkalosis

pH

7.50

PaCO2

42

HCO3-

33

Respiratory

Acidosis

Respiratory

Alkalosis

Metabolic

Acidosis

Metabolic

Alkalosisincreased normal increased

COMPENSATION• Remember with the buffering systems the

body attempts to regulate hence a state of compensation

uncompensatedpartially compensatedfully 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 pHIf 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

Fully Compensated

Ph7.35-7.45

PaCO2

35-45

HCO3-

22-26Respiratory

AcidosisNormal but <7.40

Rise Rise

Respiratory

AlkalosisNormal but >7.40

Fall Fall

Metabolic

AcidosisNormal but <7.40

Fall Fall

Metabolic

AlkalosisNormal but >7.40

Rise Rise

Partially Compensated

Ph7.35-7.45

PaCO2

35-45

HCO3-

22-26Respiratory

AcidosisFall Rise Rise

Respiratory

AlkalosisRise Fall Fall

Metabolic

AcidosisFall Fall Fall

Metabolic

AlkalosisRise Rise Rise

• The only difference between fully compensated and partially compensated is whether the pH has returned to within the normal range

RESPIRATORY ACIDOSIS

• Causes [hypoventilation]

Head injury

Narcotics

Sedatives

Spinal cord injury

Neuromuscular disease

AtelectasisPneumoniaPneumothoraxPulmonary edemaBronchial obstructionPulmonary embolusPainChest wall injury or deformityAbdominal distension

Signs and symptoms of respiratory acidosis• Dyspnea• Respiratory distress• Headache• Restlessness• Confusion• Drowsiness• unresponsiveness

• Tachycardia

• Dysrhythmias

Respiratory AlkalosisCauses [hyperventilation]• Anxiety• Fear• Pain• Fever• Sepsis• pregnancy

Signs and Symptoms

• Light-headedness

• Numbness/tingling

• Confusion

• Inability to concentrate

• Blurred vision

• Dysrythmias

• Palpitations

• Dry mouth

• Diaphoresis

• Spasms of arms and legs

Metabolic Acidosis

Causes

• Renal failure

• DKA

• Anaerobic metabolism

• Starvation

• Salicylate intoxication

Signs and Symptoms

• Headache

• Confusion

• Restlessness into lethargy

• Kusmal respirations

• Warm flushed skin

• Nausea and vomiting

Metabolic AlkalosisCauses• Antacids• Overuse of bicarbonate• Lactate as used in dialysis• Protracted vomiting• Gastric suction• High levels of aldosterone

Signs and symptoms• Dizziness• Lethargy• Disorientation• Seizure• Coma• Weakness• Muscle twitching• Muscle cramps• Tetany

• Nausea and vomiting

• Respiratory depression

• Tetany

Involuntary contraction of muscles

• Proracted

Prolonged

• Aldosterone

a hormone that increases the reabsorption of sodium ions and water and the release of potassium ions

• Atelectasis

the lack of gas exchange within alveoli, due to alveolar collapse or fluid