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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
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