Transcript Imbalances Of: Fluids, Electrolytes, & Acid

Imbalances Of:
Fluids, Electrolytes, & Acid-bases
Pathophysiology
Review of Body Fluids
Body Water
– Healthy adult
•
•
•
•
• Fluid compartments
– 2 main ones
Male = 60%
Female = 50%
Babies = 75%
Elderly = 45%
• ICF = 2/3 volume of fluid in
body
• ECF = 1/3 volume of fluid in
body
– Plasma = 20%
– Interstitial fluid = 80%
– Calculation:
• 1 Kg = 1 L water
volume
– 150# = 70Kg
– 60% of 70Kg
» =
approx
40Kg
– 40Kg = 40L
–
Calculation:
• 40L = fluid volume
– 2/3 = 25L of ICF
– 1/3 = 15L of ECF
– NB: Blood = 3-4% of weight
• Solution = Solute + Solvent
– Solution = the fluid compartment (ICF or ECF)
– Solvent = water
– Solutes:
• Electrolytes
– Charged ions
» They dissolve in water
» They can conduct an electric current
– Major cations:
» ECF = sodium
ICF = potassium
– Major anions:
» ECF = chloride, bicarbonate
ICF = proteins w/ neg charge
• Non-electrolytes
– Polar =those that are water soluble (sugars, proteins)
– Non-polar = those that are water insoluble (lipids)
• Basic concepts relating to regulation of fluid & electrolytes
– Water moves passively in response to changes in solute concentration
• Key = water follows salt
• Thus, regulation of fluid balance & electrolyte balance are intertwined
– All monitors to homeostatic balance occur in ECF and not ICF !!
• Fluid shifts occur between ICF & ECF in response to changes only in ECF
• Key to equilibrium is maintaining solute concentration (osmolality = #
solute particles in one liter of solution & is the ability of that solution to
cause osmosis) between ICF & ECF
– If change to hypertonic ECF, then water into ECF
– If change to hypotonic ECF, then water into ICF
– During transfer on nutrients (chemicals) an average 24 liters of fluid moves
out of plasma each day; 85% is reabsorbed & the remainder (4L) is the lymph
fluid that accumulates
• At the capillary level have 2 separate forces at work:
– Hydrostatic pressure --- pushes fluid out of vessels
– Colloid osmotic pressure --- pushes fluid into vessels
See Next Slide
•
Fluid balance
–
–
Important in IV daily
maintenance
Intake & output ( I &O )
Note: Insensible loss = 1000 cc/day
• The control of fluid balance
– What is monitored: Volume & Osmolality (osmotic pressure via solute conc.)
– Mechanisms:
• ADH (antidiuretic hormone) , osmoreceptors, & thirst mechanism
– Osmoreceptors in hypothalamus regulates secretion of ADH from
posterior pituitary
– The higher the osmolality, the more ADH secreted
» ADH causes: (1) thirst center to be stimulated
(2) kidneys to conserve water
• Aldosterone
– Secreted by adrenal cortex
– Causes kidneys to retain sodium (nb: water follows salt)
– Stimulated by: increase potassium, falling sodium, & renin-angiotensin
• Atrial natriuretic peptide (ANP)
– Released by distended atrial walls of heart
– Secretion caused by increased pressure and/or volume
– Antagonistic to aldosterone
Fluid Excess --- Edema
• Edema = excessive amount of fluid in interstitial compartment
• 4 main causes
– Increased capillary hydrostatic pressure
• Etiology
– Hypertension
– Increased blood volume ---- 2o to pregnancy, renal failure, CHF
– Loss of plasma proteins (esp. albumin)
• Etiology
– Kidney disease, malnutrition, malabsorption
– Obstruction of lymphatic circulation
• Etiology
– Cancer, parasitic diseases, post surgical
– Increased capillary permeability
• Etiology
– Inflammation, toxins, burns
see next slide
• Effects of edema
• Swelling------- local or
generalized
• Pitting edema
• Increase in body weight
• Functional impairment
• Pain impaired arterial
circulation (obesity)
– Pressure exerted on
arteries
Fluid deficiency --- Dehydration
• Loss is generally from ECF
– Mild dehydration = decrease of 2% in body weight
– Moderate dehydration = 5% loss of body weight
– Severe dehydration = 8% loss
• Loss of water usually accompanied by loss of electrolytes
» Remember water follows salt
– But can get 3 types of dehydration
• (1) Isotonic dehydration = equal loss of fluid & lytes
• (2) Hypotonic dehydration = loss of more lytes than water
• (3) Hypertonic dehydration = loss of more fluid than lytes
• Causes
•
•
•
•
Vomiting & diarrhea, N-G suction
Excess sweating
Diabetic ketoacidosis
Insufficient water intake
• Effects of dehydration
• Dry mucous membranes
• Decreased skin turgor
• Decreased BP
• Increased hematocrit
• Compensatory mechanisms
• Increase thirst
• Increase pulse
• Constriction of vessel to skin
» Get pale, cool skin
• Decreased urine output
• If brain cells lose water, can get
confusion, unconsciousness, & coma
– “ downer”
•
Diagnose dehydration:
– Dry tongue
– Poor skin turgor
– Concentrated urine
Electrolytes & Their Imbalances
Sodium (Na+)
• Sodium balance
– Sodium = major cation in extracellular fluid (ECF)
– Sodium = most common problem with electrolyte balance
– Key to balance: ingestion via G-I tract = excretion via kidney
• Aldosterone controls sodium levels via the kidney
– Remember aldosterone’s antagonist = ANP
– Sodium contributes to resting membrane potential
• Sodium rushing into cell via open channels causes depolarization
of nerves and muscles
Signs of sodium imbalance
1.
2.
3.
4.
hyponatremia
Weakness & fatigue
G-I: anorexia, nausea, cramps
Hypotension
Mental confusion & ? Seizures
hypernatremia
weakness & agitation
G-I: thirst, dry mucosa
hypertension & edema
(from fluid shift into brain cells)
•
Causes of hyponatremia
–
–
–
–
–
•
Excess sweating, vomiting, diarrhea
Diuretics
Renal failure
Excess water intake (water intoxication)
Hormonal imbalances
Causes of hypernatremia
–
–
–
–
Watery diarrhea
Long periods of rapid respiration
Loss of thirst mechanism
Hormonal imbalances
Electrolytes & Their Imbalances
Potassium (K+)
• Potassium balance
– Major intracellular cation
– Balance: ingestion = excretion (via kidneys)
• Aldosterone primarily controls potassium
– It exchanges potassium for sodium
• Insulin also regulates potassium
– It drives it into cells (with sugar) & thus produces
hypokalemia
• pH also affects potassium secretion
– Acidosis: more H+ in blood which finds its way into cell
& pushes K+ into blood
» Also get kidney to exchange H+ for K+
» Acidosis -gives- hyperkalemia
– Alkalosis: less H+ in blood
» Kidneys exchange K+ for H+; thus get hypokalemia
• Effects of abnormal potassium on cardiac function
• Hyperkalemia = fast repolarization; heart gets more irritable
• Hypokalemia = cell can’t repolarize & heart gets less irritable
• Effects of hyper & hypokalemia very similar
– Both give:
– Muscle weakness, & paresthesias
– Nausea
• Kidney effects:
• Hyperkalemia : oliguria, retention of H+ (become acidotic)
– Note: oliguria because of aldosterone secretion
• Hypokalemia : polyuria, excretion of H+ (become alkalotic)
– Note: polyuria because of decrease aldosterone secretion
Electrolytes & Their Imbalances
Calcium (Ca++)
• Calcium balance
–
–
–
–
Calcium is most abundant mineral in body
Calcium is important as an extracellular cation
Calcium & phosphorus have a reciprocal relationship
Calcium balance is dependent on:
» Parathyroid hormone (PTH)
» Calcitriol (active vitamin D)
» Calcitonin (from thyroid)
– 98% of calcium reabsorbed at the kidneys
• Calcium functions
–
–
–
–
Structural strength for bones & teeth
Maintains stability of nerve membrane
Required for muscle cell contraction
Necessary for blood clotting
• Hypercalcemia
– Symptoms
• SOUP
– Causes
• Hyperparathyroidism
– Most frequent cause
• Malignant tumors
• Immobility
– Via demineralization
• Milk- alkali syndrome
– Effects
• General muscle weakness
• Increase strength of heart
muscle contraction !!
• Prevention of ADH
working on the kidney
• Increase in PTH leads to
decrease bone density
• Hypocalcemia
– Symptoms
• Tetany
• Weak heartbeat
• Muscle spasms
• Convulsions
– Causes
• Not too common
• Renal failure
• Malabsorption
• Alkalosis
– Effects
• Low calcium leads to increased
membrane permeability of
nerves & get spontaneous
stimulation of skeletal muscle
(tetany)
• Weakens muscle cell
contraction
– Thus weak heart
contraction
[note opposite effects on skeletal & cardiac m.]
Other Electrolytes & Their Imbalances
• Magnesium
– Imbalances are rare
– Most is reabsorbed by kidneys
• Chloride
–
–
–
–
Primarily in ECF
99% reabsorbed in normal adult
Usually follows sodium
Note: chloride-bicarbonate shift with vomiting
• Phosphate
– Most is reabsorbed by kidneys
– Works primarily in ICF for formation of ATP & cell membranes
Acid-Base Imbalance
Physiology of acid-base balance
• Changes in pH
– Disrupt the stability of cell membrane
– Alters protein
» Alter protein structure
» Alter enzyme activity
• Normal = 7.34 – 7.45
• Acidosis more common & clinically more significant
– Remember that metabolic acids are by-products of metabolism
– Acidosis if pH < 7.35
– Clinical findings
» Coma develops
» Cardiac muscle deteriorates
» Peripheral vasodilation (decrease BP)
– Weak vs. strong acids
– Strong acids dissociate in solution freeing up more hydrogen ions
– Weak acids enter a solution & a significant number of molecules
remain intact
• Buffer systems are used to keep the body in pH balance (homeostasis)
– It consists of a weak acid (H+)and its dissociation products (an anion)
– 3 major buffer systems in human
• [1] Protein buffer system (includes hemoglobin buffer system)
– Regulates ICF & ECF (both plasma & interstitial fluid)
– Most important in ICF & hemoglobin
» Hemoglobin buffer system = carbonic anhydrase in RBC
* it absorbs CO2 from ECF & get immediate effect
– Amino acids have carboxyl group (gives up H+) and
– Amino acids have amino group(can accept H+)
• [2] Carbonic acid-bicarbonate buffer system
– Important in ECF
– Lots of carbon dioxide from metabolic acids
– It mixes with water & get carbonic acid which dissociates into H+ &
HCO3– Metabolic acids have H+ ; Our body has “bicarbonate reserve”
» Bicarbonate reserve = ample supply of bicarb in ECF
» These combine to form CO2 + H2O
» CO2 excreted via lungs
– Think of CO2 as an acid since it readily combines with water to become
carbonic acid
•
Note:
– Blood (hemoglobin) acts first
• Works on excess H+
– Kidneys act secondly
• Rids one of excess H+
– Lungs act last
• Rids one of excess HCO3-
Lung’s mechanism to regulate body’s pH
•
[3] Phosphate buffer system
»
»
Important in ICF
Phosphate is an anion but a weak acid
1.
Summary of 3 key buffer systems
Hemoglobin buffer system (protein) --- short term
2.
Carbonic acid buffer system ---- long term
3.
Phosphate buffer system
• To maintain acid- base balance you must control hydrogen ion losses & gains
– 3 key ways:
– This is done by (1) pulmonary & (2) renal mechanisms
» These are called metabolic buffer systems
– Also done by (3) buffer systems
» These are called chemical buffer systems:
• Imbalances of pH ------ 4 basic categories
– Key points
•
•
•
•
•
Excess vomiting = loss of acid & get metabolic alkalosis
Excess diarrhea = loss of bicarbonate & get metabolic acidosis
Sx of acidosis = CNS depression
Sx of alkalosis = CNS irritability
Both acidosis & alkalosis will lead to coma