1. Imbalances Of: Fluids, Electrolytes, & Acid-bases
Pathophysiology

2. Review of Body Fluids Fluid compartments Body Water Healthy adult
Male = 60%
Female = 50%
Babies = 75%
Elderly = 45%
Calculation:
1 Kg = 1 L water volume
150# = 70Kg
60% of 70Kg
= approx 40Kg
40Kg = 40L
Fluid compartments
2 main ones
ICF = 2/3 volume of fluid in body
ECF = 1/3 volume of fluid in body
Plasma = 20%
Interstitial fluid = 80%
Calculation:
40L = fluid volume
2/3 = 25L of ICF
1/3 = 15L of ECF
NB: Blood = 3-4% of weight

4. 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)

5. 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

7. Note: Insensible loss = 1000 cc/day
Fluid balance
Important in IV daily maintenance
Intake & output ( I &O )
Note: Insensible loss = 1000 cc/day

8. 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

9. Fluid Excess --- Edema
Edema = excessive amount of fluid in interstitial compartment
4 main causes
Increased capillary hydrostatic pressure
Etiology
Hypertension
Increased blood volume o to pregnancy, renal failure, CHF
Loss of plasma proteins (esp. albumin)
Kidney disease, malnutrition, malabsorption
Obstruction of lymphatic circulation
Cancer, parasitic diseases, post surgical
Increased capillary permeability
Inflammation, toxins, burns
see next slide

10. Effects of edema Swelling------- local or generalized Pitting edema
Increase in body weight
Functional impairment
Pain impaired arterial circulation (obesity)
Pressure exerted on arteries

11. 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

12. 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

14. 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

15. Signs of sodium imbalance
hyponatremia hypernatremia
Weakness & fatigue weakness & agitation
G-I: anorexia, nausea, cramps G-I: thirst, dry mucosa
Hypotension hypertension & edema
Mental confusion & ? Seizures
(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

17. 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

18. 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

19. 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

20. Hypercalcemia Hypocalcemia Symptoms Symptoms Tetany 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.]

21. 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
Works primarily in ICF for formation of ATP & cell membranes

22. Physiology of acid-base balance
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

23. 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+)

24. [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

25. 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-

26. Lung’s mechanism to regulate body’s pH

27. Summary of 3 key buffer systems
[3] Phosphate buffer system
Important in ICF
Phosphate is an anion but a weak acid
Summary of 3 key buffer systems
Hemoglobin buffer system (protein) --- short term
Carbonic acid buffer system ---- long term
Phosphate buffer system

28. 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:

29. Imbalances of pH ------ 4 basic categories

31. 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