Chapter 2
Fluid, Electrolyte, and
Acid-Base Imbalances
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Distribution of Body Fluids
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Total body water
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Intracellular fluid (ICF): Inside the cell
Extracellular fluid (ECF): Outside the cell
• Interstitial fluid – between tissues
• Intravascular fluid – in the blood vessels (plasma)
• Cerebrospinal fluid (CSF)
• Lymphatic, synovial, intestinal, biliary, hepatic, pancreatic,
pleural, peritoneal, pericardial, and intraocular fluids
• Sweat
• Urine
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Water Movement between the
ICF and ECF
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Osmolality
Osmotic forces
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Sodium for the ECF
Potassium for the ICF
Osmosis: How water moves between the ICF
and ECF compartments
When ECF osmolality changes, water moves
from one compartment to another until osmotic
equilibrium is reestablished.
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Water Movement between
Intravascular and Interstitial Fluid =
Capillary Exchange
Capillary hydrostatic
pressure (blood
pressure)
Capillary osmotic
pressure (plasma
proteins – albumin)
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Water Balance
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Body water is regulated by thirst perception and
the antidiuretic hormone (ADH)
Thirst perception
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Osmolality receptors (osmoreceptors)
• Signal posterior pituitary to release ADH
• Increase water intake
Baroreceptors
• Stimulated from depleted plasma volume
• Causes release of ADH
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Water Balance (Cont.)
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ADH
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Is released when there is an increase in plasma
osmolality or decrease in circulating blood volume.
Is also called vasopressin.
Increases water reabsorption in the nephrons of the
kidneys.
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Overview of Electrolytes
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Electrolytes are in both ECF and ICF
compartments but are in different
concentrations.
Some electrolytes are more concentrated in the
ICF compartment, as compared with the ECF
compartment.
All electrolytes move across compartments but
must be in balance for optimal health.
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Overview of Electrolytes (Cont.)
Intracellular
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Cation
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Potassium (K+)
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Anions
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Extracellular
Cation
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Phosphate
Organic ions
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Sodium (Na+)
Calcium (Ca++)
Anions
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Chloride (Cl−)
Bicarbonate (HCO3−)
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Na+ and Cl− Balance
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Sodium
Is the primary ECF cation.
Ø Regulates osmotic forces.
Ø Roles include:
• Neuromuscular irritability, acid-base balance, cellular
Ø
reactions, and transport of substances
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Is regulated by aldosterone and natriuretic peptides.
Chloride
Is the primary ECF anion.
Ø Provides electroneutrality.
Ø Follows sodium.
Ø
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Na+ and Cl− Balance (Cont.)
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Sodium regulation
Ø Renin-angiotensin-aldosterone system
Ø Aldosterone - Increases sodium reabsorption
in kidneys
Ø Natriuretic peptides - Decreases tubular
resorption, and promotes urinary excretion of
sodium
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Na+ and Cl− Balance (Cont.)
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Renin-angiotensin-aldosterone system
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Questions??
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Alterations in Water Movement:
Edema (Fluid Excess) &
Dehydration (Fluid Deficit)
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Alterations in Water Movement:
Edema
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Accumulation of fluid in the interstitial spaces
Causes
Ø Increased capillary hydrostatic pressure (venous obstruction)
Ø Decreased plasma oncotic pressure (losses or diminished production of
albumin)
Ø Increased capillary permeability (inflammation and immune response)
Ø Lymphatic obstruction (lymphedema)
Capillary hydrostatic
pressure (blood
pressure)
Capillary osmotic
pressure (plasma
proteins – albumin)
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Alterations in Water Movement:
Edema (Cont.)
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Causes of edema
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Alterations in Water Movement:
Edema (Cont.)
Clinical Manifestations
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Dependent edema
Pitting edema
Swelling and puffiness
Tight-fitting clothes
and shoes
Weight gain
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Alterations in Water Movement:
Dehydration
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Insufficient body fluid
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Inadequate intake
Excessive loss
Both
Fluid loss often measured by change in body
weight
Dehydration more serious in infants and older
adults
Water loss may be accompanied by loss of
electrolytes and proteins (e.g., diarrhea).
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Causes of Dehydration
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Vomiting and diarrhea
Excessive sweating with loss of sodium and
water
Diabetic ketoacidosis
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Loss of fluid, electrolytes, and glucose in the urine
Insufficient water intake in older adults or
unconscious persons
Use of concentrated formula in infants
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Effects of Dehydration
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Dry mucous membranes in the mouth
Decreased skin turgor or elasticity
Lower blood pressure, weak pulse, and fatigue
Increased hematocrit
Decreased mental function, confusion, loss of
consciousness
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Testing for Dehydration
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Questions??
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Alterations in Electrolyte Balance:
Sodium, Potassium and Calcium
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Sodium - Hyponatremia
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Serum sodium level <135 mEq/L
Related to sodium loss or water gain
Causes
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Losses from excessive sweating, vomiting, diarrhea
Use of certain diuretic drugs (potassium sparing)
Low-salt diet
Hormonal imbalances
• Insufficient aldosterone à Adrenal insufficiency
• Excess ADH secretion
Excessive water intake
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Effects of Hyponatremia
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Low sodium levels
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Cause fluid imbalance in compartments
• Fatigue, muscle cramps, abdominal discomfort or cramps,
nausea, vomiting
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Decreased osmotic pressure in ECF
compartment
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Ø
Fluid shift into cells
• Hypovolemia and decreased blood pressure
Cerebral edema
• Confusion, headache, weakness, seizures
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Hyponatremia and Fluid Shift into Cells
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Sodium - Hypernatremia
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Hypernatremia
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Serum sodium >145 mEq/L
Related to sodium gain or water loss
Water movement from the ICF to the ECF
• Intracellular dehydration
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Hypernatremia
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Cause is imbalance in sodium and water
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Insufficient ADH (diabetes insipidus)
• Results in large volume of dilute urine
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Loss of the thirst mechanism
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Watery diarrhea
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Prolonged periods of rapid respiration
Ø
Ingestion of large amounts of sodium without enough
water
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Effects of Hypernatremia
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Weakness, agitation
Dry, rough mucous membranes
edema
Increased thirst (if thirst mechanism is
functional)
Increased blood pressure
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Potassium
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Review of potassium
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Major intracellular cation
Serum levels are low, with a narrow range.
Ingested in foods
Excreted primarily in urine
Insulin promotes movement of potassium into cells.
Level influenced by acid–base balance
Excess potassium ions in interstitial fluid may lead to
hyperkalemia.
Abnormal potassium levels cause changes in cardiac
conduction and are life-threatening!
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Potassium - Hypokalemia
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Definition of hypokalemia
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Serum K+ < 3.5 mEq/L
Causes
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Excessive losses caused by diarrhea
Diuresis associated with some diuretic drugs
Excessive aldosterone or glucocorticoids
• Example: Cushing syndrome
Decreased dietary intake
May occur during treatment of diabetic ketoacidosis
with insulin
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Effects of Hypokalemia
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Cardiac dysrhythmias
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Interference with neuromuscular function
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Caused by impaired repolarization leading to cardiac
arrest.
Muscles less responsive to stimuli
Paresthesia―“pins and needles”
Decreased digestive tract motility
Severe hypokalemia:
Ø
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Shallow respirations
Failure to concentrate urine―polyuria
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Potassium - Hyperkalemia
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Definition of hyperkalemia
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Serum K+ > 5 mEq/L
Causes
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Renal failure
Deficit of aldosterone
“Potassium-sparing” diuretics
Leakage of intracellular potassium into extracellular
fluids
• In patients with extensive tissue damage
Displacement of potassium from cells by prolonged or
severe acidosis
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Displacement of potassium from cells by prolonged or severe
acidosis
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Effects of Hyperkalemia
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Cardiac dysrhythmias
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Muscle weakness common
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May progress to cardiac arrest.
Progresses to paralysis.
May cause respiratory arrest.
Impairs neuromuscular activity .
Fatigue, nausea, paresthesias
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Calcium
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Review of calcium
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Important extracellular cation
Ingested in food
Stored in bone
Excreted in urine and feces
Balance controlled by parathyroid hormone (PTH)
and calcitonin
Vitamin D promotes calcium absorption from intestine.
• Activated in kidneys
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Calcium - Hypocalcemia
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Causes
Ø Hypoparathyroidism
Ø Malabsorption
Ø Increased
serum pH level
Ø Renal failure
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Effects of Hypocalcemia
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Increase in the permeability and excitability of
nerve membranes
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Spontaneous stimulation of skeletal muscle
• Muscle twitching
• Carpopedal spasm
Tetany
Weak heart contractions
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Delayed conduction
Leads to dysrhythmias and decreased blood
pressure.
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Calcium - Hypercalcemia
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Uncontrolled release of calcium ions from bones
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Hyperparathyroidism
Demineralization caused by immobility
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Decrease stress on bone
Increased calcium intake
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Neoplasms―malignant bone tumors
Excessive vitamin D
Excess dietary calcium
Milk-alkali syndrome
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Effects of Hypercalcemia
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Depressed neuromuscular activity
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Interference with ADH function
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Muscle weakness, loss of muscle tone
Lethargy, stupor, personality changes
Anorexia, nausea
Less absorption of water
Decrease in renal function
Increased strength in cardiac contractions
Ø
Dysrhythmias may occur.
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Acid-Base Balance
pH—What is it?
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Negative logarithm of the H+ concentration
0
7
Increasing H+
Very acidic
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Decreasing H+
Neutral
Very alkaline
Each number represents a factor of 10.
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pH scale
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If the solution moves from a pH of 7 to a pH of 6,
then the H+ ions have increased 10-fold.
If H+ is high in number, pH is low (acidic).
If H+ is low in number, pH is high (alkaline).
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Acid-Base Balance (Cont.)
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Acids are formed as end products of protein,
carbohydrate, and fat metabolism.
To maintain the body’s normal pH (7.35–7.45)
the H+ must be neutralized by the retention of
bicarbonate or excreted.
Bones, lungs, and kidneys are major organs
involved in the regulation of acid-base
balance.
pH below 6.8 = death.
pH above 7.8 = death.
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Hydrogen Ion and pH Scale
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Acid-Base Balance (Cont.)
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Acid-base balance is mainly concerned with two
ions
1. Hydrogen (H+)
2. Bicarbonate (HCO3−)
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Alterations of hydrogen and bicarbonate
concentrations in body fluids are common in
disease processes.
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Acid-Base Balance (Cont.)
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Sources of H+ ions
Ø
CO2 diffuses into the bloodstream where the following
reaction occurs:
CO2 + H2O ßà H2CO3 ßà HCO3− + H+
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Buffering Systems
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Buffer: Something that can correct the pH
change
Located in the ICF and ECF.
Most important plasma buffering systems:
carbonic acid-bicarbonate system and
hemoglobin
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Carbonic Acid-Bicarbonate Buffering
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Operates in the lung and the kidney.
Lungs can decrease carbonic acid.
Kidneys can reabsorb or regenerate bicarbonate but do
not act as fast as the lungs.
Regulated by the Lung
Regulated by the Kidney
CO2 + H2O ßà H2CO3 ßà HCO3− + H+
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Carbonic Acid-Bicarbonate Buffering (Cont.)
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If bicarbonate decreases, then the pH decreases
and can cause acidosis.
pH can be returned to normal if carbonic acid
also decreases.
Ø
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This type of pH adjustment is called compensation.
The respiratory system compensates by
increasing or decreasing ventilation.
The renal system compensates by producing
acidic or alkaline urine.
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Decompensation
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Occurs when:
Ø
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Causative problem becomes more severe.
Additional problems occur.
Compensation mechanisms are exceeded or fail.
Requires intervention to maintain homeostasis.
LIFE-THREATENING!
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Acid-Base Imbalances
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Four categories
1. Respiratory acidosis— elevated blood CO2 as a
result of ventilation depression
2. Respiratory alkalosis— reduced blood CO2 as a
result of hyperventilation
3. Metabolic acidosis— reduced blood HCO3−
4. Metabolic alkalosis— elevated blood HCO3−, usually
as a result of an excessive loss of metabolic acids
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Respiratory Acidosis
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Acute problems
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Chronic respiratory acidosis
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Pneumonia, airway obstruction, chest injuries
Drugs that depress the respiratory control center
Common with chronic obstructive pulmonary disease
Decompensated respiratory acidosis
Ø
May develop if impairment becomes severe or if
compensation mechanisms fail.
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Metabolic Acidosis
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Excessive loss of bicarbonate ions to buffer
hydrogen
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Increased use of serum bicarbonate
Renal disease or failure
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Diarrhea―loss of bicarbonate from intestines
Decreased excretion of acids
Decreased production of bicarbonate ions
Decompensated metabolic acidosis
Ø
Additional factor interferes with compensation.
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Effects of Acidosis
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Impaired nervous system function
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Headache
Lethargy
Weakness
Confusion
Coma and death
Compensation
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Deep rapid breathing
Secretion of urine with a low pH
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Respiratory Alkalosis
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Causes
Ø
Hyperventilation
• Caused by anxiety, high fever, overdose of aspirin
• Head injuries
• Brain stem tumor
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Metabolic Alkalosis
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Causes
Ø
Increase in serum bicarbonate ion
• Loss of hydrochloric acid from stomach
• Hypokalemia
• Excessive ingestion of antacids
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Effects of Alkalosis
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Increased irritability of the nervous system
causes:
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Restlessness
Muscle twitching
Tingling and numbness of the fingers
Tetany
Seizures
Coma
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Summary
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Questions??
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