MLAB 2401: CLINICAL
CHEMISTRY
KERI BROPHY-MARTINEZ
Disorders of Acid-Base Imbalance
ACID-BASE IMBALANCES
•
•
•
•
•
pH< 7.35 = acidosis/acidemia
pH> 7.45 = alkalosis/alkalemia
The body responds to imbalances by
compensation
If balance is fully restored to 20:1 , it is termed
complete
If balance is still outside of normal limits it is
termed partial
COMPENSATION

Respiratory compensation
Occurs when underlying problem is metabolic
 See changes in pCO2
 Body responds by hyper or hypoventilation


Metabolic Compensation
Occurs when underlying problem is respiratory
 See changes in bicarbonate concentration
 Body responds by activating renal mechanisms

ACID-BASE IMBALANCE

Four categories
 Metabolic
Acidosis
 Metabolic Alkalosis
 Respiratory Acidosis
 Respiratory Alkalosis
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METABOLIC VS RESPIRATORY

Metabolic
KIDNEY
 Effects base= bicarbonate


Respiratory
LUNGS
 Effects acid= carbonic acid

METABOLIC ACIDOSIS
Bicarbonate deficit : blood concentrations of bicarb drop
below 22mEq/L
 Results in: pH drop
 Decrease in 20:1 ratio
 Causes of:

Loss of bicarbonate through diarrhea or renal dysfunction
 Accumulation of acids (lactic acid or ketones) that exceed rate of
elimination
 Failure of kidneys to excrete H+

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SYMPTOMS OF METABOLIC
ACIDOSIS
Headache,
 Rapid and deep breathing
 Lethargy
 Nausea, vomiting, diarrhea
 Coma
 Death

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COMPENSATION FOR METABOLIC
ACIDOSIS

Respiratory
Primary mechanism
 Increased ventilation



CO2 blown off
Renal
Excretion of hydrogen ions if possible
 Reabsorption of bicarbonate

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METABOLIC ALKALOSIS
Bicarbonate excess - concentration in blood is
greater than 26 mEq/L
 Results in: pH increase
 Causes of:


Loss of acid-rich fluids
Excess vomiting = loss of stomach acid
 Certain diuretics


Addition of base to the body
Excessive use of alkaline drugs
 Heavy ingestion of antacids


Decrease of base elimination

Endocrine disorders ( Cushing’s syndrome)
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COMPENSATION FOR METABOLIC
ALKALOSIS

Respiratory
Primary mechanism
 Hypoventilation

Increased retention of CO2
 Limited by hypoxia ( no oxygen)


Alkalosis most commonly occurs with renal
dysfunction, so can’t count on kidneys to excrete
excess bicarbonate
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SYMPTOMS OF METABOLIC
ALKALOSIS
Respiration slow and shallow
 Hyperactive reflexes ; tetany
 Often related to depletion of electrolytes
 Atrial tachycardia
 Dysrhythmias

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RESPIRATORY ACIDOSIS
•
•
•
Increased carbonic acid as indicated by increased pCO2
Results in: decreased pH
Causes of:
– Problems within the respiratory system
– Organs- lungs
– Obstruction in the airway or restriction of gas
exchange
– Obstructive emphysema
– Pulmonary edema/ pulmonary disease
– Depression of respiratory center in brain that controls
the breathing rate
– Drugs
– Stroke, Coma
COMPENSATION FOR RESPIRATORY
ACIDOSIS

Kidneys
 Primary mechanism
 Eliminate hydrogen ions
 Retain bicarbonate ions
SIGNS AND SYMPTOMS OF
RESPIRATORY ACIDOSIS
Breathlessness
 Restlessness
 Lethargy and disorientation
 Tremors, convulsions, coma
 Respiratory rate rapid, then gradually depressed
 Skin warm and flushed due to vasodilation caused by
excess CO2

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RESPIRATORY ALKALOSIS
•
Decrease carbonic acid indicated by decreased
pCO2
Most common acid-base imbalance
•
Results in: increased pH
•
Causes of:
•
Hypoxemia
• Stimulation of the Respiratory Center:
•
RESPIRATORY ALKALOSIS

Hypoxemia





Pulmonary disease
Congestive heart disease
Severe anemia
High-altitude exposure
Conditions that stimulate respiratory center:





Acute anxiety
Salicylate intoxication
Cirrhosis
Gram-negative sepsis
Hyperventilation syndrome
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COMPENSATION FOR RESPIRATORY
ALKALOSIS
•
Kidneys
Primary mechanism
• Conserve hydrogen ion
• Excretion of bicarbonate ion
•
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SUMMARY OF ACID-BASE DISORDERS
PRIMARY ACID/BASE DISORDERS
pCO2
pH
HCO3
Base Excess
Uncompensated
acidosis
N
D
D
D
Uncompensated
alkalosis
N
I
I
I
Partially
compensated
acidosis
D
D
D
D
Partially
compensated
alkalosis
I
I
I
I
N
I/D
I/D
Compensated
I/D
Acidosis/alkalosis
Disturbance Primary Abnormality
Compensation
Metabolic Excess endogenous
Hyperventilation lowers
Acidosis
acid depletes
pCO2,
bicarbonate
Kidney excretes excess
H+ and forms more
HCO3Respiratory Inefficient excretion
Formation of excess
Acidosis
of CO2 by the
HCO3- by kidney
lungs
Metabolic
Alkalosis
Excess plasma
bicarbonate
Kidneys excrete excess
HCO3- and form less
HCO3- and NH4,
Lungs hypoventilate
Respiratory
Alkalosis
Hyperventilation
lowers pCO2
Increased excretion of
bicarbonate by kidney
Cause
Renal failure
Ketosis
Increased lactic acid
Diarrhea
Chronic pulmonary
Diseases (COPD), such as
emphysema
Acute problems, such as
pneumonia, airway
obstruction, drugs such as
opiates, congestive heart
failure
Loss of gastric juice
Chloride depletion
Hypokalemia
Increased
corticosteroid
Increased ingestion of
antacids
Hyperventilation, such as
with severe anxiety,
fever, head injuries
Stimulation of resp.
center by drugs
Central nervous system
diseases
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REFERENCES




Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical
Chemistry: Techniques, principles, Correlations. Baltimore:
Wolters Kluwer Lippincott Williams & Wilkins.
Carreiro-Lewandowski, E. (2008). Blood Gas Analysis and
Interpretation. Denver, Colorado: Colorado Association for
Continuing Medical Laboratory Education, Inc.
Jarreau, P. (2005). Clinical Laboratory Science Review (3rd
ed.). New Orleans, LA: LSU Health Science Center.
Sunheimer, R., & Graves, L. (2010). Clinical Laboratory
Chemistry. Upper Saddle River: Pearson .
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