MLAB 2401: CLINICAL CHEMISTRYKERI BROPHY-MARTINEZDisorders 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 AcidosisMetabolic AlkalosisRespiratory AcidosisRespiratory 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

KidneysPrimary mechanismEliminate hydrogen ionsRetain 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

Partiallycompensated acidosis

D D D D

Partiallycompensated alkalosis

I I I I

CompensatedAcidosis/alkalosis

I/D N I/D I/D

Disturbance Primary Abnormality Compensation CauseMetabolic Acidosis

Excess endogenous acid depletes bicarbonate

Hyperventilation lowers pCO2,Kidney excretes excess H+ and forms more HCO3

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Renal failureKetosisIncreased lactic acidDiarrhea

Respiratory Acidosis

Inefficient excretion of CO2 by the lungs

Formation of excess HCO3

- by kidneyChronic pulmonary Diseases (COPD), such as emphysemaAcute problems, such as pneumonia, airway obstruction, drugs such as opiates, congestive heart failure

Metabolic Alkalosis

Excess plasma bicarbonate

Kidneys excrete excess HCO3

- and form less

HCO3- and NH4,

Lungs hypoventilate

Loss of gastric juiceChloride depletionHypokalemiaIncreased corticosteroidIncreased ingestion of antacids

Respiratory Alkalosis

Hyperventilation lowers pCO2

Increased excretion of bicarbonate by kidney

Hyperventilation, such as with severe anxiety, fever, head injuriesStimulation 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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