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ACID-BASE
IMBALANCE
Wan Nedra
Faculty of Medicine
YARSI University
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Teaching aims
By the end of lecture session, the students
are expected to:
Understand the underlying concept of acid-base balance in human body
To maintain a balance between acids and
bases to achieve homeostasis
Arterial blood shows the make-up of bloodbefore it is distributed to the tissues
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Regulators of Acid/Base
Buffers
Respiratory system
Renal system
Buffers:
- Primary regulators
- Act immediately
- Present in blood and tissues
- Take up extra H+ ions or release H+
- (bicarbonate, proteins, hemoglobin)
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Respiratory system
Eliminates CO2 Respiratory center in medulla controls
breathing
Incresed respiration leads to CO2eliminated from body and CO2in blood
Decresed respiratory leads to CO2eliminated from body and CO2in blood
Responds whithin minutes to hours tochanges in acid/base
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Renal System
Selected hydrogen (H+) ion and
reabsorbs bicarbonate (HCO3) ions
Reabsorbtion and secretion ofelectrolytes (Na,Cl)
Respons within hours to days
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Types of acid-base imbalance
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis
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Respiratory Acidosis
Any condition that increases blood pCO2 (above45 mmHg, pH
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Causes:
Hypoventilation:
Central nervous system
Peripheral nervous system Neuromuscular transmission
Muscle disorders
Chest wall abnormalities
Lung and airway disorders. Inhalation of CO2
Increased production of CO2
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Carbonic acid excesscaused by blood levels of
CO2above 45 mm Hg.
Hypercapniahigh levels of CO2 in blood
Acute conditions:
Adult Respiratory Distress Syndrome
Pulmonary edema
Pneumothorax
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Chronic conditions:
Depression of respiratory
center in brain that controlsbreathing ratedrugs or head
trauma
Paralysis of respiratory orchest muscles
Emphysema
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Compensation for Respiratory Acidosis
Kidneys eliminate hydrogen ion
and retain bicarbonate ion
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Signs and Symptoms of RespiratoryAcidosis
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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Treatment of Respiratory Acidosis
Restore ventilation
IV lactate solution Treat underlying dysfunction or
disease
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Respiratory Alkalosis
Respiratory alkalosis - any condition thatdecreases blood pCO2 (below 35 mmHg, pH>7.45).
This is associated with hyperventilation. Usuallythese are acute so there is no time for renalcompensation, but if prolonged, such as inacclimatization to high altitudes, there wouldprobably be renal compensation.
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Carbonic acid deficit
pCO2less than 35 mm Hg
(hypocapnea) Most common acid-base
imbalance
Primary cause is hyperventilation
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Respiratory alkalosis (cont.)Causes:
Deliberate induced hyperventilation
during anaesthesia
Some causes of hypoxiaassociated with hyperventilation
Fever
Some types of C.N.S. damage
Hysterical hyperventilation
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Conditions that stimulate respiratory center:
Oxygen deficiency at high altitudes
Pulmonary disease and Congestive heart failurecaused by hypoxia
Acute anxiety
Fever, anemia
Early salicylate intoxication
Cirrhosis
Gram-negative sepsis
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Compensation of Respiratory Alkalosis
Kidneys conserve hydrogen ion Excrete bicarbonate ion
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Treatment of Respiratory Alkalosis
Treat underlying cause Breathe into a paper bag
IV Chloride containing solution
Cl- ions replace lost bicarbonate
ions
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Metabolic Acidosis (non-respiratoryacidosis)
This (non-respiratory acidosis) is
due to increase in acids (i.e. H+
donating substances) other thanH2CO2 or decrease in base (i.e.
H+acceptors) in the blood.
Compensation is by
hyperventilation. This lowers the
PaCO2 thus deducing the any pH
change
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Metabolic acidosis (cont.)
Bicarbonate deficit - blood concentrations ofbicarb drop below 22mEq/L
Causes:
Increased alimentary or parenteral intake of acidor alimentary loss of base (Loss of bicarbonate
through diarrhea)
Accumulation of acids (lactic acid or ketones)
Failure of excretion of acid (excrete H+) or loss ofbase by the renal system (or renal dysfunction)
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Symptoms of MetabolicAcidosis
Headache, lethargy
Nausea, vomiting, diarrhea Coma
Death
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Compensation for MetabolicAcidosis
Increased ventilation
Renal excretion of hydrogenions if possible
K+exchanges with excess H+
in ECF
( H+into cells, K+out of cells)
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Treatment of Metabolic Acidosis
IV lactate solution
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Metabolic Alkalosis
Bicarbonate excess-concentration in blood is greaterthan 26 mEq/L
Causes:
Excess vomiting = loss of stomachacid
Excessive use of alkaline drugs Certain diuretics
Endocrine disorders
Heavy ingestion of antacids
Severe dehydration
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Compensation for Metabolic Alkalosis
Alkalosis most commonly occurs
with renal dysfunction, so cant
count on kidneys
Respiratory compensation difficult
hypoventilation limited by
hypoxia
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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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Treatment of Metabolic Alkalosis
Electrolytes to replace those lost IV chloride containing solution
Treat underlying disorder
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Diagnosis of Acid-BaseImbalances
1. Note whether the pH is low
(acidosis) or high (alkalosis)
2. Decide which value, pCO2orHCO3
-, is outside the normal
range andcould be thecauseof
the problem. If the cause is a
change in pCO2, the problem isrespiratory. If the cause is HCO3
-
the problem is metabolic.
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3. Look at the value that doesnt correspond to
the observed pH change. If it is inside the
normal range, there is no compensation
occurring. If it is outside the normal range,the body is partially compensating for the
problem.
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Example
A patient is in intensive care
because he suffered a severe
myocardial infarction 3 days ago.The lab reports the following
values from an arterial blood
sample:
pH 7.3 HCO3- = 20 mEq / L ( 22 - 26)
pCO2 = 32 mm Hg (35 - 45)
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Diagnosis
Metabolic acidosis With compensation
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