Acid-Base
Imbalances
Acid-Base Imbalances
• pH< 7.35 acidosis
• pH > 7.45 alkalosis
• The body response to acid-base imbalance is
called compensation
• May be complete if brought back within normal
limits
• Partial compensation if range is still outside
norms.
2
Compensation
• If underlying problem is metabolic, hyperventilation
or hypoventilation can help : respiratory
compensation.
• If problem is respiratory, renal mechanisms can bring
about metabolic compensation.
3
Acid-Base Disturbances
• When compensation is appropriate
Metabolic acidosis (↓ HCO3, ↓ pCO2)
Metabolic alkalosis (↑ HCO3, ↑ pCO2)
Respiratory acidosis (↑ pCO2, ↑ HCO3)
Respiratory alkalosis (↓ pCO2, ↓ HCO3)
Stepwise Approaches
1. History & physical examination
2. Arterial blood gas for pH, pCO2, (HCO3)
• Use the HCO3 from ABG to determine compensation
3. Serum Na, K, Cl, CO2 content
• Use CO2 content to calculate anion gap
4. Calculate anion gap
• Anion gap = {Na + K - (Cl + HCO3-)}
5. Determine appropriate compensation
6. Determine the primary cause
1. Respiratory Acidosis
• Carbonic acid excess caused by blood levels
of CO2 above 45 mm Hg.
• Hypercapnia – high levels of CO2 in blood
• Causes:
• Chronic conditions:
• Depression of respiratory center – drugs
or head trauma
• Paralysis of respiratory or chest muscles
• Emphysema
6
Respiratory Acidosis cont.
• Acute conditions:
• Adult Respiratory Distress Syndrome
• Pulmonary edema
• Pneumothorax
• Compensation for Respiratory Acidosis: the
kidneys eliminate hydrogen ion and retain
bicarbonate ion (metabolic alkalosis)
7
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
8
Treatment of Respiratory Acidosis
• Treat underlying dysfunction or disease
• Caution should be exercised in the correction
of chronic hypercapnia: too-rapid correction of
the hypercapnia can result in metabolic
alkalosis. Alkalization of the cerebrospinal fluid
(CSF) can result in seizures.
• Admit to intensive care unit (ICU) if pH (< 7.25)
• Oxygen therapy should be used with caution
because it may worsen hypercapnia
9
• Restore ventilation: invasive or non invasive
ventilation
• Bicarbonate: Infusion of sodium bicarbonate is
rarely indicated. This measure may be considered
after cardiopulmonary arrest with an extremely
low pH (< 7.0-7.1). In most other situations,
sodium bicarbonate has no role in the treatment
of respiratory acidosis.
2. Respiratory Alkalosis
• Carbonic acid deficit
• pCO2 less than 35 mm Hg (hypocapnea)
• Most common acid-base imbalance
• Primary cause is hyperventilation
11
Respiratory Alkalosis
• Conditions that stimulate respiratory center:
• Oxygen deficiency at high altitudes
• Pulmonary embolism
• Acute anxiety
• Fever, anemia
• Early salicylate intoxication
• Cirrhosis
• Gram-negative sepsis
• Compensation of Respiratory Alkalosis
• Kidneys conserve hydrogen ion
• Excrete bicarbonate ion (metabolic acidosis)
12
Treatment of Respiratory Alkalosis
• The treatment of respiratory alkalosis is primarily
directed at correcting the underlying disorder.
• Respiratory alkalosis itself is rarely life
threatening. Therefore, emergent treatment is
usually not indicated unless the pH level is greater
than 7.5.
• Breathe into a paper bag, beta blocker or
sedatives can be helpful in anxiety attacks
13
3. Metabolic Acidosis
• Bicarbonate deficit - blood concentrations of
bicarbonate drop below 22mEq/L
• Causes:
• Loss of bicarbonate through diarrhea or renal
dysfunction
• Accumulation of acids (lactic acid or ketones)
• Failure of kidneys to excrete H+
14
Symptoms of Metabolic Acidosis
• Headache, lethargy
• Nausea, vomiting, Diarrhea
• Coma
• Death
• Compensation for Metabolic Acidosis
• Increased ventilation (respiratory alkalosis)
• Renal excretion of hydrogen ions if possible
• K+ exchanges with excess H+ in ECF ( H+ into
cells, K+ out of cells)
15
Treatment of Metabolic Acidosis
• Treating the underlying conditions in high
AG states usually is sufficient in reversing
the acidosis.
• Treatment with bicarbonate is unnecessary,
except in extreme cases of acidosis when
the pH is less than 7.1-7.2.
• HCO3- can be administered intravenously to
raise the serum HCO3- level adequately to
increase the pH to greater than 7.20.
16
4. Metabolic Alkalosis
• Bicarbonate excess - concentration in blood
is greater than 26 mEq/L
• Causes:
• Excess vomiting = loss of stomach acid
• Excessive use of alkaline drugs
• Certain diuretics
• Endocrine disorders
• Heavy ingestion of antacids
• Severe dehydration
17
Symptoms of Metabolic Alkalosis
• Respiration slow and shallow
• Hyperactive reflexes ; tetany often related to
depletion of electrolytes
• Dysrhythmias
• Compensation for Metabolic Alkalosis
• Alkalosis most commonly occurs with renal
dysfunction, so can’t count on kidneys
• Respiratory compensation difficult –
hypoventilation limited by hypoxia
18
Treatment of Metabolic Alkalosis
• Treat underlying disorder
• Replace electrolytes loss
• IV sodium chloride in volume depleted patients often
need to add potassium
• Hydrochloric acid: Intravenous HCl is indicated in
severe metabolic alkalosis (pH >7.55) or when sodium
or potassium chloride cannot be administered
because of volume overload or advanced renal failure.
• Dialysis: Both peritoneal dialysis and hemodialysis can
be used with certain modifications of the dialysate to
correct metabolic alkalosis
19