Four Major Acid-Base Imbalances and Possible Etiologies
Respiratory Characteristics of Failure
Imbalance
Respiratory ↑ H2CO3 (carbonic acid)
Acidosis
level from retention of
CO2.
Caused by: decreased
ventilation and
consequent CO2
retention.
“Hypoventilation”
Respiratory ↓ H2CO3 (carbonic acid)
Alkalosis
level from excessive
expiration of CO2 and
H2O
Caused by: increased
ventilation and
elimination of CO2.
“Hyperventilation”
Net result is ↑ pH; ↓in
ionized blood calcium
concentration.
Associated Disease/Conditions
Compensation
Simple, acute respiratory acidosis results
in a low pH, or acidemia. Sleep apnea,
asthma, aspiration of a foreign object or
ARDS. Chronic respiratory acidosis is
associated with obesity hypoventilation
syndrome, COPD or emphysema, certain
neuromuscular diseases, and starvation
cachexia.
Severe, acute respiratory alkalosis results
in a high pH, or alkalemia.
Condition may be mediated centrally
(head injury, anxiety, cerebrovascular
accident, or tumors); or by peripheral
stimulation (pneumonia, hypoxemia, high
altitudes, pulmonary embolism,
congestive heart failure, or interstitial lung
disease. Also caused by aftermath of
intense exercise; anxiety reaction; early
sepsis.
Could be produced by excessive
mechanical ventilation by doctors.
Kidneys compensate by
↑ bicarb resorption,
thereby creating a
metabolic alkalosis;
which helps to ↑ the pH
(takes 3-5 days).
Impact to electrolytes
Acidosis decreases binding of calcium to
albumin and tends to increase serum
ionized calcium levels. In addition,
acidemia causes an extracellular shift of
potassium, but respiratory acidosis rarely
causes clinically significant hyperkalemia.
Decrease in ionized blood calcium
concentration.
It could cause the symptoms of
hypocalcaemia (tetany – involuntary
contraction of muscles or fainting) with
no fall in total serum calcium levels.
Metabolic Characteristics of Failure
Imbalance
Metabolic ↑ H+ (decreased pH)
Acidosis
concentration from
increased production,
increased ingestion, or
increased retention. OR…
↓HCO3- from
extracellular fluid.
(Loss of base)
Associated Disease/Conditions
Compensation
Simple, acute metabolic acidosis results in
a low blood pH, or academia. Diarrhea;
uremia; ketoacidosis from uncontrolled
diabetes mellitus (often resulting in rapid,
deep breathing called Kussmaul
respirations); toxin ingestion; starvation. A
pH under 7.1 is an emergency due to risk
of cardiac arrhythmias; may need IV
treatment of bicarb.
The lungs compensate
by ↑ ventilation and
CO2 elimination (rapid,
deep breaths) creating a
respiratory alkalosis,
which helps to ↑ pH.
High-fat, low-carbohydrate diet; drug use;
excessive bicarb loss via the kidneys or
intestinal tract; PTN without thiamin has
caused death.
Clinical tool: “Anion Gap” - The chloride
and bicarb levels are subtracted from
sodium.
Four potential buffering
systems: bicarb;
intracellular; respiratory
compensation; renal
compensation.
Impact to electrolytes
([Na+])-([Cl-]+[HCO3-]).
Metabolic
Alkalosis
↓ H+ (increased pH)
concentration from
increased losses. OR…
↑ HCO3- from abnormal
retention of base in
extracellular fluid.
Elevated anion gap > 16 mmol/l can
indicate particular types of metabolic
acidosis.
Simple, acute metabolic alkalosis results in
a high blood pH (alkalemia). Diuretics use;
increased ingestion of alkali; loss of acid
during gastric suctioning.
Loss of chloride (from villous adenoma or
diuretic use); vomiting; decreased blood
flow to the kidneys stimulates resorption
of sodium and water, increasing bicarb
resorption resulting in “contraction
alkalosis”.
Compensation occurs
mainly in the lungs
through
hypoventilation.
Due to a low extracellular potassium
concentration, potassium shifts out of
the cells. In order to maintain electrical
neutrality, hydrogen shifts into the cells,
raising blood pH. Could result in
hypokalemia.
Severe hypokalemia can also cause
alkalosis - as K moves to extracellular
fluid, H+ moves to the intracellular fluid
to maintain electroneutrality resulting in
intracellular acidosis - which increases
H+ excretion and bicarb resorption by the
kidneys.