Respiratory acidosis is an acid-base disorder caused by the accumulation of carbon dioxide in the blood due to inadequate alveolar ventilation. The condition is accompanied by a decrease in blood pH and requires the activation of multilevel compensatory mechanisms.
CausePulmonary hypoventilation leading to an excess of carbon dioxide in the body.
Key ShiftDecrease in blood pH and accumulation of carbonic acid.
Long-term DefenseRenal compensation via acidogenesis and ammoniagenesis.
Brain EffectArteriolar spasm and risk of ischemia due to altered vascular tone.
Immediate Compensatory Mechanisms
The body responds to acidification almost instantly by utilizing internal reserves:
Buffer Systems: Hemoglobin and protein buffers bind excess hydrogen ions ($H^+$).
Ion Exchange in Erythrocytes: Active exchange of intracellular bicarbonate ($HCO_3^-$) for plasma chloride ions ($Cl^-$) occurs, which helps stabilize pH.
These processes aim to neutralize the excess $H^+$ generated during the dissociation of carbonic acid.
Role of the Kidneys in Acidosis Correction
Long-term adaptation is carried out by the kidneys, which operate more slowly but more effectively:
Acidogenesis: Active excretion of hydrogen ions.
Ammoniagenesis: Synthesis and excretion of ammonium ($NH_4^+$).
Titratable Acids: Enhanced secretion of phosphates.
Sodium Reabsorption: A process coupled with $H^+$ excretion and potassium exchange.
Impact on Hemodynamics and Tissues
The pathogenesis of acidosis is closely linked to vascular reactions:
Cerebral Circulation: Increased arteriolar tone leads to spasm and ischemia.
Peripheral Tissues: The opposite effect is observed — vasodilation (decreased vascular tone).
Hypoxia: Develops due to circulatory disorders and the Bohr effect, in which the affinity of hemoglobin for oxygen changes, impairing its release to tissues.
Mnemonic
"Buffers act fast, kidneys act last": remember that chemical blood systems (erythrocytes) work first, followed by the "heavy artillery" of renal acid excretion.
Frequently asked questions
What specific diseases and pathological conditions lead to the development of respiratory acidosis?
Respiratory acidosis is caused by prolonged pulmonary hypoventilation. Sources indicate the following causes and conditions:
Chronic obstructive pulmonary disease (COPD).
Respiratory center depression by opioids.
Neuromuscular diseases.
Bronchiolar spasm.
Airway obstruction.
Pickwickian syndrome — marked alveolar hypoventilation in obese individuals, accompanied by hypercapnia and respiratory acidosis.
Hypothyroid coma — respiratory failure develops due to alveolar hypoventilation and is accompanied by progressive hypoxia and acidosis.
Reticular formation depression in overdose of narcotic analgesics, barbiturates, tranquilizers, and other neuro- and psychoactive substances, manifested by slow shallow breathing, hypercapnia, and acidosis.
Pulmonary pathology with bronchial obstruction, microcirculation impairment, inflammatory infiltration, and interstitial edema, leading to hypoxemia, hypercapnia, and respiratory acidosis.
How do blood gas parameters (PaCO2, HCO3-, BE) change in respiratory acidosis?
In respiratory acidosis, sources indicate the following changes:
Blood pH — decreases, acidosis develops.
PaCO2 — increases, hypercapnia develops.
HCO3- — during chronic compensation, kidneys retain bicarbonate over 3–5 days.
BE — dynamics of this parameter in respiratory acidosis are not described in the cited sources.
What changes in blood potassium levels develop during respiratory acidosis and why?
Respiratory acidosis is associated with an increase in extracellular $K^+$ content and the development of hyperkalemia.
The mechanism is related to potassium redistribution: intracellular acidosis stimulates the efflux of $K^+$ from cells, while simultaneously $Cl^-$ is transported into cells. Sources also indicate that a 0.1 decrease in pH increases plasma potassium concentration by 0.6 mEq/L.
What are the main clinical symptoms of hypercapnia in acute respiratory acidosis?
For gas acidosis and hypercapnic states, the cited sources indicate the following clinical manifestations:
Impaired pulmonary ventilation with signs of respiratory hypoxia.
Increased intracranial pressure — associated with cerebral arteriolar dilation and pathological arterial hyperemia in brain tissue.
Ischemia of organs and tissues, except the brain — due to arteriolar smooth muscle spasm in these organs.
Microcirculation disorders — accompanied by signs of capillary-trophic insufficiency.
Hypoxemia and tissue hypoxia.
Certain forms of respiratory pathology exhibit tachypnea, hypercapnia, and acidosis; respiratory center depression leads to slow shallow breathing, hypercapnia, and acidosis.
What is the difference between immediate and long-term compensation?
Immediate compensation (buffers, $Cl^-/HCO_3^-$ exchange) is activated instantly to neutralize $H^+$. Long-term compensation (kidneys) takes time but provides radical acid elimination.
Why does the brain suffer in respiratory acidosis?
Due to pH changes, cerebral arterioles undergo spasm, leading to ischemia and impaired tissue nutrition.
What is the Bohr effect in the context of acidosis?
This is the change in hemoglobin's affinity for oxygen. During acidosis, oxygen release to tissues is impaired, which worsens hypoxia.
Go deeper
Mechanisms of ammoniagenesis regulation in the proximal renal tubules.
Relationship between $pCO_2$ levels and respiratory center activity.
Differential diagnosis of respiratory and metabolic acidosis.
Clinical markers of the depletion of the body's compensatory reserves.