Pathogenesis of mixed disorders
Mixed forms are characterized by a unidirectional change in pH, but driven by completely different pathological mechanisms.
- Mixed acidosis in heart failure. The gas component is formed due to impaired alveolar perfusion and the development of pulmonary edema. The non-gas component has a dual nature: the metabolic shift arises from circulatory hypoxia (lactate accumulates), and the excretory renal factor joins due to renal hypoperfusion.
- Mixed alkalosis in brain injury. The gas component is due to central hyperventilation. The non-gas component is represented by excretory gastric alkalosis, which develops due to the loss of acidic contents from repeated vomiting.
Combined forms (multidirectional shifts)
In combined disorders, processes that shift the pH in opposite directions occur in the body simultaneously. The final acidity index depends on which factor dominates — metabolic or functional (the state of the lungs and kidneys).
- Chronic obstructive pulmonary disease (COPD). The disease itself causes hypoventilation and respiratory acidosis. However, glucocorticoid therapy provokes the development of excretory chloride-dependent renal alkalosis.
- Severe chronic gastroenteritis. Vomiting leads to the loss of acidic gastric contents (excretory gastric alkalosis). Concurrently, diarrhea causes the loss of alkaline intestinal juice (excretory intestinal acidosis). Such a complex picture requires constant monitoring of ABD parameters to adjust treatment.
Principles of treatment for respiratory disorders
Respiratory acidosis The main goal is to reduce the severity of or completely eliminate respiratory failure. In acute form, a set of emergency measures is necessary to restore alveolar ventilation volume. In chronic form, therapy is based on three principles:
- Etiotropic: elimination of the causes of acidosis (hypoventilation, pulmonary hypoperfusion, decreased diffusion capacity of the air-blood barrier).
- Pathogenetic: combating hypercapnia (elevated CO2 levels) by normalizing gas exchange.
- Symptomatic: relief of headache, pronounced tachycardia or bradycardia, psychomotor agitation, and excessive sweating.
Respiratory alkalosis The main goal is to eliminate CO2 deficit.
- Etiotropic treatment aims to eliminate the cause of hyperventilation.
- Pathogenetic treatment includes breathing gas mixtures with an increased CO2 content (e.g., carbogen) and correcting water-electrolyte balance with buffer solutions.
- Symptomatic treatment involves the use of anticonvulsants, cardiotropic, and vasoactive drugs.
Symptomatic therapy of non-gas alkalosis
Treatment aims to eliminate complications of the underlying disease and the alkalosis itself, as well as to relieve symptoms that worsen the condition.
- Correction of protein metabolism. Alkalosis causes a deficiency of potassium (K+), which is a crucial cofactor for proteosynthetic enzymes. K+ replenishment is necessary to normalize protein metabolism.
- Restoration of the cardiovascular system. Cardiotropic and vasoactive drugs are used to normalize cardiac contractility and vascular tone.
- Elimination of gastrointestinal dysfunction. Alkalosis causes slowed peristalsis, constipation, and impaired cavitary and membrane digestion. Enzyme preparations, components of gastric and intestinal juices, and cholinomimetics are used for correction.
To understand shifts in gastroenteritis: Vomiting removes acid (alkalosis), diarrhea removes alkali (acidosis). The final pH depends on the prevailing symptom.
Class and exam questions
What determines the final pH in combined acid-base disorders?
The final pH value depends on the dominating factor. For example, in COPD, the balance is determined by the ratio of respiratory acidosis due to hypoventilation and renal alkalosis against the background of glucocorticoid intake.
Why does heart failure lead to mixed acidosis?
Pulmonary edema and impaired alveolar perfusion cause gas acidosis. Concurrently, circulatory hypoxia leads to the accumulation of lactate, and renal hypoperfusion reduces acid excretion, forming the non-gas component.
How is carbon dioxide deficit corrected in respiratory alkalosis?
The patient is prescribed breathing of special gas mixtures with an increased partial pressure of CO2 (e.g., carbogen), and buffer solutions are administered to normalize water-electrolyte balance.
Why is potassium level correction necessary in non-gas alkalosis?
K+ ions act as a cofactor for proteosynthetic enzymes. Their deficiency, typical of alkalosis, leads to severe protein metabolism disorders.
What else to study on this topic
- Mechanisms of development of excretory chloride-dependent renal alkalosis during glucocorticoid therapy
- Pathogenesis of lactate accumulation under conditions of circulatory hypoxia
- Effect of alkalosis on cavitary and membrane digestion
- Composition and use of buffer solutions in respiratory alkalosis
- Diffusion capacity of the air-blood barrier and its role in the development of acidosis
Master the entire topic in the "Pathophysiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Mixed ABD disorders" and 4,913 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 135 video lessons on the subject
Other topics in "Chapter 13. Acid-Base Disorders"
Free video lessons: pathophysiologyShort lessons with lecture notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.