Q.99 Which ONE of the following is TRUE in case of respiratory acidosis?
(A) Increased rate of ventilation is a cause of respiratory acidosis
(B) Blood pH more than 7
(C) Increased levels of carbon dioxide in blood
(D) Acidosis can be compensated through reduction of bicarbonate levels in plasma
The correct answer is (C) Increased levels of carbon dioxide in blood.
Respiratory acidosis occurs due to hypoventilation, leading to CO2 retention and blood acidification. This question tests understanding of its hallmark feature for exams like CSIR NET Life Sciences.
Option Analysis
(A) Increased rate of ventilation
Increased ventilation, or hyperventilation, reduces blood CO2 levels and causes respiratory alkalosis, not acidosis.
(B) Blood pH more than 7
Respiratory acidosis features blood pH below 7.35 due to excess CO2 forming carbonic acid. Normal pH ranges from 7.35-7.45.
(C) Increased levels of carbon dioxide in blood
Hypoventilation causes CO2 accumulation (hypercapnia), lowering pH via the reaction CO2 + H2O → H2CO3 → H+ + HCO3-. This defines respiratory acidosis.
(D) Acidosis can be compensated through reduction of bicarbonate
Kidneys compensate by increasing plasma bicarbonate reabsorption and generation, not reducing it, to buffer excess H+.
Respiratory acidosis arises from impaired lung ventilation, causing increased CO2 levels in blood and reduced pH below 7.35. This condition, common in COPD or drug overdose, features hypercapnia as its core mechanism.
For CSIR NET aspirants, mastering respiratory acidosis MCQs hinges on recognizing CO2 retention over misconceptions like hyperventilation causes.
Key Causes
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Chronic obstructive pulmonary disease (COPD) and asthma obstruct airways.
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Neuromuscular disorders like ALS limit breathing.
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Central depression from opioids slows respiration.
Pathophysiology
CO2 buildup shifts the equilibrium: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻, raising H⁺ and dropping pH. Acute cases show rapid onset; chronic ones allow partial renal compensation via bicarbonate rise.
Compensation Mechanisms
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Acute: Intracellular buffering slightly raises HCO₃⁻ (1 mEq/L per 10 mmHg CO₂ rise).
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Chronic: Kidneys retain HCO₃⁻ over days, normalizing pH partially.
| Aspect | Acute Respiratory Acidosis | Chronic Respiratory Acidosis |
|---|---|---|
| pH | <7.35 sharply | Near normal with high HCO₃⁻ |
| PCO₂ | Elevated | Persistently high |
| HCO₃⁻ | Slight increase | Markedly increased |
Symptoms and Treatment
Symptoms include confusion, drowsiness, and headaches from hypercapnia. Treatment targets underlying causes: bronchodilators for COPD, ventilation support.
