Respiratory acid-base disorders are among the most frequently encountered clinical problems in emergency, critical care, and medical practice. They reflect a disturbance in ventilation and gas exchange, directly affecting the levels of carbon dioxide (CO2) in the blood. When the lungs fail to regulate CO2 properly, the body experiences either respiratory acidosis or respiratory alkalosis.
Understanding these conditions is crucial for clinicians, nurses, and medical students because they often indicate underlying life-threatening problems such as hypoventilation, pulmonary embolism, pneumonia, or anxiety-induced hyperventilation. ABG (Arterial Blood Gas) interpretation provides a direct insight into these imbalances.
In this guide, we’ll explore the pathophysiology, causes, signs, symptoms, and interventions of both respiratory acidosis and respiratory alkalosis.
Respiratory Acidosis
Pathophysiology
Respiratory acidosis occurs when the lungs retain too much CO2 due to inadequate ventilation. The excess CO2 combines with water to form carbonic acid, lowering blood pH.
- Primary Problem: Hypoventilation → CO2 retention
- Compensatory Mechanism: The kidneys try to correct the imbalance by excreting hydrogen ions and retaining bicarbonate (HCO3).
ABG Findings:
- pH < 7.35
- PaCO2 > 45 mmHg
Causes of Respiratory Acidosis
A helpful memory tool: “DEPRESS” breathing
- D – Drugs (opioids, sedatives) → suppress the respiratory center
- E – Edema (fluid in the lungs, impairs gas exchange)
- P – Pneumonia (mucus blocks alveolar ventilation)
- R – Respiratory center damage (e.g., trauma, stroke, tumors)
- E – Emboli (pulmonary embolism prevents CO2 elimination)
- S – Spasms of bronchi (asthma attack)
- S – Sac elasticity damage (COPD, emphysema)
All these conditions impair effective gas exchange, leading to CO2 retention.
Signs and Symptoms of Respiratory Acidosis
Respiratory acidosis symptoms often reflect hypoxia and hypercapnia (high CO2 levels).
- Low blood pressure
- Low respiratory rate (or shallow breathing)
- Increased heart rate (tachycardia)
- Restlessness and confusion
- Headache due to cerebral vasodilation
- Drowsiness, lethargy, or even coma
Interventions for Respiratory Acidosis
Management aims to restore ventilation and improve CO2 elimination.
- Administer supplemental oxygen
- Position patient in semi-Fowler’s to ease breathing
- Encourage turn, cough, and deep-breathing exercises (TCDB)
- For pneumonia: administer fluids to thin secretions + antibiotics
- Monitor potassium levels (as acidosis may cause hyperkalemia)
- If CO2 > 50 mmHg, mechanical ventilation with an endotracheal tube may be required
Respiratory Alkalosis
Pathophysiology
Respiratory alkalosis occurs when the lungs lose too much CO2 due to hyperventilation. Reduced CO2 lowers carbonic acid, raising blood pH.
- Primary Problem: Hyperventilation → CO2 loss
- Compensatory Mechanism: The kidneys excrete bicarbonate and retain hydrogen ions to balance pH.
ABG Findings:
- pH > 7.45
- PaCO2 < 35 mmHg
Causes of Respiratory Alkalosis
A simple way to recall: “TACHYPNEA”
- ↑ Temperature (fever, sepsis → increased respiratory rate)
- Aspirin toxicity (early stages cause hyperventilation)
- C – CNS disorders (stroke, brain injury stimulating respiration)
- H – Hyperventilation (anxiety, pain, panic attacks, mechanical ventilation set too high)
- Y – Hypoxemia (low oxygen levels trigger hyperventilation)
Signs and Symptoms of Respiratory Alkalosis
Symptoms are related to low CO2 and reduced calcium ionization.
- Respiratory rate > 20 breaths/min
- Tachycardia (increased heart rate)
- Lightheadedness, dizziness
- Confusion, fatigue
- Tetany and muscle twitching
- EKG changes
- Chvostek sign: twitching of facial muscles when tapping the facial nerve, due to hypocalcemia
Interventions for Respiratory Alkalosis
Treatment focuses on correcting hyperventilation and restoring CO2 balance.
Provide emotional support (for anxiety-induced hyperventilation)Correct the breathing pattern:
- Rebreathing into a paper bag (to increase CO2)
- Adjust ventilator settings if mechanically ventilated
Comparing Respiratory Acidosis and Respiratory Alkalosis
| Feature | Respiratory Acidosis | Respiratory Alkalosis |
|---|---|---|
| pH | < 7.35 | > 7.45 |
| PaCO2 | > 45 mmHg | < 35 mmHg |
| Primary Problem | CO2 retention (hypoventilation) | CO2 loss (hyperventilation) |
| Compensation | Kidneys retain HCO3 | Kidneys excrete HCO3 |
| Causes | COPD, pneumonia, asthma, drugs | Anxiety, fever, aspirin, hypoxemia |
| Symptoms | Confusion, headache, low BP, drowsiness | Lightheadedness, tetany, Chvostek sign |
| Treatment | Oxygen, airway clearance, ventilation | Rebreathing, anxiety control, electrolyte monitoring |
Clinical Relevance
- Emergency medicine: Recognizing acute respiratory acidosis in opioid overdose can save a patient’s life.
- Critical care: Identifying respiratory alkalosis due to hyperventilation syndrome prevents unnecessary intubation.
- Nursing practice: Monitoring ABGs, positioning, and providing oxygen therapy are crucial.
- Anesthesiology: Ventilator settings directly impact PaCO2 and must be closely adjusted.
Frequently Asked Questions (FAQ)
Q1: What’s the main difference between respiratory acidosis and alkalosis?
A: Acidosis is caused by CO2 retention, while alkalosis is due to CO2 loss.
Q2: Can kidneys fully correct respiratory acid-base disorders?
A: Yes, but compensation takes hours to days. Lungs act faster; kidneys provide long-term balance.
Q3: Why does respiratory alkalosis cause muscle twitching?
A: Low CO2 causes low ionized calcium, leading to neuromuscular irritability.
Q4: Which patients are at highest risk of respiratory acidosis?
A: Patients with COPD, emphysema, pneumonia, or those on sedatives/opioids.
Q5: How do you quickly treat anxiety-induced respiratory alkalosis?
A: Encourage slow breathing or have the patient breathe into a paper bag to retain CO2.
