Respiratory Acidosis & Alkalosis – Study Notes

Core Concept

• Carb & fat metabolism → CO₂ production (15,000 mmol / 336 L daily ≈ 24 balloons of CO₂).

• CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

• High CO₂ → ↑ H⁺ → acidosis

• Low CO₂ → ↓ H⁺ → alkalosis

• Lungs control CO₂ elimination.

Respiratory Acidosis

Definition: Retention of CO₂ → ↑ H⁺ → ↓ pH

Causes

1. Lung-related (ventilation/obstruction)

   • COPD (umbrella: emphysema + chronic bronchitis)

     • Emphysema: destruction of elastic tissue → airway collapse → CO₂ trapping

     • Chronic bronchitis: mucus buildup → airway narrowing → CO₂ retention

   • Asthma: airway constriction → obstruction

   • Aspiration/foreign body: blocked airway

   • Restrictive diseases: pulmonary edema, pneumonia, ARDS → thickened alveolar membrane

   • Pulmonary fibrosis: scarring → impaired diffusion

   • Pleural pathology: pneumothorax, hemothorax, pleural effusion → impaired lung expansion

2. Musculoskeletal causes

   • Chest trauma: broken ribs, flail chest

   • Spinal deformities: kyphosis, scoliosis

   • Muscular disorders: muscular dystrophy → weak inspiratory effort

3. Neurologic causes

   • Neuromuscular junction disorders

     • Myasthenia gravis (myasthenic crisis) → ACh receptor blockade

     • Botulism → blocks ACh release

   • Motor neuron diseases

     • ALS, poliomyelitis → motor neuron destruction

   • CNS issues

     • Brainstem injury/tumor → depressed respiratory center

     • Drugs: opioids, barbiturates → CNS depression

   • Other neurologic

     • Guillain-Barré (peripheral demyelination)

     • Multiple sclerosis (central demyelination)

     • Tetanus → GABA inhibition → rigid contraction (ineffective breathing)

4. Mechanical ventilation

   • Underventilation → CO₂ retention

Respiratory Alkalosis

Definition: Excess CO₂ elimination → ↓ H⁺ → ↑ pH

Causes

1. Hyperventilation (most common)

   • Anxiety/panic attack

   • Pain

   • Fever (↑ metabolism → ↑ respiratory drive)

2. Hypoxemia-induced (low O₂ → ↑ respiratory drive)

   • High altitude

   • Severe anemia (↓ O₂ carrying capacity)

   • Early pulmonary edema

   • Pulmonary embolism (early stage)

3. CNS stimulation

   • Trauma, tumor to respiratory center

   • Drugs: salicylates (aspirin) → early stages stimulate respiration → alkalosis (late stages → acidosis)

Quick Summary

• Resp Acidosis = Retaining CO₂ → from hypoventilation or impaired gas exchange

• Resp Alkalosis = Blowing off CO₂ → from hyperventilation or hypoxemia-driven overbreathing