Acid–Base Disorders

Core Explanation

Normal acid–base balance (review). Recall from biochemistry: blood pH is tightly maintained around 7.35–7.45. The body controls pH using buffers (especially bicarbonate), the lungs (which adjust CO₂, an acid when dissolved), and the kidneys (which adjust bicarbonate, HCO₃⁻, and H⁺). Disorders arise when pH drifts out of range.

Acidosis and alkalosis.

• Acidosis — blood pH is too low (below 7.35) — too acidic (excess acid or loss of base).
• Alkalosis — blood pH is too high (above 7.45) — too basic (excess base or loss of acid).

Both impair body function (enzymes/proteins are pH-sensitive — recall denaturation), and severe cases are life-threatening.

Respiratory vs. metabolic. Each disorder is classified by its cause:

• Respiratory disorders involve CO₂ (controlled by the lungs):
  • Respiratory acidosis — CO₂ builds up (e.g., from hypoventilation — not breathing enough, as in respiratory depression or COPD), making blood more acidic.
  • Respiratory alkalosis — too much CO₂ is blown off (e.g., hyperventilation), making blood more basic.
• Metabolic disorders involve bicarbonate/acids (handled by the kidneys and metabolism):
  • Metabolic acidosis — too much acid or loss of bicarbonate (e.g., diabetic ketoacidosis, lactic acidosis from poor perfusion, severe diarrhea, kidney failure).
  • Metabolic alkalosis — too much base or loss of acid (e.g., excessive vomiting — losing stomach acid).

(A memory approach: respiratory = lungs/CO₂; metabolic = kidneys/bicarbonate and metabolic acids.)

Compensation. The body tries to restore pH toward normal through compensation:

• If the problem is respiratory, the kidneys compensate (adjusting bicarbonate) — slower but powerful.
• If the problem is metabolic, the lungs compensate (adjusting breathing/CO₂) — fast (e.g., rapid deep breathing in metabolic acidosis to blow off CO₂).

Compensation helps but often doesn't fully fix the problem until the underlying cause is treated. This is why acid–base disorders point to underlying conditions that need attention.

How It Works

Acid–base disorders:

Normal blood pH ~7.35–7.45 (buffers + lungs/CO2 + kidneys/HCO3−)
ACIDOSIS = pH <7.35 (too acidic) | ALKALOSIS = pH >7.45 (too basic)
Classify by cause:
   RESPIRATORY (lungs/CO2):
      acidosis = CO2 builds up (hypoventilation, COPD)
      alkalosis = CO2 blown off (hyperventilation)
   METABOLIC (kidneys/bicarbonate & acids):
      acidosis = ↑acid / ↓bicarbonate (DKA, lactic acidosis, diarrhea, kidney failure)
      alkalosis = ↑base / ↓acid (vomiting = lose stomach acid)
COMPENSATION: respiratory problem → kidneys compensate (slow); metabolic problem → lungs compensate (fast)
   → helps, but must treat the underlying cause

Important Relationships and Comparisons

High-Yield Pre-Nursing Connections

Acid–base status is assessed by arterial blood gases (ABGs) — a key lab in critical care. Diabetic ketoacidosis (DKA) (metabolic acidosis) and lactic acidosis (from poor perfusion/shock) connect to biochemistry and are important emergencies. Respiratory acidosis ties to respiratory failure/COPD (CO₂ retention); vomiting causes metabolic alkalosis. Recognizing that the body compensates (lungs fast, kidneys slow) and that treatment targets the underlying cause guides care. This topic unifies respiratory, renal, endocrine, and metabolic concepts.

Quick Recap

• Blood pH is kept ~7.35–7.45 by buffers, the lungs (CO₂), and the kidneys (bicarbonate/H⁺).
• Acidosis = pH too low; alkalosis = pH too high — both impair function.
• Respiratory disorders involve CO₂/lungs (acidosis from hypoventilation, alkalosis from hyperventilation); metabolic disorders involve bicarbonate/acids (acidosis from DKA/lactic acidosis/diarrhea, alkalosis from vomiting).
• The body compensates (lungs fast, kidneys slow), but the underlying cause must be treated; status is assessed via ABGs.

Common Confusions

• Acidosis (pH low) vs. alkalosis (pH high).
• Respiratory = lungs/CO₂; metabolic = kidneys/bicarbonate and metabolic acids.
• Respiratory acidosis = hypoventilation (CO₂ up); respiratory alkalosis = hyperventilation (CO₂ down).
• Compensation helps but doesn't replace treating the cause (lungs compensate fast, kidneys slow).