Chapter 25: Fluids & electrolytes part 5,i

Compensation Overview

• Compensation refers to the body's response to fix a disturbance affecting blood CO₂ or H₂O levels.

• Initially, the body is uncompensated, meaning kidneys/lungs have not attempted correction.

Acid-Base Imbalances

• Four main types:

  • Respiratory acidosis

  • Respiratory alkalosis

  • Metabolic acidosis

  • Metabolic alkalosis

Compensation Mechanisms

• Bicarbonate buffer system is ineffective after a certain point; physiological buffers (lungs and kidneys) must intervene.

• Incomplete compensation: pH has not returned to normal, indicating ongoing metabolic/acidosis issues.

• Complete compensation: pH normalizes but other blood gases may remain abnormal.

Specific Conditions

Respiratory Acidosis

• pH < 7.35, elevated CO₂ (PaCO₂ > 45).

• Increase in hydrogen ion levels, kidneys attempt compensation via bicarbonate reabsorption and hydrogen ion excretion.

Respiratory Alkalosis

• pH > 7.45, CO₂ < 35.

• Decreased hydrogen ion levels, kidneys absorb hydrogen ions and secrete bicarbonate.

Metabolic Acidosis

• pH < 7.35, bicarbonate < 22.

• Co₂ levels normal; respiratory system increases ventilation to expel CO₂ and lower acidity.

Metabolic Alkalosis

• pH > 7.45; excess bicarbonate from overconsumption of antacids or loss of hydrogen ions.

• Lungs compensate by decreasing respiration to increase CO₂ levels.

Grandpa's Case Study

• Symptoms indicative of respiratory acidosis (pH: 7.25, PaCO₂: 70, HCO₃: 33).

• Evidence of compensation: elevated HCO₃ indicates renal compensation.

• Analysis of CO₂ to bicarbonate ratio determines if the imbalance is chronic or acute; chronic if CO₂ elevation corresponds to insufficient bicarbonate increase.

Exam Preparation Points

• Review arterial blood gases and compensation mechanisms.

• Understand the interplay between respiratory function and acid-base balance, especially regarding kidney and lung compensation.