Overview
This lecture explains how to interpret blood pH and distinguish between respiratory and metabolic acidosis and alkalosis, emphasizing the normal values and the systems involved.
Normal Laboratory Values
- Normal blood pH is 7.35 to 7.45.
- Normal CO2 (controlled by the lungs) is 35 to 45 mmHg.
- Normal bicarbonate (HCO3-, controlled by kidneys/metabolic system) is 22 to 26 mmol/L.
Acid-Base Disorders Overview
- There are four main acid-base disorders: respiratory acidosis, metabolic acidosis, respiratory alkalosis, and metabolic alkalosis.
- The cause (respiratory or metabolic) tells you which organ system is responsible.
Respiratory Acidosis
- Caused by the lungs not removing enough CO2, leading to pH less than 7.35.
- High CO2 levels indicate hypoventilation (slow/shallow breathing).
- Common causes include drug overdose (opiates), asthma, COPD, or airway obstruction.
Metabolic Alkalosis
- Caused by metabolic system (kidneys) leading to pH greater than 7.45.
- Abnormal handling of bicarbonate or acid loss by the body causes this state.
- The name tells you both the organ system at fault and the pH direction.
Key Terms & Definitions
- pH — A measure of acidity or alkalinity of blood; normal range is 7.35–7.45.
- CO2 (carbon dioxide) — A gas controlled by the lungs; normal range 35–45 mmHg.
- Bicarbonate (HCO3-) — Buffer controlled by the kidneys; normal range 22–26 mmol/L.
- Acidosis — Condition where blood pH is below 7.35 (acidic).
- Alkalosis — Condition where blood pH is above 7.45 (alkaline).
- Respiratory acidosis — Acidosis due to high CO2 from respiratory system failure.
- Metabolic alkalosis — Alkalosis due to metabolic system or kidney dysfunction.
Action Items / Next Steps
- Memorize normal values for pH, CO2, and bicarbonate.
- Practice determining the cause of acid-base disorders using pH and lab values.