Overview
This lecture introduces the fundamentals of acid-base disturbances in medical patients, focusing on definitions, core physiological concepts, and essential equations.
Key Definitions in Acid-Base
- "Acidemia" and "alkalemia" refer to the actual pH state in the blood; acidemia is pH < 7.35, alkalemia is pH > 7.45.
- "Acidosis" and "alkalosis" describe processes occurring in the body that tend to push pH toward acid or base, respectively.
- Multiple acid-base processes can occur simultaneously; the net effect determines the blood pH.
pH and Body Chemistry
- pH measures hydrogen ion (proton) concentration: pH = -log[H+].
- As proton concentration increases, pH decreases (becomes more acidic).
- The equation: water + CO2 ⇄ H2CO3 (carbonic acid) ⇄ H+ + HCO3- (bicarbonate) summarizes acid-base balance.
Bicarbonate and CO2 Roles
- Bicarbonate (HCO3-) is the main buffer against acid; it is mostly produced in the kidneys.
- Decreased bicarbonate means metabolic acidosis; increased bicarbonate means metabolic alkalosis.
- CO2 (carbon dioxide) is an acid regulated by the lungs; increased CO2 = respiratory acidosis, decreased CO2 = respiratory alkalosis.
The Henderson-Hasselbalch Equation
- pH = 6.1 + log([HCO3-] / (0.03 × pCO2)).
- Metabolic processes affect HCO3-, and respiratory processes affect pCO2.
Normal Values and Lab Notation
- Normal pH: 7.35–7.45.
- Normal pCO2: 35–45 mmHg (centered at 40).
- Normal HCO3-: 22–26 mEq/L (centered at 24).
- On the "chem 7" lab panel, "CO2" is the same as HCO3- (not pCO2).
- Arterial blood gas (ABG) values are listed as: pH / pCO2 / pO2 / HCO3-.
Key Terms & Definitions
- Acidemia — blood pH below 7.35.
- Alkalemia — blood pH above 7.45.
- Acidosis — process pushing pH lower (acidic).
- Alkalosis — process pushing pH higher (basic).
- Bicarbonate (HCO3-) — primary blood base, kidney-controlled.
- pCO2 — partial pressure of CO2, controlled by lungs.
- ABG — arterial blood gas test for acid-base assessment.
Action Items / Next Steps
- Review the Henderson-Hasselbalch equation and know normal lab values.
- Prepare for deeper details in subsequent lectures.