Acid/Base

Acid-Base Balance

Overview

  • Definition of Acid-Base Balance: The balance between acids and bases in the body is crucial for maintaining physiological functions.

  • Learning Objectives:

    • List the systems responsible for acid-base balance.

    • Define acidemia and alkalosis.

    • List the types of acidemia and alkalosis.

    • Identify causes of each type.

Definitions

  • Acid: Any substance that releases hydrogen ions (H+) in a solution.

  • Base: Any substance that can accept or combine with hydrogen ions in a solution.

  • Free H+: Determines acidity in body fluids.

  • pH Range: Normal arterial blood pH is 7.35-7.45, indicating acid-base balance.

  • Regulatory Systems: The acid-base balance is regulated by the kidneys, lungs, and buffering systems.

Acid-Base Imbalance

  • Definition: Imbalance occurs when the amount of acid or base exceeds the body's ability to regulate or adjust it.

  • Influential Factors:

    • Organ function

    • Toxin ingestion

    • Shifts in fluid status

    • Medical and surgical treatments

    • Prolonged imbalance can lead to increased morbidity and mortality.

Sources of Acids

  • Exogenous Sources:

    • Food

    • Acid precursors

    • Toxins

  • Endogenous Sources:

    • Normal tissue metabolism.

  • **Specific Acids Produced: ** Phosphoric and sulfuric acids produced by the metabolism of phosphate-containing substrates and sulfur-containing amino acids.

  • Accumulation of Acids: Can occur following:

    • Exercise

    • Acute illness

    • Fasting

    • Hypoventilation

  • CO2 Production: Resulting from the metabolism of carbohydrates, proteins, and fats.

Mechanisms of Acid-Base Balance

  • Kidneys:

    • Regulate hydrogen ion secretion.

    • Resorb bicarbonate (HCO3-).

  • Lungs:

    • Control alveolar ventilation, altering depth and rate of breathing.

  • Disorders Categorization: Acid-base disorders can be differentiated based on whether they arise from renal or pulmonary causes.

Types of Acid-Base Disorders

Metabolic Acidosis

  • Definition: Results from increased acid production or accumulation, or decreased base in extracellular fluid (ECF).

  • Physiological Impact: Low pH (<7.35) indicates acidemia.

  • Examples of Causes:

    • Toxin ingestion

    • Uremia (renal failure)

    • Diabetic ketoacidosis

    • Lactic acidosis

    • Excessive loss of base (HCO3-).

  • Anion Gap: Measurement of the difference between the sum of measured cations and anions in the blood.

    • Causes include:

    • Small bowel or pancreatic fistula

    • Diarrhea

    • Renal tubular acidosis.

Respiratory Acidosis

  • Cause: Caused by the lungs due to decreased ventilation leading to CO2 retention.

  • Common Causes:

    • Pneumonia

    • Chronic obstructive pulmonary disease (COPD)

    • Sleep apnea

    • Asthma

    • Adult respiratory distress syndrome (ARDS).

  • Chronic Respiratory Acidosis:

    • Caused by chronic hypoventilation due to conditions such as obesity, neuromuscular diseases, emphysema/COPD, and malnutrition.

Metabolic Alkalosis

  • Definition: Results from excess HCO3- or its precursors, excessive loss of acid, or loss of ECF with more chloride than HCO3-.

  • Physiological Impact: High blood pH (>7.45) indicates alkalemia.

  • Common Cause: Loss of acids (e.g., vomiting).

Respiratory Alkalosis

  • Cause: Results from excessive ventilation and elimination of CO2.

Compensation Mechanisms

  • Definition: When an imbalance occurs, the body attempts to restore balance by compensating for the primary disorder.

  • Example: In a patient with COPD, the arterial pH may be 7.32, and the kidneys will increase HCO3- reabsorption to raise the pH.

  • Example of Metabolic Acidosis: Increased respiration to "blow off" CO2.

  • Time for Compensations: Respiratory compensations happen faster, while renal compensations may take 3-5 days.

  • Treatment Note: It is important to identify primary disorders for effective treatment, as compensation mechanisms will then adjust in response.

Recap of Key Points

  • Normal pH Range: 7.35 - 7.45.

  • Acidemia: pH < 7.35.

  • Alkalosis: pH > 7.45.

  • Responsible Systems for Balance: Lungs, kidneys, and buffering systems.

  • Alterations in Organ Function: Can lead to imbalances.

  • Compensation: Possible for imbalances, but treatment must target the underlying primary problem.