Acid-Base Balance

• Acid-base balance is the body's mechanism to maintain arterial blood pH between 7.35 and 7.45, which is essential for normal physiological processes.

Regulatory Mechanisms

• Buffer systems, the respiratory system, and the renal system regulate acid-base balance.

Buffer Systems

• Buffers minimize pH changes by neutralizing excess acids or bases.
• Bicarbonate buffer system: This is the primary extracellular buffer, using bicarbonate (HCO3-) and carbonic acid (H2CO3) to neutralize strong acids or bases.
• Phosphate buffer system: An important intracellular buffer, particularly effective in renal tubules.
• Protein buffer system: Found both intracellularly and extracellularly; proteins like hemoglobin can bind to acids or bases.

Respiratory System

• The respiratory system regulates acid-base balance by adjusting the amount of CO2 exhaled, altering the concentration of H2CO3 in the blood.
• Increased ventilation decreases CO2 levels, raising pH (reducing acidity).
• Decreased ventilation increases CO2 levels, lowering pH (increasing acidity).

Renal System

• The kidneys regulate acid-base balance by excreting acids or bases in urine and by regulating bicarbonate reabsorption and generation.
• Kidneys can excrete excess acid (H+) or base (HCO3-) to maintain normal pH.
• Kidneys generate new bicarbonate to replenish that lost in buffering acids.

Acid-Base Imbalances

• Acidosis: pH below 7.35; Alkalosis: pH above 7.45.
• Respiratory acidosis: Caused by hypoventilation, leading to CO2 retention and decreased pH.
• Respiratory alkalosis: Caused by hyperventilation, leading to excessive CO2 excretion and increased pH.
• Metabolic acidosis: Caused by excessive production of metabolic acids or loss of bicarbonate, decreasing pH.
• Metabolic alkalosis: Caused by excessive loss of metabolic acids or increase in bicarbonate, increasing pH.

Compensation

• Compensation is the body's mechanism to return pH to normal or near-normal when an acid-base imbalance occurs.
• The respiratory system compensates for metabolic imbalances, and the renal system compensates for respiratory imbalances.

Respiratory Compensation

• In metabolic acidosis, the respiratory system increases ventilation to lower CO2 levels and raise pH.
• In metabolic alkalosis, the respiratory system decreases ventilation to increase CO2 levels and lower pH.
• Respiratory compensation occurs rapidly, within minutes to hours.

Renal Compensation

• In respiratory acidosis, the kidneys increase bicarbonate reabsorption and excretion of excess acid to raise pH.
• In respiratory alkalosis, the kidneys decrease bicarbonate reabsorption and excrete more bicarbonate to lower pH.
• Renal compensation is slower, taking several days to have a significant effect.

Mixed Acid-Base Disorders

• Mixed disorders involve concurrent respiratory and metabolic imbalances.
• Requires identifying the primary disturbances and their expected compensatory responses.

Anion Gap

• Anion gap helps diagnose the cause of metabolic acidosis.
• Calculated as: Anion gap = Na+ - (Cl- + HCO3-).
• A high anion gap indicates an excess of unmeasured acids (e.g., lactic acid, ketoacids).
• A normal anion gap indicates bicarbonate loss (e.g., diarrhea) or renal tubular acidosis.

Clinical Assessment

• Arterial blood gas (ABG) analysis is essential for diagnosing acid-base imbalances.
• ABG values include pH, PaCO2, PaO2, and HCO3-.
• Clinical history and physical examination are crucial for identifying the underlying cause of imbalances.

Treatment

• Treat the underlying cause of the acid-base imbalance.
• Severe acidosis may require bicarbonate administration; severe alkalosis may require acid administration, but these are rare.
• Support respiratory function with oxygen therapy or mechanical ventilation.
• Correct electrolyte imbalances, especially potassium.

Acidosis

• Characterized by an excess of acid in the body, leading to a decrease in blood pH below 7.35.
• Respiratory acidosis results from impaired ventilation, causing carbon dioxide retention.
• Metabolic acidosis occurs due to increased production of metabolic acids or loss of bicarbonate.
• Compensation involves the body's attempt to restore normal pH through respiratory and renal mechanisms.
• Respiratory compensation for metabolic acidosis involves hyperventilation to reduce CO2 levels.
• Renal compensation for respiratory acidosis involves increased bicarbonate reabsorption and acid excretion.

Alkalosis

• Characterized by an excess of base in the body, leading to an increase in blood pH above 7.45.
• Respiratory alkalosis results from hyperventilation, causing excessive carbon dioxide excretion.
• Metabolic alkalosis occurs due to excessive loss of acid or increased bicarbonate levels.
• Compensation involves the body's attempt to restore normal pH through respiratory and renal mechanisms.
• Respiratory compensation for metabolic alkalosis involves hypoventilation to increase CO2 levels.
• Renal compensation for respiratory alkalosis involves decreased bicarbonate reabsorption and acid retention.

Arterial Blood Gas (ABG) Interpretation

• pH: Measures the acidity or alkalinity of the blood (normal range: 7.35-7.45).
• PaCO2: Measures the partial pressure of carbon dioxide in arterial blood (normal range: 35-45 mmHg).
• HCO3-: Measures the bicarbonate concentration in arterial blood (normal range: 22-26 mEq/L).
• PaO2: Measures the partial pressure of oxygen in arterial blood (normal range: 80-100 mmHg).
• SaO2: Measures the oxygen saturation in arterial blood (normal range: 95-100%).

Steps for ABG Interpretation

• Assess the pH: Determine if the blood is acidic (pH < 7.35) or alkaline (pH > 7.45).
• Evaluate the PaCO2: Determine if the PaCO2 is within the normal range (35-45 mmHg) and whether it corresponds with the pH.
• Evaluate the HCO3-: Determine if the HCO3- is within the normal range (22-26 mEq/L) and whether it corresponds with the pH.
• Identify the primary disorder: Determine if the primary disturbance is respiratory (PaCO2) or metabolic (HCO3-).
• Assess compensation: Determine if the body is compensating for the primary disorder and whether the compensation is partial or complete.

Compensation

• Full compensation: pH is within normal range.
• Partial compensation: pH is outside normal range.
• No compensation: pH is abnormal and either pCO2 or HCO3- is abnormal.