Respiratory and Metabolic Acid-Base Imbalances

Respiratory Acid-Base Imbalances

• Acute Ventilatory Failure
  • Hypoventilation results in increased PaCO2, H2CO3, and HCO3-.
  • Decreases the HCO3-/H2CO3 ratio
  • After 24-48 hours, kidneys retain HCO3- to correct pH
  • If PaCO2 is 80 mmHg, pH should be 7.2 and HCO3- 30 mEq/L according to the normal blood buffer line
  • If pH and HCO3- levels are higher than expected, renal retention of HCO3- has occurred.
  • A low pH indicates partial compensation, a normal pH indicates complete compensation.
• Acute Alveolar Hyperventilation
  • Causes include pain and anxiety
  • Results in low PaCO2, H2CO3, and HCO3-.
  • Increases the HCO3-/H2CO3 ratio, leading to an increase in pH
• Chronic Alveolar Hyperventilation and Renal Compensation
  • Hyperventilation for more than 24-48 hours results in low PaCO2, high pH.
  • Kidneys excrete excess HCO3- in the urine to compensate.

Metabolic Acid-Base Imbalances

• Metabolic Acidosis
  • Caused by the presence of acids not related to increased PaCO2 or renal compensation.
  • Lowers both HCO3- and pH.
  • Causes:
    • Lactic acidosis (end product of anaerobic metabolism), often due to severe acute hypoxemia
    • Ketoacidosis (low insulin levels in diabetics cause low intracellular glucose levels, leading to the production of ketone bodies as alternative metabolites)
    • Renal failure
• Chronic Metabolic Acidosis and Respiratory Compensation
  • The normal response to metabolic acidosis is an increase in respiratory rate to decrease PaCO2
• Metabolic Alkalosis
  • Caused by an excess of bases in the blood.
  • Increases pH
  • Common Causes:
    • Hypokalemia: low potassium levels lead to the kidneys retaining potassium by excreting hydrogen ions (H+), resulting in an increase in blood base.
• Chronic Metabolic Alkalosis and Respiratory Compensation
  • Decreases in respiratory rate (RR) increase PaCO2, leading to a decrease in pH, compensating for the alkalosis.

Base Excess/Deficit

• Quantifies and manages non-respiratory acid-base imbalances.

Respiratory Acid-Base Imbalances

• Increased CO2: Increases PCO2, HCO3-, and H2CO3.
• Acute Ventilatory Changes: Immediately alter pH
• H2CO3 Changes: Powerful role in affecting pH compared to HCO3- changes.
• **Acute Ventilatory Failure:**Hypoventilation increases PCO2, H2CO3, and HCO3- which decreases the HCO3-/ H2CO3 ratio.
• Renal Compensation (24-48 Hours): Kidney retains HCO3- to correct pH.
• PaCO2 of 80 mmHg: pH should be 7.2 and HCO3- 30 mEq/L. Higher levels indicate renal retention of HCO3-.
• Partial Compensation: Low pH despite renal compensation.
• Complete Compensation: Normal pH.
• Acute Alveolar Hyperventilation: Pain and anxiety cause low PaCO2, H2CO3, and HCO3- leading to a larger HCO3-/H2CO3 ratio and higher pH.

Chronic Alveolar Hyperventilation and Renal Compensation

• Hyperventilation over 24-48 Hours: Low PaCO2, high pH, kidneys excrete excess HCO3- in urine.

Metabolic Acid-Base Imbalances

Metabolic Acidosis

• Low pH due to Acids: Acids unrelated to increased PaCO2 or renal compensation.
• Low HCO3- and pH: Both values are lower.

Causes of Metabolic Acidosis

• Lactic Acidosis: End-product of anaerobic metabolism; caused by severe acute hypoxemia.
• Ketoacidosis: Low insulin levels in diabetics cause low intracellular glucose levels. Increased ketones formed.
• Renal Failure:

Chronic Metabolic Acidosis and Respiratory Compensation

• Normal Response: Increased respiratory rate to decrease PaCO2.

Metabolic Alkalosis

• High pH due to Bases: Bases other than those related to CO2/HCO3- system.
• Hypokalemia: Low potassium levels cause kidneys to save potassium by excreting H+. This increases blood base levels.

Chronic Metabolic Alkalosis and Respiratory Compensation

• Decreased Respiratory Rate: Increases PaCO2, lowering pH.

Base Excess/Deficit

• Quantification and Management: Best method to quantify and manage non-respiratory acid-base imbalances.

This quiz covers the concepts of respiratory and metabolic acid-base imbalances, detailing mechanisms such as acute ventilatory failure, hyperventilation, and renal compensation. Understand how disturbances in these systems affect blood pH and bicarbonate levels. Test your knowledge on the physiological responses to these conditions.