Acid Base

Acid-Base Concepts

Learning Objectives

• Understand acid-based lab values.

• Explain the mechanism to maintain acid-based balance.

• Identify findings for the patient experiencing acid-based imbalance.

• Discuss basic nursing care for patient with acid-based disturbances.

Acid-Base Balance (pH)

• Acid: Substance containing hydrogen ions that can be liberated or released.

• Base: Substance that can trap hydrogen ions.

Normal Values

• pH: 7.35-7.45

• pCO2/PaCO2: 35-45 mmHg

• HCO3: 22-28 mEq/L

• PO2/PaO2: 80-100 mmHg

• SaO2 (O2 Saturation): 92-100%

Major Homeostatic Regulators of Hydrogen Ions

• Buffer Systems:

  • Chemical acid-based control actions.

  • Carbonic acid–sodium bicarbonate.

  • Phosphate buffer system.

  • Protein buffer system.

• Respiratory Mechanisms:

  • Increase or decrease in respiration rates affect blood pH.

• Renal Mechanisms:

  • Control of bicarbonate ions and hydrogen ions through urine.

Homeostasis Management

• Removal of H+:

  • CO2 + H2O ⇌ H₂CO₃ ⇌ H+ + HCO3-

• Addition of H+:

  • Manipulation of carbon dioxide levels affects pH.

• Respiratory Rate Influence:

  • Increased respiratory rate can compensate for acidosis by lowering CO2 and consequently increasing pH.

  • Decreased respiratory rate can exacerbate acidosis by raising CO2 and lowering pH.

  • Other buffer systems in the body also contribute to maintaining optimal pH levels.

Acid-Base Imbalances

• Acidosis:

  • Can occur from overproduction of hydrogen ions or under-elimination (retention of hydrogen ions).

  • Defined by a pH < 7.35.

  • Types include:

  • Metabolic acidosis (refer to table 12.2).

  • Respiratory acidosis.

• Alkalosis:

  • Can occur from overproduction of bicarbonate (HCO3) or under-elimination of bicarbonate.

  • Defined by a pH > 7.45.

  • Types include:

  • Metabolic alkalosis (refer to table 12.3).

  • Respiratory alkalosis.

Clinical Scenario Questions

• Question 1: A patient is brought to the emergency department with respiratory depression and has a history of COPD. What acid-base imbalance is most likely?

  • Options:

  • Metabolic alkalosis

  • Respiratory acidosis

  • Metabolic acidosis and respiratory acidosis

  • Metabolic alkalosis and respiratory alkalosis

• Question 2: The nurse is evaluating the laboratory work of a patient with uncontrolled metabolic acidosis. Which outcome would result from this condition?

  • Options:

  • pH 7.40

  • PaO2 98 mm Hg

  • Bicarbonate 38 mEq/L

  • Serum potassium 5.7 mEq/L

• Question 3: The nurse is reviewing the standing orders for a patient admitted for evaluation of chest pain, with a history of COPD and mild respiratory acidosis. Which order would the nurse question?

  • Options:

  • Encourage oral fluids

  • Keep head of bed elevated

  • Oxygen therapy at 4 L/min as needed

  • Bedrest with bathroom privileges only

Blood Gas Interpretation

• Interpret the following values:

  • pH

  • CO2

  • HCO3

Practice Problems

1. Interpretation:

   • pH = 7.16

   • PaCO2 = 69 mmHg

   • HCO3 = 23 mEq/L

2. Interpretation:

   • pH = 7.61

   • PaCO2 = 26 mmHg

   • HCO3 = 25 mEq/L

3. Interpretation:

   • pH = 7.57

   • PaCO2 = 25 mmHg

   • HCO3 = 22 mEq/L

4. Interpretation:

   • pH = 7.32

   • PaCO2 = 39 mmHg

   • HCO3 = 19 mEq/L