Acid-Base Balance and Disorders Study Notes

NR324: Adult Health I - Acid-Base Balance and Disorders

Learner Objectives

  • Review the basics of acid-base balance.
  • Interpret arterial blood gases.
  • Discuss acid-base imbalances.
  • Describe the nursing care of patients with acid-base imbalances.

Acid-Base Balance

  • Definition: The acid-base balance is a regulatory system that enables the body to maintain homeostasis, specifically by balancing the acids produced during metabolism and the bases that neutralize these acids.
  • Key Concept: It refers to the balance of hydrogen ion (H+) concentration in the blood, which determines the acidity or alkalinity of the blood.

pH Scale

  • pH Levels: The pH scale ranges from 0 to 14, with 7 being neutral.
    • Acids: 0-6 (e.g., Battery acid, Vinegar, Black coffee)
    • Neutral: 7 (Water, Human blood at 7.4)
    • Bases: 8-14 (e.g., Baking soda, Soapy water, Drain cleaner)

Acid-Base Regulation

  • Measurement: pH measures hydrogen (H+) concentration.
  • Buffering Systems:
    • Primary regulator of acid-base balance is buffering systems in the body.
  • Organs of Regulation:
    • Lungs: Excrete carbon dioxide (CO2) and water, crucial for acid-base balance.
    • Kidneys: Excrete acids via urine, return bicarbonate (HCO3-) to circulation.

Respiratory System Regulation

  • Mechanism: The lungs excrete CO2 through respiration.
  • Equation: CO2 + H2O = H2CO3 (carbonic acid).
  • Functionality: Regulates the body’s acid-base balance quickly (1-3 minutes).
  • CO2 Value: Represents the respiratory system in acid-base balance.

Renal System Regulation

  • Functionality: The kidneys help maintain acid-base balance by excreting acids and returning bases (bicarbonate) to the blood.
  • Efficiency: The renal buffer system is more efficient in balancing, though slower (takes 2-3 days).
  • HCO3- Value: Represents the renal/metabolic system in acid-base balance.

Arterial Blood Gases (ABGs)

  • Purpose: Provides information about:
    • Acid-base balance and imbalances
    • Oxygenation
    • Ventilation
  • Objective: ABGs give objective status about a patient’s acid-base and respiratory status, and ability to regulate pH.

Procedure for Obtaining ABGs

  • Sample Collection: Perform arterial puncture to obtain blood.
  • Equipment: Use a heparinized syringe, keep on ice, and send to lab immediately for analysis.
  • Who Can Draw: Specifically trained nurses (ICU, ED), respiratory therapists, or doctors.
  • Testing Complications:
    • Before Puncture: Allen’s test to check collateral circulation.
    • During Puncture: Care to prevent complications.
    • After Puncture: Apply pressure with pillow to the site.

Components of ABGs

  • pH: Measures H+ concentration
  • PCO2: Measures partial pressure of CO2 in blood (PaCO2)
  • HCO3-: Measures bicarbonate in blood
  • PO2: Measures partial pressure of O2 in blood (PaO2)
    • Low PaO2 = hypoxemia
  • SaO2: Measures O2 saturation
    • Low SaO2 = hypoxia
  • Additional Data: Includes details on PaO2 and O2 saturation status.

Normal Values of ABGs

  • pH: 7.35 – 7.45
  • PCO2: 35 – 45 mmHg
  • HCO3-: 22 – 26 mEq/L
  • PO2: 80 - 100 mmHg
  • SaO2: 95 - 100%

Interpreting ABGs

  • Step 1: Evaluate pH

    • Is it normal?
    • Less than 7.35: ACIDOSIS
    • More than 7.45: ALKALOSIS

  • Step 2: Evaluate PCO2 (Respiratory component)

    • More than 45: ACIDOSIS
    • Less than 35: ALKALOSIS
    • If normal, proceed to step 3.

  • Step 3: Evaluate HCO3- (Metabolic component)

    • Less than 22: ACIDOSIS
    • Greater than 26: ALKALOSIS

Mnemonics for ABG Interpretation

  • ROME acronym:
    • R: Respiratory (↓pH ↑CO2)
    • O: Opposite (↑pH ↓CO2)
    • M: Metabolic (↑pH ↑HCO3)
    • E: Equal (↓pH ↓HCO3)

Compensation Strategy

  • If one body system becomes unbalanced, the other may help restore pH to normal:
    • Uncompensated: pH is not normal, CO2 or HCO3 are not normal.
    • Partially Compensated: All values are abnormal.
    • Fully Compensated: pH returns to normal while CO2 and HCO3 remain abnormal.

Practical Application

  • Tic-Tac-Toe grid for understanding acid-base imbalances in patients.

Exercises for Practice

  • Exercise 1: Given pH 7.56, PaCO2 26, HCO3 22, PaO2 84: Determine if high or low, deduce alkalosis or acidosis.
  • Exercise 2: Given pH 7.23, PaCO2 37, HCO3 18, PaO2 90: Determine condition based on values.
  • Exercise 3: Given pH 7.33, PaCO2 67, HCO3 37, PaO2 78: Determine condition based on values.

Acid-Base Imbalances

  • Classifications:
    • Respiratory Acidosis
    • Respiratory Alkalosis
    • Metabolic Acidosis
    • Metabolic Alkalosis
Respiratory Acidosis
  • Definition: Caused by hypoventilation leading to CO2 retention (hypercapnia).
  • Conditions: pH < 7.35; PCO2 > 45.
  • Causes:
    • Chronic Obstructive Pulmonary Disease (COPD)
    • Atelectasis
    • Chest wall injury
    • Pneumonia, pulmonary edema, and respiratory failure.
  • Symptoms:
    • Shallow, rapid breathing evolving to bradypnea.
    • Tachycardia progressing to bradycardia and dysrhythmias.
    • Changes in LOC, skin pallor or cyanosis, and Cheyne-Stokes respirations.
  • Treatment:
    • Treat the underlying cause.
    • Maintain airway, O2 therapy, possible ventilatory support, bronchodilators, and mucolytics.
Respiratory Alkalosis
  • Definition: Caused by hyperventilation, resulting in decreased CO2.
  • Conditions: pH > 7.45; PCO2 < 35.
  • Causes:
    • Anxiety, fever, pain, kidney/liver failure, pneumonia, or pulmonary emboli.
  • Symptoms:
    • Tachypnea, chest pain, tachycardia, paresthesia, dizziness, and potential seizures.
  • Treatment:
    • Address the underlying cause, O2 therapy (non-rebreather mask), and anxiety-reducing measures.
Metabolic Acidosis
  • Definition: Associated with a deficit in bicarbonate (HCO3-).
  • Conditions: pH < 7.35; HCO3- < 22.
  • Causes:
    • Dehydration, diabetic ketoacidosis (DKA), diarrhea, lactic acidosis, renal failure, shock, starvation.
  • Symptoms:
    • Tachypnea; Kussmaul respirations; cardiovascular changes; LOC changes, warm, dry skin.
  • Treatment:
    • Address the underlying cause; may require bicarbonate replacement.
Metabolic Alkalosis
  • Definition: Associated with increased bicarbonate (HCO3-).
  • Conditions: pH > 7.45; HCO3- > 26.
  • Causes:
    • Vomiting, NG suctioning, diuretics, excess bicarbonate intake, steroids, liver disease, hypokalemia.
  • Symptoms:
    • May show normal respiratory rate or tachypnea; changes in cardiovascular and neurological status.
  • Treatment:
    • Fluid and electrolyte replacement; addressing underlying conditions.

Conclusion

  • Understanding acid-base balance is crucial for proper patient care in nursing and healthcare settings, facilitating effective treatment and management of patients with acid-base imbalances.