14.2 Acid-base balance and imbalances

Acid-base balance is crucial for maintaining normal body function. The body uses chemical buffers, respiratory adjustments, and renal mechanisms to keep blood pH between 7.35 and 7.45. Understanding these processes helps nurses identify and manage acid-base imbalances.

Metabolic and respiratory disorders can disrupt acid-base balance. Interpreting arterial blood gases and recognizing symptoms are key to diagnosing these issues. Nurses play a vital role in implementing interventions to correct imbalances and treat underlying causes.

Acid-Base Balance Regulation and Imbalances

Mechanisms of acid-base regulation

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• Acid-base balance regulation maintains normal blood pH between 7.35 and 7.45 involves chemical buffers, respiratory system, and renal system
• Chemical buffers provide immediate response to changes in pH include bicarbonate buffer system, phosphate buffer system, and proteins (hemoglobin)
• Respiratory system regulates acid-base balance by adjusting ventilation
  • Increased ventilation (hyperventilation) eliminates CO2, reducing acidity
  • Decreased ventilation (hypoventilation) retains CO2, increasing acidity
• Renal system regulates acid-base balance through excretion or retention of H+ and HCO3-
  • Excretion of H+ and retention of HCO3- helps correct acidosis
  • Retention of H+ and excretion of HCO3- helps correct alkalosis

Metabolic vs respiratory acid-base disorders

• Metabolic acidosis occurs when blood pH decreases due to increased acid production or decreased acid excretion caused by conditions like diabetic ketoacidosis, lactic acidosis, renal failure, or diarrhea and is compensated by hyperventilation to eliminate CO2
• Metabolic alkalosis occurs when blood pH increases due to increased base production or decreased base excretion caused by conditions like vomiting, diuretic use, or excess bicarbonate administration and is compensated by hypoventilation to retain CO2
• Respiratory acidosis occurs when blood pH decreases due to increased CO2 retention caused by conditions like hypoventilation, respiratory depression, airway obstruction, or COPD and is compensated by increased renal excretion of H+ and retention of HCO3-
• Respiratory alkalosis occurs when blood pH increases due to increased CO2 elimination caused by conditions like hyperventilation, anxiety, pain, or high altitude and is compensated by decreased renal excretion of H+ and increased excretion of HCO3-

Interpretation of arterial blood gases

• Arterial blood gas (ABG) components include pH which indicates overall acid-base balance, PaCO2 which reflects respiratory function, and HCO3- which reflects metabolic function
• Interpreting ABG results involves comparing values to normal ranges: pH 7.35-7.45, PaCO2 35-45 mmHg, HCO3- 22-26 mEq/L
  • Acidosis is indicated by pH < 7.35
  • Alkalosis is indicated by pH > 7.45
  • Respiratory imbalances show primary changes in PaCO2
  • Metabolic imbalances show primary changes in HCO3-
• Correlating ABG results with signs and symptoms helps identify specific disorders
  • Metabolic acidosis may present with Kussmaul breathing, fatigue, confusion, nausea, abdominal pain
  • Metabolic alkalosis may present with muscle cramps, weakness, irritability, hypoventilation
  • Respiratory acidosis may present with dyspnea, headache, confusion, cyanosis, tachycardia
  • Respiratory alkalosis may present with dizziness, lightheadedness, paresthesia, chest tightness

Nursing interventions for acid-base imbalances

• Metabolic acidosis interventions include identifying and treating the underlying cause (manage diabetes, treat sepsis), administering bicarbonate therapy as prescribed, and monitoring and replacing electrolytes as needed
• Metabolic alkalosis interventions include identifying and treating the underlying cause (manage vomiting, adjust diuretic therapy), administering acetazolamide or potassium chloride as prescribed, and encouraging oral intake of fluids and electrolytes
• Respiratory acidosis interventions include ensuring adequate ventilation and airway patency, adjusting ventilator settings to increase minute ventilation and reduce PaCO2, administering bronchodilators and mucolytics as prescribed, and encouraging deep breathing and coughing exercises
• Respiratory alkalosis interventions include identifying and treating the underlying cause (manage pain, reduce anxiety), encouraging controlled breathing techniques, and administering sedatives or analgesics as prescribed
• Monitoring fluid balance is important for all acid-base imbalances and involves assessing intake and output, monitoring urine pH and electrolytes, and adjusting fluid and electrolyte replacement based on the patient's needs and acid-base status