Metabolic Acidosis Management
Introduction to Metabolic Acidosis
- Metabolic acidosis is a primary reduction in serum bicarbonate (<22 mmol/L) associated with blood pH <7.35, where the body attempts compensation by increasing ventilation to eliminate CO2, according to the American College of Physicians 1
- The normal serum bicarbonate range is 22-26 mmol/L, though more recent evidence suggests 23-30 mEq/L to avoid missing acid-base disorders, as recommended by the National Kidney Foundation 1
Pathophysiology and Clinical Presentation
- In Chronic Kidney Disease, the kidneys' impaired ability to excrete hydrogen ions and synthesize ammonia leads to acid accumulation in the body, as stated by the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines 1
- Western dietary patterns with high animal protein, cereal, and grain consumption combined with low fruit and vegetable intake create an imbalance between nonvolatile acids and available alkali, contributing to metabolic acidosis, according to the American Heart Association 1
- Animal proteins contain sulfur-containing amino acids that produce nonvolatile acids during metabolism, which can lead to metabolic acidosis, as noted by the European Society of Cardiology 1
Diagnosis and Assessment
- The body attempts to compensate for metabolic acidosis by increasing ventilation to eliminate CO2, as explained by the American Thoracic Society 1
- Patients with severe acidosis may self-ventilate their PCO2 to very low levels as compensation for the metabolic acidosis, according to the British Medical Journal 2
- Hypotension (systolic blood pressure <80 mm Hg or <70 mm Hg if <1 year) complicates about 25% of cases presenting with severe acidosis (base deficit >15 mmol/l), as reported by the American College of Emergency Physicians 2
Treatment and Management
- Initiate sodium bicarbonate when serum bicarbonate falls below 22 mmol/L, with aggressive treatment required when levels drop below 18 mmol/L, as recommended by the National Institute of Diabetes and Digestive and Kidney Diseases 1
- Oral sodium bicarbonate (2-4 g/day or 25-50 mEq/day) divided into 2-3 doses for standard oral dosing, according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines 1
- Target maintenance is serum bicarbonate ≥22 mmol/L at all times, as stated by the American Society of Nephrology 1
Special Considerations
- Metabolic acidosis resolves with correction of hypovolemia and treatment of underlying cause, according to the Society of Critical Care Medicine 3
- Sodium bicarbonate should not be used to treat metabolic acidosis arising from tissue hypoperfusion in sepsis; instead, focus treatment on restoring tissue perfusion with fluid resuscitation and vasopressors, as recommended by the Surviving Sepsis Campaign 4
- The effectiveness of sodium bicarbonate to correct metabolic acidosis from septic shock is unsure, and acidosis may have protective effects, as noted by the American College of Chest Physicians 4
Metabolic Acidosis Diagnosis and Management
Clinical Significance and Diagnostic Approach
- The British Thoracic Society guidelines note that pH <7.35 with normal or low PCO2 should prompt investigation for metabolic acidosis, in patients with suspected metabolic acidosis, particularly those with low bicarbonate levels 5, 6
- A PO2 of 23.8 mmHg is critically low, indicating severe hypoxemia, which may contribute to lactic acidosis, and requires immediate oxygen therapy, according to guidelines from the British Thoracic Society 6
- SO2 of 37.2% indicates severe hypoxemia, requiring immediate oxygen therapy, as recommended by the British Thoracic Society guidelines 5, 6