Dr. Ahmad Shahzad
Founder | Lyallpur Diabetes Foundation
Consultant Diabetologist | Educator | Advocate for Preventive Care
Health conditions that affect the body’s delicate balance often develop silently but can have serious consequences if left untreated. One such condition is metabolic acidosis, a disorder that changes how the body manages acids and bases. It may manifest in diabetics, kidney disease or even due to infections and some medications. Since its initial symptoms can be only vague, it is essential to learn about what metabolic acidosis is, how it can occur, and what diagnosing and treating it requires to ensure overall health and avoid complications.
What is Metabolic Acidosis?
Metabolic acidosis is a health condition whereby the body fluids contain excess acid, which causes the blood pH to drop abnormally (below 7.35). It arises in case of excess acid by the body, inability of the kidneys to eliminate enough acid, or loss of bicarbonate that normally neutralizes acid in the blood.
Types of Metabolic Acidosis
Metabolic acidosis is classified primarily into two major types based on the anion gap (AG):
1. High Anion Gap Metabolic Acidosis (HAGMA)
- Marked by a greater number of unmeasured anions in the blood.
- Common causes include:
- Ketoacidosis (e.g., diabetic ketoacidosis)
- Lactic acidosis (due to tissue hypoxia or other causes)
- Renal failure (accumulation of acids normally cleared by kidneys)
- Ingestion of toxins such as methanol, ethylene glycol, salicylates, and metformin
- The anion gap rises as the acid accumulates, contributing to unmeasured anions such as lactate and ketones.
2. Normal Anion Gap Metabolic Acidosis (NAGMA) or Hyperchloremic Acidosis
- Characterized by loss of bicarbonate or inability of the kidneys to produce bicarbonate without an augmentation in unmeasured anions, resulting in a comparatively normal anion gap.
- Common causes include:
- Renal tubular acidosis (types 1, 2, and 4)
- Gastrointestinal bicarbonate loss (e.g., diarrhea, fistulas)
- Certain drug effects, like carbonic anhydrase inhibitors
- Chloride levels tend to rise to compensate for bicarbonate loss.
Subtypes of Renal Tubular Acidosis (RTA)
- Type 1 (Distal RTA): Distal tubule failure to release hydrogen ions, resulting in the retention of acid.
- Type 2 (Proximal RTA): Loss of bicarbonate due to defects in the bicarbonate reabsorption in the proximal tubule.
- Type 4 RTA: Complicated by hypoaldosteronism with the lack of ammonium excretion and hyperkalemia.
Other variants of metabolic acidosis are lactic acidosis subtypes (Type A associated with tissue hypoxia and Type B without hypoxia), and ketoacidosis associated with elevated ketone bodies due to fat metabolism.
Causes and Risk Factors
Metabolic acidosis occurs due to factors that increase acid secretion, bicarbonate loss, or failure to eliminate acid by the kidneys. Important causes and risk factors are:
Causes
- Kidney Disease: Chronic kidney disease (CKD) and acute kidney injury impairs the kidneys to eliminate acids and the ketones are accumulated.
- Diabetic Ketoacidosis (DKA): When diabetes is not controlled, the body accumulates ketone bodies that are acidic.
- Lactic Acidosis: This is the accumulation of lactic acid caused by conditions such as cancer, acute anemia, sepsis, heart failure, liver failure, excessive exercising and alcohol abuse.
- Severe Diarrhea: Causes great loss of bicarbonate that is a base neutralizing acid.
- Ingestion of Toxins: Poisoning by aspirin, ethylene glycol (antifreeze), and methanol.
- Renal Tubular Acidosis: the kidney tubules are unable to remove acid normally, which accumulates.
Risk Factors
- Chronic Illness: Diabetes, kidney disease, liver disease.
- Medications: Drugs like diuretics, certain chemotherapy agents, and aspirin.
- Dehydration: A severe loss of fluids due to illness or diarrhea may influence acid-base balance.
- Lifestyle Factors: High-fat, low-carbohydrate diets, heavy alcohol use.
- Genetic Conditions: There are unusual genetic diseases of kidney function.
- Age: Elderly people are more susceptible to this because of kidney failure.
- Other Factors: Smoking, anemia, hyperkalemia (high potassium), and certain infections (e.g., sepsis).
Altogether, metabolic acidosis may be caused by a mixture of causes and is more probable in persons with some chronic illness or a poisonous exposure.
Signs and Symptoms
The signs and symptoms of metabolic acidosis vary depending on the acid-base imbalance and the cause. Signs and symptoms include:
- Pulmonary alterations: Deep and fast breathing at the onset (Kussmaul respirations) to drive out carbon dioxide as an adaptation, which may subsequently slow and become deeper as acidosis advances.
- Neurological symptoms: Confusion, headache, lethargy, sleepiness, and in severe cases, stupor or coma.
- Cardiovascular effects: Fast heartbeat (tachycardia) and palpitations.
- Gastrointestinal: Nausea, vomiting, and appetite loss.
- General symptoms: Fatigue, weakness, and malaise.
- Special signs: Fruity-smelling breath, especially in diabetic ketoacidosis.
Mild cases can be silent, or more severe or faster acidosis develops, leading to clear clinical symptoms. Physical examination may be unpromising except insofar as it indicates the underlying disorder. Severe metabolic acidosis may precondition cardiac dysfunction, arrhythmia, and shock.
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Diagnosis of Metabolic Acidosis
The diagnosis of metabolic acidosis involves several key laboratory tests and clinical assessments:
Primary Diagnostic Tests
- Blood Tests:
- Serum bicarbonate (or serum CO2), which is usually included in a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). Less than 22 mEq/L of bicarbonate indicates metabolic acidosis.
- ABG analysis to determine blood pH, partial carbon dioxide pressure (pCO2), and bicarbonate. Low bicarbonate and pH under 7.35 confirm the metabolic acidemia.
- Anion Gap Calculation:
- Anion gap = Na – (Cl + HCO3). This helps differentiate high anion gap metabolic acidosis from normal anion gap types.
- The normal anion gap is around 12 mEq/L; values higher than this indicate high anion gap acidosis.
Additional Tests to Identify Cause
- Serum lactate to check for lactic acidosis.
- Blood ketones for ketoacidosis.
- Kidney function tests (BUN, creatinine) to assess renal impairment.
- Urinalysis to check urine pH and presence of ketones or other abnormalities.
- Toxin levels if poisoning is suspected (e.g., salicylates, methanol).
Interpretation Steps
- Confirm acidemia (pH < 7.35).
- Confirm metabolic origin by low bicarbonate and low/normal pCO2.
- Calculate the anion gap to classify metabolic acidosis.
- Determine if respiratory compensation is appropriate using Winter’s formula.
- Assess for mixed acid-base disorders if the clinical picture is complex.
Treatment and Management
Treatment and management of metabolic acidosis focus primarily on correcting the underlying cause and restoring the body’s acid-base balance.
Key Treatment Approaches
- Treat the underlying cause: This entails the management of the underlying problem or condition using interventions such as insulin, antibiotics, dialysis, or antidote ingestion.
- Nutritional care: A higher intake of fruits, vegetables and plant-based proteins may be used to decrease acidic load by supplying alkaline substances. It can also be reduced by eating fewer foods that produce acid such as meats, egg yolks, and processed cheeses. Eating habits must be individualized and guided by a professional.
- Alkali therapy: Sodium bicarbonate or sodium citrate preparations can be used to counteract excess acid, particularly in chronic metabolic acidosis, or in severe acute cases with a very low pH(e.g. below 7.2). Potassium citrate can be administered under some circumstances, but with care to prevent hyperkalemia.
- IV fluids: Fluid replacement with the right electrolytes is necessary, particularly in diabetic ketoacidosis or lactic acidosis.
- Renal replacement therapy: Hemodialysis or continuous renal replacement therapy might be required in severe cases or in cases where metabolic acidosis is not responding to normal treatment, especially in acute renal failure or toxicity.
- Other adjunctive therapies: Therapies can be vitamin supplementation (e.g., B1 in lactic acidosis), antidotes in case of poisoning, or inotropes to augment cardiac output.
Important Considerations
- The therapy depends on the severity of acidosis and disease.
- It is important to monitor to prevent such complications as electrolyte imbalances, fluid overload, or rebound alkalosis.
- Acidosis of pH 7.20 or below is in many cases severe enough to warrant intensive care.
Bottom Line
Metabolic acidosis is a severe illness and it may afflict anybody, but particularly diabetes, kidney and other chronic illness patients. Early diagnosis, early medical consultation, and prevention of underlying cause are essential in avoiding life threatening complications. Most individuals can manage metabolic acidosis and preserve their health in the long-term with adequate diagnosis, treatment, and lifestyle modifications. The most appropriate action to remain healthy is to be informed and active.