What is Metabolic Acidosis?

Metabolic acidosis is an imbalance in the body's acid-base equilibrium, where there is an accumulation of acid or a loss of the base bicarbonate, leading to various physiologic complications. It can be indicative of underlying health issues like renal dysfunction and respiratory disorders.

This article will explore the causes, symptoms, diagnosis, and treatment options for metabolic acidosis to increase awareness and understanding of the condition and empower individuals to recognize symptoms early for timely intervention.

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What is Metabolic Acidosis?

Physiology of Acid-Base Balance

pH measures the acidity or alkalinity of fluids in the body and must be between 7.35 and 7.45. A proper pH is vital for numerous physiological processes, including enzyme activity, cellular function, and protein structure to function optimally. Therefore, the body uses buffer systems and respiratory and renal compensation mechanisms to keep pH levels within the normal range.

The lungs help to regulate pH levels by controlling the levels of carbon dioxide (CO2), increasing breathing rate to expel excess CO2 when needed to maintain pH within a normal range.

When pH decreases (acidosis), the kidneys increase their excretion of hydrogen ions and reabsorb bicarbonate ions from the urine back into the bloodstream to raise blood pH. If the blood becomes too alkaline, the kidneys compensate by decreasing the excretion of hydrogen ions and increasing the excretion of bicarbonate ions to decrease blood pH over time.

For acute compensation, the bicarbonate buffer system helps to maintain the pH of the blood by using bicarbonate ions (HCO3-) to neutralize hydrogen ions (H+) to form carbonic acid, minimizing any decreases in pH. 

Definition of Metabolic Acidosis

Disruptions of these regulatory mechanisms can lead to conditions like metabolic acidosis, where the body’s pH balance is compromised, potentially resulting in adverse health effects. Metabolic acidosis occurs when excess acid accumulates in the body, disrupting its pH balance. 

Causes of Metabolic Acidosis

Metabolic acidosis can occur due to various issues, including an increased production of acids, decreased elimination of acids by the kidneys, or loss of bicarbonate base that normally helps maintain pH balance.

Renal Causes 

Conditions like chronic kidney disease and renal tubular acidosis impair the kidneys' ability to regulate acid-base balance, leading to metabolic acidosis. When the kidneys are not functioning optimally, there is reduced acid excretion and decreased bicarbonate reabsorption, causing a build-up of acid in the body, which can lead to symptoms like fatigue and confusion. 

Increased Acid Production 

Conditions like diabetic ketoacidosis (DKA), lactic acidosis, and certain types of poisonings can increase acid production and lead to metabolic acidosis. These conditions create excess acid that overwhelms the body's buffering capacity, resulting in metabolic acidosis.

• Diabetic Ketoacidosis: In some cases of uncontrolled diabetes, the body does not have enough insulin and, therefore, starts breaking down fat for energy in a process that produces ketones and acidic byproducts, leading to acidosis.
• Lactic acidosis: Lactate is a byproduct of anaerobic metabolism that can accumulate and increase acidity in the blood due to conditions like sepsis, shock, or severe hypoxia, which impair oxygen delivery to tissues.
• Poisonings: Ingestion of certain toxic substances, such as methanol, antifreeze (ethylene glycol), or salicylate, can lead to metabolic acidosis by producing toxic metabolites that increase acid levels in the body.

Loss of Bicarbonate 

If bicarbonate is lost from the body in large quantities due to severe diarrhea or other gastrointestinal conditions, metabolic acidosis can occur. With severe diarrhea, intestinal fistulas, or ileostomies, bicarbonate-rich fluids are lost from the gastrointestinal tract in the stool, decreasing the body's buffering capacity and causing a decrease in blood pH. 

Symptoms of Metabolic Acidosis

In some cases of metabolic acidosis, symptoms can build up slowly and may be hard to notice. 

General symptoms of metabolic acidosis include: 

• Rapid breathing (hyperventilation)
• Fatigue
• Confusion
• Lethargy

In more severe cases, additional symptoms can develop that indicate a medical emergency:

• Shock (low blood pressure, decreased organ perfusion)
• Coma (severe neurological impairment)

Diagnosing Metabolic Acidosis

The diagnostic process for metabolic acidosis includes laboratory blood testing and other tests to help identify underlying causes of the acid-base imbalance. The general diagnostic pathway for evaluating metabolic acidosis includes:

1. A thorough clinical history
2. Vital signs (respiratory rate, heart rate, blood pressure, oxygen saturation, and temperature)
3. A physical examination
4. Determine if the acid-base status is acidemia or alkalemia based on pH using blood testing such as blood gasses
5. Evaluation of bicarbonate (HCO3) and pCO2 to determine if the pH imbalance is due to a respiratory or metabolic cause and whether compensation is occurring
6. Investigation of underlying causes

Initial Blood Tests

• Measure pH levels: blood gas analysis (arterial [ABG] or venous) assesses pH levels in the blood. If the pH is lower than 7.35-7.45, metabolic acidosis is occurring. Typically, the ABG analysis also reveals a reduction in HCO3 and pCO2.
• Assess bicarbonate levels: serum bicarbonate levels help to evaluate the body's buffering capacity. Low bicarbonate levels (<22 mEq/L) suggest metabolic acidosis.
• Evaluate electrolytes: An electrolyte panel test measures levels of sodium, chloride, potassium, and bicarbonate in the blood. These are frequently measured as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) and may be altered in metabolic acidosis. For example, acidosis causes potassium to leave cells, which causes elevated levels in the blood (hyperkalemia) that can impair brain function, eventually resulting in coma.

Additional Testing

Once an acidosis is identified based on the pH obtained from a blood gas analysis, the underlying causes of a renal or metabolic disturbance can be investigated further to target effective treatment.

• Anion Gap: calculated by measuring the difference between levels of electrolytes that carry a positive (like Na+ and K+) and negative (Cl- and HCO3-) electrical charge. A high anion gap suggests the presence of endogenously produced acids from diabetic ketoacidosis, lactic acidosis, alcoholic intoxication, drug overdose, or renal failure causing metabolic acidosis. If the anion gap is normal, it suggests that the metabolic acidosis is due to a loss of HCO3 from the kidneys or gastrointestinal tract or a failure of the kidney to excrete potassium, as occurs in renal tubular acidosis.
• Urine tests: A urinalysis can help assess urine pH and check for signs of renal dysfunction, such as abnormal acid excretion or electrolyte imbalances.
• Specific blood tests: to further elucidate the underlying cause of metabolic acidosis, testing for blood glucose levels to evaluate suspected diabetic ketoacidosis or lactate levels to investigate lactic acidosis may be ordered. In addition, levels of suspected toxins such as methanol, ethylene glycol, or salicylate can be measured if suspected.
• Imaging studies: depending on the suspected underlying cause, imaging studies such as an abdominal ultrasound, MRI, or CT scans may be used to identify underlying causes, such as renal abnormalities or gastrointestinal conditions.

Treatment Options

Immediate Treatments

In severe cases of metabolic acidosis, immediate treatments, such as intravenous bicarbonate, fluids, or dialysis may be necessary to stabilize the patient. These can help to restore pH balance by removing excess acids and toxins from the blood and correcting electrolyte imbalances.

Addressing Underlying Causes

Additional treatment is tailored to the specific underlying causes. 

• Renal dysfunction: underlying kidney disease should be treated with medications to preserve kidney function, dialysis, or kidney transplantation.
• Diabetic ketoacidosis: hyperglycemia must be corrected with insulin therapy to prevent further acidosis and other complications.
• Gastrointestinal disorders: conditions like severe diarrhea or intestinal fistulas are addressed with fluid replacement, electrolyte correction, and management of the underlying gastrointestinal condition.

Potential Complications

If metabolic acidosis is not treated properly, it can seriously harm various organ systems with long-term health impacts. Early recognition, comprehensive management, and ongoing monitoring are essential to prevent complications and improve overall well-being.

Health Risks

• Cardiovascular Effects: acidosis and accompanying electrolyte imbalances can affect heart function, increasing the risk of arrhythmias and cardiac dysfunction.
• Muscle Weakness and Wasting: metabolic acidosis can contribute to muscle breakdown and weakness, impairing physical function and mobility.
• Bone Health: chronic metabolic acidosis can leach calcium from bones over time, contributing to osteoporosis and increased fracture risk.

Chronic Implications and Long-Term Health Issues

• Renal Damage: prolonged metabolic acidosis can damage the kidneys and cause a decline in kidney function, exacerbating metabolic acidosis in a vicious cycle.
• Growth Impairment: chronically, acidosis may impair normal growth and development in children, affecting bone growth and overall health.
• Metabolic Disorders: long-term metabolic acidosis can exacerbate insulin resistance, increasing the progression of metabolic syndrome and diabetes.
• Cognitive Impairment: acidosis and accompanying electrolyte imbalances can affect cognitive function and mental health, leading to issues like cognitive decline and depression.
• Increased Mortality Risk: if not properly managed, metabolic acidosis can cause severe complications like coma and death.

Prevention Strategies

Preventive measures and regular health check-ups can reduce the risk of developing metabolic acidosis and help optimally manage contributing conditions in individuals with diabetes, kidney disease, or gastrointestinal disorders. 

• Monitor and balance electrolyte levels: keeping electrolytes, including bicarbonate, potassium, and chloride in balance is important for avoiding complications like irregular heart rhythms and brain dysfunction and preventing the development of metabolic acidosis.
• Maintain hydration: adequate hydration and electrolyte balance are crucial to prevent dehydration, especially in people with chronic kidney disease. 
• Follow a balanced anti-inflammatory diet: an anti-inflammatory diet focused on plenty of fresh vegetables and fruits and avoiding excessive intake of acid-producing foods, such as processed meats and sugary snacks, helps to maintain a balanced acid-base status and blood sugar.
• Blood sugar management: maintaining stable blood sugar levels through medication, supplements, diet, and lifestyle adjustments can help prevent episodes of diabetic ketoacidosis and prevent metabolic acidosis.
• Avoid excessive alcohol and medications: alcohol and certain medications, such as aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), can increase the risk of metabolic acidosis. 

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Key Takeaways

• Metabolic acidosis is a serious medical condition that occurs when excess acid builds up in the blood.
• It can result from kidney dysfunction, excessive acid production, or bicarbonate loss.
• Prompt medical attention is crucial, as untreated metabolic acidosis can lead to severe complications, including cardiovascular issues, muscle weakness, and bone damage.
• Management strategies may include intravenous bicarbonate, fluid replacement, and addressing underlying causes such as diabetes or kidney disease.
• Preventive measures involve managing underlying conditions, monitoring electrolyte levels, maintaining hydration, and following a balanced anti-inflammatory diet.
• Regular health check-ups and monitoring are essential for early detection and intervention, especially for individuals with diabetes, kidney disease, or other risk factors.