Our bodies are intricate chemical factories, constantly working to produce the energy needed to power every heartbeat, breath, and thought. This process relies on a steady supply of oxygen. But what happens when cells are starved of oxygen or are unable to use it properly? In these critical situations, the body can shift to an emergency backup system that produces a byproduct called lactic acid. When this acid builds up faster than the body can clear it, it leads to a dangerous condition called lactic acidosis. This is not a disease in itself, but a sign of a severe, underlying medical problem. Lactic acidosis is a life-threatening medical emergency that signals a catastrophic failure in the body’s metabolism, requiring immediate hospital care to treat its root cause and prevent fatal outcomes.

Lactic acidosis is a serious medical condition that occurs when too much lactic acid builds up in the bloodstream. This buildup causes the pH of the blood to drop, making it too acidic. This acidity disrupts the function of nearly every organ system in the body.

To understand this condition, it is essential to know how our cells normally generate energy.

• Aerobic Metabolism: In a healthy, well-oxygenated state, our cells use a highly efficient process called aerobic metabolism. They combine glucose (sugar) and oxygen to produce large amounts of energy (in the form of a molecule called ATP) with harmless byproducts like carbon dioxide and water.
• Anaerobic Metabolism: When cells are deprived of oxygen due to shock, poor blood flow, or other causes, they switch to a less efficient, emergency backup system called anaerobic metabolism. This process can generate a small amount of energy very quickly without using oxygen, but it produces lactic acid as a major waste product.

A small amount of lactic acid is produced even under normal conditions and is efficiently cleared from the blood, primarily by the liver. Lactic acidosis occurs when there is a dramatic imbalance. Either the body produces far too much lactic acid, its ability to clear it is impaired, or both. The resulting high acid level in the blood disrupts the function of vital enzymes and proteins, leading to cellular dysfunction and organ failure.

Analogy: Think of lactic acid as the “exhaust fumes” of your cells making energy. Normally, your body’s liver and kidneys act like filters, clearing it out. But if the filter is blocked or the engine runs too hard without oxygen, fumes build up, polluting the bloodstream.

Lactic acidosis results from an imbalance between lactic acid production and clearance. In medicine, lactic acidosis is traditionally divided into two main categories, which helps doctors pinpoint the underlying problem.

Type A Lactic Acidosis: This is the most common form and results from oxygen deprivation (hypoxia or hypoperfusion). When tissues are starved of oxygen, their cells are forced into anaerobic metabolism, churning out large amounts of lactic acid.

Type B Lactic Acidosis: This category includes cases where there is no evidence of poor oxygen delivery to the tissues. Instead, the problem lies with the cells’ inability to use oxygen properly or with the body’s impaired ability to clear lactate from the blood. This can be caused by certain drugs, toxins, or systemic diseases.

You develop lactic acidosis as a direct consequence of a severe underlying illness, medication, or toxin. It is a sign that the body is in a state of extreme physiological distress.

Common Conditions Causing Type A Lactic Acidosis (Low Oxygen States):

Any condition that leads to shock or circulatory collapse can cause Type A lactic acidosis.

• Sepsis and Septic Shock: This is a leading cause. Sepsis is a life-threatening, body-wide inflammatory response to an infection. In septic shock, blood pressure plummets, and blood flow to vital organs is severely reduced.
• Cardiogenic Shock: Occurs when the heart is severely damaged and cannot pump enough blood to the body, such as after a massive heart attack or in end-stage heart failure.
• Hypovolemic Shock: Caused by a massive loss of blood or body fluids, such as from severe trauma, internal bleeding, or profound dehydration.
• Severe Respiratory Failure: Conditions like acute respiratory distress syndrome (ARDS) or a large pulmonary embolism can prevent the body from getting enough oxygen.
• Carbon Monoxide Poisoning: Carbon monoxide prevents red blood cells from carrying oxygen to the tissues.

Common Conditions Causing Type B Lactic Acidosis (Normal Oxygen States):

• Medications: Certain drugs are well-known causes.
  • Metformin: This is the most famous example. Metformin is a safe and effective first-line medication for type 2 diabetes. However, in very rare instances, it can cause a severe form called Metformin-Associated Lactic Acidosis (MALA). This almost always occurs in patients who take the medication while having significant kidney failure, as the kidneys are responsible for clearing metformin from the body. When kidney function is poor, the drug can build up to toxic levels and interfere with cellular metabolism.
  • Certain medications used to treat HIV.
• Toxins and Poisons: Ingestion of toxic substances like methanol (found in contaminated or illicit alcohol), ethylene glycol (antifreeze), or cyanide can cause severe lactic acidosis.
• Severe Liver Disease: The liver is the primary organ that clears lactate from the bloodstream. In patients with severe liver failure or cirrhosis, this clearance mechanism is impaired, allowing lactate to build up.
• Cancers: Certain blood cancers like leukemia and lymphoma can be associated with lactic acidosis.
• Thiamine (Vitamin B1) Deficiency: Severe thiamine deficiency can disrupt normal aerobic metabolism.
• Intense Exercise: It is worth noting that strenuous exercise causes a temporary and physiological lactic acidosis (the source of the “muscle burn” feeling). This is quickly cleared by a healthy body and is entirely different from the dangerous, persistent acidosis seen in critically ill patients.

Symptoms of lactic acidosis are often non-specific, but can escalate rapidly, depending on the underlying cause. However, there are some key signs that point specifically to the presence of severe metabolic acidosis.

The most prominent symptoms include:

• Rapid and Deep Breathing: This is known as Kussmaul breathing. It is not a sign of a lung problem, but rather the body’s desperate attempt to compensate for the acidic blood. By breathing rapidly and deeply, the body “blows off” excess carbon dioxide, which is an acid, in an effort to raise the blood’s pH.
• Nausea, Vomiting, and Severe Abdominal Pain.
• Profound Weakness and General Malaise.
• Changes in Mental Status: As acidosis worsens and affects the brain, a person may become confused, disoriented, excessively drowsy, or fall into a coma.

Lactic acidosis is diagnosed with blood tests, particularly measurements of lactate levels and blood pH.

• Clinical Suspicion: A doctor will suspect lactic acidosis in any critically ill patient who presents with shock, altered mental status, or signs of severe infection.
• Key Laboratory Tests: The diagnosis is confirmed with specific blood tests.
  • Arterial Blood Gas (ABG): This is a critical test where blood is drawn from an artery. It directly measures blood pH. A low pH (typically below 7.35) confirms the presence of acidosis.
  • Serum Lactate Level: This blood test directly measures lactate concentration. A high level (typically above 4 mmol/L) confirms that the acidosis is due to lactic acid.
  • Anion Gap Calculation: Doctors will also calculate the “anion gap” from a standard blood chemistry panel. A high anion gap is a strong clue that metabolic acidosis, like lactic acidosis, is present.
• Finding the Cause: Once lactic acidosis is confirmed, the medical team will immediately launch an investigation to find the underlying cause, as this is the key to treatment. This involves looking for a source of infection, performing an ECG to check for a heart attack, reviewing the patient’s medications, and possibly testing for toxins.

Treatment is urgent and focuses on supporting the patient’s vital functions while aggressively treating the root cause.

1. Treat the Underlying Cause

The acidosis will not improve unless the underlying condition driving is reversed.

• For sepsis, this means administering powerful intravenous antibiotics.
• For cardiogenic shock, this may mean emergency procedures to open a blocked coronary artery.
• For hypovolemic shock, this means giving IV fluids and blood transfusions.
• For MALA or toxic ingestions, this may mean stopping the drug and initiating emergency dialysis.

2. Supportive Care

While the root cause is being addressed, the patient will receive intensive supportive care in an ICU.

• Oxygen Therapy: To maximize oxygen delivery to the tissues.
• Intravenous (IV) Fluids: To improve circulation and blood pressure.
• Medications to Support Blood Pressure (Vasopressors): Often needed to treat shock.
• Mechanical Ventilation: A patient may need to be placed on a breathing machine to support their respiratory system and help control the blood’s acid-base balance.

3. Other Interventions

• Bicarbonate Therapy: While it seems intuitive to give an alkali like sodium bicarbonate to neutralize the acid, this is controversial and generally not recommended except in cases of extremely severe acidosis. It does not fix the underlying problem of lactate production and can sometimes have negative side effects.
• Dialysis: Hemodialysis can be used to help clear both lactate and certain toxins (like metformin or methanol) from the blood.

Outlook (Prognosis): The prognosis for a patient with lactic acidosis is often poor, not because of the lactate itself, but because it is a marker of an extremely severe, life-threatening underlying disease.

Lactic acidosis is not a disease but a critical metabolic alarm bell. It signals that the body’s cells are in a state of severe distress, either starving for oxygen or unable to use it. It is an ominous sign that arises as a complication of life-threatening conditions like sepsis, shock, or severe organ failure. The symptoms of rapid breathing, confusion, and profound weakness in a critically ill person should always raise immediate concern for this dangerous state. The key to survival lies not in treating acidosis directly, but in a rapid, aggressive, and successful treatment of the underlying cause.

• Merck Manual Professional Version. (2023). Lactic Acidosis. Retrieved from https://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/acid-base-regulation-and-disorders/lactic-acidosis
• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). (2023). Metformin. Retrieved from https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/metformin
• Cleveland Clinic. (2022). Lactic Acidosis. Retrieved from https://my.clevelandclinic.org/health/diseases/24524-lactic-acidosis
• Mayo Clinic. (2023). Lactic acidosis. https://www.mayoclinic.org