Acid-Base Balance Made Easy- AI Simulated Case-Scenario Discussions

Study Guide on Acid-Base Balance

General Principles

The normal pH range for human blood is between 7.35 and 7.45.
Acidemia is defined as a blood pH less than 7.35 while alkalemia refers to a pH greater than 7.45.
The body maintains balance using the lungs to regulate carbon dioxide and the kidneys to regulate bicarbonate.
A primary disturbance in carbon dioxide is considered a respiratory disorder and a primary disturbance in bicarbonate is a metabolic disorder.

1. Metabolic Acidosis

This abnormality is defined by a primary decrease in bicarbonate which causes the blood pH to drop below 7.35.
The respiratory system compensates by hyperventilating to blow off acidic carbon dioxide and help raise the pH.
Clinicians use Winter’s formula to calculate the expected partial pressure of carbon dioxide to determine if the respiratory compensation is appropriate.
Causes are categorized by the anion gap which is the difference between measured cations and anions.
High Anion Gap Metabolic Acidosis is often caused by the accumulation of organic acids as seen in the mnemonic MUDPILES which stands for Methanol, Uremia, Diabetic Ketoacidosis, Paraldehyde, Isoniazid or Iron, Lactic acidosis, Ethylene glycol, and Salicylates.
Normal Anion Gap Metabolic Acidosis typically results from the loss of bicarbonate through the gastrointestinal tract like in diarrhea or through the kidneys as seen in renal tubular acidosis.

2. Metabolic Alkalosis

This state involves a primary increase in bicarbonate concentration leading to a blood pH above 7.45.
Compensation occurs through hypoventilation where the lungs retain carbon dioxide to increase the acidity of the blood.
The disorder is further divided into chloride-responsive and chloride-resistant types based on the level of chloride in the urine.
Chloride-responsive alkalosis is commonly caused by the loss of gastric acid through vomiting or nasogastric suction and is treated with intravenous normal saline.
Chloride-resistant alkalosis is often associated with mineralocorticoid excess or severe potassium depletion and does not respond to saline alone.
It is critical to never give bicarbonate to a patient in metabolic alkalosis as it will worsen the condition and potentially cause lethal arrhythmias.

3. Respiratory Acidosis

This condition is characterized by an elevated partial pressure of carbon dioxide due to the lungs failing to remove it effectively which results in a low pH.
The primary cause is hypoventilation which can stem from airway obstructions like COPD, chest wall diseases, or central nervous system depression from drugs such as opioids.
The kidneys provide compensation by retaining bicarbonate and excreting hydrogen ions though this metabolic response takes several days to develop.
In cases of chronic respiratory acidosis the body may rely on a hypoxic drive to breathe so giving high-flow oxygen without ventilation support can be dangerous.
Treatment focuses on improving ventilation through the use of bronchodilators, steroids, or non-invasive positive pressure ventilation.

4. Respiratory Alkalosis

This disorder is defined by a primary decrease in carbon dioxide because the lungs are hyperventilating which increases the blood pH.
The kidneys compensate for the high pH by excreting bicarbonate over a period of hours to days.
Common causes include anxiety, pain, and fever as well as acute medical emergencies like a pulmonary embolism or early sepsis.
Patients may experience tingling sensations or paresthesias because the alkalosis causes calcium to shift into cells.
The main goal of therapy is to treat the underlying cause such as managing a panic attack with reassurance or addressing a primary infection

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