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Chemistry

Disease Correlation

Connecting acid-base disturbances with specific disease states allows for accurate diagnosis and targeted treatment. It helps you assess the patient’s condition and guide the right approach to management

  • Respiratory Acidosis
  • Respiratory Alkalosis
  • Metabolic Acidosis
  • Metabolic Alkalosis

Respiratory Acidosis

  • Definition: A condition characterized by a decrease in blood pH (< 7.35) due to an increase in arterial carbon dioxide tension (Pa\(CO_2\) > 45 mmHg) resulting from inadequate alveolar ventilation
  • Underlying Pathophysiology:
    • Inadequate alveolar ventilation causes carbon dioxide retention, leading to increased carbonic acid (\(H_2CO_3\)) concentration in the blood
    • This results in an increase in hydrogen ion (\(H^+\)) concentration and a decrease in pH
  • Common Causes
    • Chronic Obstructive Pulmonary Disease (COPD): Emphysema, chronic bronchitis
    • Central Nervous System (CNS) Depression: Drug overdose (e.g., opioids, sedatives), brainstem injury
    • Neuromuscular Disorders: Muscular dystrophy, amyotrophic lateral sclerosis (ALS), myasthenia gravis
    • Severe Pneumonia or Acute Respiratory Distress Syndrome (ARDS): Impaired gas exchange
    • Chest Wall Abnormalities: Kyphoscoliosis, flail chest
  • Laboratory Findings
    • pH: < 7.35
    • Pa\(CO_2\): > 45 mmHg
    • \(HCO_3^-\): Normal in acute respiratory acidosis; elevated in chronic respiratory acidosis (due to renal compensation)
    • Pa\(O_2\): May be decreased, depending on the underlying cause
  • Symptoms
    • Acute Respiratory Acidosis: Confusion, anxiety, restlessness, dyspnea (shortness of breath), cyanosis (bluish discoloration of the skin), headache, dizziness, cardiac arrhythmias
    • Chronic Respiratory Acidosis: Often asymptomatic or mild symptoms such as fatigue, lethargy, and sleep disturbances
  • Disease State Correlation
    • COPD: Chronic bronchitis and emphysema cause airflow obstruction, leading to carbon dioxide retention
    • Drug Overdose: Opioids and sedatives depress the respiratory center in the brain, resulting in hypoventilation
    • Neuromuscular Disorders: Muscle weakness impairs the ability to breathe effectively
    • Pneumonia and ARDS: Inflammation and fluid accumulation in the lungs impair gas exchange
    • Chest Wall Abnormalities: Restrict lung expansion and impair ventilation

Respiratory Alkalosis

  • Definition: A condition characterized by an increase in blood pH (> 7.45) due to decreased arterial carbon dioxide tension (Pa\(CO_2\) < 35 mmHg) resulting from excessive alveolar ventilation
  • Underlying Pathophysiology
    • Excessive alveolar ventilation causes carbon dioxide to be blown off, leading to decreased carbonic acid (\(H_2CO_3\)) concentration in the blood
    • This results in a decrease in hydrogen ion (\(H^+\)) concentration and an increase in pH
  • Common Causes
    • Hyperventilation Syndrome: Anxiety, panic attacks
    • Hypoxia: High altitude, severe anemia
    • Pulmonary Embolism: Stimulation of respiratory centers
    • Central Nervous System Disorders: Stroke, meningitis, encephalitis
    • Mechanical Ventilation: Excessive ventilation by a mechanical ventilator
    • Pregnancy: Hormonal stimulation of the respiratory center
    • Salicylate Poisoning: Direct stimulation of the respiratory center
  • Laboratory Findings
    • pH: > 7.45
    • Pa\(CO_2\): < 35 mmHg
    • \(HCO_3^-\): Normal in acute respiratory alkalosis; decreased in chronic respiratory alkalosis (due to renal compensation)
    • Pa\(O_2\): May be normal or decreased, depending on the underlying cause
  • Symptoms
    • Dizziness, lightheadedness, confusion, paresthesias (numbness and tingling), muscle cramps, carpopedal spasm (spasm of the hands and feet), chest pain, palpitations
  • Disease State Correlation
    • Hyperventilation Syndrome: Anxiety and panic attacks cause rapid breathing, leading to excessive carbon dioxide elimination
    • Hypoxia: Low oxygen levels stimulate the respiratory center to increase ventilation
    • Pulmonary Embolism: Blood clot in the lungs stimulates respiratory centers, leading to hyperventilation
    • Pregnancy: Progesterone and other hormones stimulate the respiratory center

Metabolic Acidosis

  • Definition: A condition characterized by a decrease in blood pH (< 7.35) due to a primary decrease in serum bicarbonate concentration (\(HCO_3^-\) < 22 mEq/L)
  • Underlying Pathophysiology
    • Loss of bicarbonate: Results in a decrease in buffering capacity and a drop in pH
    • Excess production of acids: Overwhelms the body’s buffering capacity, leading to a decrease in pH
    • Impaired excretion of acids: Leads to an accumulation of acids in the blood, lowering pH
  • Common Causes
    • Increased Acid Production:
      • Diabetic Ketoacidosis (DKA): Insulin deficiency leads to increased ketone production
      • Lactic Acidosis: Anaerobic metabolism due to shock, sepsis, or severe exercise
      • Starvation: Breakdown of fats and proteins leads to increased ketoacid production
      • Toxins: Ingestion of methanol, ethylene glycol, or salicylates
    • Loss of Bicarbonate:
      • Diarrhea: Loss of bicarbonate-rich intestinal secretions
      • Renal Tubular Acidosis (RTA): Impaired reabsorption of bicarbonate by the kidneys
    • Impaired Acid Excretion:
      • Kidney Failure: Reduced ability to excrete acids and regenerate bicarbonate
  • Laboratory Findings
    • pH: < 7.35
    • Pa\(CO_2\): Normal or decreased (due to respiratory compensation)
    • \(HCO_3^-\): < 22 mEq/L
    • Base Excess (BE): More negative than -2 mEq/L
    • Anion Gap: May be normal or elevated, depending on the cause
  • Anion Gap
    • Definition: The difference between measured cations (Na+, \(K^+\)) and anions (Cl-, \(HCO_3^-\)) in serum or plasma
    • Calculation: Anion Gap = [\(Na^+\)] + [\(K^+\)] - [\(Cl^-\)] - [\(HCO_3^-\)]
    • Normal Anion Gap: 8-16 mEq/L (with \(K^+\)), 10-20 mEq/L (without \(K^+\))
  • Disease State Correlation
    • Diabetic Ketoacidosis (DKA): Insulin deficiency leads to increased ketone production, resulting in a high anion gap metabolic acidosis
    • Lactic Acidosis: Anaerobic metabolism due to shock, sepsis, or severe exercise results in increased lactic acid production, leading to a high anion gap metabolic acidosis
    • Diarrhea: Loss of bicarbonate-rich intestinal secretions results in a normal anion gap (hyperchloremic) metabolic acidosis
    • Kidney Failure: Reduced ability to excrete acids and regenerate bicarbonate results in a high anion gap metabolic acidosis
    • Toxins:
      • Methanol: Metabolism to formic acid
      • Ethylene Glycol: Metabolism to glycolic acid and oxalic acid
      • Salicylates: Complex effects on metabolism and respiration
  • Compensation
    • Respiratory Compensation: Increased ventilation to blow off carbon dioxide and raise pH
    • Renal Compensation: Increased excretion of acid and increased reabsorption of bicarbonate over several days
  • Symptoms
    • Rapid breathing, fatigue, confusion, nausea, vomiting

Metabolic Alkalosis

  • Definition: A condition characterized by an increase in blood pH (> 7.45) due to a primary increase in serum bicarbonate concentration (\(HCO_3^-\) > 26 mEq/L)
  • Underlying Pathophysiology
    • Excess alkali administration: Overwhelms the body’s acid-base regulatory mechanisms
    • Excess loss of acid: Depletes the body’s acid stores, leading to a relative excess of bicarbonate
    • Contraction alkalosis: Volume contraction stimulates bicarbonate reabsorption in the kidneys
  • Common Causes
    • Loss of Acid:
      • Vomiting: Loss of gastric acid (hydrochloric acid, \(HCl\))
      • Nasogastric Suctioning: Removal of gastric acid
    • Excess Bicarbonate Administration:
      • Administration of Bicarbonate: During resuscitation or treatment of acidosis
      • Excessive Antacid Use: Ingestion of large amounts of antacids containing bicarbonate
    • Contraction Alkalosis:
      • Diuretic Therapy: Volume depletion stimulates bicarbonate reabsorption in the kidneys
    • Mineralocorticoid Excess:
      • Hyperaldosteronism: Increased aldosterone leads to increased sodium reabsorption and increased hydrogen ion excretion
  • Laboratory Findings
    • pH: > 7.45
    • Pa\(CO_2\): Normal or increased (due to respiratory compensation)
    • \(HCO_3^-\): > 26 mEq/L
    • Base Excess (BE): More positive than +2 mEq/L
  • Disease State Correlation
    • Vomiting: Loss of gastric acid leads to metabolic alkalosis
    • Diuretic Therapy: Volume depletion and increased aldosterone levels stimulate bicarbonate reabsorption
    • Hyperaldosteronism: Increased aldosterone levels promote hydrogen ion excretion and bicarbonate reabsorption
  • Compensation
    • Respiratory Compensation: Decreased ventilation to retain carbon dioxide and lower pH
    • Renal Compensation: Increased excretion of bicarbonate and decreased excretion of acid over several days
  • Symptoms
    • Confusion, lightheadedness, muscle cramps, nausea, vomiting

Key Terms

  • Acidosis: A condition in which the blood pH is below the normal range
  • Alkalosis: A condition in which the blood pH is above the normal range
  • Hypercapnia: The presence of abnormally high levels of carbon dioxide in the blood
  • Hypocapnia: The presence of abnormally low levels of carbon dioxide in the blood
  • Hypoxemia: A condition in which the blood oxygen level is lower than normal
  • Arterial Blood Gas (ABG): A test that measures the levels of oxygen and carbon dioxide in arterial blood
  • Partial Pressure of Oxygen (Pa\(O_2\)): A measure of the oxygen level in arterial blood
  • Partial Pressure of Carbon Dioxide (Pa\(CO_2\)): A measure of the carbon dioxide level in arterial blood
  • Bicarbonate (\(HCO_3^-\)): A major buffer in the blood
  • Base Excess (BE): A measure of the amount of acid or base needed to restore normal pH
  • Oxygen Saturation (Sa\(O_2\)): A measure of the percentage of hemoglobin saturated with oxygen
  • Respiratory Acidosis: Acidosis caused by increased carbon dioxide levels
  • Metabolic Acidosis: Acidosis caused by decreased bicarbonate levels or increased acid production
  • Respiratory Alkalosis: Alkalosis caused by decreased carbon dioxide levels
  • Metabolic Alkalosis: Alkalosis caused by increased bicarbonate levels or decreased acid levels
  • Anion Gap: The difference between measured cations and anions in serum or plasma
  • Compensation: The physiological response to an acid-base disturbance that attempts to restore normal pH
  • Estimated Glomerular Filtration Rate (eGFR): An estimate of GFR based on serum creatinine, age, sex, and ethnicity
  • Body Surface Area (BSA): The measured or calculated surface of a human body
  • Modified Allen Test: A test to assess collateral circulation in the hand
  • COPD: Chronic Obstructive Pulmonary Disease
  • CNS: Central Nervous System
  • ARDS: Acute Respiratory Distress Syndrome
  • DKA: Diabetic Ketoacidosis
  • RTA: Renal Tubular Acidosis
  • Hypoventilation: The state in which a reduced amount of air enters the lungs
  • Hyperventilation: The state of breathing too fast or too deeply
  • Paresthesias: An abnormal sensation, typically tingling or pricking (“pins and needles”), caused chiefly by pressure on or damage to peripheral nerves
  • Carpopedal Spasm: Cramps in the hands and feet
  • Lactate: An organic acid, C3H6O3, present in blood, muscle, and other tissues, formed as an end product of anaerobic glucose metabolism; it is produced in increased amounts in strenuous muscular exercise or when there is anoxia
  • Ketones: Chemicals that your liver makes when there’s not enough insulin in the blood and the body breaks down fat for energy
  • Glomeruli: Filtering units within the kidney
  • Proteinuria: The presence of excess protein in urine
  • Metabolic Disorder: Occurs when abnormal chemical reactions in the body disrupt metabolism
  • Alveolar: Relating to the alveoli of the lungs
  • Alkaline Phosphatase (ALP): A hydrolase enzyme responsible for removing phosphate groups from many different types of molecules, including nucleotides, proteins, and other phosphates
  • In Vitro: Taking place in a test tube, culture dish, or elsewhere outside a living organism
  • In Vivo: Occurring within a living organism
  • Homeostasis: The process by which organisms maintain a relatively stable internal environment
  • Pulmonary Embolism: A blood clot that occurs in the lungs
  • Transfusion: The process of transferring blood or blood products from one person to another
  • Lethargy: A state of tiredness, weariness, fatigue, or lack of energy
  • Ischemia: An inadequate blood supply to an organ or part of the body
  • Hypoxia: An inadequate oxygen supply to the cells and tissues of the body