Acid

Carbonic Acid-Bicarbonate Buffer System

• Carbonic acid (H2CO3) converts to hydrogen ions (H+) and bicarbonate ions (HCO3-).

• Process occurs when carbon dioxide (CO2) and water (H2O) mix, leading to the formation of bicarbonate or carbonic acid.

• In the presence of carbonic anhydrase, carbonic acid can dissociate into these components.

• Important for maintaining pH balance at a cellular level.

Interpretation of Arterial Blood Gases (ABGs)

• ABGs allow healthcare providers to assess acid-base balance in patients.

• Understanding how compensation works is crucial (both respiratory and renal).

Compensation Mechanisms

• General Principle: The body seeks to restore pH towards a normal level (7.35-7.45).

• Kidneys: May increase bicarbonate production when in acidosis, excreting excess H+.

• Lungs: May expel more CO2 through increased breathing rate when in acidosis.

• Compensation responses can be seen through renal function and respiratory function alterations.

Types of Acid-Base Imbalances

Acidosis

• Defined as an increase in hydrogen ion concentration and decreased pH in the blood.

Respiratory Acidosis

• Occurs with elevated carbon dioxide levels (hypercapnia) due to:

  • Pneumonia: Lungs unable to effectively exchange gases.

  • Chronic Obstructive Pulmonary Disease (COPD): Impairs alveolar function, leading to CO2 retention.

  • Drug Overdose: Affect the respiratory center, causing hypoventilation.

• Compensation: Kidneys retain bicarbonate and excrete H+ to offset acidosis.

Metabolic Acidosis

• Defined by a decrease in bicarbonate or the accumulation of hydrogen ions.

• Causes include:

  • Diarrhea: Loss of bicarbonate ions leading to acidosis.

  • Diabetic Ketoacidosis (DKA): In diabetic patients lacking insulin; fats are broken down leading to ketone production.

  • Kidney Failure: Inability to excrete acids efficiently.

• Compensation: Increased respiratory rate (hyperventilation) to blow off CO2.

Symptoms of Acidosis

• Headache, lethargy, confusion, weakness, arrhythmias.

• Severe acidosis can lead to a coma or death due to lack of oxygen to the brain and cardiac instability.

• Electrolyte imbalances, notably potassium shifts, cause hyperkalemia (increased potassium in the blood) as potassium leaves cells in exchange for hydrogen ions.

Respiratory Alkalosis

• Defined as low levels of CO2 resulting from hyperventilation.

• Causes include:

  • Anxiety: Increased respiratory rate, blowing off too much CO2.

  • Altitude: Decreased atmospheric pressure reduces CO2 levels in the blood.

• Compensation: Kidneys excrete bicarbonate to retain hydrogen ions.

Metabolic Alkalosis

• Occurs with a major loss of H+ or bicarbonate retention, typically through vomiting.

• Symptoms: Shallow, slow respirations as the body attempts to retain CO2, thus retaining acid.

• Compensation: Involves respiratory responses to retain carbon dioxide and conserve acids.

Decompensation

• Refers to when compensatory mechanisms fail, and the body can no longer maintain homeostasis.

• Often occurs when the condition worsens or additional complications arise, leading to patient deterioration.

Treatment of Acid-Base Disturbances

• Always treat the underlying cause of the disturbance.

• For dehydration, ensure hydration to restore kidney function.

• Bicarbonate therapy may be administered in severe cases of metabolic acidosis if indicated (e.g. cardiac arrest).

Importance of Electrolyte Monitoring

• Changes in acid-base status directly affect electrolyte levels, particularly potassium, which can cause serious complications.

• Know the implications of high potassium (hyperkalemia) and how it affects cardiac function.

Final Note

• Mastering the concepts of compensation in acid-base imbalances and ABG interpretation is crucial for providing effective patient care, particularly in critical situations.

• Study tables and charts related to the effects of acid-base imbalances, as referenced in textbooks, for visual aids and further understanding.