Acid-Base Balance: Buffers, Respiratory, Renal

• Normal arterial pH ranges from 7.35-7.45.
• Acid-base balance is maintained by hydrogen ion production and CO2 loss.

Buffer Systems

• Chemical buffers act as the first line of defense.
• Bicarbonate (HCO3-) is a chemical buffer that is both extracellular and intracellular.
• Phosphate is an intracellular chemical buffer.
• Protein buffers such as albumin, globulin (extracellular), and hemoglobin (intracellular) also help maintain pH.
• Buffers provide immediate response to pH fluctuations.

Respiratory System

• The respiratory system serves as the second line of defense by regulating CO2 levels.
• Increased respiratory rate "blows off" CO2, raising pH.
• Decreased respiratory rate retains CO2 which lowers pH.

Renal System

• The renal system is the slowest but strongest line of defense, taking 48-72 hours to respond.
• In cases of acidic pH, kidneys reabsorb bicarbonate (HCO3-) and excrete H+.
• In cases of basic pH, kidneys excrete bicarbonate (HCO3-).

Acid-Base Imbalances

• Acidosis is when the pH is less than 7.35.

Metabolic Acidosis

• Overproduction of H+ ions can be caused by diabetic ketoacidosis (DKA), starvation, seizures, or heavy exercise.
• Under-elimination of H+ ions can be caused by renal or liver failure.
• Over-elimination of HCO3- can occur due to diarrhea.

Respiratory Acidosis

• Respiratory depression such as drug overdose can cause respiratory acidosis.
• Inadequate chest expansion is also a cause due to muscle weakness or pain.
• Airway obstruction such as COPD, pneumonia, ARDS, or PE can cause respiratory acidosis.

Key Features of Acidosis

• Cardiovascular: Bradycardia, hypotension, delayed conduction.
• CNS: Lethargy, confusion, stupor, coma.
• Neuromuscular: Hyporeflexia, muscle weakness.
• Respiratory: Kussmaul respirations (deep, rapid).
• Integumentary (Metabolic): Warm, flushed skin.
• Integumentary (Respiratory): Pale, cyanotic, dry skin.

Acidosis Interventions

• Metabolic: Hydration, bicarbonate (only give if HCO3- is low).
• Respiratory: Airway management, oxygen, ventilation support.

Alkalosis

• Alkalosis is when the pH is greater than 7.45.

Metabolic Alkalosis

• Base excess can be due to oral bicarbonate ingestion or blood transfusions.
• Acid loss can be caused by NG suctioning or prolonged vomiting.

Respiratory Alkalosis

• Hyperventilation (CO2 loss) can be caused by anxiety, fear, or pain.

Key Features of Alkalosis

• Cardiovascular: Increased HR, Digitalis toxicity risk.
• CNS: Anxiety, irritability, Chvostek's & Trousseau's signs.
• Neuromuscular: Muscle twitching, hyperreflexia, weakness.
• Respiratory: Increased rate/depth in respiratory alkalosis; decreased respiratory effort in metabolic alkalosis.

Alkalosis Interventions

• Treat the underlying cause; monitor ABGs & electrolytes; take fall precautions.

Interpreting an ABG

• Check the pH
• pH < 7.35 is acidosis
• pH > 7.45 is alkalosis
• Check the CO2.
• CO2 > 45 indicates acidosis (respiratory cause).
• CO2 < 35 indicates alkalosis (respiratory cause).
• Check the HCO3-.
• HCO3- < 22 indicates acidosis (metabolic cause).
• HCO3- > 26 indicates alkalosis (metabolic cause).
• Determine the cause.
• If CO2 matches pH change, the cause is respiratory.
• If HCO3- matches pH change, the cause is metabolic.