Respiratory & Metabolic Acid Base

• Hydrogen ions


  Relationship with acids & bases
• Acids


  • Release hydrogen ions
• Bases

  • Accept hydrogen ions
• Substances that act as a buffer

  • Bicarbonate (carbonic acid)
  • Phosphate
  • Protein
• Acidosis


  pH < 7.35, ion concentration below
• Alkalosis


  pH 7.45 <, ion concentration above
• Systems that act as buffer systems


  • Respiratory system (lungs)
  • Renal system (kidneys)
• Respiratory system


  Regulates carbonic acid, eliminating or retaining carbon dioxide (blow off CO2)
• Renal system


  Long-term regulation of acid-base balance in body, regulating elimination of excess non-volatile acids and bicarbonate levels in ECF
• Ratio of bicarbonate to carbonic acid

  20:1; Ensures normal blood pH
• What is measured to assess acid-base balance


  • ABG's
  • PaCO2
  • PAO2
  • Serum bicarbonate
  • Base excess
• Body's way of compensating for imbalance

  Serum bicarbonate, Base excess
• Where is the assessment of acid-base pulled from


  Radial artery typically but can be from femoral or brachial artery
• Normal ranges for arterial blood gas values

  • pH: 7.35-7.45
  • Acidosis: < 7.35
  • Alkalosis: 7.45 <
  • PaCO2: 35-45 mmHg
  • Hypocapnia: < 35 mmHg
  • Hypercapnia: 45 mmHg <
  • PaO2: 80-100 mmHg
  • Hypoxemia: < 80 mmHg
  • HCO3-: 22-26 mEq/L
  • BE (Base excess): -3 to +3
• PaO2 is not the same as the statistic for a pulse oximetry
• Disorders that can cause an acid-base imbalance


  • Metabolic disorders (concentration changes in bicarbonate)
  • Respiratory disorders (concentration changes in carbonic acid)
• Primary imbalance


  Due to only 1 cause (ex. Only have diabetes)
• Mixed imbalance


  Occur from combinations of respiratory & metabolic disturbances (diabetes & emphysema)
• Treat symptoms
• Relationship between pH, PaCO2, and HCO3-


  • Respiratory (= opposite): pH is high (7.45 <), PCO2 is down (< 35); pH is low (< 7.35), PCO2 is up (45 <)
  • Metabolic (= Equal/same): pH is high (7.45 <), HCO3- is high (< 22); pH is low (< 7.35), HCO3- is low (26 <)
• Metabolic acidosis


  pH is low(7.45 <), HCO3 is low (26 <)
• #1 risk factor for metabolic acidosis

  Patients with type 1 diabetes mellitus
• Metabolic acidosis is correlated to ketoacidosis
• Other risk factors for metabolic acidosis


  • Tissue hypoxia due to shock, cardiac arrest
  • Acute or chronic renal failure (causing weight retention)
  • GI alterations such as diarrhea or intestinal suction
• Causes of metabolic acidosis


  • Accumulation of metabolic acids
  • Excess loss of bicarbonate
  • Diarrhea, ileostomy drainage, intestinal fistula
  • Biliary/ pancreatic fistulas
  • Increase in chloride levels
• In metabolic acidosis


  Increase in non-volatile acid production, Decrease acid excretion, Increase bicarbonate ions
• Body's compensation for metabolic acidosis

  Rate & depth of respirations increase eliminating additional CO2 (blow off CO2), Kussmaul breathing
• Metabolic alkalosis


  Increase in acid loss or excretion, Hypokalemia, Increased bicarbonate
• Compensatory responses for metabolic alkalosis


  Rate & depth of respirations of decrease retaining CO2
• Patient's clue to identify acid-base imbalance

  Past medical history diagnosis
• Causes of respiratory acidosis


  • Acute Respiratory Distress: Acute respiratory condition (pneumonia, pulmonary edema, acute asthma), Opiate overdose, Chest trauma
  • Chronic Respiratory Distress: Chronic respiratory conditions (COPD, cystic fibrous), Neuromuscular disease (Multiple Sclerosis)
• Body's compensation for respiratory acidosis


  Kidneys help by increasing bicarbonate to restore ratio (1 carbonic acid: 20 bicarbonate)
• Causes of respiratory alkalosis


  • Anxiety-induced hyperventilation (not blowing off CO2)
  • Fever
  • Early aspirin (salicylate) intoxication
  • Hyperventilation with mechanical ventilation
• Cause of respiratory alkalosis that can result in patient passing out

  Hyperventilation with mechanical ventilation, Autonomic nervous system kicks in by regulating breathing once passed out
• Respiratory stimulus


  Carbon dioxide; Negative feedback loop in Medulla oblongata
• Respiratory stimulus in respiratory alkalosis


  Oxygen (Maximum 2 Liters); Respiratory disease
• Body's compensation for respiratory alkalosis


  Kidneys excrete bicarbonate (CO2) & increase hydrogen ion concentration to restore ratio (1 carbonic acid: 20 bicarbonate)
• Clinical manifestations of metabolic acidosis

  • Headache, weakness, & fatigue
  • Anorexia, nausea, & vomiting
  • Declined LOC
  • Dysrhythmias & cardiac arrest
  • Deep & rapid respirations
• Diagnosis of metabolic acidosis


  • ABG's
  • Serum electrolytes
  • ECG
  • Blood glucose
  • Renal function
• Medications to treat metabolic acidosis


  • Alkaline solution, Sodium bicarbonate (given for severe acidosis)
  • IV insulin & fluid, Saline solutions & glucose