9-1

• Acid-Base Balance


  Its role in homeostasis and disease
• Maintaining Acid-Base Balance


  • Controlled by the Lungs, Kidneys and Buffers
  • Disrupted by Vomiting, Diarrhea, Respiratory Failure, Kidney Failure, Infections and Ingestions
• Maintaining Acid-Base Balance


  1. Lung

  2. Kidney

  3. Buffering

  4. Compensation

  5. Correction
• Physiological Buffers


  Oppose significant changes in pH
• Physiological Buffers


  • Bicarbonate/Carbonic acid system
  • Intracellular protein buffers
  • Phosphate buffers
• Blood pH is determined by the ratio of serum bicarbonate concentration ([HCO3-]) and partial pressure of CO2 (PaCO2)
• Metabolic acid-base disorders and secondary metabolic compensation alter [HCO3-]
• Respiratory acid-base disorders and secondary respiratory compensation alter (PaCO2)
• Subtle changes in pH cause large shifts in acid-base pair
• Proteins function within narrow spectrum of pH
• Pulmonary Compensation


  1. Peripheral chemoreceptors in the carotid bodies and central chemoreceptors in the medulla change minute ventilation

  2. Decreased pH -> increased minute ventilation -> decreased PaCO2

  3. Compensatory processes return pH toward normal over many hours, but do not fully correct pH
• Anion Gap


  Estimates unmeasured anions in plasma (albumin)
• Normal Anion Gap = 12 +/- 3 mEq/L
• Anion Gap will be used in mixed disorders
• Chronic Obstructive Pulmonary Disease (COPD)

  • Defined as a disease state characterised by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and associated with abnormal inflammatory response of the lungs to noxious particles or gases
• Causes of COPD


  • Tobacco smoke
  • Air pollution (indoor)
  • Occupational exposure
  • Genetic factors (Alpha 1 - antitrypsin deficiency)
• COPD


  • Airway obstruction
  • Airway inflammation
  • Increased mucus production
  • Increased residual volume
  • Loss of elastic re-coil
  • Dyspnoea
  • Alveolar hypoventilation
  • Hypercapnia
  • Respiratory acidosis
  • Respiratory failure
• Chronic Obstructive Pulmonary Disease - Respiratory acidosis

  1. Retention of CO2

  2. Increased retention of H+ & HCO3-

  3. HCO3- excreted by kidneys
• Chronic Obstructive Pulmonary Disease - Respiratory acidosis - Compensation

  • pH <7.35
  • pCO2 >45mm/Hg
  • HCO3- normal (uncompensated)
  • HCO3- Elevated (compensated)
• Effects of Respiratory Acidosis

  • Neuromuscular: Anxiety, Lethargy/Coma, Delirium, Seizures/Tremors, Pappiloedema
  • Cardiovascular: Arrhythmia, Tachycardia, Vasodilation
• Acid-Base Balance is an important homeostatic process
• Fluctuations in pH are buffered allowing for important biological process to be carried out
• Alterations in this balance can result from disease and disorders often affecting the compensatory organs (lung, kidneys)
• Respiratory alkalosis occurs when there is too much CO2 being exhaled or not enough CO2 produced by cells.
• Hyperventilation may occur due to anxiety, pain, fever, pregnancy, exercise, pulmonary embolism, asthma, COPD, and other lung diseases.
• The most common cause of respiratory alkalosis is hyperventilation which increases the rate and depth of breathing leading to increased expiration of CO2.
• The most common cause of respiratory acidosis is chronic obstructive pulmonary disease (COPD). COPD causes airway obstruction which makes it difficult to breathe out carbon dioxide.
• Another cause of respiratory acidosis is sleep apnea where breathing stops during sleep causing hypercapnia.
• Metabolic acidosis results from increased acid production or decreased removal of metabolically generated H+ ions.
• Metabolic acidosis results from an increase in acidic substances such as lactic acid, ketoacids, sulfuric acid, phosphoric acid, uric acid, and hydrochloric acid.
• Causes of Respiratory alkalosis

  • central causes (via respiratory centre - Stroke, Anxiety-hyperventilation syndrome, other 'supra-tentorial' causes)
  • Hypoxaemia (via peripheral chemoreceptors)
  • Pulmonary causes (via intrapulmonary receptors)
  • iatrogenic (act directly on ventilation)
• causes of respiratory acidosis

  • CO2 production & excretion
  • perfusion of lungs (Pulmonary embolism)
  • Parenchymal disease (COPD)
  • Airway obstruction
  • thorax (trauma, haemothorax)
  • failure of CNS (sedation, paralysis)