Acid Base Disturbances

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Respiratory Acidosis

  1. alveolar hypoventilation results in carbon dioxide retention and elevated PCO2.
    1. Respiratory depression due to alcohol or drugs
    2. Increased airway resistance due to asthma
    3. impaired gas exchange due to pulmonary fibrosis or severe pneumonia
    4. Loss of alveolar surface area in COPD emphysema 
    5. Muscle weakness of muscular dystrophy and other muscle diseases
  2. Increase plasma CO2
    1. Decrease HCO3 and an increase in pH 
      1. Because the problem is respiratory you dont expect respiratory compensation. 
      2. we dont have buffers as they are used up - hence your abnormal blood test
      3. So we only left with renal compensation 
        1. Excrete H+ and reabsorb HCO3, increasing pH, 
        2. COPD patients have chronic compensation
Metabolic Acidosis: Increased H+ but Decreased HCO3 - Normal alveolar exchange therefore normal PCO2
  1. Dietary and Metabolic H+ in is greater than H+ excretion - 
  2. Metabolic causes of acidosis
    1. anaerobic metabolism causes lactic acidosis
    2. excessive breakdown of fat and protein result in ketoacidosis - as in Diabetes Mellitus
  3. Dietary causes
    1. Methanol, Asprin, and ethylene glycol (antifreeze)
  4. Diarrhoea looses bicarbonate
    1. Pancreas - produces bicarbonate into the intestine to neutralise the stomach acid, and this bicarbonate is reabsorbed later. Diarrhoea prevents this reabsorption
    2. the hydrogen ion made at the same time as the bicarbonate is released into the blood stream -  in diarrhoea - there is no bicarbonate to be reabsorbed to buffer the hydrogen.
  5. Hyperventilates to compensate for increasing acidosis - normal or lower carbon dioxide
Alkalosis is uncommon 

Respiratory Alkalosis: Low HCO3 with increase pH indicates a respiratory disorder
  1. Hyperventilation - artificial ventilation 
  2. Renal compensation:
    1. Proximal renal tubule does not reabsorb bicarbonate and 
    2. the distal renal tubule secretes bicarbonate and reabsorbs Hydrogen
Metabolic Alkalosis: 
  1. 2 causes
    1. Excessive vomiting and ingesting excessive amounts of bicarbonate containing antacids
  2. Respiratory compensation - depressed ventilation, limited by hypoxia. If the PO2 falls below 60mmHg the hypoventilation ceases. 
  3. Renal compensation is the same - HCO3 not reabsorbed proximately and excreted in exchange for Hydrogen distally 

    1.  
Memory Aids

  1. MUDPILES - anion gap increased metabolic acidosis
    1. Methanol, 
    2. Uremia, 
    3. Diabetic/alcoholic starvation ketoacidosis, 
    4. Paraldehyde, 
    5. Isoprpyl alcohol/iron, 
    6. Lactic Acidosis, 
    7. Ethylene glycol, 
    8. Salicilates
  2. HARDUP - Non Anion Gap Metabolic Acidosis
    1. Hyper alimentation
    2. Acetazolamide
    3. RTA
    4. Diarrhea
    5. Ureterenteric fistula
    6. Pancreaticodudenal fistula
  3. Mixed Metabolic Acidosis
    1. Cirrhosis
    2. ASA overdose
    3. sepsis



  6. http://samedical.blogspot.com

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