Blood Gases Level 1 Tutorial: Blood Gases
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Tutorial: Blood Gases
Learn an organized approach to arterial blood gas analysis, incorporating serum and urine electrolyte values into your more advanced levels of analysis.
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Tutorial: Blood Gases The Delta Delta and Acid Base Ddx
Times Practiced
Cases Completed
1h 24m
Total Time spent
1m 24s
Average Time
The Delta Delta and Acid Base Ddx

Please see the podcast video for the explanation of the delta delta, as it is not described in the text below.

This lesson will list the causes of the following acid base disorders:
  • respiratory acidosis
  • respiratory alkalosis
  • metabolic acidosis, with an anion gap
  • metabolic acidosis, without an anion gap
  • metabolic alkalosis

Respiratory acidosis is characterized by an increase in the pCO2 secondary to hypoventilation. Therefore, anything that increases pCO2 will cause a respiratory acidosis. pCO2 elimination is determined by both the respiratory rate and the tidal volume (multiplied together, they determine the minute volume, which is volume of air moved in and out of the lungs in one minute). There are some categories of mechanisms that will cause your minute ventilation to be reduced:
  • reduced respiratory rate
    • drugs that depress the respiratory center
    • injury to the respiratory center
  • reduced tidal volume
    • increase airway resistance (asthma, COPD)
    • stiff lungs (restrictive lung disease)
    • weak respiratory muscles (spine, nerve, or musculoskeletal disorders)

Respiratory alkalosis is much less common than respiratory acidosis and is caused by hyperventilation, resulting in low pCO2. The causes of respiratory alkalosis are most commonly caused by the brain and direct lung disorders:
  • brain causes:
    • brain injury with blood around the brain (causes an acidic environment in the brain)
    • anxiety or panic attack
    • pregnancy (the brain is stimulated by hormones)
  • lung causes:
    • pulmonary embolism
    • others lung diseases (less common)

Metabolic acidosis with an anion gap is usually more dangerous than non gap metabolic acidosis. There are some mnemonics that can help you remember.

  • Methanol
  • Uremia
  • DKA (ketones)
  • Paraldehyde ingestion (very rare)
  • Iron overload and Isoniazid (very rare)
  • Lactate
  • Ethanol
  • Salicylates (ASA)
Another is KARMEL, which includes only the more common causes (therefore, more practical):
  • Ketones
  • ASA
  • Renal failure
  • Methanol
  • Ethylene glycol
  • Lactate

Metabolic acidosis without anion gap, also called non gap metabolic acidosis is caused by intake of chloride or direct loss of HCO3-.
  • Chloride intake:
    • normal saline administration
    • intravenous nutrition (called TPN or TNA)
  • HCO3- direct loss:
    • renal losses (such as renal tubular acidosis)
    • GI losses (diarrhea)

Metabolic alkalosis is categorized into chloride "responsive" (low urine chloride, < 10 mEq/L) and chloride non-responsive (high urine chloride, > 20 mEq/L). 

The chloride responsive can be summarized as all the causes that are linked by dehydration or low K+ levels (hypokalemia). The mechanism of these types of metabolic alkalosis are linked to H+ ion loss.

The chloride resistant are summarized as some part of the aldosterone system, including receptors and ion channels in the kidney related to aldosterone type functions are abnormally turned up too high. The mechanism of these types of metabolic alkalosis are linked to increased HCO3- retention.

Chloride responsive conditions are far more common than chloride resistant ones. Chloride responsive conditions can typically be corrected with administering volume and potassium (if it is low).
  • Chloride responsive (H+ ion loss, urine chloride < 10 mEq/L)
    • dehydration (from any cause)
    • hypokalemia (from any cause)
    • diuretics (because they cause dehydration and hypokalemia)
    • vomiting (lots of acid is lost with vomiting plus you get dehydrated on top of that)
  • Chloride resistant (HCO3- retention, urine chloride > 20 mEq/L)
    • hyperaldosteronism
    • Bartter Syndrome (mutation that acts like patient is getting a diuretic)
    • Gitelman syndrome (mutation that acts like patient is getting a diuretic)
    • Liddle syndrome (aldosterone receptor ion is "always open", mimics too much aldosterone)
    • eating too much salty black licorice (it contains glycyrrhizin which drops your K levels and can also give you hypertension)

Those are the lists and remember to stick with red licorice. It is safer.

And yeah ... you need to memorize all of these 5 lists of acid base disorders. They are all common and important.