VBG

When is ABG useful to investigate oxygenation?

EMKF

pulse-ox

Almost never. For patients with an adequate oximetry waveform, pulse oximetry is usually superior to ABG for measuring oxygenation. ABG is only useful to investigate oxygenation when:

  • Pulse oximetry waveform is unreliable.
  • Diagnosis of methemoglobinemia.
  • Calculation of the PaO2/FiO2 ratio to guide a specific therapeutic decision.

 

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Blood gas measurements in DKA

EMKF

  • Guidelines recommend checking an ABG or VBG in all patients with DKA.  This practice is not evidence-based and should be abandoned.
  • ABG or VBG provides little information about whether or not the patient has DKA (beyond what is already known from the serum chemistries).
  • Rather than pH, serum bicarbonate may be used to gauge the severity of acidosis.
  • There is no evidence that detecting or reacting to a very low pH is helpful.
  • Decisions about the level of ventilatory support that a patient needs can almost always be made on a clinical basis.  When in doubt, close attention to the patient with serial examination is often a sound approach.  Focus on the patient, not the blood gas.
  • VBG might be helpful in cases where it is unclear whether the patient requires intubation, or if there is a significant underlying respiratory disease (e.g. COPD or obesity hypoventilation syndrome).

 

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