Sorry doctor, the ABG machine doesn’t believe you…

The most extreme respiratory acidosis ever
Extreme respiratory acidosis

This ABG was taken on 15L/O2 min.

A loose translation:

# = uh oh
! = the patient has probably arrested in the time it took you to analyse this ABG
? = lol, that’s not possible.

It came from the left radial artery of a man in his early 70s who was referred by his GP for seeming drowsy and cold with a saturation of 71%.

He had a PMH of COPD (home oxygen) and CCF.

On arrival, he was too drowsy for a history.

On examination, there was use of accessory muscles although he seemed fatigued. There was diffuse wheeze and bilaterally reduced air entry.

The SpR treated it as a severe exacerbation of COPD.

What are the common causes of an exacerbation of COPD?

Most community-acquired infections are caused by Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Staph aureus classically causes pneumonia following influenza infection. There are also viral triggers and pollutants.

 What is best medical management?

  • initially controlled oxygen to maintain SaO2 88–92%
    adjust target range to 94–98% if the PaCO2 is normal (unless there is a history of previous NIV or IPPV) and recheck blood gases after 30–60 min
  • nebulised salbutamol 2.5–5 mg
  • nebulised ipratroprium 500 micrograms
  • prednisolone 30 mg
  • antibiotic agent (when indicated).

What are the management options in COPD with hypercapnic failure?

Hypoxic (pO2 <8kPa) Hypercapnic (pCO2 > 6kPa) Acidotic (pH < 7.35) Treatment
No No No Medical management
Yes No No Increase inspired O2
Target sats: 94-98%
Yes Yes No Titrate O2 down if pO2 > 8kPa.
Target sats: 88-92%
Yes Yes Yes NIV or intubation. May need discussion with ITU.

What are the five factors that need to assessed before starting NIV?

  • their pre-morbid state
  • the severity of the physiological disturbance
  • the reversibility of the acute illness
  • the presence of relative contraindications (see Table 1), and
  • where possible, the patient’s wishes.

The ideal COPD/NIV candidate is a well-informed, compliant patient who is able to protect his own airway. He has a reversible COPD exacerbation, and enjoyed good pre-morbid health. His pH is between 7.25 and 7.35 (if pH <7.25 invasive ventilation may be more appropriate), his pCO2 > 6kPa and he is moderately hypoxic (severe hypoxia is an indication for invasive ventilation).

The contraindications are listed below:

  • Life-threatening hypoxaemia
  • Severe co-morbidity
  • Confusion/agitation/severe cognitive impairment
  • Facial burns/trauma/recent facial or upper airway surgery
  • Vomiting
  • Fixed upper airway obstruction
  • Undrained pneumothorax
  • Upper gastrointestinal surgery
  • Inability to protect the airway
  • Copious respiratory secretions
  • Haemodynamically unstable requiring inotropes/pressors (unless in a critical care unit)
  • Patient moribund
  • Bowel obstruction

Having assessed the five criteria above, you should be able to reach a decision about what treatment options are suitable for this patient:

  • requiring immediate intubation and ventilation
  • suitable for NIV and suitable for escalation to intensive care treatment/ intubation and ventilation 
if required
  • suitable for NIV but not suitable for escalation to intensive care treatment/ intubation and ventilation
  • not suitable for NIV but for full active medical management
  • palliative care agreed as most appropriate management

I will find out more about NIV from the respiratory team and write up any clinical pearls they have in the next post.

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