pulse ox lag

4 Sep

RAGING HYPOTHETICAL:

Your next patient is a 42 yo M with COPD and severe respiratory distress, who rolls in with EMS and has an 02 sat of 77%.   You quickly decide to intubate, but immediately after doing so, the 02 sat is still sitting in the 80’s.   Your ETCO2 is working and shows a good waveform, so you should be in the right spot (trachea).  So what’s going on?

 

ONE THING TO CONSIDER…

(other than Airway, Breathing, and Circulation)

 

PULSE OX LAG

After changing someone’s oxygenation (supplemental 02, in whatever way/shape/form from nasal cannula to ETT, or removal thereof), there seems to be a lag time between their actual oxygenation (centrally) to the detection peripherally, as with an 02 sat monitor.

 

HOW LONG IS IT?

Pulse ox study (most pertinent) by Gruber et al.

  • 51 patients with nasal cannula O2 (43 monitored while O2 treatment was initiated, 18 monitored when it was discontinued)
  • Patients were placed on and/or taken off O2 via nasal cannula set at 2 or 4 L/min based on clinical indications. 
  • 02 saturation was measured at 1-minute intervals over a 30-minute period
  • Most (95%) of the patients placed on O2 attained equilibration of O2 saturation within 3.5 minutes.
  • Most (95%) of the patients taken off O2 attained equilibration of O2 saturation within 4.5 minutes.

ABG study on COPD-ers by Weinrich et al:

  • 12 patients with severe COPD on long term 02
  • FiO2 increased or decreased, and ABGs checked at increasing intervals over 34 min
  • time required to reach clinically stable values (within 1% of equilibrium values)
    • FiO2 increased: median time was 2.6 minutes and in worst case 6.8 minutes. 
    • FiO2 reduced: median time was 7.4 minutes, and in the worst case 15.6 minutes.

 

References: pulse ox study; abg/COPD study; picture

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