There’s a lot of improvising with the finger clip pulse oximetry when it’s difficult to get a good reading. Changing fingers is the obvious thing. Putting it on the ear lobe or auricle is often used. And although it looks silly, the nose can be a good place for the clip. Buccal readings, placing the clip in the lateral angle of the mouth opening, also works. Here’s one I hadn’t seen: MacGyvering a paediatric pulse ox taped to a pharyngeal airway.
The idea to tape a soft tape pulse ox to a pharygeal airway seems to come from case reports and a study taping pulse ox to LMAs. I’m not sure if these tricks measures pharyngeal or soft palate oxygenation, but both areas should be well perfused. I would think the pulse ox probe could also be places on the opposite side, to measure tongue oxygenation.
The case reports are interesting, as they get pulse trace and a saturation reading that compares well to the measured arterial saturation in patients where standard pulse oximetry didn’t give any reliable readings. Something to think about for monitoring severely shocked patients or patients with low output states.
Successful use of pharyngeal pulse oximetry with the oropharyngeal airway in severely shocked patients, Anaesthesia. 2007.
Then the LMA versions. Based on the same principal. The case studies are on two shocked patients, while the study from Anesthesia and Analgesia is on healthy, well perfused subjects, but has more detail on the technique, as well as references to papers documenting different sites of obtaining pulse oximetry, for the ones with a special interest:
Successful pharyngeal pulse oximetry in low perfusion states, Can J Anesth, 2000
A pilot study of pharyngeal pulse oximetry with the laryngeal mask airway: a comparison with finger oximetry and arterial saturation measurements in healthy anesthetized patients, Anesth Analg. 2000
Finally tried this the other day with a patient on whom we kept losing losing palpable pulses and who was too clamped down for even a temporal pulse-ox sticker – the first time I’ve ever seen that option fail. With the pharyngeal-ox it looked like there might have been a waveform on the monitor, but the patient was trying to breathe over the vent a little bit and that seemed to introduce too much baseline wander to get any sort of reading.
Still, I’m keeping it as an option for the next time we can’t get a sat anywhere else. If not for the slight movements, I think it would have given a usable waveform.
Thanks for the short case report! Luckily, most of these patients lie quite still – or we make them lie still.
Pingback: Season 2 Episode 2 – Mythbusters | GasCast
Sometimes you can try a digital block, which will vasodilate the finger and it may improve your waveform. However, this won’t help if you are vasoconstricted more proximally.