“Doctor, can you come see this patient please?”

“What’s happened?”

“Her saturations keep dropping. We keep moving the probe but the best we get is 82%.”

“What were her saturations like an hour ago?”

“Oh, you know, around 95, 96 on air.”

“How does she look?”

“She looks distressed”

“OK, be there in a bit. Put high flow oxygen on.”

It’s always the patients on the furthest ward from where you are. There’s this corridor on the way from Day Surgery unit to the rest of the hospital which has three glass walls and the floor. This looks lovely in the day, but it’s Siberia during the night. There is a door at either end of this corridor. You can leave Day Surgery through the first one, but the probability of the distal door being locked is determined by the product of how cold you are and how urgently you need to get through.

When I got there, I saw a slightly breathless 75 year old lady who was asking me  what all the commotion was about. She said she felt a little SOB, but not massively. Her RR was 18. The chest was clear.

Her radial pulse felt inconsistent. Her cap refill was less than two seconds, her BP 108/70 and her pulse 100 and irregular.

An ECG showed atrial fibrillation. This was new for her.

She had been admitted for a Hartmann’s procedure and was day 1 post operatively.

I felt that the saturations did not match up with the clinical picture, so did an ABG which showed a pO2 of 44.3 kPa. This showed that the saturations were misleading.

I later discussed this with the medical registrar. He told me that one of the commonest explanations for fluctuating saturations is atrial fibrillation. He also told me to always check the probe on my own finger if the clinical picture does not match up with the saturations.

We started her on bisprolol 1.25mg OD. She was already warfarinised for a previous PE.

Bottom line: Always go with your clinical impression over the sats machine, and get an ABG if in doubt.

Good links:

The WHO has guidance on pulse oximetry which mentions arrhythmias as a cause of false readings.