You are in the OR doing an emergency anesthetic for a pt who has a clot in their brachial artery causing a cold hand.

No relevant history and otherwise very healthy.

At the start of the case you find the pulse ox isnt working well on the finger and move it to the ear. It seems to work much better and reads 99%.

You are doing the case with an LMA, pts BP & HR are stable.

About 20 min in the pulse ox sounds like this "Bloop, Bloooooop, blooooop" and rapidly drops to 75%.

The waveform looks normal

The BP is the same as is the HR

the pt is taking TV of 200 @ 10/min.

Differentials? Actions?