How to detect an event and ensure its the first (earliest event that occurred?

Question

I am attempting to extract data from a large patient database using SQL. I need to detect when an event occurred. In this case, it will be a decrease in SpO2 by 10% from when treatment started. It needs to be the earliest time point when it decreased. Example 100%-95-92-97-88-92-89 only the 88 is what I will need. The tricky part begins as patients might have two treatments throughout care. I need to compare these treatments to observe which treatment is the best. An example of the data is below. The patient will have treatment A until treatment B starts or until the final reading and vis versa. the SpO2 values with ** are the ones I need to extract

Date	Time	SpO2	Treatment
05/19/22	18:23	100	N/A
05/19/22	18:24	95	A
05/19/22	18:25	90	N/A
05/19/22	18:26	85	N/A
05/19/22	18:27	N/A	B
05/19/22	18:27	90	N/A
05/19/22	18:28	85	N/A
05/19/22	18:29	80	N/A
05/19/22	18:30	78	N/A
05/19/22	18:31	76	N/A

What I'm hoping the final table looks like is

Date	Time	SpO2	Treatment
05/19/22	18:23	100	N/A
05/19/22	18:24	95	A
05/19/22	18:26	85	N/A
05/19/22	18:27	N/A	B
05/19/22	18:27	90	N/A
05/19/22	18:29	80	N/A

If you can please help, that would be amazing and thank you very much.