Causes of Bradypena? Low venous oxygen - advice needed

I have an extensive history: Chiari, Syringomyelia, hEDS, bilateral TOS, tethered cord, intracranial hypertension - VP shunt, spinal venous fistula, MCAS, dysautonomia, cranial cervical instability (fused skull to c4).

I did have central sleep apnoea caused my the brain later compression from and overzealous Chiari decompression (nil prior) that has been corrected with my fusion, but my breathing is so slow. Regular for me is about 8-11bpm. Oxygen seems fine, and post surgeries require oxygen for a bit and it drops even more. This has persisted for years despite multiple medication and dosage changes (on higher and lower opiates). I have severe venous compression bilaterally in almost all positions with vtos and was wondering if that may also be compressing the phrenic nerve causing the bradypena? We are really at a loss here and sometimes it’s taking a lot of effort to breathe on bad days. It’s been ignored for years because my basic sats are ok.

I have results of peripheral venous blood gases not sure if that helps

pH 7.36 ( 7.32 - 7.43 )

pO2 L 18 mm Hg ( 35 - 49 )

pCO2 49 mm Hg ( 41 - 50 )

HCO3 Actual H 28 mmol/L ( 23 - 27 )

Base Excess 2.0 mmol/L ( -3.0 - 3.0 )

O2 Saturation L 25 % ( 60 - 80 )

Lactate 1.8 mmol/L ( 0.6 - 2.0 )

Age: 39

171cm/88kgs

Nil smoker/drugs

Medications: hydromorphone, ropivicaine, clonidine - all intrathecal, metformin, ozempic, Nebivolol, ketotifin, Targin, Dantrium, Zyrtec, Famotidine.