Air carrier Captain reported a passenger suffered a medical issue and the crew discovered the blood pressure cuffs and stethoscope in the medical kit were unusable. The reporter stated this was their second event where the medical kit was unusable.

Narrative

While waiting for our aircraft to arrive; the Flight Attendants (FAs) noticed a frail passenger in the boarding area. About an hour into the flight I received a call from the FAs that the same passenger was now being attended to by three doctors. They eventually had him on the floor in the forward galley to check his vitals. The blood pressure cuff was not working; nor was the stethoscope usable because of missing pads. (This was my second occurrence of a blood pressure cuff not working) Luckily they received a blood pressure cuff from a passenger. We were in constant contact with Dispatch. The Dispatcher had advised if it came to a divert; ZZZ1 or ZZZ were our best options. Shortly after the passenger was on the floor; he deteriorated quickly. They started CPR and had the AED out. As soon as we were notified that CPR was in progress; we diverted to ZZZ. CPR was being performed by the doctors for around 25min until we reached the gate. Upon arrival at the gate; the ZZZ first responders performed CPR for another 30min. After about an hour total of CPR; first responders were able to get a pulse. They transferred the passenger to a gurney and took him to the hospital. The blood pressure cuffs in our medical kits are unusable. This is my second medical diversion where the doctors who have been gracious to help are really upset that the type of blood pressure cuff in the medical kit is useless. The stethoscope was also unusable because of missing pads.Suggestions: A different blood pressure cuff that actually works. A better check of the contents of the in-flight medical kit so that an unusable stethoscope with missing pads isn't in the kit.