While you are trying to get an<unk>  to get a crude estimate of the systolic pressure (especially if automatic cuff BP machine is not working due to BP too low) you can try one of the following:
POCUS blood pressure: inflate cuff and watch when you stop getting flow stops on ultrasound of brachial artery.
SpO2 blood pressure: inflate cuff and watch when you stop getting SpO2 on the finger.<unk>  still preferred over the above methods since these are just rough estimates.
POCUS blood pressure: inflate cuff and watch when you stop getting flow stops on ultrasound of brachial artery.
SpO2 blood pressure: inflate cuff and watch when you stop getting SpO2 on the finger.
Arterial line
Rapid infusion catheter
Sheath introducer
Pediatric central line
Intraosseous access
Central venous catheterization
Vital signs 
Pulmonary artery catheter