I will update this as I remember. Feel free to comment below any medical talk that should be added to this list.

Colonoscopy - camera test into the bottom end to look for pathologies in the bowel.

Coro+/-PCI - Coronary Angiography +/- Percutaneous Coronary Intervention: a contrast study into the heart vessels to look for blockage, plus or minus inserting stent(s) to clear said blockage.

CPR - CardioPulmonary Resuscitation: the attempt to restore a stopped heartbeat with compressions, breathing gear, plus or minus electrical shocks.

CT scan - also known as CAT scan: a (usually contrast-involved) computerised scan with radiation that provides a 3D image of the body.

Echocardiogram - also known as 'Echo': an ultrasound investigation to see how well a heart pumps and to look for heart valve problems.

MRI scan - a magnetism-based scan without radiation that provides a 3D image of the body.

OGD - OesophagoGastroDuodenoscopy, also known as upper GI endoscopy (UGIE): a camera test into the mouth and stomach to look for problems.

PPN: see TPN

RRT - Renal Replacement Therapy: a method to replace or prolong kidney function. Includes HD (Haemodialysis; a machine that filters blood) and PD (Peritoneal Dialysis; using the lining in the abdomen to filter in and out waste products).

TPN - Total Parenteral Nutrition; a non-oral way of giving the body nutrition via a plastic tube into the body. PPN is Partial Parenteral Nutrition, the partial variant.