system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we give pressors in patients with shock?

If increasing systemic vascular resistance (SVR) increases the afterload, doesn't that reduce stroke volume?
gpt
You're increasing SVR in a situation where the SVR is life-threateningly low. Increasing the SVR with vasopressin is one way your body itself manages perfusion, now it just needs help. Also when the SVR is too low, venous return would also suffer, further decreasing CO and systemic hypoxemia. 

In cardiac babies, it's not uncommon to have a fresh post-op Norwood on drips of epi, vaso, and norepi all at the same time. All work slightly differently, so you can get pretty precise BP management while minimizing side effects (like increased HR with epi, or acute kidney injury with too much vaso) since the doses are so low (0.01 mcg/kg/min)

Edit: in the above situation, you're also dealing  with a mixed systemic and pulmonary blood flow system, so you're balancing SVR and PVR. Changing things such as fiO2, RR, and TV on the vent can have just as significant an impact on BP.