How low can someone's blood pressure go before they go into cardiac arrest or shock?

SBP<90/ in shock: Shock is typically defined as a systolic BP less than 90. This is usually inadequate an explanation because the physiologic definition implies a drop in BP such that visceral organ blood flow is so reduced that mentation is altered and multisystem failure begins (with cns, renal, liver failure). Lactic acid builds up when a lack of perfusion (and hence oxygen delivery) ensues.

Time: The longer the mean BP lower than 65 the more likely.