SBP less than 90 does not mean poor perfusion, look at the Mean Arterial Pressure. Assess your patient. If this was an automatic pressure, check a manual one. Ask your patient if they are light headed, do they have a headache, do they feel dizzy or are they nauseated. Check what their previous pressures were in the last 12 or 24 hours. Are they a fresh post op, are they bleeding, is this a cardiac patient, what does their EKG show? Do they look in distress? What did they look like during a prior assessment? What medications where they given in the past 2 hours? Lots of critical thinking to be done in a minute or two prior to calling a rapid response team in. I am assuming you checked all critical possiblities of a slightly low SBP and nothing to warrant a RRT. Document your assessment and leave knowing you did what you are supposed to do.