An adult patient who sustained a severe head trauma has been intubated and is being manually ventilated via a bag-mask device at a rate of 18 breaths/minute with clear breath sounds bilaterally. the patient has received one intravenous fluid bolus of 500 ml of warmed isotonic crystalloid solution. the paco2 is 30 mm hg (4.0 kpa), and the pulse oximetry is 92%. bp is 142/70 mm hg. what is the most important intervention to manage cerebral blood flow?