EFFECT OF HYPERVENTILATION, MANNITOL, AND VENTRICULOSTOMY DRAINAGE ONCEREBRAL BLOOD-FLOW AFTER HEAD-INJURY

Therapies to lower intracranial pressure (ICP) after traumatic brain i njury (TBI) include hyperventilation (HV), intravenous mannitol (IM), and cerebrospinal fluid drainage from a ventriculostomy (DV), To deter mine the effects of these therapies on cerebral blood flow (CBF), fibe roptic oximetry was used to measure jugular venous O-2 saturation (Sjv O2) as an index of the CBF to cerebral metabolic rate for O-2 (CMRO(2) ) ratio after IM (25 g IV for more than 5 min), DV (3 min), or HV (inc rease respiratory rate by 4) therapy for elevated ICP, Assuming CMRO(2 ) is constant, changes in SjvO2 reflect changes in CBF, Continuous mea surements of SjvO2, ICP, blood pressure, artery rial O-2 saturation, a nd end-tidal CO2 were obtained in 22 patients with a Glasgow Coma Scal e score of 5.3 +/- 0.4 (mean +/- SD) in the first 5 days after TBI, Th erapy was initiated a total of 196 times when ICP was > 15 mm Hg for > 5 minutes, and measurements made at 20 minutes after treatment were c ompared with those made just before, After DV, ICP fell in 90% of the observations by 8.6 +/- 0.7 mm Hg (mean +/- SEM, n = 119); after IM, I CP fell in 90% of the observations by 7.4 +/- 0.7 mm Hg (n = 43); and after HV, ICP fell in 88% of the observations by 6.3 +/- 1.2 mm Hg (n = 14), In patients where ICP fell, SjvO2 increased by 2.49 +/- 0.7% sa turation (from 68.0 +/- 1.3%) with IM, but only by 0.39 +/- 0.4% satur ation (from 67.2 +/- 0.9%) with DV, When HV resulted in a decrease in ICP, SjvO2 decreased by 7.7 +/- 1.0% saturation (from 63.4 +/- 2.5%), The magnitude of the effect was assessed by considering the change in SjvO2 resulting from a measured change in ICP (SjvO2/ICP). For each de crease in ICP of 1 mm Hg, SjvO2 increased 0.53 +/- 0.14% saturation wi th IM, 0.10 +/- 0.10 with DV, and decreased by 1.95 +/- 0.53 with HV, In this study DV, IM, and HV effectively reduced elevated ICP after ce rebral injury, For a given change in ICP, however, LM increased the CB F to CMRO(2) ratio nearly five times as much as DV, whereas HV decreas ed this ratio in all cases, These data suggest that mannitol improves CBF while reducing ICP; HV, although effective at reducing ICP, result s in marked lowering of CBF and should be used cautiously.