Continuous cerebral compliance monitoring in severe head injury: Its relationship with intracranial pressure and cerebral perfusion pressure

Cerebral Compliance describes the ability of cranial content to accommodate volume variations. Intracranial vascular compartment is thought to be one of the most important determinants of Compliance. Cerebral perfusion pressure (CPP) has a significant influence upon the calibre of cerebral vessels and consequently, upon blood volume. This study was designed to investigate the influence of CPP on intracranial volumes balance, described by cerebral compliance, in severe traumatic brain injured patients (TBI). Nine TBIs were studied. The Spiegelberg ventricular catheter continuously measured ICP and Compliance. Compliance, CPP and ICP were digitally collected for a total of 737 hours of monitoring (44239 total data). Compliance was lower at CPP < 60 than at CPP greater than or equal to 60 (0.51 +/- 0.3 versus 0.64 +/- 0.3 ml/mmHg). The ICP level influenced the relation between CPP and Compliance. At ICP < 20 (LICP; 80.3% of data) Compliance and CPP were not significantly related. At ICP greater than or equal to 20 mmHg (HICP; 19.7% of data), Compliance varied with changes in CPP. When CPP < 60 mmHg, Compliance showed a trend to decrease as CPP decreased (R-2 = 0.85). At CPP greater than or equal to 60 mmHg Compliance decreased with CPP (R-2 = 0.83). In the range of low CPP vaso-paralysis is impending. However, when ICP is pathological, at high CPP our results may express vasodilatation instead of expected vasoconstriction from normal autoregulation.