Short-Term Volume Loading Effects on Estimated Intracranial Pressure in Human Volunteers

BACKGROUND: Short-term fluid loading is used as part of post-spaceflight medical procedures and clinical treatment in hospitals. Hypervolemia with hemodilution induced by rapid fluid infusion reportedly impaired dynamic cerebral autoregulation. However, the effects on intracranial pressure (ICP) remain unknown.Therefore, we estimated ICP noninvasively (nICP) to examine whether rapid fluid infusion would raise ICP. METHODS: Twelve healthy male volunteers underwent two discrete normal saline (NS) infusions (15 and 30 ml . kg(-1) stages, NS-15 and NS-30, respectively) at a rate of 100 ml . min(-1).The cerebral blood flow (CBF) velocity (CBFv) waveform from the middle cerebral artery obtained by transcranial Doppler ultrasonography was recorded, as was the arterial blood pressure (ABP) waveform at the radial artery obtained by tonometry. We then used these waveforms to calculate nICP, cerebral artery compliance, and the pulsatility index (PI) in an intracranial hydraulic model. RESULTS: nICP increased significantly in both infusion stages from preinfusion (preinfusion: 7.6 +/- 3.4 mmHg; NS-15:10.9 +/- 3.3 mmHg; NS-30: 11.7 +/- 4.2 mmHg). No significant changes were observed in cerebral artery compliance or PI. Although ABP did not change in any stage, CBFv increased significantly (preinfusion: 67 +/- 10 cm . s(-1); NS-15:72 +/- 12 cm . s(-1); NS-30: 73 +/- 12 cm . s(-1)). DISCUSSION: Hypervolemia with hemodilution induced by rapid fluid infusion caused increases in nICP and CBFv. No changes were observed in cerebral artery compliance or PI related to cerebrovascular impedance. These findings suggest that rapid fluid infusion may raise ICP with increased CBF.