Background The association between intracranial pressure (ICP) and different shunt valve opening pressures in relation to body positions is fundamental for understanding the physiological function of the shunt.

Objective To analyse the ICP and ICP wave amplitude (AMP) at different shunt settings and body positions in patients with hydrocephalus.

Methods In this prospective study 15 patients with communicating hydrocephalus were implanted with a ligated adjustable ventriculoperitoneal shunt. They also received a portable intraparenchymatous ICP-monitoring device. Postoperative ICP and AMP were recorded with the patients in three different body positions (supine, sitting and walking) and with the shunt ligated and open at high, medium and low valve settings. In each patient 12 10 min segments were coded, blinded and analysed for mean ICP and mean AMP using an automated computer algorithm.

Results Mean ICP and mean AMP were lower at all three valve settings compared with the ligated shunt state (p<0.001). Overall, when compared with the supine position, mean ICP was 11.5±1.1 (mean±SD) mm Hg lower when sitting and 10.5±1.1 mm Hg lower when walking (p<0.001). Mean ICP was overall 1.1 mm Hg higher (p=0.042) when walking compared with sitting. The maximal adjustability difference (highest vs lowest valve setting) was 4.4 mm Hg.

Conclusions Changing from a supine to an upright position reduced ICP while AMP only increased at trend level. Lowering of the shunt valve opening pressure decreased ICP and AMP but the difference in mean ICP in vivo between the highest and lowest opening pressures was less than half that previously observed in vitro.