Posture-related changes in the pressure environment of the ventriculoperitoneal shunt system

OBJECT: The purpose of this study is to clarify the whole pressure environment of the ventriculoperitoneal (VP) shunt system in patients with successfully treated hydrocephalus and to determine which factor of the pressure environment has a preventive effect on overdrainage. METHODS: Thirteen patients with hydrocephalus who had been treated with VP shunt therapy by using a Codman-Hakim programmable valve without incidence of overdrainage were examined. The authors evaluated intracranial pressure (ICP), intraabdominal pressure (IAP), hydrostatic pressure (HP), and the perfusion pressure (PP) of the shunt system with the patients both supine and sitting. With patients supine, ICP, IAP, and HP were 4.6 +/- 3 mm Hg, 5.7 +/- 3.3 mm Hg, and 3.3 +/- 1 mm Hg, respectively. As a result, the PP was only 2.2 +/- 4.9 mm Hg. When the patients sat up, the IAP increased to 14.7 +/- 4.8 mm Hg, and ICP decreased to-- 14.2 +/- 4.5 mm Hg. The increased IAP and decreased ICP offset 67% of the HP (42.9 +/- 3.5 mm Hg), and consequently the PP (14 +/- 6.3 mm Hg) corresponded to only 33% of HP. CONCLUSIONS: The results observed in patients indicated that IAP as well as ICP play an important role in VP shunt therapy and that the increased IAP and the decreased ICP in patients placed in the upright position allow them to adapt to the siphoning effect and for overdrainage thereby to be avoided.