gms | German Medical Science

Objective: ICP probes need to be evaluated for their reliability and accuracy prior to clinical usage. Especially telemetric devices have to be tested repeatedly in long-term studies regarding their zero point drift. A standardized model for repetitive ICP measurements with the ability of generating ICP measuring points in a relevant range is still missing.

Method: We utilized 6 female pigs (German landrace; mean body weight 59.5 ± 18.4 kg) for experiments. A ventricular catheter connected wit a burr hole reservoir was implanted. ICP was measured directly as cm H₂O within a riser tube after percutaneous cannulation of the reservoir and afterward calculated as mm Hg. Animals were placed in lateral decubitus position. A non-invasive intraperitoneal pressure (IPP) measurement was established (intra-vesical). A Veress needle was placed directly caudal to the umbilicus for generating a pneumoperitoneum. Measurements of ICP, IPP, MAP and respiratory parameters were performed at baseline IPP and after CO₂ insufflation (Endoflator, Fa. Karl Storz, Germany) over the Veress needle to IPP levels of 20 and 30 mm Hg.

Results: All procedures were performed without complications (6/n=6). Baseline IPP in lateral decubitus position referenced to median line was 9.8 (± 2) mm Hg, while corresponding ICP was 10 (± 2.2) mm Hg. After IPP elevation to 20 mm Hg, ICP increased to 18.8 (± 1.9) mm Hg. At 30 mm Hg IPP, ICP increased to 22.8 (± 2.8) mm Hg. Except peak airway pressure, all other parameters were kept constantly. Mean ICP variation in the individual subject was 13.4 (± 2.5) mm Hg, while a ICP range from minimum 9 to maximum 31 mm Hg was documented.

Conclusions: We report a large animal model that allows (I) to measure repetitively the ICP and (II) to manipulate the ICP within a large pressure range by controlled IPP changes due to pneumoperitoneum.