Is it useful to measure supratentorial ICP in the presence of a posterior fossa lesion? Absence of transtentorial pressure gradients in an animal model

Previous studies with animal models of supratentorial ICP elevation have de monstrated a pressure gradient between the supratentorial and the infratent orial compartments. The present study was designed to investigate the possi ble presence of such a gradient in the case of infratentorial ICP elevation . An inflatable infratentorial balloon catheter was implanted in seven dome stic pigs. The infratentorial ICP (ICPi) was measured in the left cerebella r hemisphere, and the supratentorial ICP (ICPs) was measured in the left ce rebral hemisphere. The corresponding pulse amplitudes (ICPi-PA, ICPs-PA) we re recorded in both compartments, and the cerebral perfusion pressure (CPP) was calculated. ICPi and ICPs values prior to balloon inflation were 4.4 ( SD 2.2) and 4.1 (SD 2.3) mm Hg, respectively, and increased to 63.1 (SD 32. 6) and 62.3 (SD 28.1) mmHg after balloon inflation. ICPi-PA rose from 3.1 ( SD 0.43) to 12.8 (SD 8.0) mmHg, and ICPs-PA rose from 3.2 (SD 0.63) to 13.0 (SD 7.1) mmHg. CPP decreased from 86.1 (SD 12.0) to 55.4 (SD 11.6) mm Hg. The paired difference between ICPi and ICPs values was 0.44 (SD 1.96) mmHg, and the paired difference of ICP amplitudes was 0.03 (SD 1.19) mmHg. All t hese differences in infratentorial and supratentorial values were statistic ally not significant. In conclusion, infratentorial ICP elevation in the pr esented pig model leads to a uniform ICP elevation in the intracranial spac e without development of a considerable pressure gradient below and above t he tentorium. In the low pressure part of the ICP curve, cerebrospinal flui d connects the compartments and contributes to the pressure equilibrium. Th e early obstruction of the foramen magnum by intruding cerebellar tissue se ems to isolate the infratentorial from the spinal compartment. In the high- pressure part of the curve, the upwards cerebellar transtentorial herniatio n takes over the pressure transfer, and the whole intracranial space can be considered as a single compartment in the pig.