Non-invasive assessment of ICP during infusion test using Transcranial Doppler Ultrasonography

Background

Transcranial Doppler (TCD) based methods have been used to estimate ICP noninvasively (nICP), however their relative accuracy varies between different types of intracranial hypertension: vasogenic, CSF circulatory or secondary to brain volumetric changes (oedema, contusion, hematoma, etc). This study aimed to compare four nICP methods in a prospective cohort of hydrocephalus patients whose CSF dynamics was investigated using infusion tests involving controllable test-rise of ICP.

Methods

FV, ICP and non-invasive ABP were recorded in 53 patients diagnosed for hydrocephalus. nICP methods were based on: I) interaction between FV and ABP using black-box model (nICP_BB); II) diastolic FV (nICP_FVd); III) critical closing pressure (nICP_CrCP) and IV) TCD-derived pulsatility index (nICP_PI). Correlation between rise in ICP (∆ICP) and ∆nICP and averaged correlations for changes in time between ICP and nICP during infusion test were investigated.

Results

All nICP formulas overestimated ICP at baseline (p<0.005): nICP_BB 10.76 (15.08-7.30); nICP_FVd 16.97 (22.56- 11.64); nICP_CrCP 18.34 (20.38-14.89); nICP_PI 16.57 (17.46-16.06). At plateau of ICP during infusion test, only nICP_BB and nICP_PI presented significant difference from ICP. From baseline to plateau, all nICPs estimators increased significantly (paired t-test, p<0.05). Correlations between ∆ICP and ∆nICP were better represented by ICPn_PI and ICPn_BB: 0.45 and 0.30 (p<0.05). nICP_FVd and nICP_CrCP presented non-significant correlations: -0.17 (p=0.21), 0.21 (p=0.13). For changes in ICP during individual infusion test ICPn_PI, ICPn_BB and ICPn_FVd presented similar correlations with ICP: 0.39±0.40, 0.39±0.43 and 0.35±0.41 respectively. ICPn_CrCP presented a weaker correlation (R=0.29±0.24). In those cases where changes of ICP related to vasogenic fluctuations (plateu wabes, B waves) overlapped rise related to CSF infusion, time- correlation between real and estimated ICP seemed to be remarkably better.

Conclusions

Out of the 4 methods, nICP_PI was the one with best performance for predicting changes in ∆ICP during infusion test, followed by nICP_BB. nICP_FVd and nICP_CrCP showed unreliable correlations. Changes of ICP observed during the test were expressed by nICP values with only a moderate correlations. Vasogenic components of ICP seemed to be easier to estimate with TCD, than component related to increased CSF circulation.