Transcranial Doppler as a screening test to exclude intracranial hypertension in brain-injured patients: the IMPRESSIT-2 prospective multicenter international study

Background Alternative noninvasive methods capable of excluding intracranial hypertension through use of transcranial Doppler (ICP tcd ) in situations where invasive methods cannot be used or are not available would be useful during the management of acutely brain-injured patients. The objective of this study was to determine whether ICP tcd can be considered a reliable screening test compared to the reference standard method, invasive ICP monitoring (ICP i ), in excluding the presence of intracranial hypertension. Methods This was a prospective, international, multicenter, unblinded, diagnostic accuracy study comparing the index test (ICP tcd ) with a reference standard (ICP i ), defined as the best available method for establishing the presence or absence of the condition of interest (i.e., intracranial hypertension). Acute brain-injured patients pertaining to one of four categories: traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), intracerebral hemorrhage (ICH) or ischemic stroke (IS) requiring ICP i monitoring, were enrolled in 16 international intensive care units. ICP i measurements (reference test) were compared to simultaneous ICP tcd measurements ( index test) at three different timepoints: before, immediately after and 2 to 3 h following ICP i catheter insertion. Sensitivity, specificity, positive (PPV) and negative predictive values (NPV) were calculated at three different ICP i thresholds (> 20, > 22 and > 25 mmHg) to assess ICP tcd as a bedside real-practice screening method. A receiver operating characteristic (ROC) curve analysis with the area under the curve (AUC) was used to evaluate the discriminative accuracy and predictive capability of ICP tcd. Results Two hundred and sixty-two patients were recruited for final analysis. Intracranial hypertension (> 22 mmHg) occurred in 87 patients (33.2%). The total number of paired comparisons between ICP tcd and ICP i was 687. The NPV was elevated (ICP > 20 mmHg = 91.3%, > 22 mmHg = 95.6%, > 25 mmHg = 98.6%), indicating high discriminant accuracy of ICP tcd in excluding intracranial hypertension. Concordance correlation between ICP tcd and ICP i was 33.3% (95% CI 25.6–40.5%), and Bland–Altman showed a mean bias of -3.3 mmHg. The optimal ICP tcd threshold for ruling out intracranial hypertension was 20.5 mmHg, corresponding to a sensitivity of 70% (95% CI 40.7–92.6%) and a specificity of 72% (95% CI 51.9–94.0%) with an AUC of 76% (95% CI 65.6–85.5%). Conclusions and relevance ICP tcd has a high NPV in ruling out intracranial hypertension and may be useful to clinicians in situations where invasive methods cannot be used or not available. Trial registration : NCT02322970 .