Vector Angle Analysis of Multimodal Neuromonitoring Data for Continuous Prediction of Delayed Cerebral Ischemia

Abstract

Background: Dysfunctional cerebral autoregulation often precedes delayed cerebral ischemia (DCI). Currently, there are no data-driven techniques that leverage this information to predict DCI in real time. Our hypothesis is that information using continuous updated analyses of multimodal neuromonitoring and cerebral autoregulation can be deployed to predict DCI.

Methods: Time series values of intracranial pressure, brain tissue oxygenation, cerebral perfusion pressure (CPP), optimal CPP (CPPOpt), ΔCPP (CPP - CPPOpt), mean arterial pressure, and pressure reactivity index were combined and summarized as vectors. A validated temporal signal angle measurement was modified into a classification algorithm that incorporates hourly data. The time-varying temporal signal angle measurement (TTSAM) algorithm classifies DCI at varying time points by vectorizing and computing the angle between the test and reference time signals. The patient is classified as DCI+ if the error between the time-varying test vector and DCI+ reference vector is smaller than that between the time-varying test vector and DCI- reference vector. Finally, prediction at time point t is calculated as the majority voting over all the available signals. The leave-one-patient-out cross-validation technique was used to train and report the performance of the algorithms. The TTSAM and classifier performance was determined by balanced accuracy, F1 score, true positive, true negative, false positive, and false negative over time.

Results: One hundred thirty-one patients with aneurysmal subarachnoid hemorrhage who underwent multimodal neuromonitoring were identified from two centers (Columbia University: 52 [39.7%], Aachen University: 79 [60.3%]) and included in the analysis. Sixty-four (48.5%) patients had DCI, and DCI was diagnosed 7.2 ± 3.3 days after hemorrhage. The TTSAM algorithm achieved a balanced accuracy of 67.3% and an F1 score of 0.68 at 165 h (6.9 days) from bleed day with a true positive of 0.83, false positive of 0.16, true negative of 0.51, and false negative of 0.49.

Conclusions: A TTSAM algorithm using multimodal neuromonitoring and cerebral autoregulation calculations shows promise to classify DCI in real time.

Keywords: Aneurysmal subarachnoid hemorrhage; Cerebral autoregulation; Classification; Machine learning; Neurocritical care.

Fig. 1

Framework of the classification algorithm. a Workflow diagram describing the steps to classify DCI. b Visualization of the angle analysis algorithm, comparing the test patient’s data (in blue) with the reference DCI+ (red) and reference DCI− (green). The TTSAM classifies the patient as DCI+ if the total error between the test vectors and DCI+ reference vectors is smaller than that between the test vectors and DCI− reference vectors. ABP mean arterial pressure, CPP cerebral perfusion pressure, CPPOpt optimal cerebral perfusion pressure, DCI delayed cerebral ischemia, ICP intracranial pressure, PbtO2 brain tissue oxygenation, PRx pressure reactivity index, TTSAM time-varying temporal signal angle measurement, ΔCPP CPP – CPPOpt.

Fig. 2

Performance of the angle analysis approach. a True positive (TP), false positive (FP), true negative (TN), and false negative (FN) of the proposed algorithm. b Balanced accuracy of the proposed algorithm was consistently over 60% starting at 105 h after the bleed day