Revolutionizing Brain Death Diagnosis: Study reveals Impact of Non-Invasive Multimodal Neuromonitoring

Recently published study focuses on the utility of non-invasive multimodal brain monitoring (NI-MMM) as an adjunctive diagnostic tool for determining brain death, particularly in challenging apnoea test scenarios. Employing various monitoring modalities-transcranial Doppler (TCD), bilateral regional cerebral oxygen saturation (rSO₂) via near-infrared spectroscopy (NIRS), optic nerve sheath diameter (ONSD), and bispectral index (BIS)-enhances the diagnostic process when clinical criteria alone are insufficient or when doubts arise among medical professionals.

Case Series Overview

In a retrospective case series involving three patients in a neuro-intensive care unit (NICU) with severe acute brain injuries and poor Glasgow Coma Scale (GCS) scores, NI-MMM was used alongside traditional evaluation methods. Despite maximal supportive treatment, patients exhibited clinical signs indicative of brain death with absent brainstem reflexes. The traditional apnoea tests were deemed unfeasible due to hemodynamic instability in all instances. NI-MMM results from the three cases exhibited a coherent alignment with brain death diagnostic criteria. The TCD assessments indicated flow reversals in both anterior and posterior cerebral circulations, a hallmark of brain death diagnosis. All three patients demonstrated a bilateral BIS of 0, corresponding to complete electrical silence and confirming the absence of brain activity. Additionally, ONSD measurements were suggestive of elevated intracranial pressure (ICP), with mean ONSD values reaching 0.69 cm, exceeding the critical threshold indicative of elevated ICP.

rSO₂ Data Findings

The rSO₂ data revealed baseline values fluctuating in the 50%-60% range, varying according to extracranial influences. In the context of the study, significant findings emerged when a forehead tourniquet was applied to mitigate the effects of extracranial blood flow. A dramatic drop in rSO₂ by 40% from baseline was observed following the removal of the tourniquet, corroborating the hypothesis of high variability based on the presence of extracranial contamination.

Case 3 Insights

Particularly noteworthy was case 3, where a challenge involving 100% FiO₂ was administered during the apnoea test. This intervention led to pronounced increases in rSO₂ values on both sides, although the increase was notably higher on the initially lower right side. This response suggests that the underlying non-metabolizing brain tissue was not utilizing the additional oxygen, further validating the absence of cerebral circulatory function. The findings highlighted the importance of interpreting trends rather than absolute rSO₂ values when ascertaining brain death, given the complexities associated with NIRS readings influenced by deoxygenated blood flow at the capillary level. Observations underscore that while a multitude of physiological parameters can aid in confirming brain death, meticulous consideration is required in their interpretation.

Conclusions and Future Directions

Conclusions drawn from the case series emphasize that NI-MMM serves as a valuable tool in the diagnostic process of brain death, especially when standard clinical diagnostic criteria may not suffice. The non-invasive nature, portability, and ease of interpretation of these monitoring modalities provide significant advantages in critical care settings. Future research and larger-scale investigations are merited to further explore the combined effectiveness of these non-invasive monitoring techniques in enhancing brain death diagnosis, particularly in complex clinical presentations.

Key Points

- -Utility of NI-MMM-: Non-invasive multimodal brain monitoring (NI-MMM) is proposed as an adjunctive diagnostic tool for determining brain death, particularly useful in challenging apnoea test situations, integrating modalities such as transcranial Doppler (TCD), regional cerebral oxygen saturation (rSO₂) via near-infrared spectroscopy (NIRS), optic nerve sheath diameter (ONSD), and bispectral index (BIS) to augment traditional clinical criteria.

- -Retrospective Case Series-: A case series involving three patients in a neuro-intensive care unit (NICU) with severe acute brain injuries demonstrated the application of NI-MMM alongside conventional methods, where traditional apnoea tests were rendered unfeasible due to hemodynamic instability, yet clinical signs indicated brain death despite maximally supportive treatment.

- -Alignment with Diagnostic Criteria-: Results from NI-MMM in all three cases were consistent with brain death diagnostics; TCD showed flow reversals in cerebral circulations, BIS measurements indicated complete electrical silence (BIS of 0), and ONSD assessments suggested elevated intracranial pressure (ICP) with mean values exceeding the critical threshold.

- -Variability in rSO₂ Measurements-: rSO₂ baseline values fluctuating between 50%-60% were influenced by extracranial factors, with a notable 40% decrease in rSO₂ following tourniquet removal, highlighting the significant impact of extracranial blood flow on NIRS measurements.

- -Case 3 Findings-: In case 3, administering 100% FiO₂ during the apnoea test led to substantial increases in rSO₂ values, especially on the initially lower right side, indicating that non-metabolizing brain tissue was not utilizing additional oxygen, thereby confirming the absence of cerebral circulatory function.

- -Conclusions and Recommendations-: NI-MMM is affirmed as a beneficial diagnostic tool for brain death under complex conditions, emphasizing the need for further research and larger-scale studies to assess the effectiveness of these non-invasive monitoring techniques in enhancing diagnostic accuracy in critical care environments.

Reference –

Rohini M. Surve et al. (2025). Role Of A Non-Invasive Multimodal Brain Monitoring Approach In Supplementing The Clinical Diagnosis Of Brain Death: Observations From A Case Series. *Indian Journal Of Anaesthesia*. https://doi.org/10.4103/ija.ija_124_24.