Comparison of a new brain tissue oxygenation measuring probe with the established standard

Introduction

Besides intracranial pressure (ICP) monitoring, brain tissue oxygenation (p_btO₂) monitoring with the Licox system (Integra Neuroscience, Germany) is on the verge of clinical routine in acute brain injury. Recently, a new p_btO₂ probe by a different manufacturer (Raumedic AG, Germany) was introduced into the market. As this new probe facilitates measurement of ICP as well, its use would reduce invasiveness of multimodal neuromonitoring. Therefore, we investigated the agreement of p_btO₂ values of both probes in patients with aneurysmal subarachnoid hemorrhage necessitating ICP and p_btO₂ monitoring.

Methods

Eight patients with p_btO₂ monitoring probes of both types implanted side by side in the same vascular territory were investigated. Multimodal monitoring data were stored online with dedicated software. Data were analyzed using the method proposed by Bland and Altman [1].

Results

The mean measurement time per patient was 8.6 days. All data pooled, the mean bias was -0.66 mmHg. The precision range (two standard deviations of the bias) was -32.9 to 32.6 mmHg. The Licox probe showed a tendency for higher values at high p_btO₂, while the Raumedic probe showed higher values at low p_btO₂. Analysis of single patients revealed no discernible pattern in the relationship of measurement values of both probes. Three of the new probes ceased to function prematurely.

Conclusion

Our data suggest that measurements of both p_btO₂ probes cannot be interchanged. No easy algorithm for conversion of measurement data from one system to the other is available. More rigorous bench testing is necessary before implementation of the new system in the clinical routine.