Limitations of threshold-based brain oxygen monitoring for seizure detection

Abstract

Background Brain tissue oxygen (PbtO 2) monitors are utilized in a threshold-based fashion, triggering actions based on the presumption of tissue compromise when PbtO 2 is less than 20 mmHg. Some early published practice guidelines suggest that seizure is a potential culprit when PbtO 2 crosses this threshold; evidence for this is not well defined. Methods Data were collected manually as part of a prospective observational database. PbtO 2 monitors and continuous electroencephalogram (cEEG) were placed by clinical protocol in aneurysmal subarachnoid hemorrhage (aSAH) or traumatic brain injury (TBI) patients with a Glasgow Coma Scale (GCS) ≤ 8. Eight patients with discrete seizures during an overlapping monitored period were identified. Probability of seizure when PbtO 2 value was <20 mmHg (and the inverse) were calculated. Results There were 343 distinct seizure episodes and 1797 PbtO 2 measurements. 8.9% of seizures were followed by a PbtO 2 value below 20 mmHg. Of all observed low PbtO 2 values, 3.8% were associated with seizure. Seizure length did not influence PbtO 2. Two patients with the highest number of seizures developed low PbtO 2 values post-seizure. Conclusions Seizures were neither associated with a PbtO 2 value of <20 mmHg nor associated with a drop in PbtO 2 value across a clinically significant threshold. However, we cannot rule out the existence of any relationship between PbtO 2 and seizure with this limited data set. Prospective research using electronically recorded data is required to more effectively examine the relationship between PbtO 2 and seizure. © Springer Science+Business Media, LLC 2011.