Drift of the Bowman Hemedex® cerebral blood flow monitor between calibration cycles.
BACKGROUND
Since its introduction into clinical practice, the Bowman Hemedex® regional cerebral blood flow (CBF) monitor has provided a valuable tool for the bedside assessment of CBF in neurointensive care. The purpose of our study was to estimate the accuracy of CBF measurements between automatically performed self-calibration cycles at regular intervals.


METHODS
We analyzed data from 75 CBF probes, predominantly implanted into patients after severe subarachnoid hemorrhage. Automatic recalibration of the regional CBF device was performed every 30 min. CBF data were averaged once per minute and the measurement cycles pooled. Statistical analysis was performed with generalized additive modeling and bootstrapping methods.


RESULTS
Mean regional CBF was 24 mL/100 g/min after calibration and showed a mean drift of 2.3 mL/100 g/min per measurement cycle (p < 0.001). In every patient, the drift over the measurement cycle followed an exponential trend, with large heterogeneity between patients (-3.67 to 12.0 mL/100 g/min). A highly significant difference in drift was found for the internal software versions of the monitoring devices (p < 0.001).


CONCLUSIONS
Data from the Bowman Hemedex® regional CBF monitor shows an upward measurement drift of clinically relevant magnitude. As the drift follows a stable exponential function over time, recalculation of drift-corrected data is possible after termination of the measurement.
Department of Neurosurgery, Charité University, Berlin, Germany. stefan.wolf@charite.de
Stefan
S
Wolf
P
P
Vajkoczy
J
J
Dengler
L
L
Schürer
P
P
Horn
D001776:Blood Circulation Time; D001783:Blood Flow Velocity / Q000502:physiology; D001831:Body Temperature; D002138:Calibration; D002540:Cerebral Cortex / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D015233:Models, Statistical; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods*; D012039:Regional Blood Flow / Q000502:physiology