Microdialysis patterns in subarachnoid hemorrhage patients with focus on ischemic events and brain interstitial glutamine levels.
BACKGROUND
This observational microdialysis (MD) study of 33 subarachnoid hemorrhage patients explores brain interstitial levels of glutamine, glutamate, lactate and pyruvate, and their relationship to clinical status and clinical course at the neurointensive care unit.


METHODS
The focus was on ischemic events, defined by clinical criteria or by radiology, and the significance of brain interstitial glutamine levels and lactate/pyruvate (L/P) ratio.


RESULTS
Eleven out of 12 periods with an ischemic MD pattern, defined as lactate/pyruvate (L/P) ratios exceeding 40, were either related to delayed ischemic neurological deficits (DIND) or CT-verified infarcts, confirming that L/P above 40 is a specific ischemic and pathological MD measure. Poor admittance WFNS grade (WFNS 4-5) patients had lower glutamine at the onset of monitoring than what good admittance WFNS grade (WFNS 1-3) patients had (P < 0.05). Interstitial glutamine increased over time in most patients. A "glutamine surge" was defined as a period where the interstitial glutamine concentration increased at least 150 microM over 12 h. Fifteen patients had a DIND and associated MD patterns were glutamine surges (n = 12) and/or L/P>40 (n = 6). Seven patients received vasospasm treatment; in five of these the only DIND-associated MD pattern was a glutamine surge. Seventy percent of the glutamine surges occurred during ongoing propofol sedation, and there was no association between extubations and glutamine surges. There was no difference in mean glutamine levels during the monitoring period between patients with favorable 6-month outcome and patients with poor 6-month outcome.


CONCLUSIONS
We suggest that an increasing interstitial glutamine trend is a dynamic sign of augmented astrocytic metabolism with accelerated glutamate uptake and glutamine synthesis. This pattern is presumably present in metabolically challenged, but yet not overt ischemic tissue.
Samuelsson
Carolina
C
Department of Neuroscience, Neurosurgery, Uppsala University Hospital, Uppsala, Sweden. Carolina.samuelsson@neurokir.uu.se
Hillered
Lars
L
Enblad
Per
P
Ronne-Engström
Elisabeth
E
D001921:Brain / Q000378:metabolism*; D002545:Brain Ischemia / Q000150:complications / Q000000981:diagnostic imaging / Q000378:metabolism*; D002544:Cerebral Infarction / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000209:etiology / Q000378:metabolism; D005260:Female; D005973:Glutamine / Q000378:metabolism*; D006801:Humans; D008297:Male; D017551:Microdialysis; D008875:Middle Aged; D008991:Monitoring, Physiologic; D013345:Subarachnoid Hemorrhage / Q000150:complications / Q000000981:diagnostic imaging / Q000378:metabolism*; D014057:Tomography, X-Ray Computed
D005973:Glutamine