Introduction: Brain hypoxia and metabolic dysfunction are associated with poor outcome in patients with severe brain injury (sBI). We sought to determine the relationship between multimodality monitoring (MMM) parameters and impaired cerebral metabolism in patients with sBI.
Methods: Data from patients with severe brain injury that underwent multi modality monitoring; intracranial pressure (ICP), brain oxygen tension (PbtO2), and transcranial oxygen saturation (NIRS) were analyzed. Goal directed therapy was to maintain ICP less than 20 mmHg, cerebral perfusion pressure (CPP) greater than 60 mmHg; PbtO2 greater than 20 mmHg, and NIRS greater than 60%. Cerebral microdialysis (CMD) samples were for a one-hour period. MMM variables were compared to cerebral microdialysis. Metabolic crisis (MC) events were defined as Lactate:Pyruvate ratio (LPR) = 25. Severe metabolic crisis (sMC) was defined as LPR = 40. Metabolic crisis was subdivided as 1. ischemic when glucose and pyruvate were below normal, 2. Mitochondrial dysfunction when pyruvate was normal or elevated.
Results: Eighteen consecutive patients were monitored for up to 5 days. Over 58,272 minutes of continuous multimodality monitoring and 1745 microdialysis periods were analyzed. Following resuscitation, multimodality monitoring goals were obtained 97% of the time. Metabolic crisis was identified in 880 (50%) of CMD samples; sMD was in 6% of CMD samples. MC was associated with mitochondrial dysfunction in 67% of the samples. When controlling only for goal MMM parameters, twenty-one (1.2%) of the CMD samples had metabolic crisis despite having goal MMM parameters.
Conclusions: Maintenance of ICP, CPP, PbtO2 and NIRS oxygen saturation does not ensure normal cerebral metabolism. Mitochondrial dysfunction appears to be a primary reason for metabolic crisis in the setting of normal MMM parameters. Studies are needed to identify interventions and therapies effective at reversing and/or protecting against mitochondrial dysfunction.
Patient Care: Understanding the causes of secondary injury will help improve outcome
Learning Objectives: Understand the role of Multimodality monitoring in severe brain injury
Understand the relationship between multi modality monitoring and cerebral metabolism
Understand the possible contributing factors to altered metabolism