Change of the zero-reference points for intracranial and arterial pressure results in altered neurocritical care management of severe traumatic brain injury patients

Background: Many TBI treatment protocols, including the Lund concept, advocate the highest point of the subarachnoid space as the zero-reference point for ICP and the level of the right atrium as zero-reference point for the mean arterial blood pressure (MAP). In 2017 the zero-reference points for ICP and MAP were both changed to the external auditory meatus (EAM) thus altering the calculated cerebral perfusion pressure (CPP) levels. We hypothesized that the ICP and MAP levels obtained from the different zero-reference points resulted in altered neurocritical care management and/or patient outcome. Methods: A retrospective analysis of ICP, CPP, MAP, medical management, mortality, and outcome in two different patient cohorts with severe TBI, treated at department of Neurosurgery, Skane University Hospital, Lund, Sweden between 2013-2016 and 2018-2022. Results: We collected more than 31 000 measurements from 49 patients between 2013-2016 and 53 patients between 2018-2022. Age and injury severity were similar in both groups. Mortality and treatment outcome according to the Glasgow Outcome Scale – Extended (GOSE) were similar. Mean ICP levels were higher (p < 0.0001) after the reference point was changed to EAM. The use of clonidine (65 % vs. 49%; p =0.17) and metoprolol (50% vs. 13%; p = 0.0002) decreased and the use of norepinephrine increased (42% vs. 98%; p < 0.0001) after changing the reference points. Conclusion: The change of the reference point to the EAM led to higher ICP levels. The use of clonidine and metoprolol was reduced and there was a large increase in the use of norepinephrine in severe TBI patients. These results show the impact of zero-reference point placement, which should be reported in TBI studies analysing ICP and CPP management.