Fig. 1

Min-by-min time trends of metrics used for studying the relationship between CPP < LLR and high ICP. The first top chart shows an example of ICP (in white) pressure–time chart. The horizontal red line identifies ICP at 20 mmHg. The second top chart shows LLR (orange) and CPP (yellow) time trends. Note that this example captures a highly dynamic time trend of LLR, which can perhaps be viewed as controversial. However, given an equally dynamic nature of TBI pathology within its acute stage, and a growing appreciation of fragility of the CA mechanism, plausibility of such an event cannot be denied. Unfortunately, owing to the lack of other relevant measurements in this case (eg CO₂), explanation for this pattern could not be fully explored. The third chart shows in red the trend for delta CPP below LLR. Delta is calculated as ‘LLR – CPP’ and shown as absolute value. The area in yellow represents Dose of CPP below LLR only when ICP is above the threshold of 20 mmHg. The bottom chart shows in red the trend for delta ICP above 20 mmHg. Delta is calculated as ‘ICP – 20’ and showed as absolute value. The area in white represents dose of ICP above 20 mmHg only when CPP is below LLR. ICP: intracranial pressure; LLR: lower limit of reactivity; CPP: cerebral perfusion pressure