Temperature variability in the day–night cycle is associated with further intracranial pressure during therapeutic hypothermia

Background: To assess whether circadian patterns of temperature correlate with further values of intracranial pressure (ICP) in severe brain injury treated with hypothermia. Methods: We retrospectively analyzed temperature values in subarachnoid hemorrhage patients treated with hypothermia by endovascular cooling. The circadian patterns of temperature were correlated with the mean ICP across the following day (ICP24). Results: We analyzed data from 17 days of monitoring of three subarachnoid hemorrhage patients that under‑ went aneurysm coiling, sedation and hypothermia due to refractory intracranial hypertension and/or cerebral vasospasm. ICP24 ranged from 11.5 ± 3.1 to 24.2 ± 6.2 mmHg. The ratio between the coefficient of variation of temperature during the nocturnal period (18.00-06.00) and the preceding diurnal period (6:00–18:00) [temperature variability (TV)] ranged from 0.274 to 1.97. Regression analysis showed that TV correlated with ICP24 (Pearson correlation = −0.861, adjusted R square = 0.725, p < 0.001), and that CP24 = 6 (4–TV) mmHg or, for 80% prediction interval, ICP24 = 23.9 − 6.22 × TV ± 1.73 × √1.06 + ((TV − 1.1)2/4.49) mmHg. The results indicate that the occurrence of ICP24 higher than 20 mmHg is unlikely after a day with TV ≥1.0. Conclusions: TV correlates with further ICP during hypothermia regardless the strict range that temperature is maintained. Further studies with larger series could clarify whether intracranial hypertension in severe brain injury can be predicted by analysis of oscillation patterns of autonomic parameters across a period of 24 h or its harmonics