Targeted temperature management and P bt O 2 in traumatic brain injury.

INTRODUCTION: Targeted Temperature Management (TTM) to normothermia is widely used in traumatic brain injury (TBI). We investigated the effects to of TTM to normothermia patients with TBI (GCS≤12) monitored with multimodality monitoring, to better understand the physiological consequences of this intervention.

RESEARCH QUESTION: In TBI patients cooled to normothermia and in which brain oxygenation deteriorates, are there changes in physiological parameters which are pertinent to brain oxygenation?

MATERIAL AND METHOD: 102 TBI patients with continuous recordings of intracranial pressure (ICP) and brain oxygen tension (Pbt O2 ) were studied retrospectively. Non-continuous arterial carbon dioxide (Pa CO2 ) and oxygen (Pa O2 ) tensions, and core body temperature (Tc ) were added. Pa O2 and Pa CO2 were also corrected for Tc . Transitions from elevated Tc to normothermia were identified in 39 patients. The 8 h pre and post the transition to normothermia were compared. Data is given as median [IQR] or mean (SD).

RESULTS: Overall, normothermia reduced ICP (12 [9-18] -11 [8-17] mmHg, p < 0.009) and Tcore (38.3 [0.3]-36.9 [0.4] o C, p < 0.001), but not Pbt O2 (23.3 [16.6]-24.4 [17.2-28.7] mmHg, NS). Normothermia was associated with a fall in Pbt O2 in 18 patients (24.5 [9.3] -20.8 [7.6] mmHg). Only in those with a fall in Pbt O2 with cooling did ICP (15 [10.8-18.5] -12 [7.8-17.3] mmHg, p = 0.002), and temperature corrected Pa CO2 (5.3 [0.5]- 4.9 [0.8] kPa, p = 0.001) decrease.

DISCUSSION AND CONCLUSION: A reduction in Pbt O2 was only present in the subgroup of patients with a fall in temperature corrected Pa CO2 with cooling. This suggests that even modest temperature changes could result in occult hyperventilation in some patients. pH stat correction of ventilation may be an important factor to consider in future TTM protocols.