Comment on: 'Hypocapnia and the injured brain: more harm than benefit'

Body temperature affects cerebral hemodynamics in acutely brain injured patients: an observational transcranial color-coded duplex sonography study

Introduction

Temperature changes are common in patients in a neurosurgical intensive care unit (NICU): fever is frequent among severe cases and hypothermia is used after cardiac arrest and is currently being tested in clinical trials to lower intracranial pressure (ICP). This study investigated cerebral hemodynamics when body temperature varies in acute brain injured patients.

Methods

We enrolled 26 patients, 14 with acute brain injury who developed fever and were given antipyretic therapy (defervescence group) and 12 who underwent an intracranial neurosurgical procedure and developed hypothermia in the operating room; once admitted to the NICU, still under anesthesia, they were re-warmed before waking (re-warming group). We measured cerebral blood flow velocity (CBF-V) and pulsatility index (PI) at the middle cerebral artery using transcranial color-coded duplex sonography (TCCDS).

Results

In the defervescence group mean CBF-V decreased from 75 ± 26 (95% CI 65 to 85) to 70 ± 22 cm/s (95% CI 61 to 79) (P = 0.04); the PI also fell, from 1.36 ± 0.33 (95% CI 1.23 to 1.50) to 1.16 ± 0.26 (95% CI 1.05 to 1.26) (P = 0.0005). In the subset of patients with ICP monitoring, ICP dropped from 16 ± 8 to 12 ± 6 mmHg (P = 0.003). In the re-warming group mean CBF-V increased from 36 ± 10 (95% CI 31 to 41) to 39 ± 13 (95% CI 33 to 45) cm/s (P = 0.04); the PI rose from 0.98 ± 0.14 (95% CI 0.91 to 1.04) to 1.09 ± 0.22 (95% CI 0.98 to 1.19) (P = 0.02).

Conclusions

Body temperature affects cerebral hemodynamics as evaluated by TCCDS; when temperature rises, CBF-V increases in parallel, and viceversa when temperature decreases. When cerebral compliance is reduced and compensation mechanisms are exhausted, even modest temperature changes can greatly affect ICP.