Background: Transcranial Doppler (TCD) is widely used to detect and follow up cerebral vasospasm after subarachnoid hemorrhage (SAH). Therapeutic hypothermia might influence blood flow velocities assessed by TCD. The aim of the study was to evaluate the effect of hypothermia on Doppler blood flow velocity after SAH.
Methods: In 20 patients treated with hypothermia (33°) due to refractory intracranial hypertension or delayed cerebral ischemia (DCI), mean flow velocity of the middle cerebral artery (MFV(MCA)) was assessed by TCD. Thirteen patients were treated with combined hypothermia and barbiturate coma and seven with hypothermia alone. MFV(MCA) was obtained within 24 h before and after induction of hypothermia as well as before and after rewarming.
Results: Hypothermia was induced on average 5 days after SAH (range 1-12) and maintained for 144 h (range 29-270). After hypothermia induction, MFV(MCA) decreased from 113.7 ± 49.0 to 93.8 ± 44.7 cm/s (p = 0.001). The decrease was independent of SAH-related complications and barbiturate coma. MFV(MCA) further decreased by 28.2 cm/s between early and late hypothermia (p < 0.001). This second decrease was observed in patients with DCI (p < 0.001), but not in patients with intracranial hypertension (p = 0.715). Compared to late hypothermia, MFV(MCA) remained unchanged after rewarming (65.6 ± 32.1 vs 70.3 ± 36.8 cm/s; p = 0.219). However, patients treated with hypothermia alone showed an increase in MFV(MCA) after rewarming (p = 0.016).
Conclusion: Therapeutic hypothermia after SAH decreases Doppler blood flow velocity in both intracranial hypertension and DCI cases. The results can be the effect of hypothermia-related mechanisms or resolving cerebral vasospasm during prolonged hypothermia.