Assessment of cerebral autoregulation from respiratory oscillations in ventilated patients after traumatic brain injury.

Phase shift (PS) between oscillations in arterial blood pressure (ABP) and transcranial Doppler (TCD) cerebral blood flow velocity (CBFV) is thought to describe cerebral autoregulation. Ventilated patients show high amplitude and regular respiratory oscillations in ABP and CBFV, allowing reliable PS measurement. We analysed recordings of ABP, CBFV and intracranial pressure (ICP) from 187 TBI patients treated at Addenbrooke's Hospital, Cambridge, UK, from 1993 to 1998. Monitored data were recorded and PS, TCD autoregulation (Mx) and pressure reactivity (PRx) were calculated using ICM+. PS was computed by peak detection in the ABP/CBFV cross-spectrum. Recordings with low coherence (<0.5), unstable respiratory rate (RR), or PS wraparound were excluded. Median RR was 14 bpm (range 10-20 bpm). Group median PS was 13° (range -37-56°). Average PS (PSa) correlated with RR (Spearman's R = -0.302, p < 0.01, and cerebral perfusion pressure (R = -0.373, p < 0.01). Correlations of PS with Mx and PRx were weak but significant (p < 0.01). Kruskal-Wallis test for outcome vs. PS was non-significant (PSa: p = 0.14, minimum PS (PSm): p = 0.27). Mann-Whitney test for mortality vs. PS was significant (p < 0.05) for PSm only. Respiratory PS responds to changes in CPP and RR and correlates weakly with CA. Respiratory PS may have some prognostic value for patients with TBI.