Table 1.
Summary of the main cerebral autoregulation indices currently used in paediatric settings.
| CA index | Signals | Calculation & interpretation | Proposed cut-off for impaired CA, unless specified otherwise |
|---|---|---|---|
| RoR (rate of autoregulation) | MAP & CBFV | (ΔCVR /Δ T): ΔABP- Rate of restoration of CBFV with respect to a dynamic drop in ABP (e.g., during seat to stand exercise) | NA 48 |
| Rate of CBFV change index (static CA) | MAP & CBFV | Percentage of change in CBFV over a unit change in ABP, induced by pharmacological means- %ΔCBFV/ΔABP | NA 142 |
| Static ARI (static autoregulation index) | MAP (or CPP) & CBFV | Calculated as a relative change in cerebrovascular resistance (CVR = ABP/CBFV, or CPP/CBFV) over relative change in ABP or CPP) respectively: %ΔCVR/%ΔABP, or %ΔCVR/%ΔCPP | <0.437–47,73,77,78,117 |
| Dynamic ARI (dynamic autoregulation index) | MAP & CBFV | Comparison of the CBFV response to a transient step change in ABP with those predicted from a parametric model at 10 different levels of CA. The step ABP change is induced by rapid deflation of thigh cuffs, however dARI could also be calculated from spontaneous waves using transfer function analysis. | 0 completely impaired CA5 Intact CA9 Overreactive CA 76 |
| Slope of autoregulatory plateau | MAP, CBFV, PaCO2 | Slope of CBFV to ABP from a linear multivariate model including ABP and PaCO2 during a provocative test (tracheal suctioning) | >0 117 |
| CBFV slope of transients | MAP & CBFV | The temporal pattern of CBFV transients on response to ABP transient, is classified according to clusters of autoregulatory response | NA 137 |
| Mx (mean index of autoregulation) Sx (systolic index of autoregulation) Dx (diastolic index of autoregulation) | CPP (or MAP) & CBFV | Person correlation coefficient between CPP and mean CBFV (Mx) (300-s window of 10-s averages). There exist several variants of the method: Mxa (using MAP instead of CPP), systolic values of ABP and CBFV (Sx), diastolic values of ABP and CBFV (Dx) | Mx: >0.4517,124 |
| PRx (pressure reactivity index) | MAP & ICP | Moving Pearson correlation coefficient between invasive MAP and ICP (300-s window of 10-s averages) | >0.352–54>0.211,51 |
| LAx (low frequency autoregulation index) | MAP & ICP | Low frequency version of PRx, based on minute-by-minute data, the period of calculations is not standardized and can range from 5 min to 2 hours. | >0.212,60–62 |
| COx (or TOx) Cerebral oximetry index orTotal oxygenation reactivity index | MAP or CPP & CrSO2 | Pearson correlation between MAP and cerebral oxygen saturation | >0.5112–115,126–128,133,138,141≥0.485,140>0.366,115>0 170 NA99,102,107,116,139 |
| MAP-CrSO2 repeated measures correlation coefficient | MAP & CrSO2 | Repeated measures correlation between epochs of MAP and cerebral oxygen saturation over a period. | NA 74 |
| MAP-cFTOE correlation coefficient | MAP & cFTOE | Pearson or Spearman correlation between cFTOE and ABP, calculated over pre-defined epochs. | ≤−0.3 121 <−0.5 115 NA 116 |
| HVx (or THx) Haemoglobin volume reactivity index orTotal haemoglobin reactivity index | MAP or CPP & tHb | Pearson correlation between 30 consecutive 10-s means of ABP and tHb | >0.3 87 |
| DCSx Diffusion correlation spectroscopy blood flow reactivity index | MAP & DCS based Blood Flow Index BFI | Pearson correlation coefficient between MAP and microvasculature blood flow, BFI, values, sampled every 7 seconds, from a period of 30–60 min | NA 96 |
| TOHRxTotal oxygenation heart rate index | Heart rate & cerebral oxygenation | Moving correlation coefficient between cerebral oxygenation and HR (300-s window of 10-s averages) | NA110,111,132,152–154 |
| Wavelet IndiceswPRxwCOx wHVx | NIRS signals or ICP & ABP | Wavelet analysis based PRx, and HVx, calculated as a cosine of the phase shift between slow waves in NIRS parameters or ICP and ABP | wPRx: >0.24 59 wCOx: >0.26 94 wHVx: >0.19 59 ; NA171 |
| MAP- CrSO2 COH | MAP & CrSO2 | Spectral coherence of slow waves analysis | ≥0.5103,129,135 ≥0.45 (low frequency) 136 ≥0.47 (very low frequency) 136 >0.3 144 NA99,102,107,139,143,147,159 |
| MAP-HbD COH | MAP & cerebral intravascular oxygenation (HbD = HbO2 – HHb) | Spectral coherence of slow waves analysis | >0.5 105 >0.384 151 NA129,160,163,175,177 |
| MAP-CrSO2 TF gain | MAP & CrSO2 | Spectral transfer function gain (TF) in slow wave frequencies (0.002–0.02) | NA102,104,134,139Mean Gain +2SD 144 |
| MAP-HbD TF gain | MAP & HbD | Spectral TF gain analysis | NA 130 |
| HVP | MAP & cerebral tHb | Cosine-transformed phase shift at maximal coherence between tHb and ABP | >0.34 162 , NA161,163 |
| Bivariate phase rectified signal averaging (BPRSA) | MAP/HR & CrSO2 | Bivariate autoregressive modelling based spectral estimation | NA 131 |
| Bivariate autoregressive spectral coherence (BiAR-COH) | MAP & CrSO2 | Bivariate autoregressive modelling based spectral estimation | >0.57 100 |
| Partial directed coherence (PDC) | MAP & CrSO2 | Bivariate autoregressive modelling based spectral estimation | >0.55 101 |
ABP: arterial blood pressure; ARI: autoregulatory index; CA: cerebral autoregulation; CBFV: cerebral blood flow velocity; cFTOE: cerebral fractional oxygen extraction; COx: cerebral oxygenation index; CPP: cerebral perfusion pressure; CrSO2: cerebral tissue oxygenation index; CVR: cerebro-vascular resistance; HbO2: oxygenated haemoglobin; dARI: dynamic ARI; HbD: haemoglobin difference; HHb: deoxygenated haemoglobin; HR: heart rate; HVx: haemoglobin volume reactivity index; HVP: haemoglobin volume phase index; ICP: intracranial pressure; LAx: low frequency autoregulation index; Mx: mean flow index; MAP: mean arterial blood pressure; NA: not available; PaCO2: partial pressure of arterial carbon dioxide; PRx: pressure reactivity index; rTHb: relative total haemoglobin; sARI: static ARI; T: time; TF: transfer function; tHb: total haemoglobin; THx: total haemoglobin reactivity index; TOHRx: total oxygenation heart rate index; wCOx: wavelet COx; wHVx: wavelet HVx; wPRx: wavelet PRx.