Deviations from PRx-derived optimal blood pressure are associated with mortality after cardiac arrest

Abstract

Aim: Pressure reactivity index (PRx) provides a surrogate measurement of cerebrovascular autoregulation (CAR). We determined whether deviations from PRx-derived optimal mean arterial pressure (MAP_opt) were associated with in-hospital mortality after adult cardiac arrest.

Methods: Retrospective analysis of post-cardiac arrest patients who had continuously recorded intracranial pressure (ICP) and MAP. PRx was calculated as a moving, linear correlation between ICP and MAP. Impaired CAR was defined as PRx ≥ 0.3. MAP_opt was calculated using a multi-window weighted algorithm. The burdens of MAP < 5 mmHg below MAP_opt (MAP_opt-5) and > 5 mmHg above MAP_opt (MAP_opt + 5) were calculated by integrating the area between MAP and MAP_opt-5 or MAP_opt + 5 curves, respectively. Univariate logistic regression tested the association between burden of MAP < MAP_opt-5 and outcome.

Results: Twenty-two patients were analyzed. Thirteen (59%) patients died before hospital discharge. Time (median [IQR]) between ROSC and monitoring initiation was 16 [14, 21] hours and duration of monitoring was 35 [22, 48] hours; neither differed between survivors and non-survivors. Median MAP_opt was 89 [85, 97] mmHg and did not differ between survivors and non-survivors (89 [83, 94] vs. 91 [85, 105] mmHg, p = 0.64). Burden of MAP < MAP_opt-5 was greater for non-survivors compared to survivors (OR 3.6 [95% CI 1.2-15.6]). Range of intact CAR (upper-lower limit) was narrower for non-survivors when compared to survivors (5 [0, 22] vs. 24 [7, 36] mmHg, p = 0.03).

Conclusion: A greater burden of MAP below PRx-derived MAP_opt-5 was associated with mortality after cardiac arrest. Non-survivors had a narrower range of intact CAR than survivors.

Keywords: Cardiac arrest; Cerebral autoregulation; Intracranial pressure; Optimal blood pressure; PRx; Post-cardiac arrest care.

Fig. 1 –

Physiologic data over 8 h of monitoring from a representative patient. The four rows depict (A) mean arterial pressure (MAP, solid black line) and intracranial pressure (ICP, dotted gray line); (B) pressure reactivity index (PRx), the gray shaded region on the PRx curve represents the burden of impaired CAR which was defined as the area below the PRx waveform and PRx threshold of 0.3, and normalized as a percentage of the monitoring duration; (C) representative PRx versus binned MAP parabolic curve demonstrating MAP_opt at the nadir of the curve and the lower and upper limits of autoregulation (LLA and ULA) where parabolic curve crosses 0.3; and (D) MAP (solid line), MAP_opt (dotted line), gray shaded region is ± 5 mmHg of MAP_opt, dark gray region is burden of MAP less than MAP_opt – 5.

Fig. 2 –

The association between magnitude and duration of MAP below MAP_opt and survival. Using minute-by-minute MAP and MAP_opt data, for each pair of a given magnitude (MAP below MAP_opt by 0 to 40 mmHg) and for a given duration (0 to 60 minutes), the ratio between number of patients who did not survive and total number of patients who experienced at least one such episode was recorded. This ratio, indicating probability of survival, is displayed such that deep red indicates higher probability of non-survival and blue indicates higher probability of survival.