Monitoring cerebral blood flow pressure autoregulation in pediatric patients during cardiac surgery

Abstract

Background and purpose: The limits of cerebral blood flow-pressure autoregulation have not been adequately defined for pediatric patients. Mean arterial blood pressure below these limits might contribute to brain injury during cardiac surgery. The purpose of this pilot study was to assess a novel method of determining the lower limits of pressure autoregulation in pediatric patients supported with cardiopulmonary bypass.

Methods: A prospective, observational pilot study was conducted in children (n=54) undergoing cardiac surgery with cardiopulmonary bypass for correction of congenital heart defects. Cerebral oximetry index (COx) was calculated as a moving, linear correlation coefficient between slow waves of arterial blood pressure and cerebral oximetry measured with near-infrared spectroscopy. An autoregulation curve was constructed for each patient with averaged COx values sorted by arterial blood pressure.

Results: Hypotension was associated with increased values of COx (P<0.0001). For 77% of patients, an individual estimate of lower limits of pressure autoregulation could be determined using a threshold COx value of 0.4. The mean lower limits of pressure autoregulation for the cohort using this method was 42+/-7 mm Hg.

Conclusions: This pilot study of COx monitoring in pediatric patients demonstrates an association between hypotension during cardiopulmonary bypass and impairment of autoregulation. The COx may be useful to identify arterial blood pressure-dependent limits of cerebral autoregulation during cardiopulmonary bypass. Larger trials with neurological outcomes are indicated.

Figure 1

LLA determination. For each subject, the average COx is plotted over ABP. A COx value of 0.4 (horizontal dashed line) is the LLA threshold used in this study. Examples A through D demonstrated an LLA. A, A 6-day-old patient with interrupted aortic arch, (LLA at 20 mm Hg); (B) a 7-month-old patient with ventricular septal defect (LLA at 40 mm Hg); (C) a 2-year-old patient with ventricular septal defect (LLA at 50 mm Hg); (D) a 7-year-old patient with anomalous right coronary artery (LLA at 45 mm Hg). Examples E and F did not demonstrate an LLA. E, A 4-month-old patient with truncus arteriosus (LLA indeterminate due to COx values inconsistently >0.4). F, A 14-year-old with cardiomyopathy (LLA indeterminate due to COx values consistently <0.4).

Figure 2

Mean ABP, rS_O2, and COx during cardiac surgery. A, Average ABP decreased during CPB and normalized after CPB. B, Average rS_O2 decreased during CPB and normalized after CPB. C, Average COx values increased during CPB and remained elevated after CPB, indicating impaired autoregulation. (**P<0.01, ***P<0.001 by Kruskal-Wallis analysis of variance and Dunn multiple comparison test).

Figure 3

A, The distribution of the COx across binned mean ABP allows visualization of the cohort autoregulation curve. A COx value of 0.4 (horizontal dashed line) is the LLA threshold used in this study. B, The distribution of time (percent of total time) spent at each increment of ABP is sorted by surgical stage. C, The average percentage of time with critical hypotension is shown for each surgical stage. On average, subjects spent 13±23%, 26±26%, and 18±26% of time before, during, and after bypass, respectively, with mean ABP <40 mm Hg (±SD, ***P<0.001 by analysis of variance [ANOVA] by Kruskal-Wallis ANOVA and Dunn multiple comparison test).

Figure 4

The individual LLA could be estimated with the COx for 77% (42 of 54) of pediatric patients and 62% (37 of 60) of adult patients. The average individual LLA for pediatric patients was 42±7 mm Hg compared with 55±14 mm Hg for adults (±SD; P<0.0001 by Mann–Whitney U test).