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.

Objective Knowledge remains limited regarding cerebral blood flow autoregulation after cardiac arrest and during post-resuscitation hypothermia. We determined the relationship of cerebral blood flow to cerebral perfusion pressure in a swine model of pediatric hypoxic-asphyxic cardiac arrest during normothermia and hypothermia and tested novel measures of autoregulation derived from near-infrared spectroscopy. Design Prospective, balanced animal study. Setting Basic physiology laboratory at an academic institution. Subjects Eighty-four neonatal swine. Interventions Piglets underwent hypoxic-asphyhxic cardiac arrest or sham surgery and recovered for 2 hours with normothermia followed by 4 hours of either moderate hypothermia or normothermia. In half of the groups, blood pressure was slowly decreased through inflation of a balloon catheter in the inferior vena cava to identify the lower limit of cerebral autoregulation at 6 hours post-resuscitation. In the remaining groups, blood pressure was gradually increased by inflation of a balloon catheter in the aorta to determine the autoregulatory response to hypertension. Measures of autoregulation obtained from standard laser-Doppler flowmetry and indices derived from near-infrared spectroscopy were compared. Measurements and Main Results Laser-Doppler flux was lower in post-arrest animals compared to sham-operated controls during the 2-hour normothermic period after resuscitation. During the subsequent 4-hour recovery, hypothermia decreased laser-Doppler flux in both the sham surgery and post-arrest groups. Autoregulation was intact during hypertension in all groups. With arterial hypotension, post-arrest, hypothermic piglets had a significant decrease in the perfusion pressure lower limit of autoregulation compared to post-arrest, normothermic piglets. The near-infrared spectroscopy-derived measures of autoregulation accurately detected loss of autoregulation during hypotension. Conclusions In a pediatric model of cardiac arrest and resuscitation, delayed induction of hypothermia decreased cerebral perfusion and decreased the lower limit of autoregulation. Metrics derived from non-invasive near-infrared spectroscopy accurately identified the lower limit of autoregulation during normothermia and hypothermia in piglets resuscitated from arrest.