Global cerebral ischemia in humans: how long is too long?

Cerebral vascular effects of aortovenous cannulations for pediatric cardiopulmonary bypass

BACKGROUND

The effects of aortovenous cannulations for pediatric cardiopulmonary bypass on cerebral blood flow velocity (CBFV) and electroencephalography (EEG) were evaluated.

METHODS

CBFV and EEG were continuously recorded before (baseline), during, and after cannulations until initiation of cooling (mean +/- 95% confidence interval). Vasopressors and/or volume replacement were administered if mean arterial pressure (MAP) decreased below 35 mm Hg. Cannulation-related EEG slowing was used as a criterion for electrocortical alteration.

RESULTS

We studied 124 children (3 days to 17 years of age). Aortic and venous cannulations decreased mean CBFV by 10+/-3% and 13+/-4%, respectively, from baseline (p < 0.001). MAP diminished (p < 0.01) by 8+/-3% and 12+/-4%, respectively, from precannulation values (53+/-2 mm Hg). Right atrial cannulation, which was often chosen because the patient was hemodynamically unstable, was more frequently associated with pharmacologic intervention when compared with superior vena cava (SVC) cannulation (p < 0.01). Transient EEG alterations (n = 20) were associated with persistently low MAP (< 30 mm Hg), low CBFV (< 69%), and aortic (n = 4) or SVC (n = 7) cannula malposition. Infants with right atrial cannulation and intervention had more frequent EEG alterations (p = 0.04). Patients requiring intervention were younger (p < 0.01) and had longer hospital stay (p < 0.01) than those without intervention.

CONCLUSIONS

Cerebral effects of cannulations are greater in young infants. This was found to be associated with low MAP during heart manipulation or consequence of cannula malpositions.

Resuscitation update for the pediatrician

Survival and neurologic outcome among pediatric patients in CPA have not improved measurably in the past decade, but the evolution of the pediatric Utstein guidelines has provided those involved in pediatric resuscitation a common language with which to exchange information and hopefully conduct meaningful research. The widespread use of the LMA may hold real promise for airway management of pediatric patients in the prehospital setting. Several of the developments in adult resuscitation, including ACD CPR and IAC CPR, seem auspicious for pediatric patients in cardiac arrest. At first glance, the widespread use of the AED would not be expected to alter the outcome of pediatric patients in CPA, but two studies suggest that ventricular fibrillation is more common in the pediatric population than originally believed, and thus the AED may have a significant role for this group of patients. The value of high-dose epinephrine remains controversial. All of these areas require research in the pediatric population before a judgment on their worth can be made. Research in pediatric resuscitation requires the study of larger populations, most feasibly with multicenter studies. How the "final rule" will influence this type of research remains to be seen. Finally, if investigators are to make real progress in improving the outcome of pediatric patients in CPA, they must concentrate their efforts on education of the lay public and enhancement of prehospital care.