The Usefulness of Near-Infrared Spectroscopy for Detecting and Monitoring Status Epilepticus After Pediatric Cardiac Surgery

HILDREN REQUIRING cardiac intensive care are at particular risk for neurologic injury, and seizures are their most common manifestations. Postoperative seizures have been reported with an incidence ranging between 4% and 15% 1-3 ; they are likely underestimated because of frequent subtle clinical expression caused by paralyzing drugs and the lack of routinely prolonged postoperative electroencephalographic (EEG) monitoring. Recently, near-infrared spectroscopy (NIRS) cerebral monitoring has been used increasingly in pediatric cardiac intensive care for assessing the adequacy of cerebral perfusion. 4,5 The authors report a case in which this technique showed its effectiveness in detecting status epilepticus (SE) occurring after cardiac surgery and characterized by the absence of any other clinical manifestations. CASE REPORT A 78-day-old female infant weighing 4 kg developed early postoperative status epilepticus after coronary stenosis correction. The patient was born with transposition of the great arteries, unique coronary ostium, and intramural coronary arteries. At the age of 19 days, an arterial switch was performed, with an uneventful postoperative course and regular discharge. At the age of 78 days, she was readmitted because of a low-cardiac-output syndrome. Echocardiographic evaluation showed severely depressed biventricular function with left ventricular ejection fraction of about 30%. Her clinical condition required immediate admission to the pediatric cardiac intensive care unit (PCICU), where she suffered from several episodes of hypotension needing mechanical ventilation and inotropic support. The patient underwent cardiac catheterization, and severe coronary ostial stenosis of both coronary arteries was diagnosed. The aortic angiography was complicated by cardiac arrest, which required prolonged cardiopulmonary resuscitation consisting of 70 minutes of external cardiac massage and 3 defibrillations at 20 J before cardiovascular function was restored. Inotropic support was administered (epinephrine, 0.3 g/kg/ min, dopamine, 10 g/kg/min, and milrinone, 1 g/kg/min), and the general condition progressively improved with reduction of metabolic acidosis, improvement of gas exchange, and hemodynamic stability. After major brain damage was excluded by cerebral evaluation, the patient underwent surgical correction of the coronary stenosis. A surgical procedure of coronary reimplantation was performed with the use of 407 minutes of cardiopulmonary bypass; after which the patient failed weaning from cardiopulmonary bypass requiring postoperative extracorporeal membrane oxygenation (ECMO). Once admitted to the PCICU, continuous hemodynamic monitoring consisted of electrocardiogram, invasive systemic arterial pressure (systolic, diastolic, and mean arterial pressure), right and left atrial pressures, transcutaneous arterial saturation (SatO2), end-tidal CO2, temperature gradient, and 2 simultaneous NIRS measurements of cerebral (central forehead probe) (cSvO2) and somatic-renal (T10 to L2 probe) (rSvO2) saturations (INVOS 300; Somatometrics, Troy, MI). Intravenous sedation was maintained with fentanyl (10 g/kg/h) and midazolam (0.1 mg/kg/h) infusions. Vecuronium bromide (0.1 mg/kg) was given when necessary. Pump flow on ECMO was maintained at 150 to 160 mL/kg/min, whereas the inspired fraction of O2 and gas flow were maintained in order to guarantee a PaCO2 of 40 mmHg and a SatO2 of 99%. Perfusion pressure was maintained stable between 40 and 50 mmHg. The baseline cSvO2 saturation was 52%, and rSvO2 was 89%. On the first postoperative day, NIRS showed significant fluctuations of cSvO2 with repetitive “spikes” despite no evidence of significant changes in blood pressure and systemic arterial saturation, suggesting the presence of seizure activity in the absence of clinical signs (Fig 1). This abnormal pattern was previously unknown by the authors’ group. The on-duty physician asked for an urgent cerebral ultrasound; it did not detect brain damage. The initial interpretation of such a pattern was hypothesized as a possible effect of the aortic cannula on cerebral blood flow; a quick examination by the on-call surgeon showed a correct cannula position. Because the patient was apparently stable with renal NIRS values at a level of about 90%, perfusion problems were excluded and a monitor artifact was suspected. The following morning an EEG was performed, as routinely prescribed by institutional protocol for ECMO patients. The EEG diagnosed the presence of SE with multifocal seizures, characterized by subcontinuous multifocal critical sequences lasting up to several minutes (Fig 2). This EEG pattern was subclinical and not associated with signs of epileptic seizures. Intravenous drugs were given in accordance with the authors’ protocol of SE treatment. Seizures persisted on the EEG despite the administration of midazolam (0.3 mg/kg), a loading dose of phenytoin (15 mg/kg), and a loading dose of phenobarbital (5 mg/kg).