The patient was a 3-month-old male with cyanotic congenital heart disease consisting of double outlet right ventricle, near absent intraventricular septum, and aortic arch hypoplasia, who had previously undergone a Norwood stage I palliation with 3.5 mm modified Blalock-Taussig shunt (see Figure 1). He presented at 3 months of age for the next stage of palliation, a cavopulmonary anastomosis (bidirectional Glenn). His weight was 5.8 kg (31% percentile) and height was 58 cm (18% percentile). Pulse oximetry demonstrated O2 saturations of 70 to 80%, which was appropriate for his lesion. Cardiac catheterization findings included a widely patent arch with estimated normal pulmonary artery (PA) pressures (mean of 12 mmHg in the RPA) by reverse pulmonary vein wedge, a BT shunt widely patent and arising from the innominate artery with flow to the branch pulmonary arteries. The preoperative CXR was unremarkable except for prior sternotomy. A preoperative echocardiogram demonstrated the above described anatomy, insignificant atrioventricular valve insufficiency, a patent modified Blalock-Taussig shunt, and patent proximal branch PA's.
Anesthesia was induced with fentanyl 50 mcg and pancuronium 1 mg, after premedication with intravenous midazolam 1 mg. After endotracheal intubation, anesthesia was maintained with a balanced anesthetic consisting of end tidal isoflurane concentrations of 0.4% and high-dose fentanyl (~100 mcg/kg) in air/oxygen mixture. A left subclavian central venous catheter was placed after induction. A right femoral arterial line was in place from earlier heart catheterization. The patient tolerated anesthetic induction, placement of invasive lines and monitors and the pre-incision period with stable hemodynamics. In addition to standard ASA monitors, bilateral cerebral and somatic oximetry (Somanetics INVOS) was monitored throughout the case. Transesophageal echocardiography (TEE) was not used. It is not our practice to use TEE for cavopulmonary anastomosis procedures or procedures in which the cardiac chambers are not opened.
 Cardiopulmonary bypass (CPB) commenced with bicaval venous cannulation at the inferior vena cava-right atrial (IVC-RA) junction and the innominate vein. The modified Blalock-Taussig shunt was ligated and divided at the initiation of cardiopulmonary bypass. The azygous vein was divided and the superior vena cava was separated from the right atrium. The bidirectional cavopulmonary anastomosis was constructed. The patient was weaned from CPB on dopamine (initially at 5 mcg/kg/min, range 0-5 mcg/kg/min) and milrinone (0.5 mcg/kg/min). Nitroprusside 0.5 mcg/kg/min, titrated to effect, was used briefly for a period of hypertension. Dexmedetomidine (0.7 mcg/kg/hr) was started during rewarming for post-op sedation. After successfully separating from cardiopulmonary bypass, O2 saturations were near 100% and the transpulmonary gradient (CVP-LAP) was 8 to 9 mmHg. The left subclavian venous line tip was visible in the superior vena cava, near the innominate vein-superior vena cava (SVC) junction. Modified ultrafiltration was performed, protamine administered, and routine decannulation and sternotomy closure were performed. The cardiopulmonary bypass time was 36 minutes.
During the postbypass period the patient had stable vital signs with invasive blood pressures (IBPs) of ~90/40, heart rates (HRs) of ~150, oxygen saturations of 80-90% on 100% FiO2, central venous pressures (CVPs) of 12, and transpulmonary gradient (CVP-LAP) of 7-9 mmHg. Cerebral and somatic saturations were unchanged from baseline and the prebypass period.
 Preparations were being made to transport the patient to the ICU when a sudden drop in SpO2 to the 60's, a sudden rise in CVP to the mid 20's, ST segment elevation, and an acute change in the patient's color (head and face became profoundly plethoric) were noted. EtCO2 was also markedly decreased although there was no change in ventilation. Bradycardia soon followed as oxygen saturations continued to decline. Cardiopulmonary resuscitation (CPR) was immediately started with chest compressions and administration of resuscitative drugs. Preparations for reopening the chest and initiating cardiopulmonary bypass (CPB) were made while CPR continued. Profound hypoxemia persisted despite good quality CPR, confirmed with an arterial pulse with compressions and adequate ventilation.
The chest was reopened during the administration of CPR with no evidence of tamponade. On examination of the superior vena cava, an abundant collection of air bubbles was visible through the wall of the vein, appearing to fill the entire superior vena cava from the pulmonary anastomosis to the innominate vein (see Figure 2). A needle was placed in the superior vena cava and a large amount of air escaped through the needle hole. Myocardial function had begun to decline despite some improvement in oxygenation, so the patient was placed emergently on cardiopulmonary bypass. Sixteen minutes had elapsed since hemodynamic collapse and initiation of full CPB. No air bubbles in the systemic circulation were observed at aortic cannulation, offering some assurance that the emboli were confined to the cavopulmonary circuit. Approximately 3 mL of air was aspirated from the SVC while the patient was on CPB. The patient was separated from cardiopulmonary bypass after 36 minutes, with hemodynamics nearly identical to those before arrest, the exception being slightly lower oxygen saturations, 80-85%. During the bypass period, efforts were made to determine the source of the emboli and prevent further expansion, but no definitive source was ever discovered. Unfortunately, echocardiography was not used during the initial procedure, so it was not available at the time of the arrest.
The patient remained stable after the second bypass period and tolerated chest closure. Systemic hypothermia was initiated Intra-op and continued for 24 hours post-op with a target temperature of 34-35 C. He was taken to the PICU in stable condition. The patient did well over the remainder of his hospital course with no discernible neurological or cardiovascular sequelae of the arrest and was discharged to home on POD 10.