Premature closure of the foramen ovale associated with aortic stenosis, left ventricular dilation with thrombus, and early mortality.

Premature foramen ovale (FO) closure has been postulated as a cause of hypoplastic left heart syndrome. We suggest that premature FO closure is also associated with left ventricular (LV) dilation and LV thrombus formation, and that FO closure in patients with aortic stenosis and LV dilation is a secondary event that occurs later in gestation than that seen with the hypoplastic left heart.

Regional blood flow distribution during extracorporeal membrane oxygenation in rabbits.

To study regional blood distribution during extracorporeal membrane oxygenation, we stabilized three groups of five rabbits each (3 to 5 kg) on venoarterial bypass at a flow rate of 30 ml/kg/min. Albumin aggregates (15 to 30 microns) labeled with technetium 99m were injected into the left ventricle during bypass (ventricle), the perfusion cannula during bypass (cannula), and the left ventricle with no bypass (control). Animals were put to death, organs were removed, and the percent distribution was determined with a gamma camera. The Student Newman-Keuls test was used for statistical comparisons. Distribution to both the heart and brain in the cannula group were decreased from control by 55% and 35%, respectively. Distribution to the brain in the ventricle group was also decreased from control by 39%. Intestinal distribution was elevated above control in the ventricle group by 37%, whereas musculoskeletal distribution was elevated 33% above control in the cannula group. No significant changes were noted for the kidneys, stomach, or liver. These data suggest that overall perfusion of some vital organs may be significantly reduced during low-flow extracorporeal membrane oxygenation, specifically in the case of the heart and brain, which may be deprived of oxygenated blood.

Prolonged extracorporeal membrane oxygenation in sheep with a hollow-fiber oxygenator and a centrifugal pump.

ECMO with a roller-pump employs two potentially thrombogenic devices: the servoregulator bladder and heat exchanger. To eliminate these we used an 0.8 m2 Capiox II hollow-fiber oxygenator ventilated with warmed humidified oxygen and a Bio-Medicus centrifugal pump with a 1/4 inch head at a flow of 250 cc/min in six sheep during 96 hr of ECMO each. Oxygenator performance and plasma Hgb were determined, as were the volume, electrolyte, and protein content of fluid accumulating in the gas phase of the oxygenator. Mean oxygen transfer was 15.78 +/- 3.15 ml/min, and mean differences in PaO2 between blood entering and leaving the oxygenator was 360 +/- 49 mmHg. Mean plasma Hgb was 24.7 +/- 12.8 mg/dl. Fluid in the gas phase of the oxygenator was less than 75 ml/day and contained no albumin, protein, sodium, potassium, or chloride. Centrifugal pumps have been associated with hemolysis at low flows, but this may have been due to the simultaneous use of silastic membrane oxygenators that have high resistance. Hollow-fiber oxygenators have been associated with early failure of gas exchange and fluid accumulation in the gas phase. This may have been due to ventilation with dry gas. We conclude that a hollow-fiber oxygenator and a centrifugal pump can provide excellent gas exchange, acceptable hemolysis, and little fluid loss.

Is heparin necessary for extracorporeal circulation?

To explore the possibility of extracorporeal circulation (ECC) without heparin, we performed veno-arterial extracorporeal membrane oxygenator procedures for a five hour period on a total of 15 rabbits in three groups. Blood flow rates were maintained at 125 ml/min with a standard roller pump through 1/4 inch PVC tubing and a 0.4 m2 SciMed membrane oxygenator. The rabbits in Group 1 received a standard dose of heparin, while no form of anticoagulation was used in Group 2. The tubing and membrane surfaces in Group 3 were modified by a glutaraldehyde crosslinked albumin-heparin complex with no systemic heparinization. Blood samples were obtained for activated clotting time, platelet count, and blood gas determinations. Circuits were evaluated for thrombosis, and samples of lung and kidney were examined histologically for emboli. There were no statistically significant differences among the three groups for any of the quantitative parameters. Moderate thrombus formation was visually detected in some areas of stagnation in the nonheparinized systems, while the albumin coating appeared to inhibit thrombus formation in regions of moderate and high blood flow. These results do not reflect any significant benefit of either the albumin-heparin coating or systemic heparinization during short-term ECC.