ASAIO transactions / American Society for Artificial Internal Organs
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To perform low blood flow extracorporeal CO2 removal (ECCO2R), the authors developed a device for extracorporeal circulation (ECC) equipped with a dialyzer for the elimination of CO2 as bicarbonate. The major problem with this method was the decrease in blood pH. To control blood pH and clarify the limit of CO2 elimination using this method, a study with apneic dogs was performed. ⋯ The CO2 was converted to bicarbonate using systemic infusion of trihydroxy-methylamino methane (THAM), and the generated bicarbonate was removed by hemodialysis. Blood flow rate in the ECC was 15 ml/kg/min, and the duration of ECC was 5 hr. During ECC, the hemodynamic parameters of the dogs were stable, and the PaCO2 remained at about 90 mmHg with a PaO2 above 350 mmHg; CO2 elimination from the airway was negligible.
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A simple, colorimetric protamine titration method was developed for rapid and precise estimation of the protamine dose required for clinical heparin reversal. The method employs azure A dye as the titration indicator, and has replaced the time consuming clotting assay in the conventional protamine titration method with a rapid colorimetric assay. ⋯ In a similar manner, the colorimetric assay can also be employed with a heparin titration procedure to quickly assess the heparin dose required for protamine reversal. This would allow physicians to exercise a quick and accurate heparin back-titration to patients who are overdosed with protamine.
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Extracorporeal techniques for respiratory support in the newborn are feasible, as the growth of neonatal extracorporeal membrane oxygenation (ECMO) has demonstrated. It has been shown, however, that even in severely damaged lungs, sufficient oxygenation and gas exchange can be maintained only by removing CO2 in an extracorporeal circuit, i.e., extracorporeal CO2 removal (ECCO2R). To demonstrate the effectiveness of CO2 removal in a bicarbonate-free hemodialysis procedure, CO2 removal was measured during routine acetate hemodialysis in 22 patients on renal replacement therapy for end-stage renal disease. ⋯ To use bicarbonate-free hemodialysis for total metabolic CO2 removal, acetate dialysate was modified with lactate, phosphate buffer, and sodium hydroxide to compensate for the bicarbonate loss. In sheep, apneic oxygenation could be achieved with blood flow rates as low as 10-15 ml/kg/min for 4-6 hours. These preliminary data suggest that a hemodialysis procedure for bicarbonate and CO2 elimination (ECBicCO2R) could be an efficient method for CO2 removal requiring much lower blood flow rates than techniques presently in use.
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To avoid the drawbacks of systemic anticoagulation during prolonged extracorporeal lung assist, a heparinization technique has been developed by which partially degraded heparin is covalently end-point attached to the surface of the equipment that constitutes the extracorporeal circuit (Carmeda Bio-Active Surface; CABS). Four patients have been treated with extracorporeal carbon dioxide elimination and low pressure-low frequency ventilation for acute respiratory failure (ARF) by means of extracorporeal equipment coated with the CBAS. The author's experience is that by using the CBAS technique it is possible to perform an extracorporeal circulation on a prolonged basis with minimal systemically administered heparin, thus avoiding the risk of major coagulation defects.