Metabolic CO₂ Removal by Dialysis: THAM vs NaOH Infusion

Abstract

New methods of respiratory support are needed to reduce the high mortality rate of acute respiratory failure. To simplify the procedures of extracorporeal CO2 elimination under apneic oxygenation, one approach is to replace the membrane lung by a hemodialyzer and to administer an alkali, since hemodialysis requires a lower blood flow rate than blood-gas exchange. This study compared the effectiveness of trishydroxymethyl aminomethane (THAM) and NaOH in this procedure. Twelve male Anglo-Poitevin dogs (25 to 33 kg) were anesthetized, curarized and mechanically hypoventilated (&Vdot;E = 41% of the control value). After not less than 15 min, a venovenous shunt was used for dialysis with blood flow of 7-10 ml. min.-1kg-1 for at least 8 hours. The dialysate contained no acetate, bicarbonate or lactate, but was alkalinized to a pH of 8-9 by the addition of NaOH. A solution of THAM (0.5 N) was infused into the right heart at the rate of 0.30 ml.min.-1kg-1 in six animals, and NaOH (0.15 N) was infused in the other six at the rate of 0.80 ml.min.-1 kg-1. The injected volumes were compensated for by an equivalent amount of ultrafiltration. Elimination of CO2 (mean †CO2 = 2.3 ml.min.-1kg-1) was the same with both methods and the difference for the electrolytes and acid-base equilibrium was only very small. However, hemolysis was six times greater with NaOH than with THAM. Despite ultrafiltration, a similar marked weight gain was observed from the second hour of the experiment in the NaOH series, but only after 7 hours with THAM. It thus appears that hemodialysis combined with alkalinisation is still too complex a procedure to be safely applied in acute or chronic pulmonary failure

Experimental High‐Volume Hemofiltration With Predilutional Tris‐Hydroxymethylaminomethane for Correction of Low Tidal Volume Ventilation‐Induced Acidosis

“…A potential drawback for the combination of THAM and RRT is the formation of lung edema noted in dogs that were treated with central venous THAM infusion and dialysis (22). In the postdilutional THAM + HVHF group, which resembles a central venous application, we also found the highest incidence of pulmonary edema formation (Fig.…”

“…The potential of using RRT for hydrogen and CO 2 removal has been reported since 1983 (19–22). Although the treatment of metabolic acidosis with RRT is a “routine” procedure in the ICU, the impact of RRT on hypercapnia has not been sufficiently investigated to date.…”

Extracorporeal CO2 removal by hemodialysis: in vitro model and feasibility

“…Based on contemporary understanding of acid-base balance, previous work by several groups have attempted to replace the bicarbonate with NaOH, Tris, and organic ions [16, 17], believing this would maintain physiological pH. However, these attempts proved unsuccessful, resulting in hemolysis, elevated pulmonary artery pressure, and metabolic acidosis, among other negative effects.…”

“…The similarities between respiratory and conventional hemodialysis provide additional benefits over membrane lung ECCO 2 R, including clinician familiarity, availability of dialysis equipment in intensive care units, and a reduced risk of air embolism. Bicarbonate removal, however, has proven challenging due to the development of metabolic acidosis, despite attempts to mitigate the acidosis by replacing the bicarbonate with bases, such as sodium hydroxide, and TRIS [1, 16, 17]. …”

Bench to bedside review: Extracorporeal carbon dioxide removal, past present and future

“…Several approaches to replace bicarbonate have been attempted using sodium hydroxide, tromethamine (THAM), and organic anions. However, fluid gain, hyperchloremic acidosis, hemolysis, cardiac arrhythmias and acid-base derangements have prevented successful long-term use [64,65]. …”