Computer‐Assisted Numerical Analysis for Oxygen and Carbon Dioxide Mass Transfer in Blood Oxygenators

Abstract

A two-dimensional numeric simulator is developed to predict the nonlinear, convective-reactive, oxygen mass exchange in a cross-flow hollow fiber blood oxygenator. The numeric simulator also calculates the carbon dioxide mass exchange, as hemoglobin affinity to oxygen is affected by the local pH value, which depends mostly on the local carbon dioxide content in blood. Blood pH calculation inside the oxygenator is made by the simultaneous solution of an equation that takes into account the blood buffering capacity and the classical Henderson-Hasselbach equation. The modeling of the mass transfer conductance in the blood comprises a global factor, which is a function of the Reynolds number, and a local factor, which takes into account the amount of oxygen reacted to hemoglobin. The simulator is calibrated against experimental data for an in-line fiber bundle. The results are: (i) the calibration process allows the precise determination of the mass transfer conductance for both oxygen and carbon dioxide; (ii) very alkaline pH values occur in the blood path at the gas inlet side of the fiber bundle; (iii) the parametric analysis of the effect of the blood base excess (BE) shows that (.)V(CO₂) is similar in the case of blood metabolic alkalosis, metabolic acidosis, or normal BE, for a similar blood inlet P(CO₂), although the condition of metabolic alkalosis is the worst case, as the pH in the vicinity of the gas inlet is the most alkaline; (iv) the parametric analysis of the effect of the gas flow to blood flow ratio (QG/QB) shows that (.)V(CO₂) variation with the gas flow is almost linear up to QG/QB = 2.0. (.)V(O₂) is not affected by the gas flow as it was observed that by increasing the gas flow up to eight times, the (.)V(O₂) grows only 1%. The mass exchange of carbon dioxide uses the full length of the hollow-fiber only if Q(G) /Q(B)> 2.0, as it was observed that only in this condition does the local variation of pH and blood P(CO₂) comprise the whole fiber bundle.

In-vitro performance of a low flow extracorporeal carbon dioxide removal circuit

“…As the sweep gas flow increases, the outlet partial pressure of CO 2 decreases and pH increases to a point that – based on the Henderson-Haselbach relationship – no further CO 2 can be eliminated. 28 In this model, with increasing sweep gas flow rates the post-membrane pH remained 7.35–7.39, reflecting these limits on CO 2 transfer with changes in pH. 28 We did not test the relationship between gas flow and membrane anatomical dead space due to condensation or an aging membrane where micro clot formation around the fibres may reduce or stop blood flow while gas is still flowing in the membrane.…”

“…28 In this model, with increasing sweep gas flow rates the post-membrane pH remained 7.35–7.39, reflecting these limits on CO 2 transfer with changes in pH. 28 We did not test the relationship between gas flow and membrane anatomical dead space due to condensation or an aging membrane where micro clot formation around the fibres may reduce or stop blood flow while gas is still flowing in the membrane. 10,29 We can only hypothesise that with greater anatomical dead space the membrane VCO 2 / gas flow relationship may be shifted to the right.…”

Effect of Impeller Design and Spacing on Gas Exchange in a Percutaneous Respiratory Assist Catheter

“…The significance of this enhancement is emphasized when considering the effect of impeller-facilitated active mixing on the mass exchange effectiveness parameter. The ratio (~0–1) of achieved CO 2 removal versus maximum possible removal normalized for blood flow rate, gas flow rate, and $p{\text{CO}}_2^{\text{INLET}}$ increases >15-fold from 0.012 to 0.203 with impeller rotation at 20 000 rpm versus passive gas exchange (i.e., 0 rpm) (33). …”

Artificial Organs 2011: A Year in Review

“…Fabio Turri and Jurandir Itizo Yanagihara (66) of the University of São Paulo, São Paulo, Brazil developed a two‐dimensional numeric simulator to predict the nonlinear, convective‐reactive, oxygen mass exchange in a cross‐flow hollow‐fiber blood oxygenator. This simulator also calculates the carbon dioxide mass exchange.…”