Evaluation of a mathematical model for blood gases and acid–base status during extracorporeal circulation

Results Surfactant properties did not change in the control group. In the CPB group, PL content increased in TA 24 hours after CPB. LA concentration dropped 4 hours after CPB (P < 0.01) but recovered within 24 hours. The PL : protein ratio of LA was decreased at 24 hours as compared with baseline (P < 0.01). The relative amount of phosphatidylglycerol in LA-PL content dropped linearly over time. The relative content of the hydrophobic SP-B and SP-C in LA increased almost threefold as compared with baseline. There were no significant changes in biophysical function of LA. Conclusions CPB in children induces profound changes in the surfactant system, involving both PL and protein components. Bio-physical function may be maintained by compensatory increases in SP-B and SP-C of LA. Objectives Blood gases and acid–base status are important parameters during extracorporeal circulation. They are controlled by the perfusionist, by varying arterial pump flow, gas flow over the oxi-genator, inspiratory oxygen fraction, and carbon dioxide content in the inspiratory gas mix. To support the perfusionist with suggestions based on a control algorithm, a reliable system description is needed. Reliability of a complex model of human acid–base and blood gas status under extracorporeal circulation was evaluated using clinical documentation data. Methods A mathematical model for blood gas and acid–base status under extracorporeal circulation was developed. This model consists of a multiple compartment model for the oxygenator, and models for arterial and venous PCO 2 , PO 2 , (including temperature-and pH-dependent shift in oxygen-binding capacity of haemoglo-bin), SO 2, bicarbonate, base excess and pH. It was implemented in a Matlab/Simulink environment. Input parameters were oxygenator type, gas flow, FiO 2 , arterial pump flow, temperature, haemoglobin concentration and haematocrit. As output parameters, venous and arterial SO 2 , PO 2 , PCO 2 and pH were analyzed. The model was tested by using clinical monitoring data during extracorporeal circulation of patients undergoing aorto-coronary bypass grafting as input data, and comparing the model output with the results of conventional blood gas analyses (Rapidlab 288 ®) retrospectively. Results Estimations of arterial PO 2 , PCO 2 and SO 2 were adequate. They followed the time course appropriately and remained within a narrow error band (Max. dev.: PO 2 <17 mmHg, PCO 2 <7 mmHg, SO 2 <0.01%). Venous PO 2 followed appropriately (Max. dev.: <4 mmHg), whereas PCO 2 (Max. dev.: <8 mmHg) did not reproduce …