The oxygenator is modelled as a classical 'Riley' three compartment lung placed either in series (VV - ECMO) or in parallel (VA - ECMO) with the patient's native lung.
By default, Qs/Qt ('Shunt Fraction') of the oxygenator at a nominal blood flow of 3.0 lpm is set to 0.08 and is varied in a linear manner according to the blood flow through the device (Segers et al).
By default, Vd/Vt (''Dead Space') of the oxygenator at a nominal blood and gas flow of 3.0 lpm is set to 0.08 (Pybus et al).
The nominal values of these parameters can be altered using the Supervisor Application.
The behaviour of the model is illustrated in the following figure in which the output of the model has been compared in real-time with data acquired from a CDI-500 'in-line' blood gas analyser from a patient on cardio-pulmonary bypass. The predicted arterial PO2 has been compared with the actual arterial PO2 during a manoeuvre where the inspired oxygen concentration to the oxygenator (green line) was reduced from 100% to ~ 60% and then returned to 100% two minutes later. The concordance between the actual and predicted readings is clearly apparent.
References:
Pybus DA, Lyon M, Hamilton J, Henderson M. Measuring the efficiency of an artificial lung: 1. Carbon dioxide transfer. Anaesth Intensive Care. 1991 Aug;19(3):421-5.
Riley RL and Cournand A. (1949) ‘Ideal’ Alveolar air and the analysis of ventilation-perfusion relationships in the lungs. J. Appl. Physiol., 1, 825-847
Segers PA, Heida JF, de Vries I, Maas C, Boogaart AJ, Eilander S. Clinical evaluation of nine hollow-fibre membrane oxygenators. Perfusion. 2001 Mar;16(2):95-106.