Therapeutic Hypothermia for Refractory Hypoxemia on Venovenous Extracorporeal Membrane Oxygenation: An In Silico Study

Patients with respiratory failure may remain hypoxemic despite treatment with venovenous extracorporeal membrane oxygenation (VV-ECMO). Therapeutic hypothermia is a potential treatment for such hypoxia as it reduces cardiac output ((Q) over dot(t)) and oxygen consumption. We modified a previously published mathematical model of gas exchange to investigate the effects of hypothermia during VV-ECMO. Partial pressures were expressed as measured at 37 degrees C (alpha-stat). The effect of hypothermia on gas exchange was examined in four clinical scenarios of hypoxemia on VV-ECMO, each with different physiological derangements. All scenarios had arterial partial pressure of oxygen (PaO2) <= 46 mm Hg and arterial oxygen saturation of hemoglobin (SaO(2)) <= 81%. Three had high Q(t) with low extracorporeal blood flow to (Q) over dot(t) ratio ((Q) over dot(EC)/Q(t)). The problem in the fourth scenario was recirculation, with normal (Q) over dot(t). Cooling to 33 degrees C increased SaO(2) to > 89% and PaO2 to > 50 mm Hg in all scenarios. Mixed venous oxygen saturation of hemoglobin as % (SvO(2)) increased to > 70% and mixed venous partial pressure of oxygen in mm Hg (P (v) over barO(2)) increased to > 34 mm Hg in scenarios with low (Q) over dot(EC)/(Q) over dot(t). In the scenario with high recirculation, S (v) over barO(2) and P (v) over barO(2) increased, but to < 50% and < 27 mm Hg, respectively. This in silico study predicted cooling to 33 degrees C will improve oxygenation in refractory hypoxemia on VV-ECMO, but the improvement will be less when the problem is recirculation.