Oxygenation in Patients With a Functionally Univentricular Circulation and Complete Mixing of Blood

Darrel P. Francis, Keith Willson, Sara A. Thorne, L. Ceri Davies, Andrew J. S. Coats
1999 Circulation  
Background-Perioperative management of patients with complete mixing of pulmonary and systemic blood centers on approximately equating pulmonary (Qp) and systemic (Qs) blood flow (Qp/QsϷ1). This empirically derived target is opposed by theoretical studies advocating a target Qp/Qs well below 1. We studied the cause of this persistent discrepancy. Methods and Results-Classic theoretical studies have concentrated on maximizing 1 of many potential combination parameters of arterial oxygen content
more » ... CaO 2 ) and systemic blood flow: total oxygen delivery (DO 2 )ϭCaO 2 ϫQs. We defined "useful" oxygen delivery as the amount of oxygen above a notional saturation threshold (Sat Thresh ): D(u)O 2 ϭcarrying capacityϫ(SaO 2 ϪSat Thresh )ϫQs. Whereas DO 2 peaks at Qp/Qs ratios Ͻ1, D(u)O 2 peaks at higher Qp/Qs ratios, nearer to (or exceeding) 1. Systemic venous saturation (which mirrors tissue oxygen tension) peaks at Qp/Qsϭ1. Conclusions-First, the standard model of single-ventricle physiology can be reexpressed in a form allowing analysis by differential calculus, which allows broader conclusions to be drawn than does computer modeling alone. Second, the classic measure DO 2 fails to reflect the fact that proportional changes in saturation and flow are not clinically equivalent. Recognizing this asymmetry by using D(u)O 2 can give a target Qp:Qs balance that better represents clinical experience. Finally, to avoid an arbitrary choice of Sat Thresh , systemic venous oxygen saturation (SsvO 2 ) may be a useful parameter to maximize: this occurs at a Qp/Qs ratio of 1. Attempts to increase DO 2 by altering Qp/Qs away from this value will inevitably reduce SsvO 2 and therefore tissue oxygenation. Oxygen delivery is far from synonymous with tissue oxygen status. (Circulation. 1999;100:2198-2203.)
doi:10.1161/01.cir.100.21.2198 pmid:10571980 fatcat:5fvx5c6bx5aihcj4jso6vqcwfm