Unrecognized pulmonary venous desaturation early after Norwood palliation confounds Qp : Qs assessment and compromises oxygen delivery

Background-Hemodynamic stability after Norwood palliation often requires ma nipulation of pulmonary vascular resistance to alter the pulmonary-to-syste mic blood flow ratio ((Q) over dot p:(Q) over dot s). (Q) over dot p:(Q) ov er dot s is often estimated from arterial saturation (SaO(2)), a practice b ased on 2 untested assumptions: constant systemic arteriovenous O-2 differe nce and normal pulmonary venous saturation. Methods and Results-In 12 patients early (less than or equal to3 days) afte r Norwood palliation, simultaneous arterial, superior vena caval (SsvcO(2)) , and pulmonary venous (SpvO(2)) oximetry was used to test whether SaO(2) a ccurately predicts (Q) over dot p:(Q) over dot s. Stepwise multiple regress ion assessed the contributions of SaO(2), SsvcO(2), and SpvO(2) to (Q) over dot p:(Q) over dot s detennination. SaO(2) correlated weakly with (Q) over dot p:(Q) over dot s (R-2 = 0.08, P < 0.05). Inclusion of SsvcO(2) and Spv O(2) improved (Q) over dot p:(Q) over dot s prediction accuracy. Pulmonary venous desaturation (SpvO(2) < 95%) was observed frequently (30%), especial ly at FiO(2) less than or equal to 0.21, but normalized with higher FiO(2) or PEEP in all patients. In 6 patients, FiO(2) was increased incrementally from 0.17 to 0.50 to determine whether this was an effective means to manip ulate (Q) over dot p:(Q) over dot s failed to change predictably with incre ased FiO(2). In 5 of 6 patients, however, higher SpvO(2) and SaO2 enhanced systemic oxygen delivery, as demonstrated by improvement in oxygen extracti on. Conclusions-SaO(2) correlated poorly with (Q) over dot p:(Q) over dot s bec ause of variability in SsvcO(2) and SpvO(2). A novel observation was that p ulmonary venous desaturation occurred frequently early after Norwood pallia tion but normalized with higher FiO(2) or PEEP. Because unrecognized pulmon ary venous desaturation confounds (Q) over dot p:(Q) over dot s assessment and compromises SaO(2) and oxygen delivery, judicious use of inspired oxyge n and PEEP may be beneficial in selected patients early after Norwood palli ation.