Unrecognized pulmonary venous desaturation early after Norwood palliation confounds Gp:Gs assessment and compromises oxygen delivery.

ABSTRACT

BACKGROUND: Hemodynamic stability after Norwood palliation often requires manipulation of pulmonary vascular resistance to alter the pulmonary-to-systemic blood flow ratio (QpQs). QpQs is often estimated from arterial saturation (SaO2), a practice based on 2 untested assumptions constant systemic arteriovenous O2 difference and normal pulmonary venous saturation. METHODS AND RESULTS: In 12 patients early (oximetry was used to test whether SaO2 accurately predicts QpQs. Stepwise multiple regression assessed the contributions of SaO2, SsvcO2, and SpvO2 to QpQs determination. SaO2 correlated weakly with QpQs (R2=0.08, P<0.05). Inclusion of SsvcO2 and SpvO2 improved QpQs prediction accuracy. Pulmonary venous desaturation (SpvO2 <95%) was observed frequently (30%), especially at FiO2 patients. In 6 patients, FiO2 was increased incrementally from 0.17 to 0.50 to determine whether this was an effective means to manipulate QpQs. QpQs failed to change predictably with increased FiO2. In 5 of 6 patients, however, higher SpvO2 and SaO2 enhanced systemic oxygen delivery, as demonstrated by improvement in oxygen extraction. CONCLUSIONS: SaO2 correlated poorly with QpQs because of variability in SsvcO2 and SpvO2. A novel observation was that pulmonary venous desaturation occurred frequently early after Norwood palliation but normalized with higher FiO2 or PEEP. Because unrecognized pulmonary venous desaturation confounds ps assessment and compromises SaO2 and oxygen delivery, judicious use of inspired oxygen and PEEP may be beneficial in selected patients early after Norwood palliation.