Background - Hemodynamic stability after Norwood palliation often requires manipulation of pulmonary vascular resistance to alter the pulmonary-to-systemic blood flow ratio (Q̇p:Q̇s). Q̇p:Q̇s 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 (≤3 days) after Norwood palliation, simultaneous arterial, superior vena caval (Ssvco2), and pulmonary venous (Spvo2) oximetry was used to test whether Sao2 accurately predicts Q̇p:Q̇s. Stepwise multiple regression assessed the contributions of Sao2, Ssvco2, and Spvo2 to Q̇p:Q̇s determination. Sao2 correlated weakly with Q̇p:Q̇s (R2=0.08, P<0.05). Inclusion of Ssvco2 and Spvo2 improved Q̇p:Q̇s prediction accuracy. Pulmonary venous desaturation (Spvo2 <95%) was observed frequently (30%), especially at Fio2 ≤0.21, but normalized with higher Fio2 or PEEP in all patients. In 6 patients, Fio2 was increased incrementally from 0.17 to 0.50 to determine whether this was an effective means to manipulate Q̇p:Q̇s. Q̇p:Q̇s 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 Q̇p:Q̇s 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 Q̇p:Q̇s assessment and compromises Sao2 and oxygen delivery, judicious use of inspired oxygen and PEEP may be beneficial in selected patients early after Norwood palliation.
- Heart defects, congenital
- Hypoplastic left heart syndrome
- Norwood operation