Is indexed preoperative superior vena cava blood flow a risk factor in patients undergoing bidirectional cavopulmonary shunt?

Background: This study evaluated the effect of a new measurement - superior vena cava (SVC) flow - and anatomic factors on postoperative arterial oxygen saturation and clinical outcome in patients who underwent bidirectional cavopulmonary shunt (BCPS). Methods: We reviewed 19 patients who underwent a BCPS between January 2009 and May 2011 who also had SVC blood flow measurements. Median age was 6 months (range, 2 to 29 months). Body weight was 7.0 ± 1.7 kg. Bilateral SVCs were present in 4. SVC flow was measured at the time of BCPS by a Transonic flow probe (Transonic Systems Inc, Ithaca, NY). SVC flow, preoperative hemodynamics, pulmonary artery size, and clinical outcome were analyzed to determine risk for morbidity and death. Results: Mean absolute and indexed pre-BCPS SVC flow was 0.65 ± 0.23 L/min and 1.63 ± 0.55 L/min/m² or 91.1 ± 30.8 mL/kg/min, respectively. In all but 1 patient, the SVC flow was increased after BCPS from 1.63 ± 0.55 to 1.99 ± 0.57 L/min/m² (p = 0.005). There was a significant positive correlation between pre-BCPS and post-BCPS SVC flow (r = 0.627, p = 0.029). Pulmonary artery size correlated with post-BCPS SVC flow (r = 0.560, p = 0.016). Two patients with preoperative SVC flow of below 1.0 L/min/m² died or required BCPS takedown. SVC size did not correlate with BCPS flow (r = 0.231, p = 0.356). Univariate analysis indicated pre-BCPS pulmonary artery pressure was a risk factor for low arterial oxygen saturation (≤ 75%) immediately after BCPS (p = 0.042) and at discharge (p = 0.030). Conclusions: A new indicator - low SVC flow, may be a marker for BCPS failure or death, suggesting that the SVC flow vs size is more important in predicting successful BCPS.