Does size matter? Larger Blalock-Taussig shunt in the modified Norwood operation correlates with better hemodynamics.

OBJECTIVE

Excess pulmonary to systemic blood flow ratio (Qp/Qs) correlates with hemodynamic instability and mortality after modified Norwood operation. Studies suggest that maximal oxygen delivery occurs at a Qp/Qs of around 1. The use of a rather small modified Blalock-Taussig shunt (MBTS) is believed to achieve this goal. However, optimal MBTS size with respect to postoperative hemodynamics remains unclear.

METHODS

Between 2/2002 and 2/2004, 20 consecutive patients underwent Norwood operation; there were 19 operative survivors: nine with a normalized MBTS area (NSA) > or = 3.3 mm2/kg (group 1) and 10 with NSA < 3.3 mm2/kg (group 2). Mean arterial pressure (MAP) and common atrial pressures (CAP), arterial and superior vena cava oxygen saturations, urinary output and inotropes recorded for the postoperative hours 0, 6, 12, 18, 24 and 48 were analyzed.

RESULTS

Hospital mortality was 11.1% (1/9) in group 1 and 30% (3/10) in group 2 (P = 0.6). For group 1 significantly higher MAP of 52+/-1.3 versus 46+/-0.8 mmHg (P < 0.001), higher urinary output of 6.2+/-0.5 versus 4.2+/-0.5 ml/kg per h (P < 0.01), lower CAP of 8+/-0.3 versus 10+/-0.4 mmHg (P < 0.001), and lower heart rate of 145+/-2.6 versus 160+/-1.6 bpm were recorded than for group 2. In group 1, lower doses of adrenaline (0.03+/-0.01 versus 0.15+/-0.01 microg/kg per min, P < 0.05) and noradrenaline (0.01+/-0.01 versus 0.13+/-0.04 microg/kg per min, P < 0.01) were needed. Although Qp/Qs was more often calculated to be > 1.5 in group 1 (51 versus 31%), arteriovenous oxygen difference and oxygen excess factor were not significantly different, indicating similar oxygen delivery.

CONCLUSIONS

Monitoring of the central venous oxygen saturations and application of afterload reduction in cases of high Qp/Qs allows the insertion of a larger MBTS without association with lower oxygen delivery. In fact, better hemodynamic status with less inotropic support was noted with a larger MBTS early after Norwood operation.