Use of Ultrasonic Flow Probe for Realtime Pulmonary Blood Flow Monitoring after Norwood Stage 1 Operation
Pranava Sinha, MD, Lok Sinha, Can Yerebakan, Richard Jonas.
Children's National Medical Center, Washington, DC, USA.
Objective(s): Postoperative management after Stage 1 Norwood is challenging because of lack of real-time monitoring of systemic and pulmonary blood flow. Novel miniaturized ultrasonic flow probes (UFP) along with use of valved femoral vein homograft (FVH) for Sano shunts (RVPAS) introduce new management options.
Methods: 264 patient-hours of continuous flow measurements across RVPAS using UFP (Transonic Systems Inc. Ithaca NY) were conducted in three patients after Norwood Stage 1 operation. A composite RVPAS was constructed using a flow-limiting proximal ePTFE graft and a distal valved FVH. The UFP was placed around the FVH segment, and remained in place until delayed sternal closure on postoperative day 3-4.
Results: Compared to flows upon admission to the ICU there was progressive decline in pulmonary blood flow to <2L/min/m2 with nadir achieved by postoperative hour 8 in all patients (p<0.05). This low flow state persisted for 40-45 hours, followed by gradual return to baseline. A second period of low flow <2L/min/m2 corresponded with aggressive diuresis employed to allow delayed sternal closure (hours 60-75 postoperatively) (Figure 1). No conventionally monitored parameters were reflective of flow changes.
Conclusions:
Continuous measurement of pulmonary blood flow is feasible with technical modification to RVPAS. Profound and prolonged low pulmonary blood flow is seen after Norwood Stage 1 operation. Continuous flow measurement allows improved management of low flow conditions and fine-tuning of postoperative therapies. 
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