Abstract Background The Norwood procedure is one of the most complex surgical interventions for neonates with hypoplastic left heart syndrome. Even after a successful operation, patients may experience haemodynamic instability, leading to poor outcomes. While the most stable haemodynamics after the Norwood procedure are achieved empirically when the pulmonary-to-systemic flow ratio (Qp/Qs) is 1.0, the theoretically optimal Qp/Qs in the post-Norwood period remains unknown. Purpose Biological measurements, including blood gases and radial artery waveforms, were collected during the postoperative period and used to develop patient-specific Norwood circulation computational fluid dynamics (CFD) models. These models were constructed at arbitrary blood draw timings, incorporating lactate levels as a marker of haemodynamic stability. This study aims to determine the optimal Qp/Qs ratio in the postoperative period following the Norwood procedure, based on lactate level variations, and to provide insights into underlying haemodynamic parameters. Methods Three neonates (three females, median age: 34 days range: 30–41 days, median body weight: 2.6 kg range: 2.5–2.7 kg who underwent the Norwood procedure were included in this study. 0–1-dimensional lumped parameter Norwood circulation CFD models were developed using patient-specific data, including radial artery pressure waveforms, lactate levels, and oxygen saturation, and were reconstructed at thirty blood draw time points by minimising the differences between the actual and standard Norwood circulation CFD waveforms using the gradient descent method. The correlation between Qp/Qs and lactate levels was analysed, and the corresponding haemodynamic parameters were automatically calculated at each time point. Results The agreement rates for mean blood pressure and arterial oxygen saturation were 96 ± 2.5%, and 97 ± 2.3%, respectively. The relationship between lactate levels and elapsed time revealed that pulmonary vascular resistance decreased (R = -0.488) and pulmonary arterial compliance increased (R = 0.350) over time. Declining lactate levels correlated with reduced pulmonary vascular resistance (R = 0.609) and increased pulmonary arterial compliance (R = -0.296). Simultaneously, right ventricular active elastance decreased (R = 0.299), suggesting reduced ventricular afterload and optimised cardiac function. The lowest lactate levels coincided with a Qp/Qs ratio of 1.45. Conclusion This study successfully developed a series of patient-specific Norwood circulation CFD models by incorporating various physiological measurements to simulate postoperative haemodynamics. The models successfully demonstrated key haemodynamic parameters following the Norwood procedure and provided a theoretically feasible approach to representing patient-specific haemodynamics. A Qp/Qs ratio of 1.45 is the most favourable value for stabilising haemodynamics in the postoperative Norwood circulation.Patient-Specific Norwood CFD model Lactate level vs Qp/Qs
Sughimoto et al. (Sat,) studied this question.