Effect of change in tidal volume on left to right shunt across ventricular septal defect in children - A pilot study

Background : Pulmonary vascular resistance, an important determinant of shunting across ventricular septal defects (VSD), rises at both extremes of lung volume. Aims : We sought to determine the effect of changes in tidal volumes (VT) on pulmonary blood flow (Qp), systemic blood flow (Qs), and shunt (Qp/Qs) in children with VSD. Setting : Single-center teaching hospital. Design : Prospective observational study. Methods : Thirty children with a mean age of 11.8 ± 5 months undergoing surgical closure of VSD were studied. Hemodynamics and shunt-related parameters were assessed using transthoracic echocardiography measured at three different VT i.e. 10, 8, and 6-ml/kg keeping the minute ventilation constant. Results : Reduction in VT from 10 to 8 to 6 ml/kg led to a reduction in gradient across VSD measuring 23.5, 20 and 13 mmHg respectively (P < 0.001). Similarly, right ventricluar outflow tract (RVOT) diameter, RVOT velocity time integral, Qp (57.3 ± 18.1, 50.6 ± 16.9, 39.9 ± 14.7 mL; P < 0.001), Qs (24.1 ± 10.4, 20.0 ± 8.7, 15.3 ± 6.9 mL; P < 0.001) and peak airway pressure (17.2 ± 1.5, 15.8 ± 1.3, 14.5 ± 1.2 cmHg; P < 0.001) showed progressive decline with decreasing VT from 10 to 8 to 6 ml/kg, respectively. However, Qp/Qs (2.4 ± 0.4, 2.6 ± 0.4, 2.6 ± 0.4) demonstrated a minor increasing trend. Conclusion : Lower V_Treduces the gradient across VSD, the pulmonary blood flow, and the peak airway pressure. Hence, ventilation with lower V_Tand higher respiratory rate maintaining adequate minute ventilation might be preferable in children with VSD. Further studies are required to confirm the findings of this pilot study.