The effects of ventilation on left-to-right shunt and regional cerebral oxygen saturation: a self-controlled trial

Background: Increase of pulmonary vascular resistance (PVR) is an efficient method of modulating pulmonary and systemic blood flows (Qp/Qs) for patients with left-to-right (L-R) shunt, and is also closely associated with insufficient oxygen exchange for pulmonary hypoperfusion. So that it might be a preferred regime of maintaining arterial partial pressure of carbon dioxide tension (PaCO2) within an optimal boundary via ventilation management in congenital heart disease (CHD) patients for the inconvenient measure of the PVR and Qp/Qs. However, the appropriate range of PaCO2 and patient-specific mechanical ventilation settings remain controversial for CHD children with L-R shunt. Methods: Thirty-one pediatric patients with L-R shunt, 1-6 yr of age, were included in this observation study. Patients were ventilated with tidal volume (V-T) of 10, 8 and 6 ml/kg in sequence, and 15 min stabilization period for individual VT. The velocity time integral (VTI) of L-R shunt, pulmonary artery (PA) and descending aorta (DA) were measured with transesophageal echocardiography (TEE) after an initial 15 min stabilization period for each VT, with arterial blood gas analysis. Near-infrared spectroscopy sensor were positioned on the surface of the bilateral temporal artery to monitor the change in regional cerebral oxygen saturation (rScO(2)). Results: PaCO2 was 31.51 +/- 0.65mmHg at VT 10ml/kg vs. 37.15 +/- 0.75mmHg at VT 8ml/kg (P < 0.03), with 44.24 +/- 0.99 mmHg at V-T 6 ml/kg significantly higher than 37.15 +/- 0.75mmHg at V-T 8 ml/kg. However, PaO2 at a VT of 6 ml/kg was lower than that at a V-T of 10ml/kg (P = 0.05). Meanwhile, 72% (22/31) patients had PaCO2 in the range of 40-50mmHg at V-T 6 ml/kg. VTI of L-R shunt and PA at V-T 6ml/kg were lower than that at V-T of 8 and 10 ml/kg (P < 0.05). rScO(2) at a V-T of 6 ml/kg was higher than that at a V-T of 8 and 10 ml/kg (P < 0.05), with a significantly correlation between rScO(2) and PaCO2 (r = 0.53). VTI of PA in patients with defect diameter > 10mm was higher that that in patients with defect diameter <= 10mm. Conclusions: Maintaining PaCO2 in the boundary of 40-50mmHg with V-T 6 ml/kg might be a feasible ventilation regime to achieve better oxygenation for patients with L-R shunt. Continue raising PaCO2 should be careful.