Effets de la ventilation mécanique avec PEP sur le shunt intracardiaque droit-gauche par un foramen ovale perméable

Abstract

• Objective : To assess the presence of a patent foramen ovale (PFO) using colloid contrast transoesophageal echocardiography in mechanically ventilated patient with and without PEEP and it repercussion on PaO 2. • Study design : Prospective open before-after trial. • Patients : Forty-nine mechanically ventilated patients with respiratory failure (PaO 2/FiO 2 < 250). • Methods : PEEP assessment before and after adding a PEEP = 10 cmH 2O. At each level of PEEP, semi-quantification of PFO was performed and arterial blood gases were withdrawn at FiO 2 = 1, with 15 min at each level. Semiquantification of the right-to-left intra cardiac shunt through a patent foramen ovale was obtained using the quantity of microbubbles in the left atrium on a basal short axis view. • Results : A PFO was detected in 11 out of 49 patients (22 %). A right-to-left shunt developed in one and worsen in three patients when PEEP was added. In patients without a PFO, PaO 2 increased significantly (from 119 ± 10 mmHg to 145 ± 10 mmHg, P < 0.001). In patients with a PFO, non significant changes occurred (118 ± 15 mmHg to 120 ± 17 mmHg). After adding PEEP, the difference between the two groups was significant (ANOVA, P < 0.05). Moreover, a PFO was present during the whole respiratory cycle in two out of 11 patients. These 2 patients exhibited a PaO 2 < 100 mmHg with or without PEEP. • Conclusion : This study suggests that mechanical ventilation with PEEP enhances an intracardiac right-to-left shunt through a PFO. This condition is responsible for the lack of improvement in blood oxygenation when PEEP is added. When a PFO is present all over the respiratory cycle, or when the oxygenation is worsened with PEEP, this positive pressure ventilation should be avoided. The deleterious consequences of mechanical ventilation on venous return may be minimized by partial ventilation and weaning from ventilator.