IVOX with gradual permissive hypercapnia: A new management technique for respiratory failure

IVOX (intravenous oxygenator and CO₂ removal device) augments venous gas exchange in patients with severe respiratory failure. Controlled hypoventilation with permissive hypercapnia reduces airway pressures during mechanical ventilation and augments CO₂ exchange through the IVOX. To quantify the additive effects of gradual permissive hypercapnia and IVOX on gas exchange and reduction of airway pressures, 13 adult sheep underwent tracheostomy and severe smoke inhalation injury. Seven were mechanically ventilated alone (control), and six had mechanical ventilation, systemic anticoagulation, and implantation of IVOX (size 7 with 0.21-m² surface area) (IVOX group). Both groups were anesthetized and paralyzed for 24 hr. In the IVOX group, minute ventilation was decreased in a stepwise fashion to produce a gradual increase in P_aCO₂, from 30 to 95 mm Hg, over 12 hr, and then sustained for an additional 12 hr. Sodium bicarbonate was given intravenously as necessary to keep arterial pH above 7.25. There were no significant differences in mean arterial pressure, cardiac output, or pulmonary artery pressure between the two groups. In the IVOX/permissive hypercapnia group, IVOX CO₂ removal increased as a linear function of P_aCO₂ (y = 0.87x + 8.99, R² = 0.80). IVOX CO₂ removal was only 40 ml/min at normocapnia (40 mm Hg) but increased to 91 ml/min when P_aCO₂ was 95 mm Hg. Both peak inspiratory pressure and minute ventilation of the IVOX/permissive hypercapnia group were significantly lower than the control group, 30 ± 4 mm Hg vs 51 ± 3 mm Hg and 3.9 ± 0.3 liters vs 8.4 ± 0.5 liters (P < 0.05) respectively. CO₂ removal by IVOX can be substantially augmented under conditions of permissive hypercapnia, reducing the ventilatory requirements in an ovine model of acute smoke inhalation injury.