Reduced ventilator pressure and improved P/F ratio during percutaneous arteriovenous carbon dioxide removal for severe respiratory failure

Objective: To evaluate the effect of percutaneous arteriovenous carbon dioxide removal (AVCO₂R) on ventilator pressures and P/F ratio in a clinically relevant large-animal model of severe respiratory failure. Summary Background Data: AVCO₂R was developed as a simple arteriovenous shunt with a commercially available low-resistance gas exchange device of sufficient surface area for near-total CO₂ removal. With an AV shunt 10% to 15% of cardiac output, AVCO₂R allows a reduction in ventilator airway pressures without hypercapnia or the complex circuitry and monitoring required for conventional ECMO. Methods: AVCO₂R was applied to a new, clinically relevant large-animal model of severe respiratory failure created by smoke inhalation and cutaneous flame burn injury. Adult sheep (n = 9, 38 ± 6 kg) received a 40% total body surface area, third-degree cutaneous flame bum and 36 breaths of cotton smoke insufflation. After injury, all animals were placed on volume-controlled mechanical ventilation to achieve Pao₂ > 60 mmHg and Paco₂ < 40 mmHg. Animals were placed on AVCO₂R within 40 to 48 hours of injury when the Pao₂/Fio₂ was < 200. Animals underwent cannulation of the carotid artery and jugular vein with percutaneous 10F arterial and 14F venous cannulas. Shunt flow was continuously monitored using an ultrasonic flow probe and calculated as a percentage of cardiac output. Results: AVCO₂R flows of 800 to 900 ml/min (11% to 13% cardiac output) achieved 77 to 104 ml/min of CO₂ removal (95% to 97% total CO₂ production) while maintaining normocapnia. Significant reductions in ventilator settings were tidal volume, 421.3 ± 39.8 to 270.0 ± 6.3 ml; peak inspiratory pressure, 24.8 ± 2.4 to 13.7 ± 0.7 cm H₂O; minute ventilation, 12.7 ± 1.4 to 6.2 ± 0.8 L/min; respiratory rate, 25.4 ± 1.3 to 18.4 ± 1.8 breaths/min; and Fio₂, 0.88 ± 0.1 to 0.39 ± 0.1. The P/F ratio increased from 151.5 ± 40.0 at baseline to 320.0 ± 17.8 after 72 hours. Conclusions: Percutaneous AVCO₂R allows near- total CO₂ removal and significant reductions in ventilator pressures with improvement in the P/F ratio.