Reduced Ventilator Pressure and Improved P/F Ratio During Percutaneous Arteriovenous Carbon Dioxide Removal for Severe Respiratory Failure

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Abstract
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. 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. 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 burn 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. 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. Percutaneous AVCO2R allows near-total CO2 removal and significant reductions in ventilator pressures with improvement in the P/F ratio.