Intravenacaval membrane oxygenation and carbon dioxide removal in severe acute respiratory failure.

STUDY OBJECTIVE: To characterize the physiologic response to, and safety of, intravenacaval membrane oxygenation and carbon dioxide removal. DESIGN: Interventional before-after study. SETTING: University teaching hospital ICU. PATIENTS: Twenty-two patients with severe acute respiratory distress syndrome (ARDS). INTERVENTIONS: Implantation of a hollow-fiber membrane oxygenator (IVOX; CardioPulmonics; Salt Lake City, Utah) into the superior and inferior venae cavae by venotomy of the right femoral or right internal jugular vein for a duration of up to 20 days. MEASUREMENTS: Hemodynamic measurements using pulmonary artery and systemic artery catheters, ventilator settings (FIO2, minute ventilation, peak inspiratory pressure, and positive end-expiratory pressure), arterial and mixed venous blood gases (pH, PCO2, PO2, and measured saturation), and clinical laboratory determinations (CBC, fibrinogen, plasma hemoglobin, complement C3 and C5) were obtained. Calculations of PaO2/FIO2 ratio and PaCO2-VE product were used to assess gas exchange efficacy. Microbiologic cultures were obtained from the device and wound following explantation. Survival to ICU discharge and hospital discharge were recorded. RESULTS: Implantation was successful in 20 of 22 patients. Gas exchange rates averaged 50.4 +/- 15.8 mL.min-1 for carbon dioxide and 71.1 +/- 20.2 mL.min-1 for oxygen. A reduction in FIO2 from 0.78 +/- 0.16 to 0.63 +/- 0.21 and in VE from 177 +/- 94 mL.kg-1.min-1 to 127 +/- 58 mL.kg-1.min-1 was possible within 4 h post-implantation. By 12 h, FIO2 was reduced to 0.57 +/- 0.18. Indices of gas exchange improved significantly after implantation, with PaO2/FIO2 ratio increasing from 79 +/- 20 to 112 +/- 47 and PaCO2-VE product decreasing from 7.6 +/- 4.2 to 4.9 +/- 2.5 within 4 h. A significant reduction in peak inspiratory pressure was achieved (45 +/- 10 to 38 +/- 9 cm H2O). Major complications were blood loss during implantation requiring transfusion in 11 patients, a retroperitoneal bleed in 1 patient, and femoral deep venous thrombosis in 4 patients, but there were no long-term sequelae or IVOX-related deaths. The ICU and hospital survival were 10/20 (50%) and 8/20 (40%), respectively. CONCLUSIONS: Intravenacaval membrane oxygen and carbon dioxide removal can provide partial respiratory support during severe respiratory failure and permit reductions in the level of mechanical ventilator support, with an acceptable safety profile.

Total extracorporeal arteriovenous carbon dioxide removal in acute respiratory failure: a phase I clinical study.

OBJECTIVE: To evaluate the safety and efficacy of pumpless extracorporeal arteriovenous carbon dioxide removal (AVCO2R) in subjects with acute respiratory failure and hypercapnia. DESIGN: A phase I within-group time series trial in which subjects underwent up to 72 h of support with AVCO2R in intensive care units of two university hospitals. PATIENTS: Eight patients with acute hypercapnic respiratory failure or hypoxemic respiratory failure managed with permissive hypercapnia. INTERVENTIONS: Extracorporeal CO2 removal was achieved through percutaneous cannulation of the femoral artery and vein, and a simple extracorporeal circuit using a commercially available membrane gas exchange device for carbon dioxide exchange. MEASUREMENTS AND RESULTS: Measurements of hemodynamics, blood gases, ventilatory settings, and laboratory values were made before initiation of AVCO2R, and at subsequent intervals for 72 h. PaCO2 decreased significantly from 90.8+/-7.5 mmHg to 52.3+/-4.3 and 51.8+/-3.1 mmHg at 1 and 2 h, respectively. This decrease occurred despite a decrease in minute ventilation from a baseline of 6.92+/-1.64 l/min to 4.22+/-.46 and 3.00+/-.53 l/min at 1 and 2 h. There was a normalization of pH, with an increase from 7.19+/-.06 to 7.35+/-.07 and 7.37+/-.05 at 1 and 2 h. These improvements persisted during the full period of support with AVCO2R. Four subjects underwent apnea trials in which AVCO2R provided total carbon dioxide removal during apneic oxygenation, resulting in steady-state PaCO2 values from 57 to 85 mmHg. Hemodynamics were not significantly altered with the institution of AVCO2R. There were no major complications attributed to the procedure. CONCLUSION: Pumpless extracorporeal AVCO2R is capable of providing complete extracorporeal removal of carbon dioxide during acute respiratory failure, while maintaining mild to moderate hypercapnia. Applied in conjunction with mechanical ventilation and permissive hypercapnia, AVCO2R resulted in normalization of arterial PCO2 and pH and permitted significant reductions in the level of mechanical ventilation.

Percutaneous extracorporeal arteriovenous CO2 removal for severe respiratory failure.

BACKGROUND: In previous animal studies, arteriovenous CO2 removal (AVCO2R) achieved significant reduction in ventilator pressures and improvement in the Pao2 to fraction of inspired oxygen ratio during severe respiratory failure. For our initial clinical experience, 5 patients were approved for treatment of severe respiratory failure and CO2 retention to evaluate the feasibility and safety of percutaneous AVCO2R. METHODS: Patients were anticoagulated with heparin (activated clotting time, 260 to 300 seconds), underwent percutaneous femoral cannulation (10F to 12F arterial and 12F to 15F venous catheters), and then were connected to a low-resistance, 2.5-m2 hollow-fiber oxygenator for 72 hours. RESULTS: Mean AVCO2R flow at 24, 48, and 72 hours was 837.4+/-73.9, 873+/-83.6, and 750+/-104.5 mL/min, respectively, with no vascular complications and no significant change in heart rate or mean arterial pressure. Removal of CO2 plateaued at an AVCO2R flow of 1086 mL/min with 208 mL/min CO2 removed. Average CO2 transfer at 24 and 48 hours was 142+/-17 and 129+/-16 mL/min. Use of AVCO2R allowed a significant decrease in minute ventilation from 7.2+/-2.3 L/min at baseline to 3.4+/-0.8 L/min at 24 hours. CONCLUSIONS: All patients survived the experimental period without adverse sequelae. Percutaneous AVCO2R can achieve approximately 70% CO2 removal in adults with severe respiratory failure and CO2 retention without hemodynamic compromise or instability.

Arteriovenous extracorporeal carbon dioxide removal: a mathematical model and experimental evaluation.

To explore the feasibility and operating limits of arteriovenous extracorporeal CO2 removal (AVCO2R) for support of acute respiratory failure, the authors developed a mathematical model to simulate (AVCO2R), evaluate the effects of several parameters used in its application, and predict the feasibility and necessary conditions for total CO2 removal. The mathematical model incorporated compartments representing blood, pulmonary alveoli, pulmonary capillaries, peripheral tissues and capillaries, and an extracorporeal gas exchange device. The model was validated against an animal model of extracorporeal CO2 removal. This model consisted of anesthetized and mechanically ventilated piglets. An extracorporeal CO2 removal device was placed by cannulation of a femoral artery and vein. Dynamic and steady state measurements of CO2 transfer were made and compared with simulations using the mathematical model. There was good agreement between experimental and simulated data, validating the mathematical model under a variety of conditions. The mathematical model was used to determine operating parameters for total CO2 removal. Relationships between extracorporeal blood flow, device diffusing capacity, and device gas sweep flow were established for CO2 removal at various levels of CO2 production. These simulations indicate that it is possible to achieve total CO2 removal using an extracorporeal shunt fraction of 10%-15% of cardiac output, a device diffusing capacity of 0.5 ml x min(-1) x torr(-1) (kg body weight)(-1), and a gas:blood flow of 5 or greater.

Nosocomial pneumonia.

Nosocomial pneumonia remains a major cause of morbidity, mortality, and significant hospital cost despite continued refinements in antimicrobial treatment, improved methods for diagnosis, and better supportive and preventive measures. While clinical experience is considerable, appreciation of the epidemiologic and pathogenic factors responsible for NP development and pathogen selection are limited, and consensus regarding optimal prevention and diagnostic and therapeutic strategies is lacking. This article reviews the recent literature with an emphasis on significance, pathogenesis, etiology, and therapy of nosocomial pneumonia.