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A Bidani

Publications and source records attributed to A Bidani.

134 records · Page 8Linked to original sources
PubMedDate not supplied

Determination of low blood flow limits for arteriovenous carbon dioxide removal.

Arteriovenous carbon dioxide removal (AVCO2R) has been shown to achieve total carbon dioxide (CO2) exchange. To determine optimal blood and gas flow parameters that can provide maximal gas exchange and evaluate the utility of AVCO2R at reduced blood flow, the authors used a low resistance membrane gas exchanger within an arteriovenous shunt in mechanically ventilated sheep. Adult female sheep (n = 5) were anesthetized and underwent placement of the gas exchange device in a simple arteriovenous shunt created between the carotid artery and common jugular vein. CO2 removal was determined as the product of the sweep gas flow (100% oxygen) and its exhaust CO2 content. Gas and blood flow were varied independently, and incremental reductions in minute ventilation (MV) were made while maintaining normocapnia. At maximally reduced ventilator settings, stepwise reductions in blood flow were made to determine the resultant changes in arterial PaCO2 at a sweep gas flow of 3 L/min. CO2 removal increased proportionally to blood flow to a maximum of 1,417 +/- 26 ml/min (19% of cardiac output) and gas flow to 3 L/min. Normal PaO2 and PaCO2 could be maintained with minimal ventilator support (MV = 16% baseline MV) at a blood flow of 500 ml/min or higher. At these maximally reduced ventilator settings, moderate hypercapnia (PaCO2 < or = 75 mmHg) resulted only when blood flow was decreased to below 500 ml/min. Optimizing AVCO2R blood and gas flow maximizes CO2 removal and allows a significant reduction in minute ventilation. In cases of severely limited blood flow, lung rest can still be realized at moderate hypercapnia. At flow rates achievable by percutaneous access, extracorporeal AVCO2R can be used to achieve lung rest during mechanical ventilation.

Adult↗
PubMedDate not supplied

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.

Animals↗
PubMedDate not supplied

Intravascular membrane oxygenator and carbon dioxide removal devices: a review of performance and improvements.

The first intravascular oxygenator and carbon dioxide (CO2) removal device (IVOX), conceived by Mortensen, was capable of removing 30% of CO2 production of an adult at normocapnia with a measurable reduction in ventilator requirements. Through studies of mathematical modeling, an ex vivo venovenous bypass circuit to model the human vena cava, animal models of severe smoke inhalation injury, and patients with acute respiratory failure, the practice of permissive hypercapnia has been established to enhance CO2 removal by IVOX. By allowing the blood pCO2 to rise gradually, the CO2 excretion by IVOX can be linearly increased in a 1:1 relationship. Experimental and clinical studies have shown that CO2 removal by IVOX can increase from 30 to 40 ml/min at a normal blood pCO2 to 80 to 90 ml/min at a pCO2 of 90 mm Hg. In addition, IVOX with permissive hypercapnia allows a significant reduction in minute ventilation and peak airway pressure. Active blood mixing to decrease the boundary layer resistance in the blood can significantly improve O2 transfer by up to 49% and CO2 removal by up to 35%. Design changes can also improve the performance of IVOX. Increased surface area with more fibers and enhanced mixing by increased fiber crimping in new prototypes of IVOX significantly increased CO2 removal. Other groups have used alternative designs to address the limited performance of intravascular gas exchange devices. With improved design and patient management, clinically meaningful gas exchange and reduction in mechanical ventilatory support may be achieved during treatment of severe respiratory failure.

Adult↗
PubMedDate not supplied

Significant enhancement of carbon dioxide removal by a new prototype IVOX.

The intravenacaval blood gas exchanger (IVOX) developed by Cardiopulmonics, Inc. has been tested in animals and in human clinical trials for partial support of gas exchange (25-30%) to allow reduction in mechanical ventilatory support and barotrauma during acute respiratory failure. After recognizing the limitations of the device and limited clinical utility of removing only 25-30% of CO2 production, the authors have made design changes in the IVOX (prototypes IIA and IIB), including increased fiber number, decreased fiber length, decreased fiber diameter, and increased crimping. Nine ewes underwent placement of the IVOX prototypes in an ovine model of severe smoke inhalation injury. A modification of the original insertion technique was used to implant the prototypes. CO2 removal was directly measured from the outlet gas. O2 exchange was calculated from IVOX on/off measurements. Neither IVOX IIA nor IIB significantly changed hemodynamics when a fluid bolus (15 ml/kg) was infused before insertion. There were no significant differences between prototypes regarding thrombosis, emboli, or incidence of bleeding complications. Both prototypes significantly improved CO2 removal (60-80%) compared with that reported for an older IVOX model. The improved gas transfer by these prototypes would serve to decrease mechanical ventilatory requirements and barotrauma in the treatment of severe respiratory failure.

Animals↗
PubMedDate not supplied

Intracorporeal CO2 removal and permissive hypercapnia to reduce airway pressure in acute respiratory failure. The theoretical basis for permissive hypercapnia with IVOX.

Initial studies have shown that the intravascular oxygenator and carbon dioxide removal device (IVOX, Cardiopulmonics, Inc., Salt Lake City, UT) removes approximately 30% of VCO2. After noting increased CO2 removal with increased venous CO2, we developed a conceptual analytical model based on data obtained from patients and laboratory experiments. Increasing the CO2 gradient across the hollow fiber membranes of IVOX increases the operating efficiency of the device. Using the patient management technique of permissive hypercapnia (limiting tidal volumes, respiratory rates, and airway pressures) serves to increase the CO2 gradient across the membrane. The conceptual analytical model predicts that a PaCO2 of 75-80 mm Hg is required to obtain a CO2 gradient that results in IVOX CO2 removal of approximately 90-100 ml CO2/min. This technique may allow a broader application of both permissive hypercapnia and IVOX in acute respiratory failure.

Acute Disease↗
PubMedDate not supplied

High flow/low resistance cannulas for percutaneous arteriovenous carbon dioxide removal.

Percutaneous cannulas with low resistance are necessary for arteriovenous carbon dioxide removal (AVCO2R) to allow highest flow at lowest pressure to maximize CO2 removal. Commercially available arterial (A) and venous (V) percutaneous cannulas (8-18 Fr) were tested for pressure/flow characteristics under conditions that simulated percutaneous AVCO2R at clinically pertinent flow rates between 200-1000 ml/min to obtain the M number previously described by Delius, et al. The Bio-Medicus (Bio-Medicus, Grand Rapids, MI) 17F A, Research Medical, Inc (RMI) (Model FEM II, Research Medical, Inc., Midvale, UT) 16F A, and RMI 18F V cannulas exhibited the lowest M numbers that correlated with low resistance to flow. The four most clinically favorable arterial cannulas (8, 10, 12, and 14 Fr), coupled with a venous cannula four French sizes larger, were used in an AVCO2R circuit in adult sheep (n = 3) at varying mean arterial pressures (MAP) between 65-105 mmHg. The 8, 10, 12, and 14 Fr arterial cannulas allowed an arteriovenous flow of 208 +/- 72, 530 +/- 37, 848 +/- 66, and 944 +/- 96 ml/min, respectively, at a MAP of 65 mmHg. An increase in MAP to 105 mmHg was associated with approximately a 41, 30, 32, and 27% increment in blood flow, respectively. In summary, an arterial percutaneous cannula of 10 Fr or larger will allow AVCO2R blood flow greater than 500 ml/min, as previously shown by Brunston et al. to achieve total CO2 removal without incurring hypercapnia.

Adult↗
PubMedDate not supplied

Organ blood flow during arteriovenous carbon dioxide removal.

Animal models of arteriovenous carbon dioxide removal (AVCO2R) have achieved lung rest during treatment of severe respiratory failure, with total CO2 removal at arteriovenous shunt flow rates of 10% to 25% of cardiac output (CO). Previously, no statistically significant changes were reported in heart rate, cardiac output, mean arterial pressure, or pulmonary arterial pressure during prolonged (7 days) AVCO2R with shunt flows to 25% of CO. In this study, to determine the effect of various shunt levels on organ blood flow, colored microspheres were used in a conscious ovine model of AVCO2R. A low resistance 2.5 m2 oxygenator was placed in a simple carotid-to-jugular arteriovenous circuit. The AVCO2R flow (Qb) was incrementally increased to 5%, 10%, 15%, 20%, and 25% of baseline CO. After equilibration, colored microspheres were injected into a left atrial catheter while reference blood was withdrawn from an arterial line at a constant rate. Organ blood flow obtained by measuring microspheres in the tissues, showed approximately a 10-20% decrease at a 5% shunt, but remained relatively unchanged thereafter at up to a 25% shunt, and was well tolerated without hemodynamic sequelae or evidence of end organ ischemia. It was concluded that AVCO2R can achieve lung rest during respiratory failure at flow rates of 10-25% CO, with a resultant mild decrease in critical organ blood flow that appears well tolerated.

Adult↗