Franco L. Fazzalari

The development of an implantable artificial lung

This report describes the development of an implantable gas exchange device. The device is composed of hollow fiber elements wound around a central open core enclosed in a compliant outer casing, offering very low resistance to blood while providing adequate gas exchange. The purpose of this study was to determine if this device design can completely support the gas exchange requirements of a large animal when the device is placed in series with the main pulmonary artery (PA). Six 40-80 kg adult sheep were used. The device was placed with vascular grafts anastomosed end to side on the proximal and distal main PA. The study began with the entire right ventricular blood flow being diverted through the device by occlusion of a snare around the PA between the vascular grafts. Total gas exchange then was provided by the device and the endotracheal tube was clamped. Results showed that this pumpless potentially implantable device is capable of completely supporting the gas exchange requirements of the experimental animals for up to 8 hours in the acute setting without significant change in cardiac index (CI) and oxygen consumption (VO2) compared with baseline. CI = 55.0 +/- 17.0 cc/min/kg versus 45.0 +/- 17.3 cc/min/kg. VO2 = 1.90 +/- 0.96 cc O2/min/kg versus 2.08 +/- 0.54 cc O2/min/kg.

Evaluation of the right atrial venous oxygen saturation as a physiologic monitor in a neonatal model

Pulmonary artery (PA) mixed venous saturation (SvO2) has become a crucial monitor in the adult intensive care unit, but is not used in neonates because of the difficulty in PA catheterization. We evaluated the possibility of utilizing the right atrial venous oxygen saturation (RAvO2), which is easily accessed in the neonate, as a monitor of the effects of mechanical ventilation and intravascular volume in an animal model selected to be the size of the human neonate. A continuous RAvO2 monitoring catheter was placed into the right atrium of 16 normal rabbits (2.2 to 4.1 kg). Oxygen delivery was manipulated by alterations in peak inspiratory pressure (PIP) (n = 6), positive end-expiratory pressure (PEEP) (n = 6), or by progressive hypovolemia (n = 4). RAvO2 decreased with onset of mechanical ventilation alone from 69% +/- 6% to 61% +/- 5% (P < .01). As the PIP was increased from 12 to 21 cm H2O, the RAvO2 progressively decreased from 59% +/- 4% to 49% +/- 6% (P < .05). As the PEEP was increased from 3 to 9 cm H2O, the RAvO2 progressively decreased from 64% +/- 5% to 33% +/- 16% (P < .01). RAvO2 approached baseline after return to continuous positive airway pressure (CPAP) of 3 cm H2O. Progressive phlebotomy to a total of 10 mL/kg resulted in a decrease in RAvO2 from 70% +/- 6% to 27% +/- 5% (P < .001). Volume resuscitation resulted in an increase in RAvO2 to near baseline. Peripheral arterial oxygen saturation remained at a constant 100% throughout each protocol.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of native mixed venous saturation during venovenous extracorporeal circulation.

&NA; The ability to monitor the match between systemic oxygen delivery and consumption using mixed venous oxygen saturation is an important component of management of critically ill patients. Mixed venous oxygen saturation is a particularly useful parameter in circumstances where systemic oxygen delivery is significantly compromised, such as the acute respiratory distress syndrome. With the advent of venovenous extracorporeal life support (ECLS) in the treatment of this condition, however, accurate measurement of true mixed venous oxygen saturation has not been available, because of this artificial elevation of venous oxygen content. Using an algebraic solution, the authors developed an equation to calculate true patient mixed venous oxygen saturation during ECLS. This is accomplished using readily obtainable data such as cardiac output, ECLS flow, ECLS circuit pre and post oxygenator blood oxygen content, pulmonary arterial oxygen saturation, and patient hemoglobin. The formula has been used in an in vitro model, simulating venovenous ECLS and native venous saturation ranging from 20‐72%, with a resulting correlation coefficient between calculated and measured saturation of 0.983 and a y intercept of 0.7. Using this new mathematical model, previously unobtainable information about the match of oxygen delivery and consumption in venovenous ECLS is now available. This information will facilitate optimal management of oxygen kinetics in patients during venovenous extracorporeal support. ASAIO Journal 1995;41:838‐841.

Cost-Effectiveness of Referring Patients to Centers of Excellence for Mitral Valve Surgery

BACKGROUNDThe 2014 American Heart Association/American College of Cardiology Valvular Heart Disease Guidelines state that mitral valve diseases should be repaired at a Center of Excellence (CoE). We evaluate the cost-effectiveness of such referrals. METHODSWe estimate patients’ life expectancy based on projected survival of patients after mitral valve surgery and develop a cost model to calculate short- and long-term benefits and costs to both patients and payers. Benefits include increased life expectancy and avoidance of medical complications for patients. Short-term costs include all upfront payments by patients and payers at the time of discharge. Long-term costs include all payments associated with the condition that prompted the surgical procedure incurred during the remainder of a patient’s life. We assess cost-effectiveness of treating patients with various ages and major comorbidities at CoEs vs non-CoEs. RESULTSFull implementation of the guidelines would result in an increase in the percentage of patients obtaining mitral valve repair instead of valve replacement from 58% to 72%. Depending on the patient’s age and comorbidities, it would also result in a 6.64% to 12.47% reduction in mortality, 7.85% to 9.97% reduction in reoperation, 9.97% to 17.16% reduction in stroke, and an average gain of 3.77 to 9.88 months of life expectancy. Finally, greater reliance on CoEs results in financial savings to payers, due to avoidance of the costs of future complications.CONCLUSIONPatients benefit from mitral valve surgery at a CoE regardless of their age or comorbidities. Payers may incur additional short-term costs when patients are referred to a CoE, but these are fully offset by long-term savings at the current repair rate gap of 24% between CoEs and non-CoEs in New York State. Redesigning co-pay structures and/or refining the set of patients who are referred to CoEs could further align the incentives of patients and payers on a case-by-case basis and achieve an even more desirable social outcome.

Measuring infant metabolism: Design and testing of a miniature gas exchange monitor

A compact closed-circuit gas exchange monitor (GEM) was built for measurement of oxygen consumption (VO2) in ventilated infants. The GEM includes a ventilator-driven slave bellows, a CO2 scrubber, one-way valves to ensure unidirectional flow, and tubing to complete the small-volume low-compliance system, which fits easily between the ventilator (VENT) and the endotracheal tube (ETT). Oxygen consumption is measured by volume loss from a spirometer attached by a one-way valve. Pressure is monitored at the airway, and the VENT is adjusted to attain the desired pressure pattern. The system was leak tested by placing a 3-kg weight on the spirometer bell (continuous positive airway pressure = 20 cm H2O) and then ventilating with peak inspiratory pressures (PIP) of 60 cm H2O without leak. Bench testing for accuracy of volume loss was checked by ventilating the device into another calibrated spirometer and achieving equal volumes. First, four rabbits were studied to determine the range of ventilator backup rates (BUR = 0 to 60), inspiratory times (IT = .2 to .6 seconds), and airway pressures (up to 40/8 cm H2O) attainable by this device. Then six fasted rabbits weighing 2.2 to 4.0 kg were anesthetized with a ketamine-rompun mixture, underwent tracheostomy, and were placed on a pressure VENT. The BUR was set at 20/min and the IT at .5 seconds. The GEM was placed between the VENT and the ETT, and the PIP was adjusted to maintain PaCO2 between 30 and 40 torr, eliminating spontaneous respiration. Oxygen consumption was measured at five-minute intervals for one hour.(ABSTRACT TRUNCATED AT 250 WORDS)