Montoya Jp

Development and application of a simplified liquid ventilator

OBJECTIVE Perfluorocarbon liquid ventilation has been shown to have advantages over conventional gas ventilation in premature newborn and lung-injured animals. To simplify the process of liquid ventilation, we adapted an extra-corporeal life-support circuit as a time-cycled, volume-limited liquid ventilator. DESIGN Laboratory study that involved sequential application of gas and liquid ventilation in normal cats and in lung-injured sheep. SETTING A research laboratory at a university medical center. SUBJECTS Eight normal cats weighing 2.7 to 3.8 kg (mean 3.1 +/- 0.5), and four lung-injured young sheep weighing 10.4 to 22.5 kg (mean 15.9 +/- 5.0). INTERVENTIONS Normal cats were supported with traditional gas ventilation for 1 hr (respiratory rate 20 breaths/min, peak inspiratory pressure 12 cm H2O, positive end-expiratory pressure 4 cm H2O, and FIO2 1.0). The lungs were then filled with perfluorocarbon (30 mL/kg) and tidal volume liquid ventilation was instituted, utilizing a newly developed liquid ventilation device. Liquid ventilatory settings were 4 secs for inspiration time, 8 secs for expiration time, 5 breaths/min for respiratory rate, and 15 to 20 mL/kg for tidal volume. Liquid ventilation utilizing this device was also applied to sheep after induction of severe lung injury by right atrial injection of 0.07 mL/kg of oleic acid, followed by saline pulmonary lavage. Extracorporeal life support was instituted to provide a stable model of lung injury. For the first 30 mins of extracorporeal support, all animals were ventilated with gas. Animals were then ventilated with 15 mL/kg of perfluorocarbon over the ensuing 2.5 hrs. MEASUREMENTS AND MAIN RESULTS In normal cats, mean PaO2 values after 1 hr of liquid or gas ventilation were 275 +/- 90 (SD) torr (36.7 +/- 10.4 kPa) in the liquid-ventilated animals and 332 +/- 78 torr (44.3 +/- 10.4 kPa) in the gas-ventilated animals (NS). Mean PaCO2 values were 40.5 +/- 5.7 torr (5.39 +/- 0.31 kPa) in the liquid-ventilated animals and 37.6 +/- 2.3 torr (5.01 +/- 0.31 kPa) in the gas-ventilated animals (NS). Mean arterial pH values were 7.35 +/- 0.07 in the liquid-ventilated animals and 7.34 +/- 0.04 in the gas-ventilated animals (NS). No significant changes in heart rate, mean arterial pressure, lung compliance, or right atrial venous oxygen saturation were observed during liquid ventilation when compared with gas ventilation. In the lung-injured sheep, an increase in physiologic shunt from 15 +/- 7% to 66 +/- 9% was observed with induction of lung injury during gas ventilation. Liquid ventilation resulted in a significant reduction in physiologic shunt to 31 +/- 10% (p < .001). In addition, the extracorporeal blood flow rate required to maintain the PaO2 in the 50 to 80 torr (6.7 to 10.7 kPa) range was substantially and significantly (p < .001) lower during liquid ventilation than during gas ventilation (liquid ventilation 15 +/- 5 vs. gas ventilation 87 +/- 15 mL/min/kg). CONCLUSIONS Liquid ventilation can be performed successfully utilizing this simple adaptation of an extracorporeal life-support circuit. This modification to an existing extracorporeal circuit may allow other centers to apply this new investigational method of ventilation in the laboratory or clinical setting.

Plasma leakage through microporous membranes : role of phospholipids

Plasma leakage through microporous membrane oxygenators is a well known complication of prolonged extracorporeal circulation. The authors hypothesized that adsorption of bipolar plasma molecules, such as phospholipids on the microporous membrane, results in formation of a hydrophilic layer over the hydrophobic surface of the membrane; this, in turn, leads to plasma leakage at normal surface tensions. A lipid phosphorus assay was used to measure phospholipid adsorption onto the fibers of microporous membrane oxygenators tested under a variety of experimental conditions. Adsorption of phospholipids on the microporous membrane was concentration dependent. Reproducible plasma leakage occurred both in vitro and in vivo, and the time to leakage was dependent on the concentration of phospholipids adsorbed upon the microporous membrane. Based upon these results, the authors conclude that adsorption of phospholipids contributes to the development of plasma leakage through microporous membrane oxygenators.

A standardized system for describing flow/pressure relationships in vascular access devices.

Catheters are usually characterized by length and external diameter only. We developed a system to describe flow-pressure characteristics with a single number, M, patterned after a Reynolds number-friction factor correlation. A simple alignment chart was constructed that can be used to determine M for catheters of regular internal diameter and given length. If tapers, side holes, or integral connectors are present, M can be determined in-vitro with water by measuring pressure drop at various flows. The chart describes flow pressure functions for blood (Hct = 0.41) if M is known. Using this system, any catheter, needle, valve seat, extracorporeal tubing, or vascular graft can be assigned a single number that describes hydrodynamic performance characteristics.

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.

Laboratory experience with a novel, non-occlusive, pressure-regulated peristaltic blood pump

Current blood pumps have potential safety problems, including the ability to generate extreme positive and negative pressures. These problems were addressed in the design and testing of a non-occlusive, peristaltic blood pump. The pump consists of a tubing of unique design (pump chamber) wrapped under tension around a rotor with rollers. The pump chamber design is such that the pump is passively filling; flow is dependent upon the pressure of the blood supply and the size of the pump chamber. Thus, negative pressures cannot be generated. With the outlet occluded, the pump produces the maximum attainable pressure, which can be set by adjusting the tension of the pump chamber around the rollers. The design characteristics make the pump suitable for prolonged use. The pump was tested in vitro for pressure safety, hemolysis, and durability. The pump prototype was used in 25 experiments involving extracorporeal circulation on sheep, with an average duration of approximately 6 hr and bypass flow rates between 0.5 and 2.0 L/min. No pump related complications occurred in any of these experiments. The pump described here is suitable for short- and long-term perfusion applications, and does not require additional pressure regulation, as do current blood pumps.