Dynamic oxygenator blood volume during prolonged extracorporeal life support.

Current methods for identification of oxygenator clotting during prolonged extracorporeal life support include visual inspection, evaluation of oxygenator resistance and oxygen exchange performance, and assessment of clotting-related laboratory parameters. However, these observations do not provide a quantitative assessment of oxygenator clot formation. By measuring changes in the dynamic oxygenator blood volume this study aimed to evaluate the relation to oxygenator resistance and oxygen transfer performance. Sixty-seven oxygenators were studied during adult extracorporeal life support. Oxygenator blood volume, oxygenator resistance, and oxygen transfer efficiency were monitored. Oxygenator blood volume decreased with increasing runtime (r = -0.462; p <0.001). There was a statistically significant, fair negative correlation between oxygenator blood volume and oxygenator resistance (r = -0.476; p<0.001) in all oxygenators, which became stronger analyzing only exchanged oxygenators (r = -0.680; p<0.001) and oxygenators with an oxygenator blood volume <187 mL (r = 0.831; p<0.001). No relevant correlation between oxygenator blood volume and O2 transfer was found. Oxygenator blood volume declined over time and was clearly associated with an increasing oxygenator resistance during prolonged extracorporeal life support, though O2 transfer was less affected.

Exhaled Breath and Oxygenator Sweep Gas Propionaldehyde in Acute Respiratory Distress Syndrome.

BACKGROUND: Oxidative stress-induced lipid peroxidation (LPO) due to neutrophil-derived reactive oxygen species plays a key role in the early stage of the acute respiratory distress syndrome (ARDS). Monitoring of oxidative stress in this patient population is of great interest, and, ideally, this can be done noninvasively. Recently, propionaldehyde, a volatile chemical compound (VOC) released during LPO, was identified in the breath of lung transplant recipients as a marker of oxidative stress. The aim of the present study was to identify if markers of oxidative stress appear in the oxygenator outflow gas of patients with severe ARDS treated with veno-venous extracorporeal membrane oxygenation (ECMO). METHODS: The present study included patients with severe ARDS treated with veno-venous ECMO. Concentrations of acetone, isoprene, and propionaldehyde were measured in inspiratory air, exhaled breath, and oxygenator inflow and outflow gas at corresponding time points. Ion-molecule reaction mass spectrometry was used to measure VOCs in a sequential order within the first 24 h and on day three after ECMO initiation. RESULTS: Nine patients (5 female, 4 male; age = 42.1 ± 12.2 year) with ARDS and already established ECMO therapy (pre-ECMO PaO2/FiO2 = 44.0 ± 11.5 mmHg) were included into analysis. VOCs appeared in comparable amounts in breath and oxygenator outflow gas (acetone: 838 (422-7632) vs. 1114 (501-4916) ppbv; isoprene: 53.7 (19.5-244) vs. 48.7 (37.9-108) ppbv; propionaldehyde: 53.7 (32.1-82.2) vs. 42.9 (24.8-122) ppbv). Concentrations of acetone, isoprene, and propionaldehyde in breath and oxygenator outflow gas showed a parallel course with time. CONCLUSIONS: Acetone, isoprene, and propionaldehyde appear in breath and oxygenator outflow gas in comparable amounts. This allows for the measurement of these VOCs in a critically ill patient population via the ECMO oxygenator outflow gas without the need of ventilator circuit manipulation.

Artificial lungs: current state and trends of clinical use and research and development.

This article describes recent progress in the field of artificial lungs, centering on the current state and trends in clinical use and research and development. Trends in the recent clinical use in Japan can be found in shipment-number-based surveys as well as in the questionnaire surveys for clinical extracorporeal membrane oxygenation (ECMO) and percutaneous cardiopulmonary support (PCPS). It is likely that the use of artificial lungs for open-heart surgery has peaked, and this can be attributed to the rapid expansion and popularization of off-pump coronary artery bypass grafting surgery. In contrast, the increase in the number of artificial lungs used in assisted circulation cases is showing significant growth. Along with such clinical trends, research and development toward next-generation systems is active in the field of assisted circulation, focusing on emergency or long-term use of PCPS or ECMO. Approaches include enhancing the performance of conventional systems in terms of long-term durability and hemocompatibility, developing a novel device by integrating the oxygenator with the blood pump, and developing an implantable type of artificial lung such as an intravenous oxygenator. Next-generation devices not only will benefit a multitude of patients but also represent an important target with the prospect for expansion of the market for artificial lungs. In the future, further expansion of research and development in this field, as well as progress in practical and clinical applications of innovative devices, is expected.

Study on mechanical circulatory support and currently available supporting parts in China.

The research and development on extracorporeal and assisted circulation in China have been painstaking. On one hand, China has the largest population of 1.3 [corrected] billion in the world, and the demands for supporting equipment are huge. On the other hand, as a developing country, China is not wealthy. It is urgent to design and fabricate affordable circulatory support parts, machines, and artificial hearts for Chinese market. In this regard, we have made our own heart-lung machine, mechanical and tissue valves, oxygenators, and artificial hearts and their improved versions. The cost of these parts is much lower as compared with those in the Western market. Although the results of clinical application are good so far, the quality of these lifesaving parts needs to be continuously improved.

A 10-year review of pediatric perfusion practice in North America.

In December 1999, 145 North American pediatric open-heart institutions were mailed an updated survey as a follow-up of two earlier surveys, 1989 and 1994. The survey consisted of 81 questions pertaining to demographics, equipment, techniques and patient monitoring. This survey, following a similar format of the two earlier surveys, provides a 10-year review encompassing both new and founded practices performed during the conduct of pediatric cardiopulmonary bypass. Responses were received from 83 hospitals, for a 57% response rate. Of the respondents, 72 were active pediatric open-heart centers, 67% performing both adult and pediatric cardiac surgery and 33% performing pediatric surgery exclusively. The mean number of pediatric cases performed in 1999 was 169, compared to 101 cases in 1989 and 145 cases in 1993. Of the 72 respondents, 51% were performing greater than 100 cases/year, whereas 3% of centers were performing under 25 cases/year. As the decade progressed, bubble oxygenators were completely replaced by their membrane counterpart. The use of ultrafiltration, reported first in the 1989 survey, has risen by over 30%. The use of colloids in the prime, specifically 25% albumin, has increased in use from 34% in 1989 to 85% in 1999. Rewarming gradients are used by 100% of respondents with a mean gradient of 9.4 degrees C between the patient and water bath. Myocardial protection has seen an increase of close to 20% in the use of blood cardioplegia. The use of safety devices is also on the rise with more centers using level detectors (79%), bubble detectors (88%) and arterial line filters (96%). Centers relying on the use of cardiac assist devices have increased by 25% since 1989. Results of this survey suggest a movement toward a higher volume of cases being performed at fewer centers. While some diversity is seen, movement toward greater homogeneity, first noted in the 1994 survey, continues in 1999.

Feasibility of a pumpless extracorporeal respiratory assist device.

BACKGROUND: Our study evaluated the efficacy and feasibility of a pumpless respiratory assist device and determined its capacity for carbon dioxide removal. METHODS: In five adult pigs the left femoral vein and artery were cannulated with a 20F cannula and connected to a low-pressure hollow-fiber artificial lung. After we had obtained baseline values of mean arterial pressure, cardiac output, and blood flow across the artificial lung, the mean arterial pressure was reduced 20% and 40% relative to baseline; in a second phase, it was raised 20% and 40. Cardiac output and artificial lung flow were simultaneously recorded. We determined the carbon dioxide removal capacity of the artificial lung by gradually increasing the arterial partial carbon dioxide tension of the animal. RESULTS: An increase of 10 mm Hg in mean arterial pressure resulted in an increase of flow of 0.14 L/min. The mean pressure drop across the artificial lung was measured at 17 +/- 9 mm Hg. The shunt flow over the artificial lung varied between 14 and 25% of the cardiac output of the animal. Depending on inlet conditions, carbon dioxide removal by the artificial lung was between 62 +/- 22 mL/L/min and 104 +/- 25 mL/L/min. CONCLUSIONS: A pumpless respiratory assist device can remove a significant proportion of the metabolic carbon dioxide production. However, adequate mean arterial pressure is mandatory to maintain sufficient flow across the device. The technique seems attractive because of its simplicity and can be used in acute lung injury in conjunction of apneic oxygenation for prolonged respiratory support.

Major findings from the clinical trials of the intravascular oxygenator.

Major clinically relevant findings have been extracted and summarized from the database developed from the international multicenter clinical trials of the intravascular oxygenator (IVOX) as a means for augmenting the deficient blood gas transfer of patients in advanced acute respiratory failure (ARF). Between February 1990 and May 1993, a total of 164 IVOX devices were utilized in 160 clinical trial patients who were hypoxemic and/or hypercarbic while receiving closed system positive pressure mechanical ventilator support at or exceeding generally accepted minimum safe levels of intensity. The average rates of oxygen and carbon dioxide transfer into and out of circulating venous blood by means of the IVOX device varied from 40-70 ml/min. Evidence of patient benefit during IVOX utilization includes improvement in blood gas partial pressures associated with decreased intensity of mechanical ventilation, improved hemodynamics in patients with mechanical ventilator depressed cardiovascular function, and decreased indices of lung dysfunction. Clinically recognized IVOX-related complications or adverse events were reported in 24.5% of the clinical trials patients. At necropsy examination of 68 clinical trials patients who died during or after IVOX utilization, forensic pathologists reported 4 cases in which IVOX utilization could have been a primary or contributing cause of death. Significant IVOX device mechanical and/or performance malfunction problems were recognized in 29 (17.7%) of the IVOX devices utilized in clinical trials. IVOX clinical trials data collected and analyzed to date indicate IVOX utilization has a favorable risk/benefit ratio in patients in severe, acute, potentially reversible ARF.

A survey of cardiopulmonary bypass perfusion practices in Australia in 1992.

Twenty-four cardiopulmonary bypass (CPB) perfusion units around Australia were surveyed to determine the characteristics of CPB perfusion as practised in Australia in 1992. Twenty completed survey forms were received. Findings were compared with those of a similar study performed by one of the authors for the year 1986. The field of CPB perfusion continues to expand both in terms of numbers of cases and increasing technological complexity. The major technological changes evident are the now clear dominance of membrane over bubble oxygenators and the proliferation of inline SvO2 monitoring devices. The greatest change in practice has been to the virtually universal use of cardioplegia. There remains considerable variation in the composition of the cardioplegia solutions used in the responding units. A range of minimum perfusion pressures for CPB is noted, whereas most units employ similar minimum perfusion flows. Methods of central nervous system and renal protection are mainly hypothermia and diuretics, respectively, with a scattering of other techniques. Staffing of CPB perfusion units is essentially unchanged since 1986 and at least five units had no medical perfusionist appointed in 1992.

A new intravascular membrane oxygenator to augment blood gas transfer in patients with acute respiratory failure.

The IVOX (intravascular oxygenator) is an intracorporeal, hollow-fibre membrane oxygenator and carbon dioxide (CO2) removal device. The IVOX is surgically placed into the vena cava via a femoral or jugular venotomy. Oxygen (O2) is pulled through the hollow fibers by a vacuum pump controlled by a flow meter. There is no extracorporeal circulation of blood. Gas exchange occurs as the patient's blood flows over several hundred hollow fibers. Inlet and outlet gas conduits exit a small skin incision for inflow of O2 and outflow of CO2. Studies in sheep and humans show that the IVOX can support approximately 30% of gas exchange requirements. The position of the IVOX in the vena cava does not affect hemodynamics or cause thromboembolic complications. It can remain in place for up to 22 days without affecting hematologic or blood chemistry parameters. The IVOX is currently undergoing clinical trials at selected medical centers in patients with acute respiratory failure.