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Carbon dioxide transfer is increased when the gas phase of a hollow fiber membrane lung is operated at hypobaric pressures. Oxygen transfer is augmented by hyperbaric pressures. However, uncoated hollow fibers transmit gas bubbles into the blood when operated at a pressure greater than 800 mmHg and may have increased plasma leakage when operated at hypobaric pressures. Ultrathin polymer coatings may avoid this problem while reducing thrombogenicity. The authors coated microporous polypropylene hollow fibers with 380 microns outer diameter and 50 microns walls using 1, 2, 3, and 4% solutions of polysulfone in tetrahydrofuran by dipping or continuous pull through. These fibers were mounted in small membrane lung prototypes having surface areas of 70 and 187 cm2. In gas-to-gas testing, the longer the exposure time to the solution and the greater the polymer concentration, the less the permeation rate. The 3% solutions blocked bulk gas flow. The coating was 1 micron thick by mass balance calculations. During water-to-gas tests, hypobaric gas pressures of 40 mmHg absolute were tolerated, but CO2 transfer was reduced to 40% of the bare fibers. Hyperbaric gas pressures of 2,100 mmHg absolute tripled O2 transfer without bubble formation.

Blind-ended, hollow fibers mounted on a pulmonary artery catheter may allow O2 and CO2 transfer in the vena cava, right ventricle, and pulmonary artery. The effects of fiber length, manifold number, and gas oscillation on mass and momentum transfer with water perfusate using mass spectrometry and mass flow controllers were studied. Manifolds with 112-196 microporous polypropylene fibers were mounted on 8 Fr multiple lumen, commercially available pulmonary artery catheters. Fiber lengths varied from 0.5 to 16 cm and surface areas from 7 to 220 cm2. Prototypes with 2 cm long fibers were constructed with 1-15 manifolds. A two manifold prototype with 8 cm long fibers and a surface area of 378 cm2 was also studied. The transfer failed to scale with manifold number because the steady gas flow was maldistributed to the manifolds. Oscillating gas pressures from 780 to 76 mmHg absolute at a rate of 40 cycles/min increased CO2 transfer up to 15-fold and O2 transfer up to 2.5-fold. Oscillation also corrected the maldistribution. Optimal fiber lengths of 3 and 1 cm for O2 and CO2, respectively, were seen with steady gas flow, and 8 cm for both with oscillatory gas flow.

This report describes the radiologic appearance of the intravenous oxygenator (IVOX), an intracorporeal CO2-O2 exchanger for use in patients with severe respiratory deficiency, and the extensive radiographic and sonographic support required for its use. Six patients aged 19-39 years who had severe adult respiratory distress syndrome (ARDS) and who were not expected to survive were selected for IVOX placement; ARDS was caused by trauma (four patients), severe pneumonia (one patient), or a fat embolus from a tibial fracture (one patient). Before insertion of the IVOX, all patients underwent evaluation of their right internal jugular vein, right common femoral vein, and inferior vena cava with real-time ultrasound (US) to ascertain vascular size. The IVOX improved oxygenation in all patients; because of such improvement, one patient survived. Use of the IVOX may become common; hence, radiologists should understand how the IVOX functions and its appropriate placement, be able to identify it on chest and abdominal radiographs, and appreciate the importance of US in placement of this device and follow-up.

In patients with severe adult respiratory distress syndrome, mechanical ventilation may not be able to ensure gas exchange sufficient to sustain life. We report the use of an intravenous oxygenator (IVOX) in five patients who were suffering from severe adult respiratory distress syndrome as a result of aspiration, fat embolism, or pneumonia. IVOX was used in an attempt to provide supplemental transfer of CO2 and O2 and thereby reduce O2 toxicity and barotrauma. All patients were tracheally intubated, sedated, and chemically paralyzed and had a PaO2 < 60 mmHg when the lungs were ventilated with an FIO2 = 1.0 and a positive end expiratory pressure of > or = 5 cmH2O. The right common femoral vein was located surgically, and the patient was systemically anticoagulated with heparin. A hollow introducer tube was inserted into the right common femoral vein, and the furled IVOX was passed into the inferior vena cava and advanced until the tip was in the lower portion of the superior vena cava. IVOX use ranged from 2 h to 4 days. In this group of patients, IVOX gas exchange ranged from 21 to 87 ml x min-1 of CO2 and from 28 to 85 ml x min-1 of O2. One of the five patients survived and was discharged from the hospital. The IVOX transferred up to 28% of metabolic gas-exchange requirements. One patient with a small vena cava showed signs of caval obstruction. Three other patients demonstrated signs of a septic syndrome after the device was inserted.(ABSTRACT TRUNCATED AT 250 WORDS)

Nine medical centers collaborated in a prospective randomized study to evaluate prolonged extracorporeal membrane oxygenation (ECMO) as a therapy for severe acute respiratory failure (ARF). Ninety adult patients were selected by common criteria of arterial hypoxemia and treated with either conventional mechanical ventilation (48 patients) or mechanical ventilation supplemented with partial venoarterial bypass (42 patients). Four patients in each group survived. The majority of patients suffered acute bacterial or viral pneumonia (57%). All nine patients with pulmonary embolism and six patients with posttraumatic acute respiratory failure died. The majority of patients died of progressive reduction of transpulmonary gas exchange and decreased compliance due to diffuse pulmonary inflammation, necrosis, and fibrosis. We conclude that ECMO can support respiratory gas exchange but did not increase the probability of long-term survival in patients with severe ARF.

Extracorporeal pumping PA-LA perfusions were carried out for 24 hrs in 5 awake, alert lambs by cannulating the main PA and the LA with large bore polyurethane cannulae. A mean of 42% of the basal cardiac was pumped through the membrane lung. When the PA occluder cuff was progressively inflated, up to 80% of the basal cardiac output was diverted to the extracorporeal circuit for short periods. Hemothorax remained a significant problem. Three lambs were electively perfused 12 hrs, 36 hrs, and 8 days without a roller pump, using a low resistance spiral coil membrane lung pumped by the RV. By inflating the occluder cuff, a mean of 55% of basal cardiac output was pumped by the RV through the membrane lung. The 8 day bypass lamb remained healthy and active without any bleeding or gross pathology. We did not observe air emboli, thromboemboli or gross infections in either group. We believe that such a mode of cannulation will eventually allow long-term perfusion of a low resistance membrane oxygenator driven directly by the RV.