Prolonged pulmonary assistance with the membrane gas-exchanger: a case report

Pumpless respiratory assistance using a membrane oxygenator as an artificial placenta: a preliminary study in newborn and preterm lambs

Newborns suffering from severe respiratory difficulties and not responding to conventional methods have been successfully treated by extracorporeal circulation with a membrane oxygenator (ECMO). However, the technique needs a highly specialized staff, excellent laboratory support, and continuous surveillance of the procedure to prevent complications. In a series of experiments on newborn and preterm lambs, we have investigated a relatively simpler technique of respiratory support that involves a pumpless arteriovenous bypass by cannulating both umbilical arteries and the umbilical vein. A highly efficient microporous membrane oxygenator (MO) with very low resistance was selected. This type of perfusion that mimics the placental circulation, besides providing an additional amount of oxygen to the blood, has proven to be very effective for CO2 extraction. Before its application in humans, however, improvements in the catheters to be inserted in the umbilical vessels, some modifications in the design of the MO, and improvements in the blood compatibility of all foreign surfaces in contact with blood are needed.

In vitro performance assessment of tubular membrane oxygenators

The definite advantage in oxygen transfer performance of staged (single, double and triple) tubular membrane oxygenators (TMO) is compared with reference to flat membrane oxygenators (Travenol or Landé Edwards). The overall construction of staged TMO with a blood mixing chamber is a very good way to destroy the blood boundary layer and modify the blood stagnant zone in the device. Four sizes of staged TMO were studied using the principle that gases dissolve in water in concentrations linearly proportional to the partial pressures of the gases when in equilibrium with the liquid. The experimental results show that the oxygen transfer rate and the corresponding overall oxygen mass transfer coefficient of staged TMO are increased by the same order as those of the reference membrane oxygenators. Furthermore the essential parameter analysis prove that oxygen transfer increases with the number of stages and decreases with the length of the blood tubular modules. The multistage design of TMO revealed an increase in the hydrodynamic resistance occurring in the apparatus. However the highest relative oxygen transfer efficiency suggests that better fluid distribution as well as better uniformity of oxygenation prevail in the staged devices.

Cardiopulmonary dynamics during arteriovenous perfusion: cardiac output, pulmonary arterial resistance, and right venticular stroke work

The effects of arteriovenous perfusion on myocardial performance, pulmonary circulatory dynamics, and organ preservation were studied in dogs in order to evaluate the applicability of arteriovenous extracorporeal membrane oxygenation for partial respiratory support. Studies were made on normally oxygenated dogs, on dogs made hypoxic by oxygen deprivation and ventilatory depression, and on dogs with pulmonary injury and moderate pulmonary hypertension induced by injection of oleic acid into the right ventricle. The latter two groups were included to assess the changes that occur in cardiopulmonary dynamics in the presence of hypoxia and pulmonary hypertension. A microchannel membrane oxygenator was employed to provide partial respiratory support to the group of animals with pulmonary injury. The results indicate that no deleterious hemodynamic changes occurred in any of the groups of animals with arteriovenous flow for periods of up to 5 hours at rates corresponding to 20 to 35% of the total cardiac output. Adequate systemic oxygenation was provided by the microchannel oxygenator at these rates of arteriovenous perfusion.

Scanning electron microscope study on flat type membrane oxygenator after prolonged extracorporeal circulation

Despite adequate anticoagulation, thrombi may develop onto any foreign surface subjected to circulating blood. Although the efficiency of membrane oxygenators can decrease, distal embolization can be more critical and dangerous. Scanning electron microscope observations carried out on the Travenol Modulung oxygenator used both on dogs and on patients for prolonged partial cardiopulmonary by-pass pointed out the following observations. Caution must be observed when translating the results from dogs to human beings. Heparin management can be delicate and critical. The problem of blood transfusion can be extremely important and must be extensively investigated.