Clinical evaluation of nine hollow-fibre membrane oxygenators

In a comparative study we investigated the performance characteristics of nine hollow-fibre oxygenators. In a clinical setting, 10 units of each type of oxygenator were tested for oxygen exchange, transoxygenator pressure drop, heat exchanger performance and blood trauma. The oxygenators included are Maxima PRF Plus, Affinity, Forte, Affinity NT, Quantum, Optima, Capiox 1.8, Hilite and Quadrox. Ninety patients scheduled for elective coronary bypass surgery were enrolled in the study. Cardiotomy suction blood was not allowed to mix with the circulating blood. Samples were taken preoperatively (t1), immediately after cooling and crossclamping of the aorta (t2), during rewarming (t3), and postoperatively (t4). The results showed that under clinical conditions all of the tested oxygenators are well capable of meeting the normal and above-normal oxygen needs. The Quantum and Affinity NT are the best performing oxygenators with respect to oxygen transfer. The Quantum oxygenator with a small membrane surface area of 1.9 m2 has also the highest oxygen transfer per square metre. A direct relationship between shunt fraction and blood flow could not be established in all oxygenators. The lowest shunt fraction at 4 litres blood flow was seen in the Maxima, Quantum and Affinity NT groups (15%). At near physiological PaO2-values, we noticed a negative influence on the shunt fraction. Large differences exist in pressure drop between the oxygenators under standardized conditions with circulating priming, as well as during bypass. The lowest pressure drop was noticed in the Quadrox and Affinity NT, the highest in the Quantum, Capiox and Optima. However, we did not measure any differences in pressure drop after cooling and during re-warming. Differences exist between the heat exchanger performances. The Quadrox oxygenator is the most efficient, while the Maxima has the smallest performance factor. It was not possible to calculate heat exchanger performance for the Hilite due to incorrect temperature measurement. The high pressure gradients in some of the devices did not result in higher haemolysis. Plasma free haemoglobin values were low in each oxygenator. There are no differences in platelet drop postoperatively. The influence on blood trauma of the higher pressure drop in some of the tested devices, in combination with the higher centrifugal pump revolutions needed to overcome this gradient, has to be studied with longer perfusion times.

The use of the Biomedicus centrifugal pump in combination with a separate reservoir with integrated heat exchanger in aneurysms of the thoracic aorta

The surgical correction of aneurysms in the descending thoracic aorta necessitates clamping the aorta both proximal and distal to the aneurysm. The affected length can vary from a few centimetres to large portions of the upper and lower descending aorta. Clamping times can vary from a few minutes to more than one hour. No matter which technique is applied, these operations are often accompanied by excessive blood loss and the need for rapid transfusion, resulting in substantial haemodynamic fluctuations. Hypothermia may become a problem in these patients because most blood warmers are unable to warm blood adequately ( greater than 35 degrees C) at high flow rates (>100 cc/min). This may result in clotting problems. For this reason, our clinic decided from November 1990 to integrate a reservoir with its own heat exchanger (Cobe) into our left-left bypass system. This system largely regulates transfusion during partial extracorporeal circulation (PECC). The advantages of such a system are that (1) the transfusion rate can be adapted to blood loss and is not dependent on the quality and quantity of the infusion systems; (2) blood products and other infusion liquids are filtered; and (3) the transfusion blood is warmed. In this article, we describe our experience with this application of PECC on three patients who suffered excessive blood loss during operations for large thoracic aneurysms.

Intermittent antegrade/selective cerebral perfusion during circulatory arrest for repair of the aortic arch

If the aortic arch requires repair or replacement due to an aneurysm or dissection, conventional cardiopulmonary bypass (CPB) is not possible during the period in which the aortic arch is excluded from the circulation. This creates a situation in which there is no cerebral circulation. The brain needs adequate protection from this ischaemic insult. Hypothermic circulatory arrest (HCA), antegrade/selective cerebral perfusion (ASCP) and retrograde cerebral perfusion (RCP) are reported to exhibit their cerebral protective capabilities during procedures involving the aortic arch. HCA can provide adequate protection in procedures of short duration and avoids the complications associated with cerebral perfusion techniques. The main disadvantage of HCA is that the 'safe' duration of circulatory arrest is not clearly defined. Topical cooling of the head may enhance cerebral hypothermia and provide additional protection. If longer periods of circulatory arrest are anticipated or occur unexpectedly, we suggest that ASCP can offer improved cerebral protection by providing adequate brain perfusion and improved cerebral cooling. By using a coronary sinus perfusion catheter as a carotid artery cannula, it is not necessary to snare or clamp the carotid arteries. This technique minimizes the chance of damaging the carotid arteries. In this report, we describe our set-up and ASCP perfusion protocol for the surgical repair of an aortic arch aneurysm.