Alois Philipp

Pumpless extracorporeal lung assist and adult respiratory distress syndrome

We report use of a pumpless extracorporeal lung assist-a safe and effective method in the management of severe acute respiratory failure that allows an extracorporal gas-exchange without the use of a pump.

Pumpless extracorporeal lung assist – experience with the first 20 cases

OBJECTIVEnLong-term extracorporeal lung assist is limited by a significant mechanical blood trauma resulting in bleeding and hemolysis. To reduce the drawbacks of extracorporeal lung assist a new technique has been developed, by which the driving force for the extracorporeal circuit derives from the patients arterio-venous pressure gradient (pumpless extracorporeal lung assist). The aim of this clinical study was to test the feasibilty and effectiveness of pumpless extracorporeal lung assist in patients with acute respiratory distress syndrome.nnnMETHODSnTwenty patients (41+/-16 years) with acute respiratory distress syndrome of various causes and failing respirator therapy were enrolled. The minimum hemodynamic requirements included a cardiac output (CO) >6 l/min and mean arterial pressure (MAP) >70 mmHg. Pumpless extracorporeal lung assist was established using a short circuit arterio-venous shunt including a special designed low-resistance membrane oxygenator which was placed between the patients legs.nnnRESULTSnAt the time of inclusion FiO(2) in all patients was 1.0 (paO(2) 45.9+/-7 mmHg, paCO(2) 58.9+/-17 mmHg). After 24 h of pumpless extracorporeal lung assist FiO(2) was reduced to 0.8+/-0.1. A significant improvement in oxygenation (paO(2) 84.1+/-21 mmHg, P<0.05) and CO(2) removal (paCO(2) 32.7+/-5 mmHg, P<0.05) was notable. The mean extracorporeal flow was 2.6+/-0.6 l/min, which represented approximately 25% of the patients mean CO (10.8+/-2 l/min). The median assist time was 12+/-8 (1-32) days. Fifteen out of twenty patients were weaned off pumpless extracorporeal lung assist. Five out of twenty patients died while on the system (four sepsis, one ventricular fibrillation). Three out of twenty patients died after successful weaning on day 8, 30, and 50, respectively. Twelve out of twenty patients were discharged in a healthy state (overall survival 60%). Technical problems included thrombosis of the venous cannula (n=5), thrombus formation within the membrane oxygenator (n=2), membrane oxygenator plasma leakage (n=2), and membrane oxygenator contamination with Candida albicans. No bleeding complication was observed.nnnCONCLUSIONnPumpless extracorporeal lung assist is feasible and effective in a selected group of patients with acute respiratory distress syndrome but preserved hemodynamic function. By eliminating the pump and reducing the tubing length blood trauma can be minimized. Being very simple the system entails fewer risks of technical complications and also facilitates nursing care.

Deep hypothermia and circulatory arrest for surgery of complex intracranial aneurysms.

OBJECTIVEnSome intracranial aneurysms may not be operable by conventional neurosurgery due to their location or morphology. Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest renders surgery of these complex aneurysms possible. Brain temperatures can be measured directly in this setting.nnnMETHODSnEight patients with complex intracranial aneurysms were operated on with the aid of CPB. Femoro-femoral bypass with heparin-coated circuit components was used in all cases. Venous drainage was augmented by a centrifugal pump in six patients and by a newly developed vacuum technique in two patients. Temperatures were monitored by probes in brain, tympanum, nasopharynx, bladder, rectum, arterial and venous blood. These measurements were recorded on-line together with those of cerebral oxygen saturation, AP, CVP and PAP. Blood gas analyses and an EEG were also performed continuously.nnnRESULTSnOutcome was excellent in seven patients, in one patient moderate neurological disability occurred. Mean time on cardiopulmonary bypass was 160 (117-215) min, for cooling to a brain temperature of 18 degrees C 33 (20-47) min, and for total circulatory arrest 27 (15-45) min. Additionally, terminal brain arteries were clamped for up to 68 min in four patients. No cardiac complications were observed. Actual brain temperatures were best reflected by the tympanum probes (max. deviation 2 degrees C), whereas temperatures measured in bladder or rectum exhibited deviations of up to 10 degrees C. EEG activities were arrested between brain temperatures of 19 and 26 degrees C.nnnCONCLUSIONSnComplex intracranial aneurysms can be treated successfully using deep hypothermic circulatory arrest. Extensive monitoring adds to the speed and safety of the procedure. The resulting comparative measurements of temperatures at different body sites including brain, EEG, and other variables may be of general relevance for operations employing deep hypothermia and circulatory arrest.

Heparin-Coated Equipment Reduces the Risk of Oxygenator Failure

BACKGROUNDnThe development of an abnormal pressure gradient (APG) across the oxygenator is the most common cause of oxygenator failure during cardiopulmonary bypass. This necessitated changing the oxygenator in 4 patients in this series. A retrospective analysis of conditions predisposing to APG was performed.nnnMETHODSnOne thousand nine hundred fifty-nine operations with cardiopulmonary bypass were performed in adults. A range of membrane oxygenators was used subject to availability; 769 oxygenators were heparin-coated and 1,190 were uncoated. The pressure gradient across the oxygenator was measured under standardized conditions. An APG was defined as a gradient of greater than twice the mean.nnnRESULTSnAn APG occurred in 44 uncoated and 3 heparin-coated oxygenators (p < 0.001). The mean age was higher for the APG group (p < 0.001). Fibrin deposits in the arterial line filter were noted in 45 patients. Logistic regression revealed that only fibrin deposition in the arterial line filter and the use of uncoated oxygenators were significantly associated with APG.nnnCONCLUSIONSnWe conclude that a heparin-coated oxygenator effectively prevents APG. This adds significantly to the safety of open heart operations.

Hybrid management of aortic rupture and lung failure: pumpless extracorporeal lung assist and endovascular stent-graft.

Acute traumatic aortic rupture represents a potentially life-threatening situation. Because of the extremely high early mortality, emergency surgical repair used to be the preferred method of treatment. This group of patients usually is seen with a wide variety of injuries and comorbid conditions, all of which have a major impact on surgical outcome. We present an alternative hybrid approach that combines on-site placement of pumpless extracorporeal lung assist, subsequent patient transfer, and endovascular stent-graft implantation. This procedure may be a potentially useful strategy to reduce the comorbidity and the mortality of both lesions.

Miniaturisierte Herz-Lungen-Maschine

In den 1990er Jahren wurden Nebenwirkungen der EKZ zunehmend diskutiert. Infolgedessen wurde die Koronaroperation am schlagenden Herzen (»offpump coronary artery bypass«, OPCAB) und ein Ende der Herz-Lungen-Maschine bei der Koronarchirurgie propagiert. Bald zeigte sich jedoch, dass der technischen Herausforderung nicht jeder Herzchirurg gewachsen war und die OPCAB-Chirurgie keine besseren Ergebnisse lieferte als das konventionelle Verfahren. Trotzdem blieb der Wunsch nach einem weniger traumatischen Operationsverfahren. So entstand die minimierte EKZ als Mittelweg zwischen OPCAB und konventioneller Operationstechnik (Albes 2008). Sie verbindet den Sicherheitsstandard einer EKZ mit einer minimierten Nebenwirkungsrate.

Physiologie der EKZ

Eine EKZ wird zur Aufrechterhaltung der Herz-Kreislauf-Funktion im Rahmen von Herzoperationen und bei kardialem und pulmonalem Versagen eingesetzt. Sie hat dem zufolge einen erheblichen Einfluss auf die Hamodynamik und auf den Gasaustausch. Die Optimierung der Hamodynamik erfolgt durch eine Adjustierung des Pumpenflusses, wahrend der Gasaustausch uber den Oxygenator geregelt wird. Der Blutfluss uber die kunstlichen Oberflachen erfordert eine Antikoagulation und schadet auf Dauer der Endorganfunktion. Ein langerer Herzstillstand ist nur unter Verwendung kardioplegischer Losungen moglich.