Recent experience of high trans-oxygenator pressure gradient. In May this year we had two occurrences of high trans-oxygenator pressure resulting in oxygenator change out. In this presentation I would like to look at published reports of this phenomenon to inform future practice. Keith Kincaid CCP, Leeds General Infirmary.

8 different membrane oxygenator systems. (Ann Thorac Surg 1998;65:1310 –2) Heparin-Coated Equipment Reduces the Risk of Oxygenator Failure Alexander Wahba, MD, Alois Philipp, BS, Renate Behr, and Dietrich E. Birnbaum, MD Department of Cardiothoracic Surgery, University of Regensburg, Regensburg, Germany Single centre audit 1995-7. 8 different membrane oxygenator systems. Bypass temperature ranging from 34 to 25°C, cold crystalloid cardioplegia. High trans–oxygenator pressure defined as twice the gradient for the type. In 1998 Wahba described the phenomenon from an audit of their data at University of Regensburg. They used data from 1995 to 97 and had used 8 different oxygenator systems at temperature from 25 to 32 degC with cold crystalloid cardioplegia. they defined high trans-oxygenator pressure as twice the expected gradient for the device, flow and haematocrit.

Incidents of high trans-oxygenator pressure. (Ann Thorac Surg 1998;65:1310 –2) Heparin-Coated Equipment Reduces the Risk of Oxygenator Failure Alexander Wahba, MD, Alois Philipp, BS, Renate Behr, and Dietrich E. Birnbaum, MD Department of Cardiothoracic Surgery, University of Regensburg, Regensburg, Germany Incidents of high trans-oxygenator pressure. 1194 uncoated oxygenators - 44 incidents ( ̴4%). 769 heparin coated – 3 incidents ( ̴0.4%). 4 changed out for rising pressure gradient. Fibrin deposits seen in most arterial line filters. 2 patients suffering the 44 incident died – “seemingly unrelated”. No correlations other than absence of coating. Suggests uncoated stainless steel heat exchangers as element affected. They described 44 instances in 1200 cases with uncoated oxygenators, a rate of 4%, I don’t ever remember seeing this phenomenon at anything like 4%. and only 3 instances in 760 heparin coated systems. A rate of 0.4% 4 oxygenators out of the 47 instances were changed out ,with the reasons given concern for rising pressure and essentially “clinical choice.” Interestingly theirs is the only report of fibrin strands appearing in nearly all the arterial filters. 2 of the 47 affected patients died from Quote “seemingly unrelated causes” A young man treated for massive pulmonary embolism died from multi-organ failure on day 2 and a 68 year old woman having CABG died on day 12 of small and large bowel gangrene.

18 different types of membrane oxygenator used Perfusion 2001; 16: 271–278 Oxygenator thrombosis: worst case after development of an abnormal pressure gradient – incidence and pathway Hans P Wendel Clinic for Thoracic, Cardiac and Vascular Surgery, Eberhard-Karls-University, Tuebingen, Alois Philipp Clinic for Cardiothoracic Surgery, University of Regensburg, Norbert Weber Clinic for Thoracic, Cardiac and Vascular Surgery, Eberhard-Karls-University, Tuebingen, Dietrich E Birnbaum Clinic for Cardiothoracic Surgery, University of Regensburg and Gerhard Ziemer Clinic for Thoracic, Cardiac and Vascular Surgery, Eberhard-Karls-University, Tuebingen In 2001 Wendel described the incidence in a larger group of patients from the same location. I’m not completely clear but I think they include the previously described patients. The incident rate remained the same 4% in a larger number of uncoated oxygenators, but was a tiny 1 incident in 3000 coated oxygenators. Of the 111 incidents, 12 oxygenators were changed out. There were no comments of patient harm. Between 1995 and 2000 18 different types of membrane oxygenator used 2562 uncoated oxygenators, 110 incidents (4%). 12 oxygenators replaced. 3036 heparin coated, 1 incident (0.03%), not replaced.

More common in patients with:- Non O blood type. Perfusion 1999; 14: 425-435 Oxygenator thrombosis: an international phenomenon Jennifer Schaadt. Department of Perfusion, Westroxbury VA Hospital, Massachusetts. Broad description of high trans-oxygenator pressure including detail of possible causes. More common in patients with:- Non O blood type. High factor VIII, von Willebrand factor and fibrinogen. Low D dimers. Abnormal cryoprecipetation implicated. Sudden withdrawal of asprin. Starting in heat exchanger and spreading. This review by Scmidt in 2000 gives detailed description of possible triggers and development of the phenomenon and recounts both European and American experience. Her conclusions include that it is more common in :- non O blood type, with high levels of factor VIII, von Willebrand factor and fibrinogen. And low levels of d dimer. abnormal cryopecipates studies are implicated. Along with sudden withdrawal of asprin Thrombosis starts in Heat exchanger and spreads.

All centres experienced at least 1 incident (0.1 to 2%). Perfusion 2003; 18: 25-30 Normal and abnormal trans-oxygenator pressure gradients during cardiopulmonary bypass Anthony Richard Fisher, Mya Baker, Mike Buffin, Patrick Campbell, Stephen Hansbro, Steven Kennington, Angela Lilley and Michael Whitehorne Heart and Lung Department, Harefeld Hospital, Harefeld, London, UK; Department of Clinical Perfusion, Nottingham City Hospital, Nottingham, UK; Perfusion Department, Northern General Hospital, Shef.eld, UK; Perfusion Department, Glasgow Royal In.rmary, Glasgow, UK; Department Clinical Perfusion, Leeds General In.rmary, Leeds, UK; Department of Clinical Perfusion, Derriford Hospital, Plymouth, UK; Department of Perfusion, Royal Brompton Hospital, London, UK; Cardiothoracic Unit, Kings College Hospital, London, UK In 2003 Tony Fisher published a prospective survey of 8 UK centres using 9 different systems covering 3684 patients. All centres reported at least one instance with 16 reported in all, a rate of 0.4% 3 oxygenators were changed out. He classified the phenomenon into 3 types based on the time course of the pressure rise. The most common pattern was to initially have a normal gradient, rising over 10 to 20 minutes and falling at 45 to 60 minutes. He did observe that the obstruction did not re-appear in the replacement oxygenator. Published 2003, prospective survey of 3684 cases in 8 centres using 9 different oxygenators All centres experienced at least 1 incident (0.1 to 2%). 16 incidents (0.4%), 3 oxygenators changed out. Classified into 3 subgroups based on time of onset and reversibility with time. Most commonly, initially normal, rising after 10 minutes and reducing after 45 minutes.

Case 1 Resternotomy for aortic root enlargement and replacement in young adult. Fully coated circuit and aprotinin Post heparin act > 700sec Aortic cannulation Bleeding during surgical dissection, bypass then further dissection. Oxygenator gradient initially normal, rising over 10 minutes. At 20 minutes, partially rewarm, wean from bypass and oxygenator change out. No re-occurrence of obstruction. No further change to management. Recovery as expected. Our first patient was an 18 year old for resternotomy for elective Aortic Root Replacement. We routinely use a fully coated circuit. Aprotinin was used and the post heparin ACT was >700 seconds. The aorta was cannulated. There was bleeding associated with venous cannulation so bypass was started and then further surgical dissection. The oxygenator gradient was initially normal but at 10 minutes was more than twice expected. The inlet pressure was around 650mmHg The patient was weaned off bypass with adequate pressures and the oxygenator changed. Back on to bypass and the operation progressed normally and post operative coarse was uneventful and within initial expectations.

Case 2 2 days later. 66 year old for MV Repair. Uneventful progress to bypass. Post heparin ACT >480 seconds. Again initially normal oxygenator gradient. High by 10 minutes. Oxygenator changed at 20 minutes, under circulatory arrest at 32degC. No re-occurrence of obstruction. No further change in patient management. Uneventful recovery. 2 days later We had a 66 year old for elective mitral valve repair. There was uneventful progress to bypass. Post-heparin ACT was >480. Again the oxygenator blood pressure gradient was normal but was very elevated at 10 minutes, by which time cardioplegia had been given and the heart was open. Following a discussion with clinicians the oxygenator was changed out under circulatory arrest at 32degC. After restarting bypass the was no further change to patient management and the patient had an uneventful recovery with no delay to extubation, icu discharge or discharge home.

We had no written policy to cover this event. Perfusionist’s contemporaneous documentation of pressures, times, recommendations and decisions was light at best. Perfusionist’s concerns were primarily about affects on circuit and embolism. Change outs are reflected upon and practiced. Completed quickly. Hearsay comment of arrest of 40 seconds. My observations of these events. We had no written policy to address this phenomenon despite having part of Tony Fishers survey. And we still don’t. The contemporaneous perfusion documentation around the events was light at best. The perfusionists spoke about uncertainty of effects of the high pressure on the circuit and of concerns of embolism. We do reflect upon and practice change outs and they were said to have been completed smoothly and quickly. A hearsay comment was the arrest was 40 seconds. We reviewed our practice in a department safety meeting. The minutes of which say we should in future “only” “recommend” continued monitoring of the situation with failure of adequate oxygenation as the trigger for further intervention.

Survey of members incidents, accidents and safety for 2011 and 2012. Jpn J Extra-Corporeal Technology 43(1) :1-12, 2016 The current status of the safety management in practices of cardiopulmonary bypass: Focus to the report of JaSECT safety survey 2013. Koji Takai, Makoto Anno, Makato Sonoda, Kiyoshi Yoshida. Survey of members incidents, accidents and safety for 2011 and 2012. 552 perfusionists surveyed, 77% response rate covering 70,000 cases. Section covering high trans- oxygenator pressure. Following earlier recommendation, 93% measure oxygenator inlet pressure. 51 instances of reported high inlet pressure, a rate of only 0.07%. Oxygenator changed out 29 times, continued monitoring 22 times. References to Hiraki et al who investigated 24 instances in 1033 cases without oxygenator change. A more recent description of phenomenon was described this year in the journal of the Japanese Society of Extra-Corporeal Circulation based on their safety survey of 2013. 520 perfusionists were surveyed with a response of 77% covering 70,000 cases. There was a section of the questionnaire covering high trans-oxygenator pressure. Following an earlier recommendation 93% of perfusionists monitored oxygenator inlet pressure. There were 51 reported instances of high gradients, a rate of o.o7%, perhaps the type of thing to be under-reported. The oxygenator was change out 22 times- a high proportion, but still many instances when it wasn’t. Interestingly they briefly describe a paper by Hiraki with claiming 22 instances of high trans-oxygenator pressure in 1000 cases with none changed out, and comment of detailed investigation of each event. Unfortunately I can’t find access to the paper or an abstract.

Summary Many reports of high trans-oxygenator pressure at a low incidence rate. Many changed out. With most commonly reported reason related to pressure Many instances of continued monitoring (and preparation). No reports of harm associated with occurrence of high trans-oxygenator pressure gradients. Oxygenator change out can be a risky procedure and would be much more common if every instance of high pressure gradient resulted in change out. In summary. There are many reports of high trans-oxygenator pressure gradient at a low and variable incident rate. Many have been changed out, with no re-occurrence in the new oxygenator. But many more have not. There are no reports of harm attribute to these incidents. Oxygenator change can be a risky and uncertain procedure so perhaps not something you would contemplate for every instance of high trans-oxygenator pressure. (in 1980s America Kurusz reported 23 deaths from 365 a year oxygenator changes ) With apparent benign outcomes based on the lack of reports of harm should we be replacing oxygenators on this indication alone at all? If it involves circulatory arrest. Thank you.