Mark Kurusz

Anticoagulation practices during neonatal extracorporeal membrane oxygenation: survey results:

To ascertain current anticoagulation management during neonatal extracorporeal membrane oxygenation (ECMO), a telephone survey was undertaken of all active ECMO (n = 81, 100% response rate) centres in the USA. Hospital policies regarding federal regulations governing laboratory tests [Clinical Laboratory Improvement Amendment (CLIA) 1988] were determined along with specific patient anticoagulation strategies and use of specific activated coagulation time (ACT) equipment. More than 90% of the respondents use the Hemochron device (International Technidyne Corp, Edison, NJ, USA) while the remaining centres use the Hemotec device (Medtronic Hemotec, Inc, Englewood, CO, USA). Quality control (QC) testing is performed by most centres, but there is no consensus regarding frequency of testing nor methods for dealing with abnormal results. Nearly one-half of the centres use beef lung-derived heparin and the other half use porcine intestinal-derived heparin. One-half of the programmes had a minimum heparin dose despite the ACT value, but the range varied significantly. Four out of five respondents reported that heparin dosages were dictated strictly by ACT results, and 63% will temporarily stop heparin administration for high ACT results, bleeding and/or surgery. Approximately one-third of the centres perform proficiency testing of the equipment in compliance with CLIA 1988. In conclusion, there appears to be no consensus regarding commitment to a QC programme among active ECMO centres.

Percutaneous cardiopulmonary bypass for cardiac emergencies.

Percutaneous cardiopulmonary support systems (PCPS) are compact, battery-powered, portable heart-lung machines that can be implemented rapidly in any area of the hospital using thin-walled cannulae inserted via the femoral vessels. PCPS provides temporary circulatory support by actively aspirating blood from the patient’s venous system using a centrifugal pump and hollow fiber membrane oxygenator for gas exchange. A review of clinical reports has delineated several indications for emergent applications, with the most frequent being cardiac arrest (CA) or cardiogenic shock (CS). Survival is more likely in patients with CS (40%) compared to CA (21%). Implementation of PCPS after unwitnessed CA or cardiopulmonary resuscitation > 30 min yields a patient survival rate of < 10%. The likelihood of patient survival after emergent PCPS is most often related to the patient undergoing a definitive anatomic surgical repair such as coronary artery bypass or pulmonary embolectomy. If the need for circulatory support extends beyond 6 h, conversion to conventional long-term extracorporeal membrane oxygenation or a ventricular assist device is recommended.

Technique of controlled reperfusion of the transplanted lung in humans

BACKGROUNDnReperfusion injury remains a significant and sometimes fatal problem in clinical lung transplantation. Controlled reperfusion of the transplanted lung using white cell-filtered, nutrient-enriched blood has been shown recently to significantly ameliorate reperfusion damage in a porcine model. We modified this experimental technique and applied it to human lung transplantation.nnnMETHODSnApproximately 1,500 mL of arterial blood was slowly collected in a cardiotomy reservoir during the lung implant, and mixed to make a 4:1 solution of blood:modified Buckberg perfusate. This solution was passed through a leukocyte filter and into the transplant pulmonary artery for 10 minutes, at a controlled rate (200 mL/min) and pressure (less than 20 mm Hg), immediately before removal of the vascular clamp.nnnRESULTSnFive patients underwent lung transplantation (1 bilateral, 4 single lung) using this technique. All patients were ventilated on a 40% fraction of inspired oxygen within a few hours and extubated on or before the first postoperative day.nnnCONCLUSIONSnControlled reperfusion of the transplanted lung with white cell-filtered, nutrient-enriched blood has given excellent functional results in our small initial clinical series.

Bubbles and bypass: An update

Bubbles in the bloodstream are not a normal condition -yet they remain a fact of cardiopulmonary bypass (CPB), having been extensively studied and documented since its inception some 50 years ago. While detectable levels of gaseous microemboli (GME) have decreased significantly in recent years and gross air embolism has been nearly eliminated due to increased awareness of etiologies and technological advances, methods of use of current perfusion systems continue to elicit concerns over how best to totally eliminate GME during open-heart procedures. A few studies have correlated adverse neurocognitive manifestations associated with excessive quantities of GME. Newer techniques currently in vogue, such as vacuum-assisted venous drainage, low-prime perfusion circuits, and carbon dioxide flooding of the operative field, have, in some instances, exacerbated the problem of gas embolism or engendered secondary complications in the safe conduct of CPB. Doppler monitoring (circuit or transcranial) primarily remains a research tool to detect GME emanating from the circuit or passing into the patients’ cerebral vasculature. Newer developments not yet widely available, such as multiple-frequency harmonics, may finally provide a tool to distinguish particulate microemboli from GME and further delineate the clinical significance of GME.

Effect of the Trendelenburg Position on the Distribution of Arterial Air Emboli in Dogs

We examined the effects of buoyancy on the distribution of arterial gas bubbles using in vitro and in vivo techniques in dogs. A simulated carotid artery preparation was used to determine the effects of bubble size and vessel angle on the velocity and direction of bubble movement in flowing blood. Because buoyancy tends to float bubbles away from dependent areas, bubble velocity would be expected to decrease as the vessel angle increased. We found that larger bubbles increased in velocity in the same direction as the blood flow at 0-, 10-, and 30-degree vessel angles and decreased when the vessel was positioned at 90 degrees. Smaller bubbles did not change velocity from 0 to 30 degrees and increased in velocity in the same direction as blood flow at 90 degrees. In 10 anesthetized dogs, we studied the effects of 0-, 10-, 15-, and 30-degree Trendelenburgs position on carotid artery distribution of gas bubbles injected into the left ventricle or ascending aorta. Regardless of the degree of the Trendelenburg position, the bubbles passed into the carotid artery simultaneously with passage into the abdominal aorta. We conclude that the forces of buoyancy do not overcome the force of arterial blood flow and that the Trendelenburg position does not prevent arterial bubbles from reaching the brain.

Improved left ventricular unloading and circulatory support with synchronized pulsatile left ventricular assistance compared with continuous-flow left ventricular assistance in an acute porcine left ventricular failure model.

OBJECTIVEnControversy exists regarding the optimal pumping method for left ventricular assist devices. The purpose of this investigation was to test the hypothesis that pulsatile left ventricular assist synchronized to the cardiac cycle provides superior left ventricular unloading and circulatory support compared with continuous-flow left ventricular assist devices at the same level of ventricular assist device flow.nnnMETHODSnSeven male pigs were used to evaluate left ventricular assist device function using the TORVAD synchronized pulsatile-flow pump (Windmill Cardiovascular Systems, Inc, Austin, Tex) compared with the Bio-Medicus BPX-80 continuous-flow centrifugal pump (Medtronic, Inc, Minneapolis, Minn). Experiments were carried out under general anesthesia, and animals were instrumented via a median sternotomy. Hemodynamic measurements were obtained in the control state and with left ventricular assistance using the TORVAD and BPX-80 individually. Left ventricular failure was induced with suture ligation of the mid-left anterior descending coronary artery, and hemodynamic measurements were repeated.nnnRESULTSnDuring left ventricular assist device support, mean aortic pressure and total cardiac output were higher and left atrial pressure was lower with pulsatile compared with continuous flow at the same ventricular assist device flow rate. During ischemic left ventricular failure, pulsatile left ventricular support resulted in higher total cardiac output (5.58xa0± 1.58 vs 5.12xa0± 1.19, Pxa0<xa0.05), higher mean aortic pressure (67.8xa0± 14 vs 60.2xa0± 10, Pxa0<xa0.05), and lower left atrial pressure (11.5xa0± 3.5 vs 13.9xa0± 6.0, Pxa0<xa0.05) compared with continuous flow at the same left ventricular assist device flow rate.nnnCONCLUSIONnSynchronized, pulsatile left ventricular assistance produces superior left ventricular unloading and circulatory support compared with continuous-flow left ventricular assist at the same flow rates.

Air embolism during cardiopulmonary bypass

Sudden and unexpected death during an operation is a calamity which never fails to strike terror to the heart of the boldest surgeon. Although death is a frequent and familiar visitor wherever human beings exist, nevertheless its sudden and unforeseen advent conveys with it more than the usual halo of sadness, and when such a scene transpires in the operating room it leaves impressions which neither time nor space can erase ... Believing that it is good practice to prepare for war in time of peace, I intend on this occasion to call your attention to one of the most dreaded and, I may add, one of the most uncontrollable causes of sudden death I

Paediatric perfusion practice in North America: an update

In August 1994, an updated survey questionnaire was mailed to each paediatric open-heart surgery programme in North America as a follow-up to the 1989 paediatric survey. The survey requested demographic data, equipment selection criteria and specific perfusion techniques for paediatric patients. The earlier survey revealed a wide range of clinical practice. Data from the recent survey were compared with the 1989 survey to identify current programme demographics and trends in equipment use and techniques. Responses were received from 125 hospitals (110 active programmes and 15 programmes that do not perform paediatric open-heart surgery) for a response rate of 74%. Of the 110 active centres, 77 perform both adult and paediatric cardiac surgery, and 33 perform paediatric surgery exclusively. Forty-three centres reported that they perform paediatric cardiac transplantation, an increase from 35 centres in 1989. Total caseload increased by more than 8% per year from 1988 to 1994. In 1994, 18% of the patients were operated upon during the first month of life (versus 15% in 1989), and 46% were operated on during the first year of life (versus 45% in 1989) While the 1989 survey was characterized by a high degree of heterogeneity in equipment and techniques, the recent survey reveals a trend toward homogeneity among respondents. The use of membrane oxygenation and arterial line filtration has become universal, and there was an increase in the use of all types of safety devices in the cardiopulmonary bypass circuit.

Cooling Gradients and Formation of Gaseous Microemboli With Cardiopulmonary Bypass: An Echocardiographic Study

BACKGROUNDnPrevious studies demonstrated gas emboli formation during rewarming from hypothermia on cardiopulmonary bypass when the temperature gradient exceeded a critical threshold. It also has been suggested that formation of arterial gas emboli may occur during cooling on cardiopulmonary bypass when cooled oxygenated blood exiting the heat exchanger is warmed on mixture with the patients blood. The purpose of this study was to determine under what circumstances gas emboli formation would occur during cooling on cardio-pulmonary bypass.nnnMETHODSnEight anesthetized mongreal dogs were placed on cardiopulmonary bypass using a roller pump, membrane oxygenator, and arterial line filter. For emboli detection, we positioned a transesophageal echocardiographic probe at the aortic arch distal to the aortic cannula and Doppler probes at the common carotid artery and the arterial line. Cooling gradients between normothermic blood and cooled arterial perfusate of 5 degrees, 10 degrees, 15 degrees, 20 degrees, and 0 degree C (isothermal controls) were investigated. In addition to preestablished temperature gradients, we investigated the effect of rapid cooling (maximal flow through the heat exchanger at a water bath temperature of 4 degrees C) after the initiation of normothermic cardiopulmonary bypass.nnnRESULTSnMinimal gas emboli were detected at the aortic arch at gradients of 10 degrees C or greater. The incidence of emboli was related directly to the magnitude of the temperature gradient (p < 0.01). No emboli were detected at the carotid artery. During rapid cooling, no emboli were observed either at the aorta or at the carotid artery.nnnCONCLUSIONSnCooling gradients of 10 degrees C or greater may be associated with gas emboli formation, but they may be of limited clinical significance because no emboli were detected distal to the aortic arch. During the application of rapid cooling, no emboli formation was observed.

Review article : Gaseous microemboli: a review:

... it is necessary that the air should be dispersed in small particles, so as to be almost dissolved, and imperceptibly mixed therewith. For if they once extricate themselves from the embrace of these particles of blood, and one particle of air meets with another; like small globules of quicksilver, they immediately coalesce into larger globules, and forming to themselves a kind of coat from the viscid serum