Perfusion safety: new initiatives and enduring principles.

Perfusion safety has been studied and discussed extensively for decades. Many initiatives occurred through efforts of professional organizations to achieve recognition, establish accreditation and certification, promote consensus practice guidelines, and develop peer-reviewed journals as sources for dissemination of clinical information. Newer initiatives have their basis in other disciplines and include systems approach, Quality Assurance/Quality Improvement processes, error recognition, evidence-based methodologies, registries, equipment automation, simulation, and the Internet. Use of previously established resources such as written protocols, checklists, safety devices, and enhanced communication skills has persisted to the present in promoting perfusion safety and has reduced current complication rates to negligible levels.

Technique of controlled reperfusion of the transplanted lung in humans.

BACKGROUND: Reperfusion 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. METHODS: Approximately 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. RESULTS: Five 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. CONCLUSIONS: Controlled reperfusion of the transplanted lung with white cell-filtered, nutrient-enriched blood has given excellent functional results in our small initial clinical series.

Laboratory testing of femoral venous cannulae: effect of size, position and negative pressure on flow.

Femoral venous cannulae (17-28 French) were tested to compare flows obtained by their placement in a simulated inferior vena cava (IVC) or right atrium (RA) and by varying drainage pressures using gravity siphon drainage or a centrifugal pump in the venous line. The circuit consisted of conventional tubing and equipment including a segment of thin-walled latex tubing to simulate the IVC connected to a flexible reservoir to simulate the RA. The test fluid was a 40% glycerin solution. Flow was measured at height differentials of 30-60 cm (cannula-to-inlet of hard-shell venous reservoir) and with a -10 to -80 mmHg negative pressure created by the centrifugal pump. A roller pump returned the test fluid to a flexible bag to maintain a filling pressure of 0-1 mmHg. Flow increased modestly with an increasing height differential. When negative pressure was applied with the centrifugal pump, flow increased 10% and 18% (IVC and RA positions, respectively) compared to gravity siphon drainage conditions. There also was a tendency for flow to plateau or cease when the centrifugal pump was used at higher levels of negative pressure or when larger cannulae were used. We conclude: (1) position of smaller cannulae in the RA yield better flows than when the cannulae are larger and placed in the IVC; (2) smaller-sized cannulae are capable of achieving higher flows when the centrifugal pump is used; (3) cannulae must be properly positioned to achieve maximum flow; (4) the centrifugal pump will augment flow, but should be regulated to avoid extreme negative pressures; and (5) cannula design has no demonstrable effect on flow.

Cooling gradients and formation of gaseous microemboli with cardiopulmonary bypass: an echocardiographic study.

BACKGROUND: Previous 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 patient's blood. The purpose of this study was to determine under what circumstances gas emboli formation would occur during cooling on cardio-pulmonary bypass. METHODS: Eight 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. RESULTS: Minimal 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. CONCLUSIONS: Cooling 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.

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.

Simple technique of left heart bypass.

Left heart bypass is typically established by left atrial appendage cannulation. We report a technique using inferior pulmonary vein cannulation, which is technically simpler. We have used this technique in 20 cases with reliable venous inflow.

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.

Reversal of anticoagulation without protamine using a heparin removal device after cardiopulmonary bypass.

Protamine sulfate is routinely administered after cardiopulmonary bypass to reverse systemic heparinization, but may cause a severe hypotensive reaction in as many as 2% of patients. Research Medical, Inc., has developed an extracorporeal venovenous heparin removal device (HRD) for use in patients at high risk for a protamine reaction. Circulation through the HRD removes heparin by hollow fiber plasma separation and selective sorption of anionically charged heparin to a polycationically charged poly-L-lysine ligand coupled to a agarose substrate. The heparin depleted plasma then reenters the whole blood pathway and is returned to the patient through the double lumen catheter in the right atrium. To evaluate the HRD in a clinically relevant model, cardiopulmonary bypass was performed in pigs using RA-Ao cardiopulmonary bypass (120 min) with systemic heparinization (300 IU/kg), a nonpulsatile pump with a membrane oxygenator, and systemic hypothermia (28 degrees C). Group 1 (HEP n = 7) had no intervention to neutralize the heparin; Group 2 (HRD n = 7) used the HRD. After 19.7 +/- 4.2 min of circulation through the HRD, the activated clotting time had returned to baseline, whereas the pigs in the HEP group were still anticoagulated (activated clotting time = 396 +/- 152 sec; time to baseline was 124 +/- 9 min). There were no significant differences between groups with respect to hemodynamics, hematocrit levels, leukocyte profiles, or platelet counts, HRD is an effective heparin removal device in a pig model of cardiopulmonary bypass and awaits a phase I clinical trial in humans.

Pediatric myocardial protection in the United States: a survey of current clinical practice.

A nationwide survey of institutions in the United States that perform congenital heart disease surgery was conducted to obtain an overview of the current use of myocardial protection in pediatric patients (aged 0-16 years). One hundred and one (55%) of 183 institutions responded, completing a 4-page questionnaire about pediatric cases in 1989. A total of 12,072 cases were represented. Caseloads ranged from 7 to 498 at these institutions (mean 124, median 30). Cardioplegia was used by 100 institutions (44 blood, 45 crystalloid, 11 both). Administration was guided by formulas alone in 69 and by clinical criteria alone in 32. A wide variety of compositions of cardioplegic solutions was found with no preference for any particular type. No correlation between caseloads and cardioplegic solutions was found. Hypothermia was used by all institutions, with a mean of 25.8 +/- 3.5 degrees C for a simple ventricular septal defect closure. Deep hypothermia and circulatory arrest were used in 3048 cases (25.2%). A clear trend indicated that circulatory arrest was used more frequently in larger institutions (p less than 0.0001). Fibrillation as a strategy was used in 45 institutions. Twenty-five institutions changed cardioplegia technique during 1989. The findings suggest that, even though no consensus exists about its ideal composition, cardioplegia in conjunction with hypothermia is currently the strategy most often used for pediatric myocardial protection.

Development and current status of a new intracorporeal membrane oxygenator (IVOX).

The IVOX (intravascular oxygenator) is an intracorporeal, hollow-fibre membrane oxygenator and carbon dioxide (CO 2) removal device. The IVOX is surgically placed into the vena cava via a femoral or jugular venotomy. Oxygen (O 2) is pulled through the hollow fibres by a vacuum pump controlled by a flow meter. There is no extracorporeal circulation of blood. Gas exchange occurs as the patient's blood flows over several hundred hollow fibres. Inlet and outlet gas conduits exit a small skin incision for inflow of 0 2 and outflow of CO 2. Studies in sheep show that the IVOX can support approximately 30% of gas exchange requirements. The position of the IVOX in the vena cava does not affect haemodynamics or cause thromboembolic complications. It can remain in place for up to 22 days without affecting haematologic or blood chemistry parameters. The IVOX is currently undergoing clinical trials at selected medical centres in patients with acute respiratory failure.