Perfusion

'For many reasons clinicians hesitate to employ mechanical devices of unproved efficacy except in the most critically ill patients and then only as a desperate measure. These approaches accounted for a substantial lag time between intra-aortic balloon pump availability and widespread utilization. Ventricular assist devices, recently approved for initial clinical trials, face the same dilemmas'. Norman, 1977.¹

An arterial line filter (Swank High Flow 6000) was used during extracorporeal circulation (ECC) in 21 of 45 patients undergoing coronary artery bypass grafting, to study haematological effects. The mean age was 60 (41-69) years. All patients had obstructions of at least three coronary artery branches. Average ECC and aortic crossclamp times, drainage via chest tubes until the first day after surgery, total transfusions of blood products and haemolysis did not differ in the two groups. After 90 minutes of ECC, leukocyte counts were significantly lower in the filter group whereas haematocrit, counts of erythrocytes, lymphocytes and platelets, platelet volume, fibrinogen concentration and fibrinopeptide A were similar. Release of β-thromboglobulin and platelet factor 4 were significantly higher in the filter group. No clinically significant adverse haematological effects were observed with use of the arterial line filter, although there were indications of more pronounced platelet damage in the filter group.

Longer perfusion and clamp times are associated with greater mortality and morbidity. We studied the factors which correlate with the duration of perfusion time, clamp time and nonclamp perfusion time in 1078 patients having coronary bypass surgery. Perfusion time correlated significantly (P≤ 0.05) with female sex, ejection fraction, left ventricular diastolic pressure, number of distal anastomoses, incomplete revascularization, atherosclerotic aorta, aorto-iliac-femoral occlusive disease and date of operation. Only the number of distal anastomoses, incomplete revascularization, atherosclerotic aorta, ejection fraction and date of operation correlated significantly (P≤ 0.05) with perfusion time with multiple regression analysis. Factors significantly (P≤ 0.05) correlating with nonclamp perfusion time included age, ejection fraction, left ventricular end diastolic pressure, number of distal anastomoses, incomplete revascularization, atherosclerotic aorta and aorto-iliac-femoral occlusive disease. Multiple regression analysis showed that only ejection fraction, number of distal anastomoses, incomplete revascularization and atherosclerotic aorta significantly (P≤ 0.05) contributed to the predication of nonclamp perfusion time. The individual correlates (P≤ 0.05) of clamp time included age (negative correlation), female sex, ejection fraction, height, weight, body surface area, number of distal anastomoses, incomplete revascularization, atherosclerotic aorta and date of operation. Multiple regression analysis shows that clamp time correlates significantly (P ≤ 0.05) with the number of distal anastomoses, date of operation, age, incomplete revascularization, atherosclerotic aorta and female sex.

Comparative mitochondrial ultrastructural changes during myocardial ischaemic periods have been assessed when using four different solutions: Bretschneider's solution (BS) (K+ = 10 mEq/l) at 4°C; St Thomas's hospital solution (STS) (K⁺ = 20 mEq/l) at 4°C; standard Ringer's solution (SRS) (K⁺ = 2.7 mEq/l) at 4°C; blood potassium cardioplegic solution (BPS) (K⁺ = 21 mEq/l) at 15°C.

BS (n = 8), STS (n = 10), SRS (n = 8) and BPS (n = 8) were infused in 34 patients undergoing aortic valve replacement (n = 17) or aortocoronary bypass grafting (n = 17), after aortic crossclamping, either in the aorta or in both coronary ostia, until the septal myocardial temperature reached 10-13°C for crystalloid solutions or 15°C for blood cardioplegia. Myocardial biopsies were taken from the left ventricular apex, on a beating heart, at the beginning and end of bypass.

To assess the degree of ischaemic injury, an ultrastructural evaluation of the mitochondria was done and four histological classes have been defined: class I- dense matrix and cristae; class II — occasional mitochondrial swelling; class III — decrease in matrix density with extensive swelling; class IV — severe swelling and/or rupture of matrix.

This study showed that: (1) only the St Thomas's and Bretschneider's solutions provide a rapid electromechanical asystole; (2) isolated hypothermic crystalloid solution with low potassium concentration (standard Ringer) is not sufficient either to induce cardiac arrest or to prevent detrimental mitochondrial changes; (3) Bretschneider's solution appears to provide the best ultrastructural mitochondrial preservation during myocardial ischaemia.

The following is a design for a simple, inexpensive combination positive/negative pressure monitor, with applications in neonatal extracorporeal membrane oxygenation (ECMO).

Negative (venous) pressure in the ECMO tubing circuit is monitored in the traditional reservoir volume-sensing manner, with a 5cc reservoir and associated sensing circuitry. Positive (arterial) pressure is measured by any manufacturer's blood pressure transducer/amplifier combination. The analogue signal relating to this pressure is routed from the amplifier to the ECMO pressure monitor for comparison to a reference value. If the positive pressure exceeds this reference value (indicating an overpressure situation) or the pillow collapses (indicating excess negative pressure), respective audible and visual alarms are activated and power to the blood (roller) pump is removed. When the alarm situation is remedied, power is automatically restored to the pump.

The ECMO pressure monitor affords great sensitivity, accuracy and dependability. It is adaptable to most roller pump driven ECMO systems and blood pressure monitors. The device can be assembled by a competent electronics technician, at an approximate parts cost of US$325.00.

During the past two years at the University of Modena, 72 sheep underwent cardiopulmonary bypass (CPB) for various open-heart surgical procedures. An effective protocol for anaesthesia and CPB was developed in these animals. Routine barbiturate induction and maintenance anaesthesia with isofluorane and a pressure-regulated ventilator have minimized anaesthetic problems. The type of priming fluid used was the major factor in overcoming the problems associated with haemodilution effects, clotting insufficiency and postperfusion lung syndrome. Pump flows of 60ml.kg ^-1 bodyweight.min^-1 seem to give adequate circulatory support during heart-lung bypass. A technical report and the pharmacological support protocols used successfully in 66 of the 72 animals during a two-year period are presented.