Microembolizatoins during heart surgery under extracorporeal circulation

OBJECTIVE: By means of transcranial Doppler sonography (TCD), microembolic signals (MES) representing embolic events can be registered during cardiac surgery and extracorporeal circulation in a considerable number of patients. We conducted the present study to determine the neuro-psychiatric consequences of MES. METHODS: 25 patients scheduled for elective aorto-coronary bypass grafting (ACBG; n = 10) or aortic valve replacement (AVR; n = 15) were studied pre- and postoperatively with neuropsychiatric testing. Results were related to the number of MES noted intraoperatively. In addition, we registered the intraoperative changes of middle cerebral artery blood flow velocity, mean arterial pressure, arterial blood gases, haemoglobin and haematocrit. Statistics included t-test, two-way analysis of variance, Mann-Whitney-U-test and Spearman correlation with p < 0.05 considered significant. RESULTS: Regarding demographic data and intraoperative parameters, both study groups (ACBG vs. AVR) were comparable except for age. AVR patients showed significantly more MES than those undergoing ACBG (p < 0.012) which was most pronounced in the late state of surgery (aortic clamp off; p < 0.0003). However, MES counts did not correlate with neuropsychiatric test results. CONCLUSIONS: In contrast to recent reports, we were unable to show a deterioration of postoperative neuropsychiatric state related to high intraoperative MES count in our patients. Future TCD studies should focus on the differentiation between gaseous emboli and particles even in the clinical setting, as the latter may well play a major role for the development of cerebral dysfunction following cardiac surgery and extracorporeal circulation.     

Comparative studies of glycoprotein Ib in heparin coated and nonheparin coated extracorporeal circulation circuits

Contact between blood and artificial materials has various effects on blood. Impairment of platelet function is an especially important and well known effect, but its precise mechanism is not clearly understood. The authors constructed a circulation model to investigate the effect of extracorporeal circulation on platelet membrane glycoproteins (GPs), especially GP Ib, and to compare the changes in GP Ib in heparin coated (group C) and nonheparin coated (group N) circuits. As determined by flow cytometry, GP Ib in both groups decreased on initiating circulation, but the decrease in group N was significantly larger than that in group C. There was no observed change in GP IIb/IIIa levels in either group. The extent of shear stress induced platelet aggregation significantly decreased during circulation in both groups. Decreases in the extent of shear stress induced platelet aggregation were significantly less with the use of heparin coated circuits. In addition, the amount of GP Ib in the high speed pellet decreased progressively during circulation in both groups. In contrast, the amount of GP Ib in the Triton insoluble (low speed) pellet increased dramatically during circulation. However, expression of GP Ib in the Triton soluble platelet fraction was low in both groups. From the results, it was concluded that the cause of the decrease in platelet function during extracorporeal circulation is attributable to the internalization of GP Ib from the platelet surface inside the platelet. It also can be said that a heparin coated circuit is one effective means of controlling this change.     

Virtual extracorporeal circulation process

Virtual instruments for an extracorporeal circulation (ECC) process were developed to simulate the reactions of a patient to different artificial perfusion conditions. The computer simulation of the patient takes into account the hydraulic, volume, thermal and biochemical phenomena and their interaction with the devices involved in ECC (cannulae dimensions, oxygenator and filter types, pulsatile or continuous pump and thermal exchangers). On the basis of the patient's initialisation data (height, weight, Ht) and perfusion variables (pump flow rate, water temperature, gas flow rate and composition) imposed by the operator, the virtual ECC monitors simulated arterial and venous pressure tracings in real time, along with arterial and venous flow rate tracings, urine production tracing and temperature levels. Oxyhemoglobin arterial and venous blood saturation together with other related variables (pO2, pCO2, pH, HCO3 are also monitored. A drug model which allows the simulation of the effect of vasodilator and diuretic drugs is also implemented. Alarms are provided in order to check which variables (pressure, saturation, pH, urine flow) are out of the expected ranges during the ECC simulation. Consequently the possibility of modifying the control parameters of the virtual devices of the ECC in run-time mode offers an interaction mode between the operator and the virtual environment.     

Changes in the shape of erythrocytes during use of extracorporeal circulation

The behavior of red cell shape of circulating blood was investigated following operations using the heart-lung machine by different quantitative methods. It was discovered, that the schistocytes (light microscopy) and echinocytes (scanning electron microscopy) significantly increases. The changes in erythrocyte shape are comprehended as summary effect of erythrocyte damage by the extracorporeal system and discussed in relation to the loss of phospholipid components of the erythrocyte membrane.     

Natriuresis and atrial natriuretic factors during extracorporeal circulation for cardiac surgery

At the end of cardiopulmonary bypass (CPB) diuresis and natriuresis are widely modified. Those are classically due to the CPB conditions (mean arterial pressure, non pulsatile flow, hypothermia, long duration ...). Previous studies showed no evidence of these modifications being due to variations of hormones such as vasopressin, renin or aldosterone. The atrial natriuretic factor, cardiac hormone mainly known for its natriuretic effect, would contribute to explain these facts. This study includes 17 patients NYHA I or II without any renal dysfunction or diabetes mellitus. They were scheduled for cardiac surgery under CPB (valvular replacement or aortocoronary bypass). Sampling times were: TO: after induction of anaesthesia and before surgical incision; T1: during steady CPB; T2: 30 min after CPB release. At each time were obtained: diuresis, osmolar and free water clearance, fractional excretion of sodium, haematocrit, plasma concentration of ANF (pANF), and right atrial pressure and capillar wedge pressure in case of aortocoronary graft. FeNa at the end of CPB is significantly linked to the osmolar clearance and the CPB duration. FeNa evolution is parallel with pFAN evolution. At the end of CPB pFAN is first linked to cardiac rate, then to CPB duration. Cardiac filling pressures after and before CPB are not different. pANF after CPB cannot be attributed to these pressures. Numerous factors are involved in the renal sodium elimination. An evident statistic link between pANF and FeNa is then difficult to demonstrate. Their parallel evolution is coherent and suggests that ANF is the main hormone of natriuresis at the end of CPB. ANF secretion factors at the end of CPB remain unclear. This study emphasizes the involvement of cardiac rate and CPB duration in pANF increase at the end of CPB.     

Pulsatile augmentation device for extracorporeal circulation

A device has been designed, constructed, and tested to provide pulsatile pressure/flow to a standard extracorporeal bypass circuit. The pulsatile augmentation device is pneumatically driven similar to an artificial heart ventricle except that there are no valves. It is constructed of polyurethane by vacuum forming and high frequency welding. Drivers used are a modified Arrow-Kontron intraaortic balloon pump or the Utah artificial heart driver. In vitro testing with fresh bovine blood demonstrated acceptable blood compatibility and hemodynamic function. In vivo testing for 4 h in a right and left heart extracorporeal bypass circuit showed good pulse augmentation in pulmonary and systemic bypass circuits. The device shows promise for adding pulse to standard cardiopulmonary bypass and to extracorporeal right heart circulatory assist circuits.     

Role for preliminary and continuous hemodialysis during extracorporeal circulation in infants and children

The efficacy of both preliminary and continuous hemodialysis during extracorporeal circulation (ECC) was evaluated in the pediatric population. Preliminary hemodialysis of the priming solution was initiated in eight children (HD-I group), while both preliminary and continuous hemodialysis during ECC was performed in another eight children (HD-II group). The control group which consisted of eight children did not undergo hemodialysis. Urine volume during ECC, perfusion pressure, and water balance were measured and compared among the three groups. In the HD-I and HD-II groups, the total urine volume during ECC was greater than in control group, but there was no significant difference. In the control group, the perfusion pressure temporally decreased after the pump was operating for five minutes, but the perfusion pressures remained stable in the HD-I and HD-II groups. Therefore, preliminary hemodialysis appears to prevent the "initial drop" seen in perfusion pressures. Water balance in the control group tended to be in positive balance, but both the HD-I and HD-II groups appeared to be in negative balance. Significant differences between HD-I and HD-II in contrast to the control group (p < 0.05) and p < 0.04, respectively) were observed. Preliminary hemodialysis is useful during ECC in infants and children because by maintaining perfusion pressure urine output remains adequate while a net negative water balance is achieved. Preliminary hemodialysis will increase the continuous hemodialysis in infants who are subjected to prolonged extracorporeal circulation.     

Individual responses to heparinization for extracorporeal circulation

It has been proposed that wide variations in individual response to heparin lead to deficiencies in popular heparinization protocols for extracorporeal circulation (ECC). Thirty-nine patients undergoing open cardiac operations with ECC were anticoagulated with the heparinization protocol in use at St. Thomas' Hospital. The coagulation state was monitored with the blood activated recalcification time (BART) test. Wide variations in heparin dose-response and heparin activity-decay curves were observed. No patient was underheparinized, but many had markedly prolonged BART's. The total dose of heparin declined because BART monitoring allowed elimination of incremental heparin doses up to 180 minutes of ECC. Adequate reversal with protamine was achieved in all patients regardless of response to herparin. Alternative approaches for heparinization for ECC can be developed with the aid of rapid tests of the intraoperative coagulation state.     

Lipid peroxidation injury to red blood cells during extracorporeal circulation: mechanism and protection

Twelve dogs were subjected to cardiopulmonary bypass with membrane oxygenator for 120 minutes. The effect of lipid peroxide injury on red blood cells was studied by measurement of plasma and erythrocyte membrane lipid peroxide, deformabioity of erythrocyte, plasma free hemoglobin, superoxide dismutase, Na(+)-K(+)-ATPase and Ca(2+)-Mg(2+)-ATPase of erythrocytes. The effect of vitamin E on red blood cells was also investigated. The findings indicated that vitamin E might protect red blood cells from lipid peroxide injury during extracorporeal circulation. The mechanism of damage effect of lipid peroxide and the protective effect of vitamin E on red blood cells were briefly discussed.     

Adult placenta: heparin bonded extracorporeal life support systems

The results of a dynamic study of the soluble interleukin-2 receptor (SIL-2R) expression, interleukin-2 (IL-2) production and natural killer cell factor (NKCF) activity before and after operation in 24 bladder carcinoma patients were reported. The SIL-2R expression level in the patients was significantly higher, the IL-2 production and NKCF activity were remarkably lower than those of controls. Furthermore, the higher the stage of the tumor, the higher the level of the SIL-2R. There was a period of immune suppression after operation. The results suggest that the changes of the SIL-2R expression level, IL-2 production and NKCF activity are closely related to the prognosis of patients with bladder carcinoma.     

Metabolic aspects of acute cerebral hypoxia during extracorporeal circulation and their modification induced by acetyl-carnitine treatment

Following their previous research experiences in human tissue hypoxia, in the present study the authors. investigated the metabolic effects of acute brain hypoxia in a group of patients in course of extracorporeal circulation for aorto-pulmonary bypass. One hundred subjects were treated, half with a placebo and half with acetyl-carnitine to evaluate the effects of oxidative stress in some brain plasmatic metabolites and to verify the effect of acetyl-carnitine on the tissue energy capacity. The levels of lactate, pyruvate, succinate and fumarate showed a significant imbalance due to hypoxia, while the acetyl-carnitine treatment confined the metabolic gradients within physiological limits. This means that during the course of extracorporeal circulation brain hypoxia plays a pathological role assuming the typical picture of cellular oxidative damage and the acetyl-carnitine antagonizes these deleterious effects of hypoxia by a protective mechanism on the energy processes and then on the cellular enzymic activities. In this regard, the d-tyrosine levels, considered as a proteolytic index, confirm the action of acetyl-carnitine on the cell morpho-functional integrity.     

Distribution of systemic blood flow during normothermic extracorporeal circulation (evaluation by radioactive microsphere method)

The aim of this study was to point out a hemisphere asymmetry in focal brain-damaged patients and a hand asymmetry in normals on halving binocularly a horizontal line. 50 left hemisphere and 53 right hemisphere patients (both subdivided by presence/absence of visual field defect) and 50 controls (divided by the hand they used to carry out the task) were employed. 4 differently long segments made up the test material and the error scores with respect to the geometric midpoint were worked out by means of parametric statistical procedures. It turned out that: (i) healthy subjects committed a mean leftward displacement, regardless of the hand they used. All the same, only the halving error committed by the right hand is significant keeping as reference the geometric midpoint of the segment; (ii) left and right hemisphere-damaged patients committed halving errors, that are opposite in direction, leftward for the former and rightward for the latter; (iii) the behaviour of right patients with visual field defects is the only to be significantly different from that of the corresponding controls. Our findings point to prevailing importance of the right hemisphere mainly of its posterior areas, in the halving task.     

Modifying risk for extracorporeal circulation: trial of four antiinflammatory strategies

BACKGROUND: Despite recent rediscovery of beating heart cardiac surgical techniques, extracorporeal circulation remains appropriate for most heart operations. To minimize deleterious effects of cardiopulmonary bypass, antiinflammatory strategies have evolved. METHODS: Four state-of-the-art strategies were studied in a prospective, randomized, preoperatively risk stratified, 400-patient study comprising primary (n = 358), reoperative (n = 42), coronary (n = 307), valve (n = 27), ascending aortic (n = 9), and combined operations (n = 23). Groups were as follows: standard, roller pump, membrane oxygenator, methylprednisolone (n = 112); aprotinin, standard plus aprotinin (n = 109); leukocyte depletion, standard plus a leukocyte filtration strategy (n = 112); and heparin-bonded circuitry, centrifugal pumping with surface modification (n = 67). RESULTS: Analysis of variance, linear and logistic regression, and Pearson correlation were applied. Actual mortality (2.3%) was less than half the risk stratification predicted mortality (5.7%). The treatment strategies effectively attenuated markers of the inflammatory response to extracorporeal circulation. Compared with the other groups the heparin-bonded circuit had highly significantly decreased complement activation (p = 0.00001), leukocyte filtration blunted postpump leukocytosis (p = 0.043), and the aprotinin group had less fibrinolysis (p = 0.011). Primary end points, length of stay, and hospital charges, were positively correlated with operation type, age, pump time, body surface area, stroke, pulmonary sequelae, predicted risk for stroke, predicted risk for mortality, and risk strata/treatment group interaction (p = 0.0001). In low-risk patients, leukocyte filtration reduced length of stay by 1 day (p = 0.02) and mean charges by $2,000 to $6,000 (p = 0.05). For high-risk patients, aprotinin reduced mean length of stay up to 10 fewer days (p = 0.02) and mean charges by $6,000 to $48,000 (p = 0.0007). CONCLUSIONS: These pharmacologic and mechanical strategies significantly attenuated the inflammatory response to extracorporeal circulation. This translated variably into improved patient outcomes. The increased cost of treatment was offset for selected strategies through the added value of significantly reduced risk.     

Cardiac pacemaker infection: surgical management with and without extracorporeal circulation

BACKGROUND: Pacemaker infections are rare, but serious complications of pacemaker therapy. The generator pocket, the pacing leads, or both may be involved. METHODS: We report on 12 patients with infected pacemaker systems. Four patients suffered from localized generator pocket infections, 6 had infected leads, and 2 patients had both. Pacemaker systems were completely removed in all patients. When the infection was limited to the generator pocket, the pacemaker system was removed at the original implantation site. Extracorporeal circulation was employed for the explantation of infected pacing leads. RESULTS: No complications occurred in patients with localized generator pocket infections. One patient with infected leads who was preoperatively already in a serious clinical condition died of septic shock in the early postoperative period; another patient died of pulmonary complications after tricuspid valve replacement 14 months after pacemaker explantation. No recurrent infections were observed. CONCLUSIONS: Explantation of the complete pacemaker system has proved a reliable method to eradicate infection. Complications have been rare, except in patients in a critically ill state who undergo cardiopulmonary bypass.     

Total respiratory support with tidal flow extracorporeal circulation in adult sheep

A novel pressure gated tidal flow extracorporeal circulation (TF ECC) device was developed, and it was hypothesized that it could provide total respiratory support in apneic adult sheep without adverse hemodynamic or cardiac effects. The circuit consisted of a single lumen cannula, computer driven tubing occluders gated by circuit pressure, a nonocclusive peristaltic blood pump, a spiral coiled membrane lung, and a heat exchanger. Six paralyzed, anesthetized adult sheep were instrumented and TF ECC was instituted via cannulation of the right atrium. Total respiratory support was provided by the circuit during an apneic period of 6 hours. Echocardiography was performed with the animal instrumented (baseline) and after 2 hours of TF ECC. Circuit blood tidal volume was 172.6 +/- 18.0 cc, resulting in a TF ECC flow of 71.1 +/- 10.1 cc/kg/min. At the end of the study period, PaCO2 was 35.5 +/- 7.6 mmHg, paO2) was 91.2 +/- 30.6 mmHg, and pulmonary artery oxygen saturation (SPAO2) was 95 +/- 5%. Hemodynamic stability was maintained with no significant differences at baseline and after 6 hours in mean arterial pressure, mean pulmonary artery pressure, or heart rate noted. Echocardiographic evaluation showed preserved fractional shortening of the left ventricular (LV) septal-lateral dimension (baseline 32.4 +/- 11.4%; 2 hours 34.8 +/- 8.4%). This study demonstrates TF ECC provides total respiratory support without adverse hemodynamic effects, and preserved LV function.