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.     

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.     

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.     

The monitoring of heparin activity during extracorporeal circulation

Heparin activity was assessed in 11 patients who underwent extracorporeal circulation for open-heart surgery. The activated partial thromboplastin time (A-PTT), thrombin time, protamine sulphate titration and factor Xa inhibition assay were used. The patients received heparin 3 mg/kg body weight, and 20 mg/450 ml blood was added to the pump. When the operative procedure was extended beyond 100 minutes patients received an additional 1,5 mg heparin/kg body weight. Protamine sulphate in a dose of 1,5 mg/1 mg heparin, was given to neutralize the heparin activity. The A-PTT was the easiest test which gave reliable results. The factor Xa inhibition assay measured heparin levels most precisely and mirrored the A-PTT results in all but one instance. These results indicate that the protocol employed produced adequate anticoagulation for the bypass procedure in all the patients. Protamine sulphate failed to neutralize heparin adequately after bypass in the 3 patients who received additional heparin during the surgical procedure. The monitoring of heparin activity during and after extracorporeal circulation is a desirable addition to open-heart surgical treatment.     

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.     

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.     

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.     

A simple test procedure for detection of micro-bubbles in extracorporeal blood circulation

A new contrast medium for the ultrasonic examination of the human heart was recently approved by the German medical authorities. It has proved useful for investigating the sensitivity of air detectors in detecting microbubbles measuring only a few microns in the extracorporeal line. Although the contrast medium, originally intended to be injected undiluted into the human blood circulation, was considerably diluted, microbubbles were detected by the ultrasonic air detector far below the danger limit.     

Cerebral outcome after extracorporeal circulation. Comparison between prospective and retrospective evaluations

The cerebral outcome of 100 consecutive patients who had cardiac valvular replacement was evaluated by comparing the results of prospective neurological examination with retrospective data. The latter showed that the overall prevalence of cerebral abnormalities was 6% (4% among survivors) up to ten days postoperatively and 9% thereafter. This contrasts with the 35% (37% among survivors) obtained by careful neurological investigations that showed five patients with residual signs one year after operation. Electroencephalographic and neuropsychological studies disclosed additional patients who had subclinical involvement. The results question the reportedly ever-falling cerebral complication values claimed particularly in retrospective studies and reflect what is missed when using rough clinical criteria. There is no justification in overlooking slight clinical or even subclinical dysfunction, since the elimination of them is the only acceptable criterion of cerebral safety in cardiac operations.     

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.     

Personal experience with management of extracorporeal circulation in patients with asymptomatic carotid arteriosclerosis

The authors describe in following paper their own group of patients with asymptomatic but hemodynamically significant carotid disease operated under cardiopulmonary bypass on. Current studies recommend the "alpha-stat" regime as the optimal strategy of CPB conduction to ensure intraoperative cerebral protection. This study was done to verify this idea. 284 consecutive patients admitted for elective coronary surgery underwent a non-invasive Doppler scanning of extracranial carotid arteries. Twenty seven patients (10%) had significant carotid disease. All patients underwent coronary surgery as the first procedure. There was no cerebral complication in this group of patients and neurological status of these patients postoperatively was the same as it was preoperatively. This study shows that CPB in patients with hemodynamically significant carotid disease can be achieved without impairment of central nervous system with "alpha-stat" regime of perfusion.     

Treatment of auricular fibrillation after correction of rheumatic heart disease under extracorporeal circulation

Of 372 patients operated on for rheumatic valvular defects under extracorporeal circulation, 221 patients had chronic atrial fibrillation. In 41 patients, the duration of arrhythmia ranged from a few months to 2 years. Sinus rhythm was recovered in 22 patients, using quinidine and electric-impulse treatment, and 19 patients have maintained it continuously for many years. Factors contributing to stable and lasting sinus rhythm are an adequate correction of the defect, inactive rheumatic process, and the duration of atrial fibrillation not exceeding 1-2 years. The optimum time for sinus rhythm recovery is 2-6 months after surgery. Sinus rhythm recovery prior to surgical correction of the defect is not recommended.     

EEG evaluation of patients undergoing extracorporeal circulation under analgesic and electrohypoalgesia with auricular acupuncture

Electroencephalograms recorded 12 hours before and 12 hours after heart surgery in ECC and moderate hypothermia (30 degrees) are evaluated. Two groups of patients were studied: - the first group was composed of those undergoing analgesic anaesthesia; - the second group of those undergoing electroencephalograms by means of auricular acupuncture. In the first group the postoperative EEG was dominated by long "theta" and "delta" waves characteristic of the deep sedation of analgesic anaesthesia. In the second the EEG displayed a "theta" rhythm interspersed with trains of "alpha" waves, similar to that of a tired, but alert person. The pathological traces with signs of diffused, hemispheric or cerebral distress, do not bear any relationship to the type of anaesthesia, but to the type of disease, which had increased the probability of thrombo-embolic, and/or ischaemic risk.