TUESDAY AFTERNOON, APRIL 29,1980

2:00 P.M. Scientific Sessions - Continental Ballroom

24. Extending the Limits of Hemodilution on Cardiopulmonary Bypass Using Stroma-Free Hemoglobin Solution

WILLIAM Y. MOORES*, FRANKDEVENUTO*,

WILLIAMH. HEYDORN*. RICHARD B. WEISKOPF*,

MARKBA YSINGER and JOE R. UTLEY, San Diego,

and San Francisco, California

Recent increased interest in blood conservation and tissue perfusion during cardiopulmonary bypass has heightened the importance of achieving an optimal level of hemodilution with the lowest hematocrit that adequately meets tissue oxygen requirements. To help meet this objective we utilized 10 swine to evaluate the ability of stroma-free hemoglobin solution (SFHS) to support myocardial performance at a hematocrit level of 5%. All animals were placed on normothermic, total and right-heart bypass (RHBP, controlled rate, pre-load and after-load) for evaluation of stroke volume (SV, ml/beat), coronary blood flow (CBF, ml/min/100g tissue), arterial-coronary sinus oxygen difference (A-CSOjA, Vols %) myocardial oxygen consumption (MVO₂, ml/min/100g tissue), lactate extraction (LE, %) and mass spectrometrically measured myocardial tissue gases during a control period at a hematocrit level of 28%. We divided the 10 animals into 2 equal groups who underwent exchange transfusion to a hematocrit of 5% using either 1% SFHS (Gp I) or 1% bovine albumin solution (Gp II). All tests were repeated during these experimental conditions.

Results (mean ± S.E.): Myocardial performance following albumin solution exchange (Gp II) could not be sustained on RHBP and these animals had a SV of 0 at an LVEDP of 14 torr. SFHS animals (Gp I) had a significant Irop in SV at 14 torr following exchange (20 ± 3 vs. 10 ± 4, P<0.025), but this 50% performance level could be sustained. CBF rose and MVO₂ fell in both groups, although the statistically non-significant mean differences were less with SFHS. A-CSO₂Afell significantly (P<0.05) with albumin solution (7.3 ± 1.4 vs. 2.2 ± 0.2) and non-sig-nificantly with SFHS (5.6 ± 0.7 vs. 4.1 ± 1.4). Lactate production occurred in both groups, but was greater with albumin (34 ± 11%) than with SFHS (3 ± 32%). No changes in myocardial tissue gases were noted in either group.

Conclusion: Although myocardial performance decreased and some lactate production occurred with SFHS, we believe these comparative results provide promise in the eventual utilization of an oxygen carrying agent such as SFHS to extend the limits of hemodilution to a hematocrit of 5% or less.

*By invitation

25. Massive Air Embolism during Cardiopulmonary Bypass: Causes, Prevention and Management

NOEL L. MILLS and JOHN L. OCHSNER, New Orleans, La.

Massive air embolism during Cardiopulmonary bypass is a frightening complication requiring immediate response and carrying strong medico-legal implications. From July 1971 to July 1979 there were eight instances of massive air embolism during 3620 Cardiopulmonary bypass operations. Five such accidents from other institutions are included in this report. Causes were (1) inattention to reservoir level, (2) reversal of pump head tubing or direction of pump head rotation, (3) unexpected resumption of heartbeat, (4) inadequate steps to remove air after cardiotomy, (5) high flow suction deep in a pulmonary artery, (6) defective oxygenator, (7) use of a pressurized cardiotomy reservoir, and (8) inadvertent detachment of oxygenator during bypass. Prevention includes a systematic check of pump suckers and perfusion lines before bypass, a sensing device on the oxygenator reservoir, secure fixation of the oxygenator and avoidance of traffic around pump equipment, immediate cessation of pump and inspection for abnormal noise, use of standard maneuvers to remove air from the heart and carotid compression with resumption of heartbeat.

Immediate management of massive air embolism consists of dee'p Tren-delenberg position with a large stab wound in the ascending aorta for retrograde drainage from the cerebrovascular bed. Temporary retrograde perfusion through the superior vena cava may also be used. Subsequent steps are hypothermia with the resumption of Cardiopulmonary bypass, elevation of blood pressure, steroids, ventilation with 100% oxygen, and deep barbiturate anesthesia.

Of the 13 patients, there were 4 instantaneous deaths. Cerebral injury which resolved within a 2-month period occurred in 3 patients. The remainder had no neurologic sequelae. Nonfatal cerebral air injury may be associated with prolonged convalescence yet complete recovery, as compared to embolism from debris, clot, etc., which offers a poorer prognosis.

*By invitation

26. Perioperative Myocardial Infarction and Shock: Successful Management with an LVAD

WILLIAM F. BERNHARD, SHUKRI F. KHURI*,

ROBERT L. BERGER, ERNEST M. BARSAMIAN*,

MICHAEL C. FISHBEIN*, and JAMES G. CARR*,

Boston, Massachusetts

Postoperative circulatory support (CS) with a pneumatic, xenograft-valved left ventricular assist device (LVAD) was employed in 17 cardiopul-monary bypass (CPB) dependent patients unresponsive to catecholamines and an intra-aortic balloon pump. The device (stroke volume 75 mis) was interposed between the left ventricular apex and ascending aorta, and provided a mean (pulsatile) flow of 2.3 ± 0.2 L/min/M² for periods of 2-180 hours (without anticoagulation). Cardiogenic shock secondary to a myocardial infarction was identified histologically in 10/17 patients (biopsy or autopsy) who survived for 72 hours or longer. Evidence of improvement in ventricular function was documented in seven of these after 48 hours, employing serial determinations of cardiac output (thermal dilution) or radionuclide (99mTc) gated blood pool scans. Six patients recovered sufficiently to undergo pump removal, and three remain well 11, 17 and 18 months post-resuscitation. The other three expired prior to hospital discharge 5-30 days postoperatively.

Deaths were secondary to a hemorrhagic diathesis (HD) in 9/17 patients, renal failure (2), sepsis (2), and congestive failure (1). The HD (diffuse bleeding from all suture lines) was the result of prolonged CPB (mean 5.6 ± 0.4 hours) utilized to complete the operation and attempt cardiac resuscitation. It was associated with erythrocyte trauma including elevated plasma hemoglobin concentrations and erythrocyte mechanical fragility values (60-200 mgm%). However, if renal function was not impaired, these values rapidly decreased to normal (12 hours). Thrombocytopenia (25-40 x 10³mm³) and abnormal platelet function were also evident and persisted until device removal. The functional derangement was characterized by reduced platelet dense body content (consistent with lysis or release of granules), and marked impairment of 14C-serotonin release at thrombin-to-platelet concentrations of 0.013-0.02 /m/10⁸ platelets. Conclusion: Effective management of severe left ventricular dysfunction could be accomplished with an LVAD, but earlier application of the device, to reduce CPB time, is essential if the associated HD is to be avoided.

*By invitation

27. A New Approach to the Treatment of Aortic Dissection

ALAIN CARPENTIER*, ALAIN DELOCHE*,

JEAN-NOEL FABIANI*, SYLVAIN CHAUVAUD*,

REMI NOTTIN*, JOHN RELLAND* and CHARLES DUBOST,

Paris, France

In spite of continued progress in surgical technique and myocardial protection, aortic dissection remains associated with a high incidence of early and late mortality. Actuarial survival at 8 years varied between 33 to 50% depending of the type of dissection as reported by the Stanford Group at the last A.A.T.S. Meeting. This poor prognosis may be at least partially explained by 2 factors : 1) The Dacron graft anastomoses involve the dissected areas which may lead to excessive bleeding or disruption, 2) A large segment of the dissected aorta is left in place which may lead to recurrent dissection, rupture or ischemia.

The following approach has been developed to overcome these drawbacks: 1) The Dacron graft anastomoses are performed on the non-dissected zones of the aorta, 2) The dissected aorta is totally and progressively excluded from the systemic circulation by flow inversion and subsequent thrombosis.

In type III dissection involving the descending aorta, the operation is performed through a median sternotomy, which may be prolonged by a median laparotomy, without extracorporeal circulation. A Dacron graft is placed between the non dissected ascending aorta to a non dissected zone of the diaphragmatic or abdominal aorta. A permanent clamp is placed on the aorta distal to the left subclavian artery effectively reversing the flow in the descending aorta and the dissected areas which are progressively excluded from the circulation by an intravascular thrombosis. In type I dissections, involving the entire thoracic aorta, the Dacron graft is first anastomosed to the distal aorta. Revascularization of the cerebral and brachial arteries is then achieved without extracorporeal circulation by a bifurcated graft laterally implanted on the main Dacron graft. Finally, the proximal end of the Dacron graft is anastomosed to the aortic annulus contouring the coronary ostia using an extracorporeal circulation.

Experimentation in animal have been carried out to study the conditions and extent of the thrombosis after flow reversal in the descending aorta.

4 patients were operated on for either type III (2 cases) or type I dissection (2 cases). Post-operative investigations and clinical follow-up up to 16 months support the concept of flow reversal and thromboexclusion in the surgical treatment of type I and III aortic dissection.

*By invitation

28. Reduction of Operative Heat Loss and Pulmonary Secretions in Neonates Using Heated and Humidified Anesthetic Gases

ERIC W. FONKALSRUD, SELMA CALMES* and

LARRY BARCLIFF*, Los Angeles, California

Humidified ventilation reduces the incidence of atelectasis and the difficulty removing tracheobronchial secretions in nonanesthetized infants requiring respiratory support; however, this technique has not been widely used for neonates receiving general anesthesia (GA). Hypothermia with consequent increased oxygen utilization and acidosis is a common sequella following GA in neonates despite the use of various external heating techniques.

During the past 3 years, 42 neonates undergoing surgical repair of major congenital malformations, including 28 thoracic operations, (18 full term, 24 premies) received heated (37°C) and humidified (100% saturated) anesthetic ventilation (HHV) for 1 to 3 hours with a mixture of O₂, room air, N₂O, and halothane via a Baby Bird Respirator with minimal external heating. During the past 4 years, a comparable group of 38 neonates with major anomalies underwent surgical repair under general anesthesia using the same anesthetic mixtures but with dry gases at room temperature (22 to 24°C) and with a heating mattress and an overhead infrared heating lamp (SV). The mean rectal T of infants given HHV decreased 0.38°C during the operation, whereas the mean T decreased 1.15°C in the SV infants. Twenty-three of the infants with HHV, but only 2 of the SV babies experienced heat gain by the end of the operation (p<0.05). Blood gas determinations during and shortly after operation were better in the HV infants compared to the SV babies. The mean period of post anesthetic intubation with ventilatory support was shorter in the HHV infants. Postoperative atelectasis or pneumonia occurred in only 9 of the SV group and in 2 of the HHV infants. Pulmonary secretions in the HHV infants were less voluminous and tenacious than in SV infants.

Since previous studies have shown that HHV does not interfere with anesthetic gas uptake it appears that this technique may be a useful adjunct to the currently used methods of neonatal anesthesia,

INTERMISSION - 45 MINUTES

VISIT EXHIBITS

*By invitation

TUESDAY - APRIL 29,1980

4:00 P.M. Executive Session (Limited to Active and Senior Members) - Continental Ballroom

6:30 P.M. President's Reception - Continental Ballroom