Stephen A. Mills

A Prospective Study of Sternal Wound Complications

Eight hundred seventy patients were enrolled in a prospective study to identify risk factors for sternal wound complications following open-heart operations. The 0.8% incidence of major sternal complications was similar to that reported in the literature by other centers. The effects of age, sex, weight, operative time, type of procedure, resident versus attending surgeon, prolonged ventilatory support, reoperation for bleeding, external cardiac massage, and Dacron versus wire suture for sternal closure were assessed by stepwise logistic regression. Prolonged ventilation and female sex both strongly increased the risk of major sternal complications. Age and weight exerted lesser, but statistically significant, effects on the incidence of such complications. None of the other factors was associated with an increased risk of major sternal complications.

Cerebral injury and cardiac operations

Cerebral complications constitute the leading source of morbidity and disability after cardiac operations. The incidence of stroke after coronary artery bypass grafting has increased in tandem with the mean age of the patient population. Although many cerebral deficits resolve with time, others remain sources of disability for otherwise functional patients and detract from an otherwise successful procedure. The clinical spectrum of cerebral complications includes both neurologic and neuropsychologic deficits. Neurologic deficits include fatal cerebral injury, stroke, impaired level of consciousness, and seizures. The incidence of these deficits is 1% to 6%. Neuropsychologic deficits refer to cognitive changes, and are quantitated with tests of memory and learning and speed of visual-motor response. The incidence of these deficits is 60% to 80% at 1 week after operation and 20% to 40% at 8 weeks after operation. Central nervous system complications after cardiac operations have been attributed in large part to the effects of cardiopulmonary bypass on the brain. Potential mechanisms include macroembolization of air or particulate matter; microembolization of gas, fat, aggregates of blood cells, platelets or fibrin, and particles of silicone or polyvinylchloride tubing; and inadequate cerebral perfusion pressure. Methods of assessment include those applied during the procedure (clinical observation, assessment of cerebral blood flow and metabolism, intraoperative electroencephalography, transcranial and carotid Doppler echography, quantitative embolic measurement, and fluorescein angiography) and those performed to measure outcome (neurologic and neuropsychologic testing, computed tomographic scans, magnetic resonance imaging, and cerebrospinal fluid studies). Much of the literature regarding cerebral injury and cardiopulmonary bypass is descriptive, relating patient risk factors to the incidence of postoperative stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of cerebral blood flow to changes in carbon dioxide tension during hypothermic cardiopulmonary bypass

Changes in cerebral blood flow (CBF) in response to changes in Pa were measured by intraaortic injection of133Xe in 12 patients during hypothermic (23–30°C) cardiopulmonary bypass. In each patient, CBF was determined at two randomly ordered levels of Paco2 obtained by varying the rate of gas inflow into the pump oxygenator (Group I, n = 6) or by varying the percentage of CO2 added to the gas inflow (Group II, n = 6). Nasopharyngeal temperature, mean arterial pressure, pump-oxygenator flow, and hematocrit were maintained within a narrow range. In group I, a Paco2 (uncorrected for body temperature) of 36± 4 mmHg (mean ± SD) was associated with a CBF of 13 ± 5 ml.100 g−1·min−1, while a Paco2 of 42 ± 4 mmHg was associated with a CBF of 19± 10 ml · 100 g−1·min−1. In group II, a Paco2 of 47 ± 3 mmHg was associated with a CBF of 20± 8 ml. 100 g−1·min−1, and a Paco2 of 53± 3 mmHg was associated with a CBF of 26 ± 9 ml. 100 g−1·min−1. Within group I, the difference in CBF was significant (p < 0.05); within group II, the difference in CBF was significant at the P < 0.002 level. All CBF measurements were lower than those reported for normothermic, unanesthetized subjects of similar age. The response of the cerebral circulation to changes in CO2 tension was well-maintained during hypothermic cardiopulmonary bypass. CBF increased by an average of 1.07 ± 1.19 (SD) ml. 100 g−1·min−1·mmHg−1increase in temperature-uncorrected Paco2 in Group I, and by 1.05 ± 0.54 ml · 100 g−1·min−1· mmHg−1increase in group II.

Predictive Value of Blood Clotting Tests in Cardiac Surgical Patients

Abstract This study ptospectively evaluated numerous tests of clolting function in 897 consecutive adult cardiac surgical patients over 18 months. This included coronary operation, valve replacement, and reoperative patients. The tests included activated clotting time, activated partial thromboplastin time, prothrombin time, thiombin time, fibrinogen, fibrin/fibrinogen degradation products, platelet count, and Dukes earlobe bleeding time. Other variables such as age, sex, and cardiopulmonary bypass duration were included in the multivariate analysis. Statistically significant correlations were found between 16-hour mediastinal drainage and activated partial thromboplastin time, fibrinogen, activated clotting time, fibrin/fibrinogen degradation products, platelet count, and prothrombin time. Scatter plots indicate that these relationships, although statistically significant, had little predictive value and were largely significant is a result of the large number of patients in each group, which permitted weak correlations to reach statistical significance. The best multivariate model constructed could explain only 12% of the observed variation in postoperative blood loss. Because the predictive values of the tests are so low, it does not appear sensible to screen patients routinely using these clotting tests shortly after cardiopulmonary bypass.

Surgical implications in malignant cardiac disease.

Despite the rarity of primary malignant tumors of the heart (0.0017 to 0.03% of large postmortem series) and the infrequency of clinical signs and symptoms (0 to 50%) of the more common metastatic cardiac tumors, many cardiothoracic surgeons at some time will encounter a patient with one of these two conditions. A review of the medical literature yielded 28 cases of primary cardiac tumors, 10 of secondary tumors, and 12 of carcinoid heart disease treated surgically and followed sufficiently for retrospective evaluation. We summarized those cases and made the following conclusions. Primary malignant tumors of the heart are occasionally resectable, although cure is unlikely; survival may be enhanced by postoperative irradiation but probably not by postoperative chemotherapy. For patients with secondary malignant tumors of the heart, surgical intervention is rarely of benefit except for establishing a tissue diagnosis, effecting artificial cardiac pacing, decompressing symptomatic pericardial effusions, or reducing an obstructive tumor mass. Patients with carcinoid heart disease affecting the valves may derive benefit from valve replacement or repair. Thus, in selected patients with malignant cardiac disease, surgical intervention may be feasible and should always be among the therapeutic options considered.

Risk Factors for Cerebral Injury and Cardiac Surgery

Cerebral complications represent the leading cause of morbidity after cardiac operations. With the growing awareness of their social and economic importance, increasing attention is being given to their prevention. In the coronary artery bypass population, advanced age (> or = 75 years) is associated with an 8.9% neurologic deficit rate. Mortality is increased ninefold in the elderly patient with a neurologic deficit. Cardiopulmonary bypass has long been recognized as a cause of neuropsychologic deficits. Emboli are thought to be the causal agent. Retinal microvascular lesions during cardiopulmonary bypass as well as recent demonstration of widespread pathologic subcapillary arteriolar dilatations in the brain after cardiopulmonary bypass have been documented. Despite widespread interest in cerebral blood flow and neurologic deficits, there is no convincing evidence that defines a critically low or dangerously high level of flow. The ascending aorta represents a leading source of embolic neurologic injury. The use of intraoperative ultrasound to identify the diseased aorta may result in alternative operative strategies in an effort to minimize emboli and improve neurologic outcome. Existing literature offers conflicting views on optimal management of carotid artery stenosis in the coronary artery surgical patient. A trend that combined carotid endarterectomy and coronary artery bypass may often be appropriate will need confirmation through a multicenter clinical trial. Open cardiac surgical procedures, particularly in the aged population, carry a significant increased risk of adverse neurologic outcome. Postoperative arrhythmias may result in embolic neurologic deficit. A further understanding of risk factors for cerebral injury will be of value in developing therapeutic approaches to this major clinical problem.

Radial Artery-to-Aorta Pressure Difference after Discontinuation of Cardiopulmonary Bypass

To test whether the radial artery-to-aorta pressure gradient seen in some patients after cardiopulmonary bypass (CPB) is due to reduction in hand vascular resistance, the authors compared pressures in the ascending aorta with pressures in the radial artery before and after CPB in 12 patients. They increased hand vascular resistance by briefly occluding the radial and ulnar arteries at the wrist and recorded that effect on the radial artery-to-aorta pressure relationship. They also recorded the effect of wrist compression on radial artery pressures before and after CPB in 38 patients not having aortic pressure measurements. Before CPB in the first 12 patients, the radial systolic arterial pressure (SAP) was significantly higher (P less than 0.05) than the ascending aortic SAP, and wrist compression did not significantly affect that difference (P greater than 0.05). After CPB, the radial artery and aortic SAPs were not statistically different (P greater than 0.05), but wrist compression restored the higher radial artery SAP. The mean arterial pressure (MAP) was equal in four patients and 1-3 mmHg higher or lower in eight patients before CPB, and wrist compression did not alter those relationships. After CPB, MAP was equal in four patients; radial MAP was 1-3 mmHg higher or lower in six patients, and 7 and 10 mmHg lower in the last two patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgical progress: surgical management of infective endocarditis.

Infective endocarditis of bacterial or fungal origin may arise in either the left or the right heart and can involve both natural and prosthetic valves. The diagnosis is based primarily upon clinical criteria and positive blood cultures, but serial electrocardiograms, fluoroscopy, and two-dimensional echocardiograms may also be helpful. The initial treatment should consist of antibiotic therapy and is itself often adequate in effecting cure. However, careful observation during antibiotic treatment is mandatory, since the development of congestive heart failure due to valvular obstruction or destruction can be an indication for surgical intervention. Other surgical indications include a failure to respond to antibiotic therapy, pulmonary or systemic emboli, evidence of abscess involving the valvular ring (particularly prevalent with prosthetic valve endocarditis), Brucella infection, and the onset of conduction disturbances. The goals of surgical treatment are removal of infective tissue, restoration of valve function, and correction of associated mechanical disorders. The results are surprisingly good, especially for a condition of this severity.

Hypercarbia depresses cerebral oxygen consumption during cardiopulmonary bypass.

No human studies have systematically examined the relations among PaCO2, cerebral blood flow, and the cerebral metabolic rate for oxygen during hypothermic cardiopulmonary bypass. We varied PaCO2 during hypothermic (26-28 degrees C) cardiopulmonary bypass and estimated the cerebral metabolic rate for oxygen by multiplying cerebral blood flow (measured using xenon-133 clearance) by the cerebral arteriovenous difference in oxygen contents. Patients were randomly assigned to either of two methods of managing PaCO2 (uncorrected for body temperature). In group 1 (PACO2 32-48 mm Hg, n = 13) the mean +/- SD cerebral metabolic rate for oxygen was 0.40 +/- 0.11 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 36 +/- 2.0 mm Hg and 0.40 +/- 0.14 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 45 +/- 2 mm Hg. and 49-72 mm Hg, n = 12) the mean +/- SD cerebral metabolic rate for oxygen was 0.31 +/- 0.09 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 55 +/- 3 mm Hg and 0.21 +/- 0.07 ml O2 X 100 g-1 X min-1 at a mean +/- SD PaCO2 of 68 +/- 2 mm Hg. Group 2 values differed significantly from those in Group 1 (p less than 0.05). In both groups, cerebral blood flow increased as PaCO2 increased. During cardiopulmonary bypass, increasing PaCO2 increases cerebral blood flow and decreases the cerebral metabolic rate for oxygen.

Mitral valve operation via an extended transseptal approach

The extended transseptal approach to the mitral valve has been used for 71 consecutive procedures. Four patients died; none had complications directly attributable to the exposure. Twenty underwent a primary reparative procedure; 30, a primary replacement procedure; and 21, a repeat procedure. Despite division of the sinus node artery, 26 of 32 patients with sinus rhythm preoperatively had sinus rhythm postoperatively; 4 had atrial fibrillation postoperatively. Twenty-seven of 37 patients with atrial fibrillation preoperatively had atrial fibrillation postoperatively; 8 had sinus rhythm postoperatively. Because the exposure provided by this extended transseptal approach is superior to that of standard approaches, we now use it routinely for mitral valve operations.