Faculty Bibliography

Sternal wound infections developed following 77 (0.97%) of 7,949 operative procedures involving median sternotomy at New York University Medical Center from 1976 to 1984. Risk factors associated with the development of a sternal wound infection included combined revascularization and valve replacement, early reexploration for bleeding, prolonged low cardiac output syndrome, and prolonged ventilatory support (greater than 24 hours). Concomitant infection at other sites with the same organism as cultured from the sternum was present in 42% of the patients. Thirty-seven patients (48%) were treated with radical debridement followed by closed antibiotic irrigation. In 31 other patients (40%), the wounds were debrided and left to heal by open granulation. Both initial treatments had equally high success rates (78.4% and 74.2%, respectively). However, the open granulation method resulted in a hospital stay that was an average of 10 days longer than the closed antibiotic irrigation method. Muscle flaps were used to expedite healing of open granulation in 9 patients. Analysis of the results of different treatment strategies revealed that if debridement was accomplished within 20 days of the initial cardiac procedure, 76% of the patients could be successfully treated with closed antibiotic irrigation. Conversely, if treatment was delayed for longer than 20 days, 81% of the patients were treated with open granulation (p less than 0.001). Also noted was an inverse relationship between the serum blood urea nitrogen (BUN) level and the success rate of initial treatment with closed antibiotic irrigation. Patients with a serum BUN level of less than 40 mg/dl at the time of debridement had a 90% success rate as opposed to a success rate of 38% when the BUN level was 40 mg/dl or greater. The data presented suggest the following conclusions. Early diagnosis is crucial to successful treatment of sternal wound infection. When diagnosis can be established within 20 days, 80% of infections can be eradicated by the simple approach of debridement and closed antibiotic irrigation. When diagnosis is delayed, however, prompt debridement followed by muscle flaps is the procedure of choice. Open granulation alone, while successful, unnecessarily prolongs the hospital course

The relative merits of adding a 'pulsatile' component to flow during cardiopulmonary bypass (CPB) has long generated controversy, the resolution of which has been hampered by lack of quantification of the 'pulsatility' delivered by different devices. The present experimental series had two goals: to quantify the 'pulsatility' of blood flow during CPB in terms of pulse rate and pulsatility index (PI) and to examine which aspects of a 'pulsed flow' provide clinical benefits. A flow waveform can be expressed in terms of its baseline rate and its PI, the sum of the square of its harmonics components divided by the square of the mean flow. We used PI to quantify the pulsatility of blood flow in the descending thoracic aorta and used changes in the serum lactate level as an indication of end organ flow. In one experimental series seven adult mongrel dogs were placed on roller pump CPB at a constant flow of 100 ml/kg/min. After a 20-minute stabilization period a roller pump wave and three different pulse shapes (generated by a computer-controlled hydraulic pump) were evaluated for 15 minutes each. The pulse wave shapes were graded, with C being the sharpest and A the least sharp. In a second series six other dogs were placed on CPB and were subjected to roller pump perfusion and three pulse waves of identical shape but at different rates. The results indicated that a combination of a minimum PI of 1.88 and a minimum rate of 80 bpm were necessary to significantly reduce lactate production as compared with roller pump perfusion. Thus the same mean flow can have very different physiologic effects depending on how it is delivered. This quantification method permits direct comparison of different 'pulsatile waveforms' and provides a means for identification of optimal pulsatile flow

Although prompt institution of reperfusion following coronary artery occlusion has been shown to limit myocardial infarct size, significant 'reperfusion injury' may result. We investigated in a canine model whether maintenance of the left ventricle in an unloaded state during the initial reperfusion period following acute myocardial ischemia would result in greater limitation of infarct size or modify the development of reperfusion injury. Group I (control, n = 6) underwent 6 hours of occlusion of the left anterior descending coronary artery without further intervention. In both Group II (n = 6) and Group III (n = 6), the snare was released after 2 hours and hearts were reperfused for 4 hours. In Group III only, the left ventricle was maintained in an unloaded state throughout the entire reperfusion interval via pulsatile left atrial-femoral artery bypass. The results showed that reperfusion of the left ventricle in an unloaded state resulted in significantly improved limitation of both infarct size (area of infarct/area at risk = 16.6% for Group III versus 72.0% for Group I and 55.4% for Group II, p less than 0.001) and area of microvascular damage (area of microvascular damage/area at risk = 4.8% for Group III versus 30.6% for Group II, p less than 0.001). These results indicate that although myocardial reperfusion of the type provided by thrombolysis and/or angioplasty techniques does result in limitation of infarct size when compared to no reperfusion, this limitation is not optimal unless the left ventricle is unloaded during the initial reperfusion period

In the present study, we examined the effects of various levels of oxygen tension on spinal cord blood flow while using somatosensory evoked potentials to monitor spinal cord sensory function during hypoxia. In this experiment, six adult, mongrel dogs were heparinized and placed on right atrial-femoral artery bypass with an oxygenator in the bypass circuit. The aorta was cross-clamped proximal to the left subclavian artery, and bypass flow and fluid balance were adjusted so as to maintain a distal aortic perfusion pressure of greater than 80 mm Hg. Oxygen flow to the oxygenator was lowered by graded decrements to provide decreasing levels of oxygen tension, which ultimately approached pure venoarterial bypass. Each successive oxygen level was maintained for 30 minutes. Spinal cord blood flow was measured with radioactive microspheres, and latency and amplitude of somatosomatic evolved potentials were continuously monitored. The somatosensory evolved potential signal was invariably present as long as the distal aortic pressure was greater than 80 mm Hg; there were several transient hypotensive episodes (less than 5 minutes), which were accompanied by reversible loss of somatosensory evolved potentials. The spinal cord blood flow increased from 13.6 to 119.7 ml/100 gm/min as the distal oxygen tension fell to a mean value of 30 mm Hg, while latency of somatosensory evolved potentials increased 19.3% and amplitude decreased 43.3%. These results suggest the following conclusions: (1) In response to hypoxia, spinal cord blood flow dramatically increases and somatosensory evolved potentials deteriorate (increase in latency and decrease in amplitude). (2) However, during prolonged hypoxia, spinal cord sensory function can be maintained by sufficiently high flow rates and perfusion pressures. (3) Somatosensory evolved potentials can be used to monitor continuously spinal cord sensory function under these conditions