Definition of the safe lower limits of aortic resection during surgical procedures on the thoracoabdominal aorta: use of somatosensory evoked potentials.

The technique of intraoperative monitoring of somatosensory evoked potentials was applied to a canine model of spinal cord ischemia in an attempt to determine the safe lower limits of aortic resection during thoracic aortic surgery. Fifteen animals underwent left thoracotomy with institution of partial left atrial/femoral artery bypass for maintenance of distal aortic perfusion after proximal descending thoracic aortic exclusion. In Group I animals (n = 6, control), no further interventions were performed so that the effect of exclusion of vessels noncritical to spinal cord blood supply could be assessed by measurements of spinal cord blood flow and somatosensory evoked potentials. In Group II animals (n = 8), the level of distal aortic exclusion was progressively lowered until loss of somatosensory evoked potential (critical vessel exclusion) occurred. The effect of critical vessel exclusion on spinal cord blood flow was then assessed. Exclusion of multiple vessels noncritical to spinal cord blood supply (Group I) had no effect on spinal cord blood flow or function (somatosensory evoked potentials). Exclusion of vessels critical to spinal cord blood supply resulted in significant spinal cord ischemia (83.4% flow reduction, probability [p] less than 0.05 versus baseline) and ischemic spinal cord dysfunction (loss of somatosensory evoked potential).(ABSTRACT TRUNCATED AT 250 WORDS)

Time course of effective interventional left heart assist for limitation of evolving myocardial infarction.

Previous work has shown that if pulsatile left atrial-femoral artery bypass is instituted after occlusion of the left anterior descending coronary artery for from 15 minutes to 2 hours, it can significantly limit the size of the infarct resulting 4 hours later. This study investigated whether pulsatile left atrial-femoral artery bypass begun after more clinically pertinent periods of initial ischemia can still significantly limit infarct expansion. After baseline measurements of hemodynamics, tension-time index, and regional myocardial blood flow in 73 open-chest, adult dogs, the left anterior descending coronary artery was ligated for 15 minutes or 1, 2, 4, or 6 hours of unprotected ischemia. In the five control groups, the initial ischemic period was merely extended for another 4 hours. In the five experimental groups, the animals were placed on pulsatile left atrial-femoral artery bypass for another 4 hours after the initial ischemic period. At the end of each procedure, gentian violet was used to identify the area at risk of infarction, and triphenyltetrazolium chloride was used to delineate the area of infarct. The results showed a significant reduction in the area of infarct as a percentage of the area at risk in each bypass group compared with its control group for all ischemic periods of less than 6 hours. These findings suggest that the maximum permissible ischemic time delay for myocardial salvage by pulsatile left atrial-femoral artery bypass is one which is pertinent in a clinical setting. The results justify continued attempts to develop appropriate techniques for percutaneous application of this modality to patients with an evolving myocardial infarction.

The factors influencing early patency of coronary artery bypass vein grafts: correlation of angiographic and ultrastructural findings.

To test the hypothesis that suboptimal preparation of saphenous veins may adversely affect early patency of aorta-coronary artery bypass grafts, a nonrandomized prospective study was undertaken comparing two methods of saphenous vein preparation prior to grafting. Forty recatheterizations were performed during the postoperative hospital stay (approximately 10 days) in two groups of asymptomatic patients who had undergone isolated coronary artery bypass grafting. Veins from patients in Group I were bathed in autologous, heparinized blood at 20 degrees C and distended to 80 mm Hg, prior to grafting. The veins from Group II patients were prepared in an identical manner, except that the bathing solution consisted of heparinized electrolyte solution with added papaverine (0.6 mg/lg). Segments of vein from each group were obtained prior to grafting and preserved in 3% glutaraldehyde for subsequent electron microscopic studies. Operative technique in both groups of patients was identical and all procedures were performed by the same surgeons. Comparison of patients in Group I and II revealed no significant difference in the number of diseased vessels per patient (3.1 versus 3.4), number of grafts per patient (2.9 versus 2.9), native vessel diameter (1.9 versus 1.7 mm), and postoperative graft flows (65 versus 68 cc/min). However, early postoperative graft patency in Group II patients was 93% versus 80% in patients in Group I (p less thn 0.01). Electron microscopic analysis revealed severe spasm of venous smooth muscle in the blood-stored veins causing intraluminal smooth muscle cell cytoplasmic protrusions with resultant endothelial separation and desquamation. Formation of fibrin-platelet microaggregates was common. These findings were not present in the solution-treated veins. In view of these ultrastructural findings, and the highly significant difference in patency rates, we have abandoned all blood storage techniques and now prepare saphenous veins by soaking them in a clear bathing medium with added heparin and papaverine. Long-term follow-up of these patients is currently in progress and may reveal even more dramatic results than we have heretofore observed.

Cardiac output determination after cardiac operation. Lack of correlation between direct measurements and indirect estimates.

Ninety-two mean thermodilution cardiac indices were determined in 25 patients following cardiac operations. Arterial and venous blood gases, hematocrit, body temperature, central venous pressure, left atrial pressures, urine output, heart rate, and mean arterial pressure were simultaneously recorded. Six variables, arterial and venous pH, arterial and venous PCO2, venous PO2, and temperature, showed significant simple correlations with cardiac index, but the degree of correlation was inadequate for use of these variables as reliable indices of cardiac function. When stepwise multiple regression analysis was performed, two variables, venous PO2 and left atrial pressure were associated with the best correlation with cardiac index, such that CI = 0.073 PO2V -- 0.060 LAP + 1.39 (r = 0.60, p less than 0.001). When measured values for venous PO2 and left atrial pressure were substituted into this equation, a "predicted" value for cardiac index could be obtained with only slightly improved reliability. The data indicate that indirect estimation of cardiac output by measurement of the various laboratory parameters described above is not sufficiently reliable for clinical use. The importance of obtaining direct measurements of cardiac output by thermodilution or other means in order to properly evaluate postoperative cardiac function is stressed.

Venoarterial bypass: a technique for spinal cord protection.

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.

Quantification of pulsatile flow during cardiopulmonary bypass to permit direct comparison of the effectiveness of various types of "pulsatile" and "nonpulsatile" flow.

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.

Blood potassium cardioplegia administration. Comparison of myocardial protection offered by three techniques.

To investigate the best method of administration of blood potassium cardioplegia, 19 dogs were studied while undergoing 120 minutes each of aortic crossclamping (myocardial temperature, less than 15 degrees C). Group 1 (six dogs) underwent a single 120-minute period of aortic crossclamping with the heart protected by multiple reinjections (1,000 mL every 30 minutes) of blood potassium cardioplegia solution (potassium chloride, 30 mEq/L; pH, 8; temperature, less than 15 degrees C). Group 2 (six dogs) underwent four separate 30-minute periods of aortic crossclamping, but allowing hearts to beat in a nonworking state for 20 minutes at 35 degrees C between each arrest interval. Hearts in group 3 (seven dogs) were initially arrested as described above, following which a continuous infusion (75 mL/min; KCl, 10 mEq/L) of blood potassium cardioplegia solution was maintained throughout the arrest period. Measurements of myocardial metabolism, ventricular function, regional blood flow, and ultrastructure were carried out before arrest and 30 minutes after final unclamping. Analysis of the data revealed no significant benefit of one method over another, with the exception that adenosine triphosphate level was least preserved with intermittent unclamping and reperfusion. Because continuous perfusion techniques are more cumbersome than multidose reinjection, and intermittent aortic crossclamping lengthens total cardiopulmonary bypass time, we favor the simplest approach, multidose reinjection during a single uninterrupted period of aortic crossclamping.

Intrathecal perfusion of an oxygenated perfluorocarbon prevents paraplegia after aortic occlusion.

A canine model was used to evaluate the effects of continuous intrathecal perfusion of an oxygenated perfluorocarbon emulsion on systemic and cerebral hemodynamics and neurologic outcome after 70 minutes of normothermic aortic occlusion. Twelve mongrel dogs were instrumented to monitor proximal and distal arterial blood pressure, cerebrospinal fluid pressure, spinal cord perfusion pressure, and somatosensory evoked potentials. The intrathecal perfusion apparatus consisted of two perfusing catheters, placed in the intrathecal space through a laminectomy, and a draining catheter percutaneously inserted in the cisterna cerebellomedullaris. The aorta was cross-clamped just distal to the left subclavian artery for 70 minutes. Animals were randomized into two groups: group 1 (n = 6) animals were treated with intrathecal perfusion of saline solution, whereas group 2 (n = 6) animals received oxygenated Fluosol-DA 20%. Data were acquired at baseline, during the cross-clamp period, and after reperfusion. Normothermic Fluosol or saline solution was infused at a rate of 15 mL/min beginning 15 minutes before cross-clamping and continued throughout the ischemic interval. There was no difference in proximal arterial blood pressure (97.2 versus 95.4 mm Hg; p > 0.05) or distal arterial blood pressure (14.6 versus 15.0; p > 0.05) between the two groups throughout the cross-clamp interval. Cerebrospinal fluid pressure rose significantly in both groups with the onset of intrathecal perfusion of either saline solution or Fluosol (7 +/- 1 versus 24 +/- 5 and 8 +/- 1 versus 40 +/- 4 mm Hg, respectively; p < 0.05). The rise in cerebrospinal fluid pressure was sustained throughout the perfusion interval in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental and clinical assessment of the adequacy of partial bypass in maintenance of spinal cord blood flow during operations on the thoracic aorta.

We studied both experimentally and clinically the efficacy of partial bypass techniques in maintaining spinal cord blood flow and physiological function during surgical procedures on the thoracoabdominal aorta. We attempted to define the level of distal aortic pressure required to safely ensure normal neurological function in the absence of critical intercostal occlusion. Six dogs underwent left thoracotomy with baseline measurements of spinal cord blood flow and spinal cord impulse conduction (somatosensory evoked potentials). Following exclusion of the entire descending thoracic aorta from the left subclavian artery to the T-13 level, partial left atrium-femoral artery bypass was instituted, and baseline levels of proximal and distal aortic pressure were maintained during a 30-minute stabilization period. Mean distal aortic pressure then was progressively altered at 30-minute intervals to 100, 70, and 40 mm Hg. Measurements of spinal cord blood flow and somatosensory evoked potential were repeated at the end of each interval for comparison with baseline. No significant changes in spinal cord blood flow or somatosensory evoked potential were observed in any animal with a distal aortic pressure greater than or equal to 70 mm Hg. With a pressure of 40 mm Hg, normal flow and somatosensory evoked potentials were maintained in 5 of the 6 dogs. Loss of somatosensory evoked potential, with simultaneous loss of spinal cord blood flow at the T-6 level, occurred in 1 dog. Restoration of distal aortic pressure to 70 mm Hg in all animals resulted in immediate return of somatosensory evoked potential. Loss of somatosensory evoked potential routinely occurred in animals with a distal aortic pressure less than 40 mm Hg. Clinically, 9 patients have undergone operation for lesions of the thoracoabdominal aorta using shunt or bypass techniques. Normal somatosensory evoked potentials were preserved in 7 patients with maintenance of adequate distal aortic pressure (greater than or equal to 60 mm Hg) without evidence of postoperative neurological deficit. Two patients showed hypotensive somatosensory evoked potential loss (distal aortic pressure less than 40 mm Hg). Prolonged distal hypotension (85 minutes of aortic cross-clamping) in the latter resulted in paraplegia. We conclude that maintenance of a distal aortic pressure greater than 60 to 70 mm Hg will uniformly preserve spinal cord blood flow in the absence of critical intercostal exclusion. Should distal aortic pressure be inadequate, early reversible changes in the somatosensory evoked potential will alert the surgeon. Failure to institute measures to reverse these changes may result in paraplegia.

Prevention of ischemic spinal cord injury following aortic cross-clamping: use of corticosteroids.

Prior to proximal aortic cross-clamping, baseline measurements of spinal cord blood flow and function were done. Blood flow was evaluated with radioactive microspheres and function determined by assessment of somatosensory evoked potential (SEP). Group 1 (N = 6) animals had aortic cross-clamping for 5 minutes after ischemic spinal cord dysfunction (SEP loss) was documented. Group 2 (N = 9) underwent aortic cross-clamping for 10 minutes after loss of SEP. Group 3 (N = 6) also underwent 10 minutes of cross-clamping after initial SEP loss, but were treated intravenously with methylprednisolone (30 mg per kilogram of body weight) 10 minutes prior to cross-clamping and again 4 hours postoperatively. After release of the cross-clamp, the animals were allowed to recover and serial evaluations of spinal cord blood flow and neurological status were carried out for seven days. Group 1 animals recovered uneventfully without evidence of neurological injury. Group 2 animals sustained a 67% incidence of permanent spastic paraplegia (p = 0.02 versus Group 1). In contrast, methylprednisolone-treated animals sustained no clinically detectable neurological injury (p = 0.02 versus Group 2). Measurements of spinal cord blood flow at the time of SEP loss revealed similar degrees of spinal cord ischemia in all groups. No significant differences were observed in the duration of aortic cross-clamping prior to SEP loss among the three groups. The data indicate that short periods of cross-clamping (5 minutes) following SEP loss are well tolerated, whereas longer periods (10 minutes) are associated with a high incidence of paraplegia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebrospinal fluid drainage and steroids provide better spinal cord protection during aortic cross-clamping than does either treatment alone.

We investigated whether intravenous methylprednisolone (30 mg/kg) before 30 minutes of aortic cross-clamping and after 4 hours could enhance the effects of cerebrospinal fluid drainage on spinal cord perfusion pressure and postoperative paraplegia when proximal blood pressure was controlled with sodium nitroprusside and partial exsanguination. Dogs were randomized into three groups: group 1 (n = 6), control; group 2 (n = 7), steroids; and group 3 (n = 6), steroids with cerebrospinal fluid drainage. During aortic cross-clamping, blood pressure proximal to the clamp decreased significantly in each group compared with baseline (p less than 0.05), but did not differ among groups (group 1 = 82.2, group 2 = 82.1, group 3 = 86.6 mm Hg, p greater than 0.05). Mean distal pressure decreased from systemic values to 8.4, 8.5, and 3.7 mm Hg, respectively, after aortic cross-clamping (p less than 0.05); these values did not differ from one another (p greater than 0.05). During aortic cross-clamping, cerebrospinal fluid pressure in groups 1 and 2 did not differ significantly compared with baseline (12.2 versus 8.2, 14.2 versus 10.7 mm Hg, p greater than 0.05), whereas in group 3 the baseline cerebral spinal fluid pressure of 10.7 mm Hg decreased to 0.4 mm Hg (p less than 0.05). Spinal cord perfusion pressure in group 3 was significantly higher than in groups 1 and 2 (3.3 versus -3.9 and -5.7 mm Hg, p less than 0.05), but did not differ between groups 1 and 2 (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased release of cyclic adenosine monophosphate into jugular vein in response to isoproterenol administration.

Catecholamine administration elevates plasma cyclic AMP (cAMP) levels but the source of the cAMP is unknown. To determine possible sources, plasma cAMP levels were determined in blood vessels across the head, liver, kidney and lung in anesthetized dogs infused with the beta-adrenergic agonist, isoproterenol. Only the head showed an increased release of cAMP into the blood. The kidneys removed cAMP from the blood while liver and lung showed no change. This in vivo demonstration of release of cAMP from the head represents contributions from brain and facial muscles and may be a useful approach to study brain involvement in the action of various hormones and drugs.

Effect of hematocrit on regional oxygen delivery and extraction in an adult respiratory distress syndrome animal model.

BACKGROUND: The purpose of this prospective, randomized, controlled study was to investigate the effects of hematocrit (Hct) on regional oxygen delivery and extraction following induction of adult respiratory distress syndrome (ARDS) in an animal model. METHODS: Animals were instrumented to monitor central venous pressure (CVP), systemic mean arterial pressure (MAP), pulmonary artery occlusion pressure (PAOP), and cardiac output (CO) and to measure blood flow in the renal, hepatic, and superior mesenteric arteries and portal vein. ARDS was induced, positive end expiratory pressure (PEEP) applied and CO was maximized with volume loading and epinephrine infusion. Data were acquired at baseline (BL) and at Hct levels ranging from 25% to 50%. RESULTS: Systemic DO(2) increased steadily and significantly with increased Hct. Systemic O(2) extraction ratio (O(2)ER) decreased significantly with increasing Hct until a threshold value of 40%, after which further increases in Hct did not cause a statistically significant decrease in O(2)ER. Similarly, renal and hepatic DO(2) increased and O(2)ER decreased in a statistical significant manner with transfusions up to a Hct of 35%. In the splanchnic circulation blood transfusions did not cause any statistically significant increase in DO(2), and O(2)ER showed no decrease after an Hct of 35%. Systemic, renal, hepatic, and splanchnic VO(2) were not affected by changes in Hct. Blood viscosity decreased from a baseline value of 2.9+/-0.2 centipoise at a Hct of 38% to 2.3+/-0.1 centipoise at a Hct of 25% (P<0.05). Viscosity increased progressively with increasing hematocrits and reached the value of 4.2+/-0.2 centipoise at an Hct of 50% (P<0.05 versus Hct 30%, 35%, 40%, 45%). CONCLUSIONS: Based on the results of this non-supply-dependent animal model we conclude that a progressive increase in Hct up to 40% causes a corresponding increase in systemic DO(2) associated with a decrease in O(2)ER. However, there is no improvement in renal, hepatic, and splanchnic DO(2) and O(2)ER after a threshold Hct of 35%. All other factors being the same, an Hct greater than 35% may in fact cause a decrease in blood flow rate and change in blood flow characteristics as a consequence of increased blood kinematic viscosity, which may alter and compromise cellular oxygen transfer.

Prolonged lactate clearance is associated with increased mortality in the surgical intensive care unit.

BACKGROUND: Failure of arterial serum lactate to achieve normal levels has been associated with an increased mortality among medical and trauma patients. At our institution the ability of the patient to normalize arterial serum lactate has been utilized as an end point of resuscitation. In this study, we examine the correlation between length of time to lactate normalization and mortality. METHODS: The charts of 95 consecutive surgical intensive care unit (SICU) patients requiring hemodynamic monitoring or therapy were reviewed retrospectively. Hemodynamic, demographic, and laboratory data were recorded. Patients were stratified by lactate normalization time, and a subgroup analysis of survivors and nonsurvivors was performed by univariate and multivariate analysis. RESULTS: Patients not achieving a normal lactate level sustained a 100% hospital mortality rate. Those clearing between 48 and 96 hours sustained a 42.5% mortality rate. Patients normalizing in 24 to 48 hours had a 13.3% mortality rate, and those clearing in less than 24 hours had a mortality rate of 3.9%. Subgroup analysis by survival revealed differences in time to lactate clearance, initial blood pressure, and initial lactate on univariate analysis. On multivariate analysis only time of lactate clearance was found to differ. CONCLUSIONS: Prolongation of lactate clearance is associated with increasing mortality. Failure of a patient to normalize lactate is associated with 100% mortality. Measurement of arterial serum lactate is a simple and effective predictor of outcome and end point of therapy.

Control of proximal hypertension during aortic cross-clamping: its effect on cerebrospinal fluid dynamics and spinal cord perfusion pressure.

Postoperative paraplegia remains the most devastating complication of surgery of the descending and thoraco-abdominal aorta. Control of the proximal hypertension that follows cross-clamping of the thoracic aorta to repain aneurysms of the descending and thoraco-abdominal aorta is necessary to prevent left ventricular failure, myocardial infarction, and hemorrhagic cerebral events. Both pharmacological and mechanical modalities used to control central hypertension during aortic occlusion affect cerebrospinal fluid dynamics and spinal cord perfusion pressure. Sodium nitroprusside (doses >5 microg/kg/min), the most widely used pharmacological agent, decreases spinal cord perfusion pressure because it increases cerebrospinal fluid pressure and decreases blood pressure distal to the aortic cross-clamp. This effect cannot be prevented by drainage of cerebrospinal fluid. Nitroglycerin also decreases spinal cord perfusion pressure, but its effects on cerebrospinal fluid dynamics can be countered by drainage of cerebrospinal fluid. Active distal perfusion with left atrial-femoral artery bypass can provide adequate perfusion of the circulation distal to the aortic cross-clamp while simultaneously reducing cerebrospinal fluid pressure. This approach can maintain mesenteric and spinal cord blood flow, therefore preventing the multiple organ dysfunction syndrome caused by release of cytokines from the splanchnic district and decreasing the incidence of postoperative paraplegia from spinal cord ischemia. In cases of limited retroperfusion, partial exsanguination and cerebrospinal fluid drainage can be used in conjunction with left atrial-femoral artery bypass to prevent rises in cerebrospinal fluid pressure and maintain spinal cord blood flow above the threshold necessary to prevent neurological injury. The use of oxygenated perfluorocarbons in the subarachnoid space to provide passive oxygenation of the spinal cord during aortic occlusion remains experimental and requires further investigation.

Pericardiotomy improves left ventricular compliance during sepsis-induced pulmonary artery hypertension.

Sepsis-induced pulmonary artery hypertension (SIPAH) causes an increase in right ventricular (RV) afterload, dilatation of the RV, leftward shift of the interventricular septum (IVS), and therefore decreases left ventricular compliance (LVC). This study was designed to evaluate the role of pericardiotomy during SIPAH as an alternative to vasodilators (which cause a detrimental increase in shunt fraction) to improve LVC. Systemic and pulmonary hemodynamics, pulmonary function, RV, and LVC were acquired at baseline (BL), during SIPAH with closed pericardium (PAHCP) and after opening the pericardium (PAHOP). Systemic hemodynamics and pulmonary function did not change significantly during the experiment. The infusion of live bacteria induced a significant rise in mean pulmonary artery pressure from 16 +/- 5.3 at BL to 36.8 +/- 3.3 and 35.0 +/- 6.4 mm Hg during PAHCP and PAHOP, respectively, (P less than 0.05). Pulmonary vascular resistance index and right ventricular stroke work index (RVSWI) displayed a similar rise in response to SIPAH (P less than 0.05 vs BL). Pericardiotomy did not affect pulmonary hemodynamics or RVSWI. Right ventricular contractility did not increase following pulmonary hypertension while the pericardium was closed (440 +/- 78 vs 410 +/- 125, P less than 0.05); however, it rose, although not significantly, to 615 +/- 326 after pericardiotomy. RV time tension index displayed a rise during SIPAH with the pericardium intact and returned to baseline values after pericardiotomy; however, these changes were not significant. RVC did not change significantly throughout the experiment. In contrast, LVC decreased significantly after SIPAH and significantly improved after pericardiotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

An on-line system for delivery of blood cardioplegia.

A simplified system for delivery of cold blood potassium cardioplegia was tested in 12 experimental animals subjected to 180 minutes of aortic cross-clamping. This on-line system utilized blood drawn from the pump oxygenator which was volumetrically combined with a pre-mixed electrolyte solution (9 parts blood: 1 part drug). A separate heat exchanger was employed to deliver the cardioplegic infusate at 10-15 degrees C. Use of this system permits accurate regulation of infusate potassium concentration, pH, injection pressure and flow rate. Less than one minute is required to obtain an unlimited quantity of arrest solution at steady state values for these parameters. The efficacy of this method of delivery of blood cardioplegia was verified by biochemical and functional studies which revealed no significant changes in myocardial ATP, ultrastructure, compliance, or ventricular function after 3 hours of crossclamping. It is concluded that this system offers a safe and more simplified method of delivering blood cardioplegia than heretofore available.

Release of particulate matter from extracorporeal tubing: ineffectiveness of standard arterial line filters during bypass.

Microemboli resulting from extracorporeal circulation have been considered to be a cause of organ dysfunction after cardiopulmonary bypass. A scanning electron microscopic study was carried out to quantitate the number of nonbiological particles which escape capture by the arterial line filter in a standard extracorporeal circulation circuit. Five different lots of polyvinylchloride (PVC) tubing from the same manufacturer were used in closed circuit extracorporeal pump set-ups consisting of a typical length of PVC tubing, a cardiotomy reservoir, and an arterial line filter (Pall 40 microns (mu)). A liter of Plasmalyte was circulated through this set-up for 15 minutes at 2 liters/minute with the pump head set at almost total occlusion. The circulated Plasmalyte from each pump line was then collected and passed through a 0.22 mu Millipore filter. Numerous particles ranging from 5-40 mu in diameter were observed on the surface of the filters. A mean of 51.2 particles/mm2 of filter was found after the first recirculation period. By extrapolation the mean total number of particles contained in the Plasmalyte was calculated to be 70,943. A second similar 15 minute rinse on the same pump set-ups revealed the release of a mean of 51.0 particles/mm2, or a mean total number of 70,665 particles. Analysis of variance showed no significant difference in the number of particles produced by the first compared with the second recirculation period but there were significant differences (P less than .05) between the numbers of particles produced by the different lots of tubing. This study demonstrates that commonly employed tubing packs and standard roller pump designs for extracorporeal circulation are associated with continuous release of particulate matter (5-40 mu) which is not removed by the arterial line filters most often employed. These particles seem to be released at a constant rate which makes an initial pre-bypass filtration run ineffective. Such particles can only be removed by continuous use of lower porosity filters in the pump circuit. The clinical significance of these large numbers of small particles is unknown, but they may contribute to the multi-organ failure often seen in prolonged (greater than 2 hour) periods of cardiopulmonary bypass.