Prostacyclin Usage for Spinal Cord Protection During Experimental Thoracic Aortic Cross-Clamping

The risk of paraplegia associated with thoracic aortic cross-clamping is high even when various methods of spinal cord protection are used. In this study prostacyclin 12 (PGI2) was selected as an agent to reduce the spinal cord injury because of its vasodilator, antiaggregant, and cytoprotective properties.

Twelve dogs underwent sixty-minute aortic occlusion. Six dogs received PGI2 whereas the other 6 did not (controls). PG12 administration was started at a rate of 5 ng/kg/minute five minutes before aortic occlusion. This dosage was increased to 25 ng/kg/minute during aortic occlusion. PGI2 at a dosage of 5 ng/kg/minute was maintained for a period of five minutes after the aortic occlusion was released.

Three dogs in the control group were paraplegic. There were no paraplegic dogs in the PGI2 group. Distal aortic perfusion pressure was 31 ± mmHg in the PGI2 group and 22 ±3 in the control group (P <0.008).

As a result of this study the authors conclude that PGI2 is a valuable agent for decreasing the risk of spinal cord injury during thoracic aortic cross-clamping lasting sixty minutes.

Experimental inhibition of protamine cardiotoxicity by prostacyclin

Twelve animals (26+/-5 kg) were subjected to the study. In this experimental study, the authors used prostacyclin to inhibit the toxic metabolite release during protamine administration. Animals were divided into two equal groups. Six animals received prostacyclin (the prostacyclin group), and the other six animals did not receive any additional treatment (the control group). All cardiac output and biochemical measurements were evaluated at baseline; before cardiopulmonary bypass; and at 5, 30, and 60 minutes after protamine administration. The measured cardiac index showed that the hearts treated with prostacyclin had satisfactory preservation of left ventricular function. Metabolic and biochemical data showed that the tumor necrosis factor level was raised significantly in the control group (20.75+/-2.2 in the control group and 13.75+/-2.5 pg/mL in the prostacyclin group). Also, E and P selectin levels were elevated in the control group, but this change was less marked in the prostacyclin group. In addition, the intracellular adhesion molecule-1 (ICAM-1) level was significantly higher in the control group than in the prostacyclin group (9.26+/-2.13 in the control group and 5.13+/-1.66 ng/mL in the prostacyclin group). The authors observed that prostacyclin inhibited the toxic mediator release during heparin reversal with protamine. This inhibition is one way of protecting the myocardium reserves from protamine cardiotoxicity.

Beneficial Effects of Aminophylline on Ischemia-Reperfusion in Isolated Rabbit Heart

Eighteen rabbit hearts were arrested for 3 hours with cardioplegic solution at 4°C, followed by reperfusion with oxygenated perfusion solution at 37°C for 2 hours. Six control hearts received no drug during arrest or reperfusion (group 1). Six hearts received 3 mg·L−1 aminophylline during the arrest period (group 2). Six hearts received 3 mg·L−1 aminophylline during the reperfusion period (group 3). Effects of aminophylline were evaluated in terms of the pressure-volume relationship, coronary flow, myocardial oxygen extraction, and lactate release before cardioplegic arrest and after 1 and 2 hours of reperfusion. End-diastolic pressure at constant volume after 2 hours of reperfusion was 19 ± 2.63 mm Hg in group 1, 14 ± 1.7 mm Hg in group 2, and 19 ± 2.55 mm Hg in group 3 (p < 0.05 for group 2 versus groups 1 and 3). End-systolic pressure at constant volume after 2 hours of reperfusion was 81 ± 3.55 mm Hg in group 1, 90 ± 2.95 mm Hg in group 2, and 84 ± 3.47 mm Hg in group 3 (p < 0.05 for group 2 versus groups 1 and 3). Oxygen extraction was significantly higher and release of lactate was significantly lower in group 2 compared to groups 1 and 3. The results indicate that aminophylline administration during cardioplegic arrest improved systolic and diastolic function and had a beneficial effect on metabolic recovery.

Preservation of myocardial metabolism in acute coronary artery occlusions with retrograde coronary sinus perfusion and iloprost

A total of 12 healthy mongrel dogs were subjected to the study. The left anterior descending artery was occluded. The occlusion was done for 15 min. At the end of this period, without removing the occlusion, the heart was retroperfused for 3 h. Then, occlusion was removed and reperfusion was supplied. Animals were divided into two equal groups. Six animals received iloprost and the other six control did not receive any additional treatment. In the iloprost group, the drug was administered into the coronary sinus. After 15 min following occlusion, iloprost was infused at a rate of 50 microg/min continuously. Cardiac output (CO), mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), heart rate (HR), pulmonary capillary wedge pressure (PCWP), right atrium pressure (RAP), myocardial oxygen extraction (MOE) and myocardial lactate extraction (MLE) parameters were examined in the two groups, before and during retroperfusion and during the reperfusion (1-4 h). Iloprost retroperfusion (50 microg/min) was started at the fifteenth minute of occlusion and continued till the end of the observation period (3 h). The measured hemodynamic data showed that the hearts treated with iloprost had satisfactory preservation of cardiac function. At the end of the reperfusion period cardiac output was 1.5 +/- 0.06 L/min in the control and 1.7 +/- 0.04 L/min in the iloprost group (P < 0.05). At the end of the reperfusion period, tumor necrosis factor level was raised significantly in the control group (P < 0.05). Myocardial lactate release was also high in the control group (P < 0.05). CPK-MB release was low in the iloprost group (P < 0.05). We conclude that retrogradely administered iloprost reduced the risk of myocardial injury and it is probable that this drug effectively distributes to the area of myocardium at risk.

Cardiovascular effects of enoximone and epinephrine on heparin reversal with protamine in conscious dogs

OBJECTIVE

To compare enoximone with epinephrine as treatments for the cardiotoxic effects of protamine sulfate.

STUDY DESIGN

Prospective randomized study.

ANIMAL POPULATION

12 healthy cross-bred dogs weighing 23 +/- 4 kg.

METHODS

The dogs were anesthetized with xylazine and ketamine to allow instrumentation. Femoral arterial and venous catheters were inserted for pressure monitoring and to allow drug infusion. A thermodilution catheter mounted with a fast response thermistor was inserted into the pulmonary artery via the jugular vein to measure cardiac output and right ventricular volumes. Heparin 300 units/kg followed by protamine 4.5 mg/kg were administered 45 minutes after the xylazine/ketamine. Four animals were not treated (controls), four received enoximone, and four were given epinephrine. Cardiopulmonary parameters were monitored for a period of 30 minutes.

RESULTS

Cardiac index was 104 +/- 15 mL/kg/min in the enoximone group, 72 +/- 13 mL/kg/min in the epinephrine group, and 63 +/- 10 mL/kg/min in the control group (P < .05 enoximone versus control and epinephrine). Right ventricular end systolic volume was 18 +/- 3, 27 +/- 4, and 29 +/- 6 mL in the enoximone, epinephrine, and control groups (P < .05 enoximone versus control and epinephrine). There were no differences in mean arterial pressure or pulmonary and systemic vascular resistance between the groups.

CONCLUSION AND CLINICAL RELEVANCE

In this study, enoximone was more effective than epinephrine at reversing the hemodynamic changes associated with protamine sulfate administration.

Comparison of the effects of enoximone and isoproterenol on protamine cardiotoxicity in anesthetized dogs

In this study we investigated the effects of isoproterenol and enoximone on protamine cardiotoxicity because administration of protamine for heparin reversal during open heart surgery depresses left ventricular function. Eighteen mongrel dogs were entered into this study. After induction of general anesthesia and a stabilization period, a thermodilution catheter was inserted via the jugular vein. Another 2 catheters were inserted into the left ventricle and femoral artery. Heparin and protamine were used in all animals. Heparin dosage was 300 U/kg, and protamine dosage was 4.5 mg/kg. The animals were divided into 3 groups. Six animals received enoximone (5 micrograms/kg per min), 6 animals received isoproterenol (0.05 microgram/kg per min), and 6 animals received no inotropic agent. Measurements were performed before treatment, 5 min after protamine administration, and at 15-min intervals for 1 h. Cardiac output (CO), mean arterial pressure, pulmonary capillary wedge pressure, first derivative of left ventricular pressure (1 +/-) left ventricular systolic pressure, and heart rate were measured. CO was 1582 +/- 34 ml/min in the isoproterenol group (I + P), 1684 +/- 61 ml/min in the enoximone group (E + P), and 1471 +/- 37 ml/min in the protamine group (P) (p < 0.05 E + P vs I + P and P) 60 min after protamine administration. The first derivative of left ventricular pressure (dP/dt) was 1995 +/- 61 mmHg/sec in the I + P group, 2320 +/- 85 mmHg/sec in the E + P group, and 1816 +/- 48 mmHg/sec in the P group (p < 0.05 E + P vs I + P and P). In our experimental study, the isoproterenol and protamine combination did not increase hemodynamic activity. However, isoproterenol alone significantly increased hemodynamic activity as determined by dP/dt values. Protamine administration impairs the effects of beta agonists on the myocardium. In the protamine group, CO and pressure-dependent values were significantly reduced. Isoproterenol administration did not reverse this deterioration because of the loss of the beta-receptor activity. Inotropic agents acting through the beta-adrenergic system have partial effects on myocardium. Enoximone, a phosphodiesterase inhibitor, reverses deterioration of cardiac function after protamine administration because it increases myocardial function via the phosphodiesterase system.

Iloprost added to the cardioplegic solutions improves myocardial performance

A total of 12 mongrel dogs were divided into two equal groups. Six animals received IIoprost and the other 6 animals did not receive any additional treatment. In the Iloprost group, Iloprost was added to the cardioplegic solution (25 ng). Also, Iloprost was used (10 ng/kg/min.) 5 min. before and after cross-clamping. All cardiac output and biochemical measurements were evaluated before cross-clamp and 15 min., 1 h, and 4 h after cross-clamp. The measured dp/dt shows that the hearts treated with Iloprost preserved left ventricular function. Comparison of contractility indices between the groups revealed that contractile recovery was 59% in the control group and 71% in the Iloprost group (p < 0.05). Tumor necrosis factor (TNF) alpha level was significantly elevated in the control group (p < 0.001). Its level was 22.2 +/- 2.2 pg/mL in the control group and 13.8 +/- 1.0 pg/mL in the Iloprost group. E- and P-selectin levels were elevated in the control group (p < 0.001). ICAM-1 level was also elevated in the control group. ICAM-1 level was 17.7 +/- 1.8 ng/mL in the control group and 8.5 +/- 1.8 ng/mL in the Iloprost group. The Iloprost that was added to the cardioplegic solution and low dose administration during the pre- and post-ischemic period inhibits the toxic mediator release from endothelium-leukocyte interaction and reduces the severity of ischemia-reperfusion injury.

Comparison of Enoximone with Dopamine after Protamine Reversal of Heparin

This study compared the effects of enoximone with those of dopamine on myocardial function after protamine administration for the reversal of heparin. Twelve dogs were intubated and given 300 IU/kg heparin. A femoral artery cannula and two venous cannulae were inserted, and the animals were placed on hypothermic (28°C) cardiopulmonary bypass. The hearts were arrested for one hour with cold crystalloid cardioplegic solution and the animals were rewarmed to 36°C. After weaning from bypass, the heparin was neutralized with 4.5 mg/kg protamine sulfate. The dogs were divided into 3 groups: a control group (group C) received only protamine, another group (group D) received dopamine 10 μg/kg/min and protamine, and the third group (group E) received enoximone 10 μg/kg/min and protamine. Cardiac output was 1,320 ± 50 mL/min in group C, 1,420 ± 30 mL/min in group D, and 1,540 ± 10 mL/min in group E. We concluded that enoximone is an effective drug for relieving the adverse effects of protamine on the myocardium.

Effects of Prostacyclin on Hemodynamics after Intestinal Ischemia-Reperfusion

Ten rabbits underwent 30 minutes of superior mesenteric artery occlusion to assess the release of tumor necrosis factor, subcellular damage, and hemodynamic changes after intestinal ischemia-reperfusion injury. Five were treated with prostacyclin 5 ng/kg/min 5 minutes before the arterial occlusion. It was increased to 25 ng/kg/min during occlusion, decreased to 5 ng/kg/min for the first 5 minutes of reperfusion, and then discontinued. A control group of 5 rabbits did not receive any pharmacological agent. Specimens were obtained from the small intestine for electron microscopy after 10 minutes and after 60 minutes of reperfusion, while simultaneous blood samples were collected for measurement of tumor necrosis factor. Minimal changes were seen in tissue from the prostacyclin group but severe mitochondrial damage and vacuolation occurred in the control group. The tumor necrosis factor level was 11.97 ± 3.17 U/mL in the control group and 5.06 ± 2.19 U/mL in the prostacyclin group, one hour after the end of mesenteric occlusion ( p < 0.05). Hemodynamic status, assessed by central venous and arterial pressures, was much more affected in the control group than in the prostacyclin group. Mean arterial pressure was 71 ± 5 mm Hg in the control group, and 91 ± 6 mm Hg in the prostacyclin group ( p < 0.05). Central venous pressure was 5.3 ± 0.9 mm Hg in the control group and 2.3 ± 0.7 mm Hg in the prostacyclin group ( p < 0.05). We conclude that intravenous prostacyclin reduced the severity of reperfusion injury occurring during the early period of reperfusion by inhibiting the release of the toxic mediator tumor necrosis factor, thus decreasing distant organ injury.

Beneficial effects of prostacyclin treatment on reperfusion of the myocardium

A total of 20 patients with coronary artery disease were studied in order to assess the benefits of prostacyclin administration on reperfusion of the ischaemic myocardium after cardiopulmonary bypass. Ten received prostacyclin (25 ng/kg per min) while ten were untreated controls. There was no difference between groups with regard to age, preoperative ejection fraction and aortic cross-clamping times. There were no in-hospital deaths in either group. The administration of prostacyclin significantly altered the metabolic side effects of reperfusion followed by hypothermic cardioplegic arrest. Myocardial oxygen consumption after cardiopulmonary bypass was significantly higher in the prostacyclin-treated group than in controls (18.5 ml versus 13 ml; P < 0.01). Prostacyclin treatment significantly reduced the leucocyte activity: leukotriene B4 concentrations were 58 pmol/l in prostacyclin-treated patients compared with 93 pmol/l in controls (P < 0.01). Such recovery of metabolic status during reperfusion resulted in better haemodynamic function in patients receiving prostacyclin.