Role of controlled cardiac reoxygenation in reducing nitric oxide production and cardiac oxidant damage in cyanotic infantile hearts.

Cardiopulmonary bypass (CPB) is used increasingly to correct cyanotic heart defects during early infancy, but myocardial dysfunction is often seen after surgical repair. This study evaluates whether starting CPB at a conventional, hyperoxic pO2 causes an "unintentional" reoxygenation (ReO2) injury. We subjected 2-wk-old piglets to ventilator hypoxemia (FIO2 approximately 0.06, pO2 approximately 25 mmHg) followed by 5 min of ReO2 on CPB before instituting cardioplegia. CPB was begun in hypoxemic piglets by either abrupt ReO2 at a pO2 of 400 mmHg (standard clinical practice) or by maintaining pO2 approximately 25 mmHg on CPB until controlling ReO2 with blood cardioplegic arrest. The effects of abrupt vs. gradual ReO2 without surgical ischemia (blood cardioplegia) were also compared. Myocardial nitric oxide (NO) production (chemiluminescence measurements of NO2- + NO3-) and conjugated diene (CD) generation (spectrophotometric A233 measurements of lipid extracts) using aortic and coronary sinus blood samples were assessed during cardioplegic induction. 30 min after CPB, left ventricular end-systolic elastance (Ees, catheter conductance method) was used to determine cardiac function. CPB and blood cardioplegic arrest caused no functional or biochemical change in normoxic (control) hearts. Abrupt ReO2 caused a depression of myocardial function (Ees = 25 +/- 5% of control). Functional depression was relatively unaffected by gradual ReO2 without blood cardioplegia (34% recovery of Ees), and abrupt ReO2 immediately before blood cardioplegia caused a 10-fold rise in cardiac NO and CD production, with subsequent depression of myocardial function (Ees 21 +/- 2% of control). In contrast, controlled cardiac ReO2 reduced NO production 94%, CD did not rise, and Ees was 83 +/- 8% of normal. We conclude ReO2 injury is related to increased NO production during abrupt ReO2, nullifies the cardioprotective effects of blood cardioplegia, and that controlled cardiac ReO2 when starting CPB to correct cyanotic heart defects may reduce NO production and improve myocardial status postoperatively.

Combined heart-kidney transplantation after total artificial heart insertion.

We present the first single-center report of 2 consecutive cases of combined heart and kidney transplantation after insertion of a total artificial heart (TAH). Both patients had advanced heart failure and developed dialysis-dependent renal failure after implantation of the TAH. The 2 patients underwent successful heart and kidney transplantation, with restoration of normal heart and kidney function. On the basis of this limited experience, we consider TAH a safe and feasible option for bridging carefully selected patients with heart and kidney failure to combined heart and kidney transplantation. Recent FDA approval of the Freedom driver may allow outpatient management at substantial cost savings. The TAH, by virtue of its capability of providing pulsatile flow at 6 to 10 L/min, may be the mechanical circulatory support device most likely to recover patients with marginal renal function and advanced heart failure.

Studies of hypoxemic/reoxygenation injury: with aortic clamping. XII. Delay of cardiac reoxygenation damage in the presence of cyanosis: a new concept of controlled cardiac reoxygenation.

Twenty-one immature piglets (< 3 weeks old) underwent 30 minutes of aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia. Six piglets underwent hyperoxemic cardiopulmonary bypass and blood cardioplegia without preceding hypoxemia (control). Fifteen piglets became hypoxemic (oxygen tension about 25 mm Hg) for up to 2 hours by decreasing ventilator fraction of inspired oxygen to 6% to 7% before cardiopulmonary bypass. Of these, six piglets underwent 5 minutes of abrupt hyperoxemic uncontrolled reoxygenation by starting cardiopulmonary bypass at oxygen tension of about 400 mm Hg before they received oxygen tension of about 400 mm Hg blood cardioplegia. Nine others underwent controlled cardiac reoxygenation by starting cardiopulmonary bypass at ambient oxygen tension (about 25 mm Hg) followed 5 minutes later by 30 minutes of cardiopulmonary bypass at normoxemic oxygen tension (about 100 mm Hg) before raising oxygen tension to about 400 mm Hg. Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance by conductance catheter, oxidant damage was estimated by measuring transcoronary conjugated diene levels to detect lipid peroxidation, and antioxidant reserve capacity was determined by measuring malondialdehyde produced from myocardium incubated with the oxidant t-butylhydroperoxide. Hyperoxemic cardiopulmonary bypass and blood cardioplegia preserved myocardial function and produced no oxidant damage in nonhypoxemic piglets. In contrast, uncontrolled reoxygenation at oxygen tension about 400 mm Hg, followed by blood cardioplegia, resulted in marked conjugated dienes production (42 +/- 4* vs 3 +/- 1) A233 nm/min/100 g during blood cardioplegic induction, reduced antioxidant reserve capacity malondialdehyde at 4 mmol/L t-butylhydroperoxide; 1342 +/- 59* vs 958 +/- 50 nmol/g protein) and caused profound myocardial dysfunction; end-systolic elastance recovered only 21% +/- 2%* despite a blood cardioplegic regimen that was cardioprotective in nonhypoxemic piglets. Conversely, controlled cardiac reoxygenation reduced lipid peroxidation (conjugated dienes production was 2 +/- 1**), restored antioxidant reserve capacity (malondialdehyde at 4 mmol/L t-butylhydroperoxide; 982 +/- 88**), and allowed near-complete (83 +/- 8%**) functional recovery. We conclude that reoxygenation of the hypoxemic immature heart by initiating conventional hyperoxemic cardiopulmonary bypass causes oxidant damage characterized by lipid peroxidation, reduced antioxidant reserve capacity, and results in functional depression that nullifies the cardioprotective effects of blood cardioplegia. These changes can be reduced by starting cardiopulmonary bypass at the ambient oxygen tension of the hypoxemic subject and delaying subsequent reoxygenation until blood cardioplegic induction by controlled cardiac reoxygenation (*p < 0.05 vs control; **p < 0.05 vs uncontrol reoxygenation) and analysis of variance.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VII. Counteraction of oxidant damage by exogenous antioxidants: coenzyme Q10.

Coenzyme Q10 (CoQ10) is a natural mitochondrial respiratory chain constituent with antioxidant properties. This study tests the hypothesis that CoQ10 administered before the onset of reoxygenation on cardiopulmonary bypass, can reduce oxygen-mediated myocardial injury and avoid myocardial dysfunction after cardiopulmonary bypass. The antioxidant properties of CoQ10 were confirmed by an in vitro study in which normal myocardial homogenates were incubated with the oxidant, t-butylhydroperoxide. Fifteen immature piglets (< 3 weeks old) were placed on 60 minutes of cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (oxygen tension about 400 mm Hg). Ten others became hypoxemic on cardiopulmonary bypass for 30 minutes by lowering oxygen tension to approximately 25 mm Hg, followed by reoxygenation at oxygen tension about 400 mm Hg for 30 minutes. In five piglets, CoQ10 (45 mg/kg) was added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation, and five others were not treated (no treatment). Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance (conductance catheter), oxidant damage (lipid peroxidation) was assessed by measuring conjugated diene levels in coronary sinus blood, and antioxidant reserve capacity was determined by measuring malondialdehyde in myocardium after cardiopulmonary bypass incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant damage and allowed complete functional recovery. Reoxygenated hearts (no treatment) showed a progressive increase in conjugated diene levels in coronary sinus blood after reoxygenation (2.3 +/- 0.6 A233 nm/0.5 ml plasma at 30 minutes after reoxygenation) and reduced antioxidant reserve capacity (malondialdehyde: 1219 +/- 157 nmol/g protein at 4.0 mmol/L t-butylhydroperoxide), resulting in severe postbypass dysfunction (percent end-systolic elastance = 38 +/- 6). Conversely, CoQ10 treatment avoided the increase in conjugated diene levels (2.1 +/- 0.6 vs 1.1 +/- 0.3, p < 0.05 vs no treatment), retained normal antioxidant reserve (896 +/- 76 nmol/g protein, p < 0.05 vs no treatment), and allowed nearly complete recovery of function (94% +/- 7%, p < 0.05 vs no treatment). We conclude that reoxygenation of the hypoxemic immature heart on cardiopulmonary bypass causes oxygen-mediated myocardial injury, which can be limited by CoQ10 treatment before reoxygenation. These findings imply that coenzyme Q10 can be used to surgical advantage in cyanotic patients, because therapeutic blood levels can be achieved by preoperative oral administration of this approved drug.

Studies of hypoxemic/reoxygenation injury with aortic clamping: XI. Cardiac advantages of normoxemic versus hyperoxemic management during qardiopulmonary bypass.

The conventional way to start cardiopulmonary bypass is to prime the cardiopulmonary bypass circuit with hyperoxemic blood (oxygen tension about 400 mm Hg) and deliver cardioplegic solutions at similar oxygen tension levels. This study tests the hypothesis that an initial normoxemic oxygen tension strategy to decrease the oxygen tension-dependent rate of oxygen free radical production will, in concert with normoxemic blood cardioplegia, limit reoxygenation damage and make subsequent hyperoxemia (oxygen tension about 400 mm Hg) safer. Thirty-five immature (3 to 5 kg, 2 to 3 week old) piglets underwent 60 minutes of cardiopulmonary bypass. Eleven control studies at conventional hyperoxemic oxygen tension (about 400 mm Hg) included six piglets that also underwent 30 minutes of blood cardioplegic arrest. Of 25 studies in which piglets were subjected to up to 120 minutes of ventilator hypoxemia (reducing fraction of inspired oxygen to 5% to 7%; oxygen tension about 25 mm Hg), 11 underwent either abrupt (oxygen tension about 400 mm Hg, n = 6) or gradual (increasing oxygen tension from 100 to 400 mm Hg over a 1-hour period, n = 5) reoxygenation without blood cardioplegia. Fourteen others underwent 30 minutes of blood cardioplegic arrest during cardiopulmonary bypass. Of these, nine were reoxygenated at oxygen tension about 400 mm Hg, and five others underwent normoxemic cardiopulmonary bypass and blood cardioplegia (oxygen tension about 100 mm Hg) with systemic oxygen tension raised to 400 mm Hg after aortic unclamping. Measurements of lipid peroxidation (conjugated dienes and antioxidant reserve capacity) and contractile function (pressure-volume loops, conductance catheter, end-systolic elastance) were made before and during hypoxemia and 30 minutes after reoxygenation. Hyperoxemic cardiopulmonary bypass did not produce oxidant damage or reduce functional recovery after cardiopulmonary bypass in nonhypoxemic controls. In contrast, abrupt and gradual reoxygenation without blood cardioplegia produced significant lipid peroxidation (84% increase in conjungated dienes), lowered antioxidant reserve capacity 68% +/- 5%, 44% +/- 8%, respectively, and decreased functional recovery 75% +/- 6% (p < 0.05), 66% +/- 4% (p < 0.05). Similar impairment followed abrupt reoxygenation before blood cardioplegic myocardial management, because conjungated diene production increased 13-fold, antioxidant reserve capacity fell 40%, and contractility recovered only 21% +/- 2% (p < 0.05). Conversely, normoxemic induction of cardiopulmonary bypass and blood cardioplegic myocardial management reduced conjungated diene production 73%, avoided impairment of antioxidant reserve capacity, and resulted in 58% +/- 11% recovery of contractile function.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. III. Comparison of the magnitude of damage by hypoxemia/reoxygenation versus ischemia/reperfusion.

The immature heart is more tolerant to ischemia than the adult heart, yet infants with cyanosis show myocardial damage after surgical correction of congenital cardiac defects causing hypoxemia. This study tested the hypothesis that the hypoxemic developing heart is susceptible to oxygen-mediated damage when it is reoxygenated during cardiopulmonary bypass and that this hypoxemic/reoxygenation injury is more severe than ischemic/reperfusion stress. Fifteen Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) underwent 60 minutes of 37 degrees C cardiopulmonary bypass. Five piglets (control) were not made ischemic or hypoxemic. Five underwent 30 minutes of normothermic ischemia (aortic clamping) and 25 minutes of reperfusion before cardiopulmonary bypass was discontinued. Five others underwent 30 minutes of hypoxemia (bypass circuit primed with blood with oxygen tension 20 to 30 mm Hg) and 30 minutes of reoxygenation during cardiopulmonary bypass. Functional (left-ventricular contractility) and biochemical (levels of plasma and tissue conjugated dienes and antioxidant reserve capacity) measurements were made before ischemia/hypoxemia and after reperfusion/reoxygenation. Cardiopulmonary bypass (no ischemia or hypoxemia) caused no changes in left-ventricular function or coronary sinus levels of conjugated dienes. The tolerance to normothermic ischemia was confirmed, inasmuch as left-ventricular function returned to 108% of control values and coronary sinus levels of conjugated dienes did not rise after reperfusion. Conversely, reoxygenation raised plasma levels of conjugated dienes in coronary sinus blood in the hypoxic group 57% compared with end-hypoxic levels (p < 0.05 versus end-hypoxic levels and versus ischemia, by analysis of variance). Antioxidant reserve capacity showed the lowest levels (highest production of malondialdehyde) in the hypoxemic group (51% higher than control values; p < 0.05 by analysis of variance). These biochemical changes were associated with a 62% depression of left-ventricular function after bypass because end-systolic elastance recovered only 38% of control levels (p < 0.05 by analysis of variance). These data confirm the tolerance of the immature heart to ischemia and reperfusion and document a hypoxemic/reoxygenation injury that occurs in immature hearts reoxygenated during bypass. Hypoxemia seems to render the developing heart susceptible to reoxygenation damage that depresses postbypass function and is associated with lipid peroxidation. These findings suggest that starting bypass in cyanotic immature subjects causes an unintended reoxygenation injury that may potentially be counteracted by adding antioxidants to the prime of the extracorporeal circuit.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. IV. Role of the iron-catalyzed pathway: deferoxamine.

This study tests the hypothesis that an iron chelator, deferoxamine, can reduce oxygen-mediated myocardial injury and avoid myocardial dysfunction after cardiopulmonary bypass by its action on the iron-catalyzed Haber-Weiss pathway. Twenty-one immature 2- to 3-week-old piglets were placed on cardiopulmonary bypass for 120 minutes, and five piglets served as biochemical controls without cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (cardiopulmonary bypass control). Sixteen others became hypoxemic while undergoing cardiopulmonary bypass for 60 minutes by lowering oxygen tension to about 25 mm Hg, followed by reoxygenation at oxygen tension about 400 mm Hg for 60 minutes. Oxygen delivery was maintained during hypoxemia by increasing cardiopulmonary bypass flow and hematocrit level. In seven piglets deferoxamine (50 mg/kg total dose) was given both intravenously just before reoxygenation and by a bolus injection (5 mg/kg) into the cardiopulmonary bypass circuit; nine others were not treated (no therapy). Myocardial function after cardiopulmonary bypass was evaluated form end-systolic elastance (conductance catheter) and Starling curve analysis. Myocardial conjugated diene production and creatine kinase leakage were assessed as biochemical markers of injury, and antioxidant reserve capacity was determined by measuring malondialdehyde in postcardiopulmonary bypass myocardium incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant or functional damage. Conversely, reoxygenation (no therapy) raised myocardial conjugated diene levels and creatine kinase production (conjugated diene: 3.5 +/- 0.7 absorbance 233 nm/min/100 g, creatine kinase: 8.5 +/- 1.5 U/min/100 g; p < 0.05 versus cardiopulmonary bypass control), reduced antioxidant reserve capacity (malondialdehyde: 1115 +/- 60 nmol/g protein at 4 mmol/L t-butylhydroperoxide; p < 0.05 versus control), and produced severe post-bypass dysfunction (end-systolic elastance recovered only 39% +/- 7%, p < 0.05 versus cardiopulmonary bypass control). Deferoxamine avoided conjugated diene production and creatine kinase release and retained normal antioxidant reserve, and functional recovery was complete (95% +/- 11%, p < 0.05 versus no treatment). These findings show that iron-catalyzed oxidants may contribute to a reoxygenation injury and imply that deferoxamine may be used to surgical advantage.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VI. Counteraction of oxidant damage by exogenous antioxidants: N-(2-mercaptopropionyl)-glycine and catalase.

This study tests the hypothesis that antioxidants administered before reoxygenation can reduce oxygen-mediated damage and improve myocardial performance. Of 25 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg) five underwent 60 minutes of cardiopulmonary bypass without hypoxemia (control group), and five others underwent 30 minutes of hypoxemia on cardiopulmonary bypass with a circuit primed with oxygen tension about 25 mm Hg blood followed by reoxygenation on cardiopulmonary bypass (no treatment). In vitro studies were performed to obtain the optimal dosage of the antioxidants N-(2-mercaptopropionyl)-glycine and and catalase to be used in subsequent in vivo experimental studies; cardiac homogenates were incubated in 0 to 5 mmol/L concentrations of the oxidant t-butylhydroperoxide and malondialdehyde production was measured. Fifteen piglets were made hypoxemic on cardiopulmonary bypass for 30 minutes, and the antioxidants N-(2-mercaptopropionyl)-glycine at either 30 or 80 mg/kg body weight or N-(2-mercaptopropionyl)-glycine, 30 mg/kg body weight, and catalase, 50,000 U/kg body weight, were added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation. Left ventricular contractility, which was expressed as end-systolic elastance, was measured by conductance catheter before hypoxemia and after reoxygenation. Myocardial antioxidant reserve capacity was determined after reoxygenation by incubating cardiac homogenates in the oxidant t-butylhydroperoxide and measuring subsequent malondialdehyde elution. The in vitro bioassay studies showed a dose-dependent reduction of lipid peroxidation with N-(2-mercaptopropionyl)-glycine, with maximal benefits of a 40% decrease and malondialdehyde elaboration occurring with N-(2-mercaptopropionyl)-glycine and catalase compared with untreated cardiac homogenates. Cardiopulmonary bypass (no hypoxemia) caused no oxidant damage or changes in contractile function after cardiopulmonary bypass. Reoxygenation without treatment raised conjugated diene levels 57%,* lowered antioxidant reserve capacity 51%,* and was associated with only 38%* recovery of contractile function (p < 0.05 vs control). In contrast, treatment with antioxidants avoided lipid peroxidation, maintained antioxidant reserve capacity, and resulted in a dose-dependent improvement in left ventricular contractility with complete recovery occurring in N-(2-mercaptopropionyl)-glycine and catalase-treated piglets (*p < 0.05 vs no treatment). This study confirms the occurrence of hypoxemic/reoxygenation injury in immature hearts placed on cardiopulmonary bypass and shows that biochemical and functional damage can be counteracted by adding antioxidants to the cardiopulmonary bypass priming fluid. Contractile function improved in a dose-dependent manner, and oxygen-mediated damage could be avoided by mercaptopropionyl glycine/catalase treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies of hypoxemic/reoxygenation injury: without aortic clamping. VIII. Counteraction of oxidant damage by exogenous glutamate and aspartate.

Previous studies show that (1) hypoxemia depletes immature myocardium of amino acid substrates and their replenishment improves ischemic tolerance, (2) reoxygenation on cardiopulmonary bypass causes oxygen-mediated damage without added ischemia, and (3) this damage may be related to the nitric oxide-L-arginine pathway that is affected by amino acid metabolism. This study tests the hypothesis that priming the cardiopulmonary bypass circuit with glutamate and aspartate limits reoxygenation damage. Of 22 immature Duroc-Yorkshire piglets (< 3 weeks old), five were observed over a 5-hour period (control), and five others underwent 30 minutes of CPB without hypoxemia (cardiopulmonary bypass control). Twelve others became hypoxemic by reducing ventilator inspired oxygen fraction to 6% to 7% (oxygen tension about 25 mm Hg) before reoxygenation on cardiopulmonary bypass for 30 minutes. Of these five were untreated (no treatment), and the cardiopulmonary bypass circuit was primed with 5 mmol/L glutamate and aspartate in seven others (treatment). Left ventricular function before and after bypass was measured by inscribing pressure-volume loops (end-systolic elastance). Myocardial conjugated diene levels were measured to detect lipid peroxidation, and antioxidant reserve capacity was tested by incubating cardiac muscle with the oxidant t-butylhydroperoxide to determine the susceptibility to subsequent oxidant injury. CPB (no hypoxemia) allowed complete functional recovery without changing conjugated dienes and antioxidant reserve capacity, whereas reoxygenation injury developed in untreated hearts. This was characterized by reduced contractility (elastance end-systolic recovered only 37% +/- 8%*), increased conjugated diene levels (1.3 +/- 0.1 vs 0.7 +/- 0.1*), and decreased antioxidant reserve capacity (910 +/- 59 vs 471 +/- 30 malondialdehyde nmol/g protein at 2 mmol/L t-butylhydroperoxide*). In contrast, priming the cardiopulmonary bypass circuit with glutamate and aspartate resulted in significantly better left ventricular functional recovery (75% +/- 8% vs 37% +/- 8%*), minimal conjugated diene production (0.8 +/- 0.1 vs 1.3 +/- 0.1*), and improved antioxidant reserve capacity (726 +/- 27 vs 910 +/- 59 malondialdehyde nmol/g protein*) (*p < 0.05 vs cardiopulmonary bypass control). We conclude that reoxygenation of immature hypoxemic piglets by the initiation of cardiopulmonary bypass causes myocardial dysfunction, lipid peroxidation, and reduced tolerance to oxidant stress, which may increase vulnerability to subsequent ischemia (i.e., aortic crossclamping). These data suggest that supplementing the prime of cardiopulmonary bypass circuit with glutamate and aspartate may reduce these deleterious consequences of reoxygenation.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. IX. Importance of avoiding perioperative hyperoxemia in the setting of previous cyanosis.

This study of an in vivo infantile piglet model of compensated hypoxemia tests the hypothesis that reoxygenation on hyperoxemic cardiopulmonary bypass produces oxygen-mediated myocardial injury that can be limited by normoxemic management of cardiopulmonary bypass and the interval after cardiopulmonary bypass. Twenty-five immature piglets (< 3 weeks old) were placed on 120 minutes of cardiopulmonary bypass and five piglets served as a biochemical control group without cardiopulmonary bypass. Five piglets underwent cardiopulmonary bypass without hypoxemia (cardiopulmonary bypass control). Twenty others became hypoxemic on cardiopulmonary bypass for 60 minutes by lowering oxygen tension to about 25 mm Hg. The study was terminated in five piglets at the end of hypoxemia, whereas 15 others were reoxygenated at an oxygen tension about 400 mm Hg or about 100 mm Hg for 60 minutes. Oxygen delivery was maintained during hypoxemia by increasing cardiopulmonary bypass flow and hematocrit level to avoid metabolic acidosis and lactate production. Myocardial function after cardiopulmonary bypass was evaluated from end-systolic elastance (conductance catheter) and Starling curve analysis. Myocardial conjugated diene production and creatine kinase leakage were assessed as biochemical markers of injury, and antioxidant reserve capacity was determined by measuring malondialdehyde after cardiopulmonary bypass in myocardium incubated in the oxidant, t-butylhydroperoxide. Cardiopulmonary bypass without hypoxemia caused no oxidant or functional damage. Conversely, reoxygenation at an oxygen tension about 400 mm Hg raised myocardial conjugated diene level and creatine kinase production (CD: 3.5 +/- 0.7 A233 nm/min/100 g, creatine kinase: 8.5 +/- 1.5 U/min/100 g, p < 0.05 vs cardiopulmonary bypass control), reduced antioxidant reserve capacity (malondialdehyde: 1115 +/- 60 nmol/g protein at 4.0 mmol t-butylhydroperoxide, p < 0.05 vs control), and produced severe postbypass dysfunction (end-systolic elastance recovered only 39% +/- 7%, p < 0.05 vs cardiopulmonary bypass control). Lowering oxygen tension to about 100 mm Hg during reoxygenation avoided conjugated diene production and creatine kinase release, retained normal antioxidant reserve, and improved functional recovery (80% +/- 11%, p < 0.05 vs oxygen tension about 400 mm Hg). These findings show that conventional hyperoxemic cardiopulmonary bypass causes unintended reoxygenation injury in hypoxemic immature hearts that may contribute to myocardial dysfunction after cardiopulmonary bypass and that normoxemic management may be used to surgical advantage.

Studies of hypoxemic/reoxygenation injury: with aortic clamping. X. Exogenous antioxidants to avoid nullification of the cardioprotective effects of blood cardioplegia.

This study tests the hypothesis that reoxygenation of cyanotic immature hearts when starting cardiopulmonary bypass produces an "unintended" reoxygenation injury that (1) nullifies the cardioprotective effects of blood cardioplegia and (2) is avoidable by adding antioxidants N-(2-mercaptopropionyl)-glycine plus catalase to the cardiopulmonary bypass prime. Twenty immature piglets (2 to 3 weeks) underwent 30 minutes of aortic clamping with a blood cardioplegic solution that was hypocalcemic, alkalotic, hyperosmolar, and enriched with glutamate and aspartate during 1 hour of cardiopulmonary bypass. Of these, six piglets did not undergo hypoxemia (blood cardioplegic control) and 14 others remained hypoxemic (oxygen tension about 25 mm Hg) for up to 2 hours by lowering ventilator fraction of inspired oxygen before reoxygenation on cardiopulmonary bypass. The primary solution of the cardiopulmonary bypass circuit was unchanged in eight piglets (no treatment) and supplemented with the antioxidants N-(2-mercaptopropionyl)-glycine (80 mg/kg) and catalase (5 mg/kg) in six others (N-(2-mercaptopropionyl)-glycine and catalase). Myocardial function (end-systolic elastance), lipid peroxidation (myocardial conjugated diene production), and antioxidant reserve capacity were evaluated. Blood cardioplegic arrest produced no biochemical or functional changes in nonhypoxemic control piglets. Reoxygenation caused an approximate 10-fold increase in conjugated production that persisted throughout cardiopulmonary bypass, lowered antioxidant reserve capacity 86% +/- 12%, and produced profound myocardial dysfunction, because end-systolic elastance recovered only 21% +/- 2%. Supplementation of the cardiopulmonary bypass prime with N-(2-mercaptopropionyl)-glycine and catalase reduced lipid peroxidation, restored antioxidant reserve capacity, and allowed near complete functional recovery (80% +/- 8%).** Lipid peroxidation (conjugated diene) production was lower during warm blood cardioplegic reperfusion than during induction in all reoxygenated hearts, which suggests that blood cardioplegia did not injure reoxygenated myocardium. We conclude that reoxygenation of the hypoxemic immature heart causes cardiac functional and antioxidant damage that nullifies the cardioprotective effects of blood cardioplegia that can be avoided by supplementation of the cardiopulmonary bypass prime with antioxidants (*p < 0.05 vs blood cardioplegic control; **p < 0.05 vs reoxygenation).

Studies of hypoxemic/reoxygenation injury: with aortic clamping. XIII. Interaction between oxygen tension and cardioplegic composition in limiting nitric oxide production and oxidant damage.

This study tests the interaction between oxygen tension and cardioplegic composition on nitric oxide production and oxidant damage during reoxygenation of previously cyanotic hearts. Of 35 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg), six underwent 30 minutes of blood cardioplegic arrest with hyperoxemic (oxygen tension about 400 mm Hg), hypocalcemic, alkalotic, glutamate/aspartate blood cardioplegic solution during 1 hour of cardiopulmonary bypass without hypoxemia (control). Twenty-nine others were subjected to up to 120 minutes of ventilator hypoxemia (oxygen tension about 25 mm Hg) before reoxygenation on CPB. To simulate routine clinical management, nine piglets underwent uncontrolled cardiac reoxygenation, whereby cardiopulmonary bypass was started at oxygen tension of about 400 mm Hg followed by the aforementioned blood cardioplegic protocol 5 minutes later. All 20 other piglets underwent controlled cardiac reoxygenation, whereby cardiopulmonary bypass was started at the ambient oxygen tension (about 25 mm Hg), and reoxygenation was delayed until blood cardioplegia was given. The blood cardioplegia solution was kept normoxemic (oxygen tension about 100 mm Hg) in 10 piglets and made hyperoxemic (oxygen tension about 400 mm Hg) in 10 others. The cardioplegic composition was also varied so that the cardioplegic solution in each subgroup contained either KCl only (30 mEq/L) or components that theoretically inhibit nitric oxide synthase by including hypocalcemia, alkalosis, and glutamate/aspartate. Function (end-systolic elastance) and myocardial nitric oxide production, conjugated diene production, and antioxidant reserve capacity were measured. Blood cardioplegic arrest without hypoxemia did not cause myocardial nitric oxide or conjugated diene production, reduce antioxidant reserve capacity, or change left ventricular functional recovery. In contrast, uncontrolled cardiac reoxygenation raised nitric oxide and conjugated diene production 19- and 13-fold, respectively (p < 0.05 vs control), reduced antioxidant reserve capacity 40%, and contractility recovered only 21% of control levels. After controlled cardiac reoxygenation at oxygen tension about 400 mm Hg with cardioplegic solution containing KCl only, nitric oxide and conjugated diene production rose 16- and 12-fold, respectively (p < 0.05 vs control), and contractility recovered only 43% +/- 5%. Normoxemic (oxygen tension of about 100 mm Hg) controlled cardiac reoxygenation with the same solution reduced nitric oxide and conjugated diene production 85% and 71%, and contractile recovery rose to 55% +/- 7% (p < 0.05 vs uncontrolled reoxygenation). In comparison, controlled cardiac reoxygenation with an oxygen tension of about 400 mm Hg hypocalcemic, alkalotic, glutamate/aspartate blood cardioplegic solution reduced nitric oxide and conjugated diene production 85% and 62%, respectively, and contractility recovered 63% +/- 4% (p < 0.05 vs KCl only).(ABSTRACT TRUNCATED AT 400 WORDS)

Normoxic cardiopulmonary bypass reduces oxidative myocardial damage and nitric oxide during cardiac operations in the adult.

OBJECTIVE: Hyperoxic cardiopulmonary bypass is widely used during cardiac operations in the adult. This management may cause oxygenation injury induced by oxygen-derived free radicals and nitric oxide. Oxidative damage may be significantly limited by maintaining a more physiologic oxygen tension strategy (normoxic cardiopulmonary bypass). METHODS: During elective coronary artery bypass grafting, 40 consecutive patients underwent either hyperoxic (oxygen tension = 400 mm Hg) or normoxic (oxygen tension = 140 mm Hg) cardiopulmonary bypass. At the beginning and the end of bypass this study assessed polymorphonuclear leukocyte elastase, nitrate, creatine kinase, and lactic dehydrogenase, antioxidant levels, and malondialdehyde in coronary sinus blood. Cardiac index was measured before and after cardiopulmonary bypass. RESULTS: There was no difference between groups with regard to age, sex, severity of disease, ejection fraction, number of grafts, duration of cardiopulmonary bypass, or ischemic time. Hyperoxic bypass resulted in higher levels of polymorphonuclear leukocyte elastase (377 +/- 34 vs 171 +/- 32 ng/ml, p = 0.0001), creatine kinase 672 +/- 130 vs 293 +/- 21 U/L, p = 0.002), lactic dehydrogenase (553 +/- 48 vs 301 +/- 12 U/L, p = 0.003), antioxidants (1.97 +/- 0.10 vs 1.41 +/- 0.11 mmol/L, p = 0.01), malondialdehyde (1.36 +/- 0.1 micromol/L,p = 0.005), and nitrate (19.3 +/- 2.9 vs 10.1 +/- 2.1 micromol/L, p = 0.002), as well as reduction in lung vital capacity (66% +/- 2% vs 81% +/- 1%,p = 0.01) and forced 1-second expiratory volume (63% +/- 10% vs 93% +/- 4%, p = 0.005) compared with normoxic management. Cardiac index after cardiopulmonary bypass at low filling pressure was similar between groups (3.1 +/- 0.2 vs 3.3 +/- 0.3 L/min per square meter). [Data are mean +/- standard error (analysis of variance), with p values compared with an oxygen tension of 400 mm Hg.] CONCLUSIONS: Hyperoxic cardiopulmonary bypass during cardiac operations in adults results in oxidative myocardial damage related to oxygen-derived free radicals and nitric oxide. These adverse effects can be markedly limited by reduced oxygen tension management. The concept of normoxic cardiopulmonary bypass may be applied to surgical advantage during cardiac operations.

Changing patterns of patients undergoing emergency surgical revascularization for acute coronary occlusion. Importance of myocardial protection techniques.

Between 1977 and 1992 a total of 163 consecutive patients underwent emergency coronary artery bypass grafting after acute coronary occlusion (94% after failed angioplasty). Patients were divided into four groups according to the method used for myocardial protection. The crystalloid cardioplegia group included 30 patients operated on from 1977 to 1980; the hypothermic fibrillation group included 60 patients (1980 to 1986); the blood cardioplegia group included 36 patients (1986 to 1989); and the blood cardioplegia with controlled reperfusion group included 37 patients (1989 to 1992). Preoperative data, ischemic time interval, collateral blood flow, intraoperative data, regional wall motion, global ejection fraction, myocardial infarct-specific electrocardiographic changes, enzyme release, rhythm disturbances, mortality, prevalence of intraaortic balloon pumping, and inotropic support were assessed in this retrospective study. Our data indicate that the current spectrum of patients undergoing emergency coronary artery bypass grafting after acute coronary occlusion are at a significantly higher risk compared with those 15 years ago, that is, increase in age (53 +/- 1 versus 59 +/- 2 years; p < 0.05), three-vessel disease (38% versus 3%; p = 0.004), acute occlusion of the left main coronary artery (11% versus 0%; p = 0.02), preoperative cardiogenic shock (35% versus 3%; p = 0.007), prevalence of acute two-vessel occlusion (22% versus 3%; p = 0.05), prevalence of previous infarction (59% versus 23%; p = 0.04), and duration of ischemia (3.0 +/- 0.2 versus 4.1 +/- 0.3 hours; p < 0.05). Despite the increase in patients with severely compromised ventricular function during recent years, the overall hospital mortality decreased to 5% (2/37) when maximal protection of the ischemic and remote myocardium was performed (preoperative intraaortic balloon pump, combined antegrade/retrograde substrate-enriched blood cardioplegia, warm induction, controlled reperfusion, prolonged vented bypass). Single-vessel disease was always associated with a low mortality, whereas mortality could be reduced with controlled blood cardioplegia in patients with multivessel disease (6%) and cardiogenic shock (15%). The immediate return of regional contractility in the previously ischemic area after controlled reperfusion might serve as an explanation for these favorable results. After unmodified blood reperfusion, normokinesis or slight hypokinesis occurs in only 34% to 46% in the early postoperative period (1 to 4 weeks) in comparison with 86% after controlled blood cardioplegia reperfusion (p < 0.05). We conclude that there is a significant increase in risk factors in patients undergoing emergency coronary artery bypass grafting and that improved methods of intraoperative myocardial protection are needed for these compromised patients.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. II. Evidence for reoxygenation damage.

This study tested the hypothesis that the developing heart is susceptible to oxygen-mediated damage after reintroduction of molecular oxygen and that this "unintended" reoxygenation injury causes lipid peroxidation and functional depression that may contribute to perioperative cardiac dysfunction. Among 49 Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) 15 control studies were done without hypoxemia to test the effects of the surgical preparation (n = 10) and 60 minutes of cardiopulmonary bypass (n = 5). Twenty-nine piglets underwent up to 2 hours of ventilator hypoxemia (with inspired oxygen fraction reduced to 6% to 7%) to lower arterial oxygen tension to approximately 25 mm Hg. Five piglets did not undergo reoxygenation to determine alterations caused by hypoxemia alone. Twenty-four others received reoxygenation by either raising ventilator inspired oxygen fraction to 1.0 (n = 12) or instituting cardiopulmonary bypass at oxygen tension 400 mm Hg (n = 12). Ventilator hypoxemia produced sufficient hemodynamic compromise and metabolic acidosis that 18 piglets required premature reoxygenation (78 +/- 12 minutes). To avoid the influence of acidosis and hemodynamic deterioration during ventilator hypoxemia, five others underwent 30 minutes of hypoxemia during cardiopulmonary bypass (circuit primed with blood at oxygen tension 25 mm Hg) and 30 minutes of reoxygenation (oxygen tension 400 mm Hg) during cardiopulmonary bypass. Biochemical markers of oxidant damage included measurement of coronary sinus and myocardial conjugated dienes to determine lipid peroxidation and antioxidant reserve capacity assessed by incubating myocardial tissue in the oxidant t-butylhydroperoxide. Functional recovery was determined by inscribing pressure volume loops to determine end-systolic elastance and Starling curves by volume infusion. No biochemical or functional changes occurred in control piglets. Hypoxemia without reoxygenation did not change plasma levels of conjugated dienes, but lowered antioxidant reserve capacity 24%. Reoxygenation by ventilator caused refractory ventricular arrhythmias in two piglets (17% mortality), raised levels of conjugated dienes 45%, and reduced antioxidant reserve capacity 40% with recovery of 39% of mechanical function in the survivors. Comparable biochemical and functional changes occurred in piglets undergoing ventilator hypoxemia and/or cardiopulmonary bypass hypoxemia and reoxygenation on cardiopulmonary bypass. We conclude that hypoxemia increases vulnerability to reoxygenation damage by reducing antioxidant reserve capacity and that reoxygenation by either ventilator or cardiopulmonary bypass produces oxidant damage with resultant functional depression that is not a result of cardiopulmonary bypass. These findings suggest that initiation of cardiopulmonary bypass in cyanotic immature subjects causes an unintended reoxygenation injury, which may increase vulnerability to subsequent ischemia during surgical repair.

Studies of hypoxemic/reoxygenation injury: without aortic clamping. V. Role of the L-arginine-nitric oxide pathway: the nitric oxide paradox.

This study tests the hypothesis that nitric oxide, which is endothelial-derived relaxing factor, produces reoxygenation injury via the L-arginine-nitric oxide pathway in hypoxemic immature hearts when they are placed on cardiopulmonary bypass. Twenty 3-week-old piglets undergoing 2 hours of hypoxemia (oxygen tension about 25 mm Hg) on a ventilator were reoxygenated by initiating cardiopulmonary bypass (oxygen tension about 400 mm Hg). Five animals were not treated, whereas the pump circuit was primed with the nitric oxide-synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 4 mg/kg) in five piglets. L-Arginine, the substrate for nitric oxide, was administered in a fivefold excess (20 mg/kg), together with L-NAME in five piglets (L-NAME and L-arginine), and given alone in five other piglets (L-arginine). Five normoxemic, instrumented piglets served as a control group, and five others underwent 30 minutes of cardiopulmonary bypass without preceding hypoxemia. Left ventricular contractility was determined as end-systolic elastance by pressure-dimension loops. Myocardial conjugated dienes were measured as a marker of lipid peroxidation, and the antioxidant reserve capacity (malondialdehyde production in tissue incubated with t-butylhydroperoxide) was measured. Nitric oxide level was determined in coronary sinus plasma as its spontaneous oxidation product, nitrite. Cardiopulmonary bypass per se did not alter left ventricular contractility, cause lipid peroxidation, or lower antioxidant capacity. Reoxygenation without treatment depressed cardiac contractility (end-systolic elastance 38% +/- 12% of control*), raised nitric oxide (127% above hypoxemic values), increased conjugated dienes (1.3 +/- 0.2 vs 0.7 +/- 0.1, control*), and reduced antioxidant reserve capacity (910 +/- 59 vs 471 +/- 30, control*). Inhibition of nitric oxide production by L-NAME improved end-systolic elastance to 84% +/- 12%,** limited conjugated diene elution (0.8 +/- 0.1 vs 1.3 +/- 0.2, no treatment**), and improved antioxidant reserve capacity (679 +/- 69 vs 910 +/- 59, no treatment**). Conversely, L-arginine counteracted these beneficial effects of L-NAME, because left ventricular function recovered only 24% +/- 6%,* conjugated dienes were 1.2 +/- 0.1,* and antioxidant reserve capacity was 826 +/- 70.* L-Arginine alone caused the same deleterious biochemical changes as L-NAME/L-arginine and resulted in 60% mortality. The close relationship between postbypass left ventricular dysfunction (percent end-systolic elastance) and myocardial conjugated diene production (r = 0.752) provides in vivo evidence that lipid peroxidation contributes to myocardial dysfunction after reoxygenation.(ABSTRACT TRUNCATED AT 400 WORDS)

Controlled limb reperfusion in patients having cardiac operations.

HYPOTHESIS: Severe limb ischemia in patients having cardiac operations may occur after intraaortic balloon pump insertion, prolonged femoral vessel cannulation, percutaneous cardiopulmonary bypass, dissecting aneurysms, or emboli. Normal blood reperfusion can cause a postischemic syndrome that increases morbidity and mortality. This clinical study is based on an experimental infrastructure patterned after controlled cardiac reperfusion. (1) It tests the hypothesis that controlled limb reperfusion (i.e., modifying the composition of the initial reperfusate and the conditions of reperfusion) reduces the local and systemic complications seen after normal blood reperfusion. (2) It reports initial clinical application of this strategy in three cardiac surgery centers. METHODS: Controlled limb reperfusion was applied to 19 patients with signs of severe prolonged unilateral or bilateral ischemia (including paralysis, anesthesia, and muscle contracture); six patients (32%) were in cardiogenic shock. The mean ischemic duration was 26 +/- 6 hours. The reperfusion method includes a 30-minute infusion into the distal vessels of a normothermic reperfusate solution mixed with the patient's arterial blood (obtained proximal to the obstruction) in a 6:1 blood/reperfusate ratio. Data are mean +/- standard error of the mean. RESULTS: Sixteen patients (84%) survived with salvaged and functional limbs at the time of discharge. No renal, cardiac, pulmonary, cerebral, or hemodynamic complications developed in the survivors. The three deaths occurred in patients undergoing controlled limb reperfusion while in profound postoperative cardiogenic shock; neither postischemic edema nor contracture developed in any of them. CONCLUSIONS: These findings show that controlled limb reperfusion can be applied readily with standard equipment that is used for cardiac surgery and may salvage limbs while reducing postreperfusion morbidity and mortality.

Cardiopulmonary dysfunction produced by reoxygenation of immature hypoxemic animals supported by cardiopulmonary bypass. Prevention by intravenous metabolic pretreatment.

This study tests the hypothesis that reoxygenation injury is produced when cardiopulmonary bypass is initiated in immature hypoxemic piglets and that it causes cardiopulmonary dysfunction that can be avoided by intravenous metabolic treatment before and during cardiopulmonary bypass. Of 18 immature Yorkshire-Duroc piglets (aged < 3 weeks), six were anesthetized, instrumented, and observed for 5 hours (control animals). Twelve piglets underwent up to 2 hours of hypoxemia (arterial oxygen tension = 20 to 30 mm Hg) before initiation of reoxygenation on cardiopulmonary bypass. Six received an intravenous metabolic infusion solution (mercaptopropionyl glycine, catalase, aspartate, glutamate, glucose/insulin), which was started before and continued during cardiopulmonary bypass. Hypoxia produced an initial hyperdynamic response (39% increase in cardiac index; p < 0.05) followed by progressive hemodynamic deterioration, necessitating premature initiation of bypass in 8 of 12 hypoxemic piglets (67%). Reoxygenation-induced injury (assessed 30 minutes after cardiopulmonary bypass) was characterized by 39% reduction of stroke work index (p < 0.05), increased myocardial lipid peroxidation (79% increase of conjugated dienes; p < 0.05), 254% increase in pulmonary vascular resistance index (p < 0.05), 22% decrease in static lung compliance (p < 0.05), and 50% decrease in arterial/alveolar oxygen tension ratio (p < 0.05). These reoxygenation changes were avoided by intravenous metabolic treatment. We conclude that the reoxygenation of immature hypoxemic piglets by initiating cardiopulmonary bypass results in cardiopulmonary dysfunction that may increase vulnerability to subsequent ischemia (i.e., aortic crossclamping). The cardiopulmonary reoxygenation changes are preventable by intravenous metabolic treatment before and during cardiopulmonary bypass needed for cardiac repair.

Delayed cardioplegic reoxygenation reduces reoxygenation injury in cyanotic immature hearts.

BACKGROUND: Hypoxemic developing hearts are susceptible to oxygen-mediated damage that occurs after reintroduction of molecular oxygen. This unintended hypoxemic/reoxygenation injury leads to lipid peroxidation and membrane damage and may contribute to postoperative cardiac dysfunction. Biochemical and functional status are improved by delaying reoxygenation on cardiopulmonary bypass (CPB) until cardioplegic arrest. METHODS: Six immature piglets (3 to 5 kg) without hypoxemia underwent 30 minutes of cardioplegic arrest during 1 hour of CPB. Fourteen others underwent 2 hours of hypoxemia on ventilator before reoxygenation on CPB. Reflecting our clinical routine, 9 were reoxygenated on CPB for 5 minutes followed by 30 minutes of cardioplegic arrest and 25 minutes of reperfusion. The other 5 were put on hypoxemic CPB for 5 minutes, before being reoxygenated during cardioplegic arrest for 30 minutes followed by 25 minutes of reperfusion. RESULTS: Cardioplegic arrest (no hypoxemia group) caused no functional or biochemical changes. In contrast, by preceding hypoxemia with subsequent reoxygenation on CPB (no treatment group) we found 39.5% decrease in antioxidant reserve capacity, 1,212% increase in myocardial conjugated diene production, significant increase in coronary sinus blood conjugated dienes, and an 81% reduction of left ventricular contractility, all of which were statistically significant (p < 0.05) when compared with the no hypoxemia group. Conversely, delaying reoxygenation until cardioplegic arrest (treatment group) resulted in 33.1% improvement in antioxidant reserve capacity, 91.7% less conjugated diene production, lower coronary sinus blood conjugated diene levels, and a 95% improved contractility, all of which were significant (p < 0.05) when compared with the no treatment group. CONCLUSIONS: A reoxygenation injury associated with lipid peroxidation and decreased postbypass contractility occurs in cyanotic immature hearts when reoxygenated on CPB. Delaying reoxygenation until cardioplegic arrest by starting CPB with ambient partial pressure of oxygen results in significantly improved myocardial status.

Pulmonary vasoconstriction due to impaired nitric oxide production after cardiopulmonary bypass.

BACKGROUND: Pulmonary hypertension is a serious complication after cardiopulmonary bypass (CPB). This study tests the hypothesis that CPB provokes oxidant-mediated pulmonary endothelial dysfunction, leading to reduced nitric oxide (NO) production and pulmonary vasoconstriction. METHODS: Twelve piglets underwent 2 hours of CPB. In 6 of them, CPB prime was supplemented with N-mercaptopropionylglycine and catalase, whereas the others were not treated. Left and right ventricular function were evaluated from end-systolic elastance and Starling analysis. Pulmonary vascular resistance and transpulmonary NO production (measuring NO2-, NO3-) were determined to assess pulmonary endothelial function. RESULTS: Cardiopulmonary bypass caused a significant increase in pulmonary vascular resistance (83 +/- 12 to 212 +/- 30 dynes.cm-5.s kg-1, p < 0.05), associated with a reduction of NO production (8.8 +/- 1.4 to 2.5 +/- 0.5 mumol/min, p < 0.05) and depressed right ventricular function (56 +/- 12% of control), whereas N-mercaptopropionylglycine and catalase added to the CPB allowed a substantial improvement of these deleterious effects of CPB. CONCLUSIONS: Cardiopulmonary bypass impairs pulmonary NO production, resulting in pulmonary vasoconstriction and right ventricular dysfunction, which can be reduced by antioxidants. These findings imply the validity of NO inhalation therapy for postoperative pulmonary hypertension as a supplementation of endogenous endothelium-derived relaxing factor.