Cardiac surgery and inhaled nitric oxide: indication and follow-up (2-4 years)

Effect of Inhaled Nitric Oxide on Hemodynamics in Lambs with 1½ Ventricle Circulation

Inhaled nitric oxide (NO) is widely used to treat postoperative pulmonary hypertension in congenital heart disease. It is believed that NO increases cardiac output (CO) by decreasing pulmonary vascular resistance (PVR), leading to increased left ventricular preload. However, the effect of NO on CO in patients with 1½ ventricle circulation remains unclear. To evaluate this, a superior cavopulmonary (SCP) shunt was constructed in 10 juvenile sheep. A PTFE graft was inserted between the superior vena cava (SVC) and the main pulmonary artery (PA). The SVC was clamped at the right atrial junction to establish a 1½ ventricle circulation. Flows, pressures, and arterial blood gases were recorded before and during inhalation of NO. Mean arterial pressure (46.6 ± 5.4 to 44.6 ± 5.9 mm Hg; p = 0.06) and left atrial pressure (4.0 ± 2.5 to 4.0 ± 2.3 mm Hg; p = 1.0) did not change. Mean PA pressure (13.6 ± 2.4 to 11.7 ± 2.9 mm Hg; p = 0.006) and PVR (5.47 ± 2.99 to 4.54 ± 2.61 Wood Units; p = 0.037) decreased significantly. SVC flow (24.8 ± 11.3 to 22.0 ± 9.7 ml/min/kg; p = 0.09) did not change, and CO decreased (140.2 ± 37.2 to 132.1 ± 39.2 ml/min/kg; p = 0.033). Arterial PO2 improved (103.72 ± 29.30 to 132.43 ± 47.02 mm Hg; p = 0.007). In this 1½ ventricle model, NO surprisingly decreased cardiac output (CO) and did not increase left ventricular preload.

Inhaled therapy for the management of perioperative pulmonary hypertension

Patients with pulmonary hypertension (PH) are at high risk for complications in the perioperative setting and often receive vasodilators to control elevated pulmonary artery pressure (PAP). Administration of vasodilators via inhalation is an effective strategy for reducing PAP while avoiding systemic side effects, chiefly hypotension. The prototypical inhaled pulmonary-specific vasodilator, nitric oxide (NO), has a proven track record but is expensive and cumbersome to implement. Alternatives to NO, including prostanoids (such as epoprostenol, iloprost, and treprostinil), NO-donating drugs (sodium nitroprusside, nitroglycerin, and nitrite), and phosphodiesterase inhibitors (milrinone, sildenafil) may be given via inhalation for the purpose of treating elevated PAP. This review will focus on the perioperative therapy of PH using inhaled vasodilators.

Hypoplastic left heart syndrome: current considerations and expectations

In the recent era, no congenital heart defect has undergone a more dramatic change in diagnostic approach, management, and outcomes than hypoplastic left heart syndrome (HLHS). During this time, survival to the age of 5 years (including Fontan) has ranged from 50% to 69%, but current expectations are that 70% of newborns born today with HLHS may reach adulthood. Although the 3-stage treatment approach to HLHS is now well founded, there is significant variation among centers. In this white paper, we present the current state of the art in our understanding and treatment of HLHS during the stages of care: 1) pre-Stage I: fetal and neonatal assessment and management; 2) Stage I: perioperative care, interstage monitoring, and management strategies; 3) Stage II: surgeries; 4) Stage III: Fontan surgery; and 5) long-term follow-up. Issues surrounding the genetics of HLHS, developmental outcomes, and quality of life are addressed in addition to the many other considerations for caring for this group of complex patients.

Genetic variation in the mitochondrial enzyme carbamyl-phosphate synthetase I predisposes children to increased pulmonary artery pressure following surgical repair of congenital heart defects: a validated genetic association study

Increased pulmonary artery pressure (PAP) can complicate the postoperative care of children undergoing surgical repair of congenital heart defects. Endogenous NO regulates PAP and is derived from arginine supplied by the urea cycle. The rate-limiting step in the urea cycle is catalyzed by a mitochondrial enzyme, carbamoyl-phosphate synthetase I (CPSI). A well-characterized polymorphism in the gene encoding CPSI (T1405N) has previously been implicated in neonatal pulmonary hypertension. A consecutive modeling cohort of children (N=131) with congenital heart defects requiring surgery was prospectively evaluated to determine key factors associated with increased postoperative PAP, defined as a mean PAP>20 mmHg for at least 1h during the 48h following surgery measured by an indwelling pulmonary artery catheter. Multiple dimensionality reduction (MDR) was used to both internally validate observations and develop optimal two-variable through five-variable models that were tested prospectively in a validation cohort (N=41). Unconditional logistic regression analysis of the modeling cohort revealed that age (OR=0.92, p=0.01), CPSI T1405N genotype (AC vs. AA: OR=4.08, p=0.04, CC vs. AA: OR=5.96, p=0.01), and Down syndrome (OR=5.25, p=0.04) were independent predictors of this complex phenotype. MDR predicted that the best two-variable model consisted of age and CPSI T1405N genotype (p<0.001). This two-variable model correctly predicted 73% of the outcomes from the validation cohort. A five-variable model that added race, gender and Down's syndrome was not significantly better than the two-variable model. In conclusion, the CPSI T1405N genotype appears to be an important new factor in predicting susceptibility to increased PAP following surgical repair of congenital cardiac defects in children.

Inhaled nitric oxide use in bidirectional Glenn anastomosis for elevated Glenn pressures

BACKGROUND

Children frequently undergo bidirectional Glenn anastomosis in the staged surgical management of single ventricle physiology. The purpose of our study was to investigate the role of inhaled nitric oxide therapy in children with marked elevations in Glenn pressures after this surgery.

METHODS

A retrospective study over a 30-month period was performed. The effect of inhaled nitric oxide therapy was analyzed in children with marked elevations of Glenn pressures resulting in decreased systemic perfusion. Effects on Glenn pressures, respiratory indices, and systemic perfusion were evaluated after initiation of nitric oxide therapy and compared with baseline parameters.

RESULTS

Sixteen patients were placed on nitric oxide therapy for marked elevations of Glenn pressures (22.4 +/- 3.9 mm Hg). In the 11 responsive patients, there were significant reductions in Glenn pressures (from 22.4 mm Hg to 17.1 mm Hg, p < 0.001) and significant improvement in partial pressure of oxygen to fraction of inspired oxygen ratio (from 49 to 74.3, p = 0.001) and oxygenation index (from 17 to 12, p = 0.005). There was simultaneous significant reduction in inotrope score (from 14.9 to 11.4, p < 0.001) and fluid volume support (from 11.4 mL/kg to 2.3 mL/kg, p < 0.001) in the responsive patients. Five patients that failed to show any response were found, subsequently, to have an anatomic lesion.

CONCLUSIONS

Inhaled nitric oxide produces significant reduction in Glenn pressures and improvement in systemic perfusion and pulmonary gas exchange in patients with marked elevations of Glenn pressures after bidirectional Glenn anastomosis. Patients who fail to respond should be investigated for an anatomic lesion.

Neonatal physiology of the functionally univentricular heart

The neonate with functionally univentricular physiology presents unique challenges to the cardiac team. An integrated approach that applies working knowledge of cardiac anatomy, cardiopulmonary physiology, and basic principles of intensive care is essential to guide management of each individual patient. This requires cooperative and constructive involvement of a surgical, medical, nursing and respiratory care team experienced in the management of such patients. In the neonate with this physiology, systemic oxygen delivery is optimized by manipulating pulmonary and systemic resistances, augmenting total cardiac output, and utilizing strategies for ventilation that preserve optimal pulmonary recruitment.

Single-ventricle physiology

The patient with single-ventricle physiology presents a significant challenge to the intensive care team at all stages of management. An integrated approach that applies a working knowledge of cardiac anatomy, cardiopulmonary physiology, and the basic principles of intensive care is essential to guide management for each individual patient. This management requires cooperative and constructive involvement of surgeons, cardiologists, and intensivists, as well as a nursing and respiratory care team experienced in the management of single-ventricle patients. The outcome of each stage of palliation for single-ventricle lesions should continue to improve as new ideas are developed and as older ideas are subjected to rigorous scientific analyses.

Effect of cardiopulmonary bypass on urea cycle intermediates and nitric oxide levels after congenital heart surgery

OBJECTIVE

To test the hypothesis that cardiopulmonary bypass used for repair of ventricular septal defects and atrioventricular septal defects would decrease availability of urea cycle intermediates including arginine and subsequent nitric oxide availability.

STUDY DESIGN

Consecutive infants (n = 26) undergoing cardiopulmonary bypass for repair of an unrestrictive ventricular septal defect or atrioventricular septal defect were studied. Blood samples were collected immediately before surgery, immediately after surgery, and 12 hours, 24 hours, and 48 hours after surgery. Urea cycle intermediates, including citrulline, arginine, and ornithine, were measured by amino acid analysis. Nitric oxide metabolites were measured by means of the modified Griess reaction.

RESULTS

Cardiopulmonary bypass caused a significant decrease in the urea cycle intermediates arginine, citrulline, and ornithine at all postoperative time points compared with preoperative levels. The ratio of ornithine to citrulline, a marker of urea cycle function, was elevated at all postoperative time points compared with preoperative values, indicating decreased urea cycle function. Nitric oxide metabolites were significantly decreased at all postoperative time points except for 48 hours, compared with preoperative levels.

CONCLUSIONS

Cardiopulmonary bypass significantly decreases availability of arginine, citrulline, and nitric oxide metabolites in the postoperative period. Decreased availability of nitric oxide precursors may contribute to the increased risk of postoperative pulmonary hypertension.

Inhaled nitric oxide in cardiology

Inhaled nitric oxide (INO) allows selective pulmonary vasodilatation with rapidity of action. It is effective in the acute management of reversible pulmonary hypertension in cardiac medical and surgical patients and is also useful in assessing the pulmonary vasodilator capacity in patients with chronic pulmonary hypertension. This review will examine the role of INO in the management of cardiac patients, compared to alternatives where available. The use of INO in cardiac failure, post-operative cardiac patients, patients with congestive cardiac failure or congenital heart disease will also be reviewed. Newer alternatives with prolonged pulmonary activity and simpler administration are also discussed.