Inhaled nitric oxide in patients with critical pulmonary perfusion after Fontan-type procedures and bidirectional Glenn anastomosis

A complicated Glenn procedure: risk factors and association with adverse long-term neurodevelopmental and functional outcomes

OBJECTIVES

To determine potentially modifiable risk factors for a complicated Glenn procedure (cGP) and whether a cGP predicted adverse neurodevelopmental and functional outcomes. A cGP was defined as post-operative death, heart transplant, extracorporeal life support, Glenn takedown, or prolonged ventilation.

METHODS

All 169 patients having a Glenn procedure from 2012 to 2017 were included. Neurodevelopmental assessments were performed at age 2 years in consenting survivors (n = 156/159 survivors). The Bayley Scales of Infant and Toddler Development-3rd Edition (Bayley-III) and the Adaptive Behavior Assessment System-2nd Edition (ABAS-II) were administered. Adaptive functional outcomes were determined by the General Adaptive Composite (GAC) score from the ABAS-II. Predictors of outcomes were determined using univariate and multiple variable linear or Cox regressions.

RESULTS

Of patients who had a Glenn procedure, 10/169 (6%) died by 2 years of age and 27/169 (16%) had a cGP. Variables statistically significantly associated with a cGP were the inotrope score on post-operative day 1 (HR 1.04, 95%CI 1.01, 1.06; p = 0.010) and use of inhaled nitric oxide post-operatively (HR 7.31, 95%CI 3.19, 16.76; p < 0.001). A cGP was independently statistically significantly associated with adverse Bayley-III Cognitive (ES -10.60, 95%CI -17.09, -4.11; p = 0.002) and Language (ES -11.43, 95%CI -19.25, -3.60; p = 0.004) scores and adverse GAC score (ES -14.89, 95%CI -22.86, -6.92; p < 0.001).

CONCLUSIONS

Higher inotrope score and inhaled nitric oxide used post-operatively were associated with a cGP. A cGP was independently associated with adverse 2-year neurodevelopmental and functional outcomes. Whether early recognition and intervention for risk of a cGP can prevent adverse outcomes warrants study.

Outcome of obstructed total anamalous pulmonary venous connection (TAPVC) repair patients with milrinone versus milrinone and inhaled nitric oxide (INO): A prospective randomized observational study

Background

Obstructed total anomalous pulmonary venous connection (TAPVC) typically present with severe cardiovascular decompensation and requires urgent surgical management. Pulmonary arterial hypertension (PAH) is a major risk factor affecting mortality. Perioperative management focuses on providing inotropic support and managing potential pulmonary hypertensive episodes. Milrinone and inhaled nitric oxide (iNO) efficiently reduce pulmonary artery pressure (PAP) and help to improve the outcome. The aim was to determine the outcome of patients with high PAP with milrinone alone and a combination of iNO and milrinone.

Material and Method

After ethical committee approval, the study was conducted over a period of 3 years in 80 patients with obstructed TAPVC repair. A total of 80 patients having severe PAH (supra systemic arterial pressure) randomly divided into two groups with 40 patients in each (M & MN). Group M (milrinone) patients received milrinone and Group MN (milrinone & iNO) patients received both milrinone (after opening aortic cross clamp) and iNO (post operative ICU). Ventilation time, hospital stay, ICU stay, complications, in hospital mortality were compared between both groups.

Result

Ventilation time, Intensive Care Unit (ICU) stay, hospital stay for group M was 8.02 ± 5.74 days, 11.25 ± 7.33 day, 14.92 ± 8.55 days, respectively, and for group MN was 5.02 ± 1.78 days, 8.27 ± 3.24 days, 10.3 ± 3.18 days, respectively. In hospital mortality for group M and MN was 10% and 2.5%, respectively. P value for each variable was significant < 0.05 (except mortality).

Conclusion

Most of the patients with obstructed TAPVC had severe PAH. Management of severe PAH with a combination of milrinone with iNO had a better outcome than milrinone alone.

The pulmonary vascular bed in patients with functionally univentricular physiology and a Fontan circulation

Fontan palliation represents one of the most remarkable surgical advances in the management of individuals born with functionally univentricular physiology. The operation secures adult survival for all but a few with unfavourable anatomy and/or physiology. Inherent to the physiology is passive transpulmonary blood flow, which produces a vulnerability to adequate filling of the systemic ventricle at rest and during exertion. Similarly, the upstream effects of passive flow in the lungs are venous congestion and venous hypertension, especially marked during physical activity. The pulmonary vascular bed has emerged as a defining character on the stage of Fontan circulatory behaviour and clinical outcomes. Its pharmacologic regulation and anatomic rehabilitation therefore seem important strategic therapeutic targets. This review seeks to delineate the important aspects of pulmonary artery development and maturation in functionally univentricular physiology patients, pulmonary artery biology, pulmonary vascular reserve with exercise, and pulmonary artery morphologic and pharmacologic rehabilitation.

Superior Cavopulmonary Connection: Its Physiology, Limitations, and Anesthetic Implications

The superior cavopulmonary connection (SCPC) or "bidirectional Glenn" is an integral, intermediate stage in palliation of single ventricle patients to the Fontan procedure. The procedure, normally performed at 3 to 6 months of life, increases effective pulmonary blood flow and reduces the ventricular volume load in patients with single ventricle (parallel circulation) physiology. While the SCPC, with or without additional sources of pulmonary blood flow, cannot be considered a long-term palliation strategy, there are a subset of patients who require SCPC palliation for a longer interval than the typical patient. In this article, we will review the physiology of SCPC, the consequences of prolonged SCPC palliation, and modes of failure. We will also discuss strategies to augment pulmonary blood flow in the presence of an SCPC. The anesthetic considerations in SCPC patients will also be discussed, as these patients may present for noncardiac surgery from infancy to adulthood.

Post-Extubation Inhaled Nitric Oxide Therapy via High-Flow Nasal Cannula After Fontan Procedure

In 2014, our hospital introduced inhaled nitric oxide (iNO) therapy combined with high-flow nasal cannula (HFNC) oxygen therapy after extubation following the Fontan procedure in patients with unstable hemodynamics. We report the benefits of HFNC-iNO therapy in these patients. This was a single-center, retrospective review of 38 patients who underwent the Fontan procedure between January 2010 and June 2016, and required iNO therapy before extubation. The patients were divided into two groups: patients in Epoch 1 (n = 24) were treated between January 2010 and December 2013, receiving only iNO therapy; patients in Epoch 2 (n = 14) were treated between January 2014 and June 2016, receiving iNO therapy and additional HFNC-iNO therapy after extubation. There were no significant differences between Epoch 1 and 2 regarding preoperative cardiac function, age at surgery, body weight, initial diagnosis (hypoplastic left heart syndrome, 4 vs. 2; total anomalous pulmonary venous return, 5 vs. 4; heterotaxy, 7 vs. 8), intraoperative fluid balance, or central venous pressure upon admission to the intensive care unit. Epoch 2 had a significantly shorter duration of postoperative intubation [7.2 (3.7-49) vs. 3.5 (3.0-4.6) hours, p = 0.033], pleural drainage [23 (13-34) vs. 9.5 (8.3-18) days, p = 0.007], and postoperative hospitalization [36 (29-49) vs. 27 (22-36) days, p = 0.017]. Two patients in Epoch 1 (8.3%), but none in Epoch 2, required re-intubation. Our results suggest that HFNC-iNO therapy reduces the duration of postoperative intubation, pleural drainage, and hospitalization.

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.

The Pulmonary Circulation in the Single Ventricle Patient

In recent decades, survival of children with complex congenital heart disease has improved considerably. Specifically, children with a variety of congenital heart defects resulting in ‘single ventricle’ physiology can now undergo palliative surgery that allows survival beyond the neonatal period, and in many cases into adulthood, despite having a single functional ventricular pumping chamber supplying both the pulmonary and systemic circulation. Our growing understanding of the functionally univentricular heart has resulted in freedom from Fontan failure of >50% at 25 years post-Fontan. Yet there is still a fair amount of knowledge to be gained, specifically as it relates to the pulmonary circulation in this group of patients. Knowledge gaps relate not only to the pulmonary circulation after Fontan operation, but also at each stage of the single ventricle surgical palliation, including the native physiology prior to any intervention. The pulmonary circulation is affected by multiple issues related to the single ventricle, including specific details of the anatomy unique to each patient, any intervention(s) undertaken, and potential complications such as aortopulmonary collaterals, protein losing enteropathy, plastic bronchitis, venovenous collaterals, pulmonary arteriovenous fistulae, ventricular dysfunction, pulmonary venous stenosis, and more. This chapter will review the current knowledge with regard to the pulmonary circulation in the single ventricle patient, primarily after the Fontan operation. Additionally, it is our hope to help the practitioner assess the pulmonary circulation in the single ventricle patient; we will also discuss the evidence behind and approach to treatment strategies in order to optimize the pulmonary circulation in this complex group of patients.

Clinical-Physiological Considerations in Patients Undergoing Staged Palliation for a Functionally Single Ventricle

OBJECTIVES

The objectives of this review are to discuss the pathophysiology of the circulation with a functionally univentricular heart, with a focus on the unique physiologic characteristics, which provide the underpinnings for the management of these complex patients.

DATA SOURCE

MEDLINE and PubMed.

CONCLUSIONS

The circulation of the patient with a functionally univentricular heart displays unique physiologic characteristics, which are quite different from those of the normal biventricular circulation. There are profound differences within the heart itself in terms of ventricular function, interventricular interactions, and myocardial architecture, which are likely to have significant implications for the efficiency of ventricular ejection and metabolism. The coupling between the systemic ventricle and the aorta also displays unique features. The 3D orientation of the Fontan anastomosis itself can profoundly impact cardiac output, although the "portal" pulmonary arterial bed is a crucial determinant of overall cardiovascular function. As a result, disease-specific approaches to improve cardiovascular function are required at all stages during the care of these complex patients.

Pulmonary Hypertension

OBJECTIVES

To review the clinical classification, diagnosis, and pathophysiology of pulmonary hypertension in children, emphasizing the role of right ventricular function, ventricular interaction, and congenital heart disease in the evolution and progression of disease, as well as management strategies and therapeutic options.

DATA SOURCE

MEDLINE, PubMed.

CONCLUSIONS

Critically ill children with pulmonary hypertension associated with congenital heart disease are a high-risk population. Congenital cardiac defects resulting in either increased pulmonary blood flow or impaired pulmonary venous drainage predispose patients to developing structural and functional aberrations of the pulmonary vasculature. Mortality from pulmonary hypertension is most directly related to right ventricular failure.

Risk Factors for Longer Hospital Stay Following the Fontan Operation

OBJECTIVES

Children with functional single ventricle undergoing the Fontan operation consume considerable resources. The purpose of this study is to evaluate pre- and intraoperative risk factors for longer hospital stay and to describe the perioperative course at a single institution over a 15-year period.

DESIGN

Retrospective cohort study.

SETTING

A single pediatric cardiac ICU.

PATIENTS

All consecutive patients undergoing a first-time Fontan operation from 2000 to 2014.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Prolonged length of stay was defined as hospital stay greater than 75 percentile at our institution after surgery. Of 218 patients who met inclusion criteria, median length of stay was 10 days (interquartile range, 8-14 d); prolonged length of stay was defined greater than or equal to 15 days. Independent pre- and intraoperative risk factors for prolonged length of stay included higher hemoglobin (odds ratio, 1.29; p = 0.003), higher mean pulmonary artery pressure (odds ratio, 1.14; p = 0.037), and lower aortic saturation (odds ratio, 0.92; p = 0.008) in the entire group. When patients with hepatic vein inclusion (following previous Kawashima) were excluded, higher hemoglobin (odds ratio, 1.24; p = 0.027), lower aortic saturation (odds ratio, 0.92; p = 0.017), and placement of a fenestration (odds ratio, 2.438; p = 0.021) were associated with prolonged length of stay. Fifty-eight patients (26.6%) had major complications defined by Pediatric Cardiac Critical Care Consortium. Placement of a fenestration (odds ratio, 2.297; p = 0.014) and longer aortic cross-clamp time (odds ratio, 1.015; p = 0.003) were independently associated with Pediatric Cardiac Critical Care Consortium major complications.

CONCLUSIONS

In this series, 75% of patients had a postoperative length of stay less than or equal to 2 weeks. Preoperative factors suggesting worse hypoxemia/decreased pulmonary blood flow (higher hemoglobin and lower oxygen saturation) and increased pulmonary artery pressure were associated with prolonged length of stay. These findings may help risk stratify this complex patient population, provide more accurate family counseling, and provide preliminary data for changes in preoperative timing of the Fontan and/or changes to postoperative management strategies for those at high risk for increased ICU morbidity.

Effect of Inhaled Nitric Oxide on Blood Flow Dynamics in Patients After the Fontan Procedure Using Cardiovascular Magnetic Resonance Flow Measurements

Invasive hemodynamic studies have shown that nitric oxide (NO), a selective pulmonary vasodilator, can lower pulmonary vascular resistance in Fontan patients. Because oximetry-derived flow quantification may be unreliable, we sought to detect changes in blood flow within the Fontan circulation after inhalation of NO using cardiovascular magnetic resonance (CMR). Thirty-three patients (mean age 12.8 ± 7.0 years) after the Fontan procedure underwent CMR as part of their routine clinical assessment. Standard two-dimensional blood flow measurements were performed in the Fontan tunnel, superior vena cava (SVC) and ascending aorta (AAO) before and after inhalation of 40 ppm NO for 8-10 min. Systemic-to-pulmonary collateral (SPC) flow was calculated as AAO - (SVC + tunnel). Heart rate (82 ± 18 to 81 ± 18 bpm; p = 0.31) and transcutaneous oxygen saturations (93 ± 4 to 94 ± 3 %; p = 0.13) did not change under NO inhalation. AAO flow (3.23 ± 0.72 to 3.12 ± 0.79 l/min/m(2); p = 0.08) decreased, tunnel flow (1.58 ± 0.40 to 1.65 ± 0.46 l/min/m(2); p = 0.032) increased, and SVC flow (1.01 ± 0.39 to 1.02 ± 0.40 l/min/m(2); p = 0.50) remained unchanged resulting in higher total caval flow (Qs) (2.59 ± 0.58 to 2.67 ± 0.68 l/min/m(2); p = 0.038). SPC flow decreased significantly from 0.64 ± 0.52 to 0.45 ± 0.51 l/min/m(2) (p = 0.002) and resulted in a significant decrement of the Qp/Qs ratio (1.23 ± 0.23 to 1.15 ± 0.23; p = 0.001). Inhalation of NO in Fontan patients results in significant changes in pulmonary and systemic blood flow. The reduction in SPC flow is accompanied by a net increase in effective systemic blood flow suggesting beneficial effects of pulmonary vasodilators on cardiac output, tissue perfusion and exercise capacity.

Postoperative care of the adult with congenital heart disease

An increasing number of children with congenital heart disease survive to adulthood, but many adults require surgical intervention and can present complex management challenges in the perioperative period. This review will address common considerations that surgeons, anesthesiologists, and intensivists are likely to face in caring for this growing population.

Pulmonary vasodilator therapy and early postoperative outcome after modified Fontan operation

Although mortality is low after the modified Fontan procedure, there is a significant percentage of patients with prolonged postoperative recovery. The objective of this study is to evaluate the usefulness of postoperative administration of oral sildenafil and inhaled nitric oxide on early postoperative outcome. A prospective interventional and comparison study with a historical cohort was conducted. Between January, 2010 and March, 2013, 16 patients received oral sildenafil during immediate modified Fontan postoperative period. Inhaled nitric oxide was also administered if the patient was kept intubated 12 hours after surgery. Early postoperative outcome was compared with a historical cohort of 32 patients on whom the modified Fontan procedure was performed between March, 2000 and December, 2009. Postoperative administration of sildenafil and nitric oxide had no influence on early postoperative outcome after the modified Fontan procedure in terms of duration of pleural effusions, mechanical ventilation time, length of stay in the ICU, and length of hospital stay.

Common carotid artery to internal jugular vein shunt for managing hypoxemia after a cavopulmonary shunt

In the present report, we discuss a patient who developed persistent hypoxemia after an attempt at Fontan completion failed. As a bail-out procedure, a left common carotid artery to left internal jugular vein shunt was constructed, after which the hypoxemia was relieved.

Review of inhaled nitric oxide in the pediatric cardiac surgery setting

Surgical intervention for congenital heart disease (CHD) can be complicated by pulmonary hypertension (PH), which increases morbidity, mortality, and medical burden. Consequently, postoperative management of PH is an important clinical consideration to improve outcomes. Inhaled nitric oxide (iNO) is a widely accepted standard of care for PH and has been studied in the context of cardiac surgery for CHD. However, large randomized, double-blind, placebo-controlled, multicenter clinical trials in pediatric patients are limited. This review will provide an overview of the clinical studies in this setting and will discuss general treatment considerations to facilitate a better understanding of the clinical use of iNO for PH after pediatric cardiac surgery.

Inhaled Nitric Oxide for Elevated Cavopulmonary Pressure and Hypoxemia After Cavopulmonary Operations

Background. Elevated cavopulmonary pressure early after surgical creation of cavopulmonary connections is an important hemodynamic problem with grave prognostic significance. We examined the effect of administration of inhaled nitric oxide (iNO) to patients with elevated cavopulmonary pressure in the early postoperative period. Methods. We retrospectively reviewed data pertaining to all 14 patients with superior (n = 6) and total (n = 8) cavopulmonary connections who were treated with iNO in the early postoperative period during an interval of six years. Changes in the cavopulmonary pressure, the transpulmonary gradient, and the oxygen saturation after the institution of iNO were evaluated. The preoperative characteristics of the patients were compared to those of a control group of patients with cavopulmonary operations not treated with iNO postoperatively. Results. Twelve hours after the initiation of iNO therapy, significant reduction in the cavopulmonary pressure (16.6 ± 3.5 mm Hg vs 18.1 ± 2.3 mm Hg, P = .006), reduction in the cavopulmonary gradient (7.0 ± 3.5 mm Hg vs 9.8 ± 3.7 mm Hg, P = .009), and elevation of the arterial oxygen saturation (84.5% ± 6.0% vs 78.7% ± 5.9%, P = .001) were observed. Linear correlation analysis confirmed tendencies for reduction in the cavopulmonary pressure ( P = .13), reduction in the cavopulmonary gradient ( P = .02), and elevation of the oxygen saturation ( P = .10). Compared to the control group, the treated patients tended to have higher preoperative pulmonary arterial pressures (PAPs) 17 (11-30) mm Hg versus 12 (10-25) mm Hg, P = .10; higher pulmonary vascular resistance (PVR) 2.04 (0.27-6.94) Wood units versus 1.02 (0.49-5.20) Wood units, P = .37; and longer bypass times 154 (41-218) versus 91 (15-276) minutes, P = .13. Conclusions. Administration of iNO was associated with diminuition of cavopulmonary pressure and transpulmonary gradient and increasing oxygen saturation in our small group of patients. In our experience selected patients with preoperatively elevated PAP above 17 mm and PVR above 2 Wood units can undergo cavopulmonary operations with iNO treatment early postoperatively.

Urgent cesarean delivery and prolonged ventilatory support in a parturient with Fontan circulation and undiagnosed pseudocholinesterase deficiency

A parturient with Fontan circulation required general anesthesia for urgent cesarean delivery and subsequent prolonged postoperative ventilation for newly-diagnosed pseudocholinesterase deficiency. Anesthetic management necessitated a thorough understanding of the hemodynamic principles of the Fontan circulation and physiologic adaptations during surgical delivery and recovery in the intensive care unit.

Pediatric pulmonary arterial hypertension: current and emerging therapeutic options

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare disease in neonates, infants and children that is associated with significant morbidity and mortality. An adequate understanding of the controlling pathophysiologic mechanisms is lacking and although mortality has decreased as therapeutic options have increased over the past several decades, outcomes remain unacceptable.

AREAS COVERED

This review summarizes the currently available therapies for neonates, infants and children with PAH and describes emerging therapies in the context of what is known about the underlying pathophysiology of the disease.

EXPERT OPINION

All of the currently approved PAH therapies impact one of three endothelial-based pathways: nitric oxide-guanosine-3'-5'cyclic monophosphate, prostacyclin or endothelin-1. The beneficial effects of these agents may relate to their impact on pulmonary vascular tone, and/or their antiproliferative and antithrombotic properties. Fundamental advances in PAH therapy are likely to relate to: i) a better understanding of PAH subpopulations, allowing for therapies to be better tailored to individual patients and pathophysiologic processes; and ii) therapies that promote the regression of advanced structural remodeling.

Pulmonary hypertension in congenital shunts

Pulmonary arterial hypertension frequently arises in patients with congenital heart disease. The vast majority present with congenital cardiac shunts. Initially these may manifest as left-to-right (i.e. systemic-to-pulmonary) shunts. The natural history of disease progression involves vascular remodeling and dysfunction that lead to increased pulmonary vascular resistance and, finally, to the development of Eisenmenger's syndrome, which is the most advanced form. The anatomical, pathological and structural abnormalities occurring in the pulmonary circulation of these patients are, to some extent, similar to those observed in other forms of pulmonary arterial hypertension. This understanding has recently led to significant changes in the management of Eisenmenger's syndrome, with the introduction of treatment specifically targeting pulmonary vascular disease. Early closure of the cardiac shunt remains the best way of preventing pulmonary vascular lesions. However, it is still not clear which preoperative parameters predict safe and successful repair, though hemodynamic evaluation is still routinely used for assessment. Postoperative pulmonary hypertension, both in the immediate period after surgical repair and during long-term follow-up, remains a real therapeutic challenge. The clinical situation of a single ventricle with Fontan circulation also presents difficulties when pulmonary vascular lesions are present. This article reviews pulmonary hypertension associated with congenital shunts and discusses a number of the specific problems encountered.

Inhaled nitric oxide and related therapies

Children with congenital heart defects are at risk for perioperative pulmonary hypertension if they require corrective or palliative surgery in the first week of life or if they have defects associated with significant pulmonary overcirculation. In addition, children undergoing cavopulmonary connections for single ventricle lesions require low pulmonary vascular resistance for surgical success. Treatment of perioperative pulmonary hypertension with inhaled nitric oxide has become standard therapy in many centers. Related drugs that increase nitric oxide synthesis, including arginine and citrulline, have also been studied in the perioperative period. In this article, previous clinical trials of inhaled nitric oxide, intravenous arginine, and intravenous and oral citrulline in children with perioperative pulmonary hypertension or elevated pulmonary vascular resistance after a cavopulmonary connection are reviewed. In addition, recommendations are presented for each agent on the clinical use in the perioperative setting including clinical indications, assessment of clinical effect, and length of therapy.

Mechanical ventilation strategy following Glenn and Fontan surgeries: On going challenge!

The Glenn and Fontan operations put the pulmonary and systemic circulations in series. It has been shown that positive pressure ventilation (PPV) decreases pulmonary blood flow (PBF) and cardiac output (CO), and negative pressure ventilation (NPV) significantly improves PBF and CO. If early extubation is not achievable, the postoperative ventilator management strategy should aim at promoting PBF and CO by lowering pulmonary vascular resistance (PVR) and intrathoracic pressure. Multiple ventilator strategies have been evaluated to optimize this physiology, including high frequency ventilation, hyperventilation post Glenn, hypoventilation post Glenn with buffered pH, and the use of inhaled nitric oxide as an adjunct therapy for mechanical ventilation. In this review, the results of these studies will be reviewed and discussed.

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.

Intraoperative and postoperative risk factors for prolonged mechanical ventilation after pediatric cardiac surgery

BACKGROUND

Early extubation after cardiac surgery in children is feasible; however, predictors of prolonged mechanical ventilation (MV) should be recognized as soon as possible.

METHODS

At a tertiary pediatric cardiac center, prospective case series analyses were carried out with a total of 411 patients within 1 year of cardiac surgery. Perioperative factors were evaluated for strength of association with duration of MV > 61 h (medium, MMV) and > 7 days (long, LMV). Two multiple regression models were performed for both cut-off points: one model considered factors identified until 24 h postoperation, the other was performed with all parameters.

RESULTS

One hundred and three patients (25%) were still intubated after 61 h; 38 patients required LMV and they occupied 33% of total intensive care unit (ICU) bed days. If factors occurring until 24 h after surgery were analyzed, duration of cardiopulmonary bypass (CPB), intraoperative transfusion, post-CPB arterial oxygen tension (PaO2/FiO2), and fluid intake on the first day were found to be associated with MMV. Urea nitrogen value, nitric oxide treatment, delayed sternal closure, and tracheobronchomalacia, measured at the same point of time, were independent predictors of LMV. Of all the studied clinical predictors, MMV was associated with pulmonary hypertensive events, delayed sternal closure, peritoneal dialysis, nonvascular pulmonary problems, low output syndrome and fluid intake, while urea nitrogen (24 h), postsurgical neurological events, nitric oxide, tracheobronchomalacia, pulmonary hypertensive events and cardiac reoperations were identified as determinants of LMV.

CONCLUSIONS

Causes of MV after surgery are heterogeneous, vary with time, and have variable impact on the duration of MV.

Analytical Identification of Ideal Pulmonary-Systemic Flow Balance in Patients With Bidirectional Cavopulmonary Shunt and Univentricular Circulation

Background— In the present study, we extended previous mathematical modeling work on patients with bidirectional cavopulmonary (“bidirectional Glenn”) anastomosis to assess the potential utility of several descriptors of oxygen status. We set out to determine which of these descriptors best represents the overall tissue oxygenation. We also introduce a new descriptor, S o 2 min, defined as the lower of the superior and inferior vena cava oxygen saturations.

Methods and Results— The application of differential calculus to a model of oxygen physiology of patients with bidirectional Glenn allowed simultaneous assessment of all possible distributions of blood flow and metabolic rate between upper and lower body, across all cardiac outputs, total metabolic rates, and oxygen-carrying capacities. When total cardiac output is fixed, although it may intuitively seem best to distribute flow to maximize oxygen delivery (total, upper body, or lower body), we found that for each variable, there are situations in which its maximization seriously deprives flow to the upper or lower circulation. In contrast, maximizing S o 2 min always gives physiologically sensible results. If the majority of metabolism is in the upper body (typical of infancy), then oxygenation is optimized when flow distribution matches metabolic distribution. In contrast, if the majority of metabolism is in the lower body (typical of older children and during exercise), oxygenation is optimal when flows are equal.

Conclusions— In patients with bidirectional cavopulmonary anastomosis, because there is a tradeoff between flow distribution and saturation, it is unwise to concentrate on maximizing oxygen delivery. Maximizing systemic venous saturations (especially S o 2 min) is conceptually different and physiologically preferable for tissue oxygenation.

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.

Nitric Oxide in Pulmonary Arteriovenous Malformations and Fontan Procedure

Pulmonary arteriovenous malformations are a well documented complication of superior cavopulmonary (Glenn) connections. We report the successful management of a case of severe hypoxemia in the early postoperative period of a patient who underwent the Fontan operation. The patient had previously been diagnosed with pulmonary arteriovenous malformations; the use of inhaled nitric oxide was followed up with reversal of life-threatening hypoxemia. At 6-month postoperative follow-up, the patient was asymptomatic with near normal aortic saturation.

Postoperative management in patients with complex congenital heart disease

Life-threatening problems occur in the neonate and infant after cardiac surgery because of the interplay of diminished cardiac output (CO), increased metabolic demand, inflammatory responses to cardiopulmonary bypass, and maladaptive responses to stress. Therefore, the postoperative management of patients with complex congenital heart defects is directed at optimization of oxygen delivery to maintain end-organ function and promote wound healing. Traditionally, assessment of circulation in the postoperative congenital heart patient has depended on indirect assessment of CO using parameters such as blood pressure, pulses, capillary refill, and urine output. Because of the limitations of indirect and observer-dependent assessment of CO, we rely on objective measures of tissue oxygen levels for the complex postoperative patient. We have found that continuous monitoring of the mixed venous saturation (SvO2) allows for identification of acute changes in systemic oxygen delivery and frequently precedes other indicators of decreased CO. The postoperative patient can be expected to have a period of decreasing CO, and the need for intervention should be anticipated because critical low output syndrome will develop in a subset of patients. Strategies for postoperative care are developed based on the diagnosis and procedure, but optimizing SvO2 is a consistent goal. A uniform approach to airway maintenance, vascular access, and drug infusions, all universal concerns during the perioperative period, minimizes the potential for these predictable and necessary interventions to result in morbidity or mortality. Management of the postoperative single ventricle patient targets stabilization of the systemic vascular resistance through the use of vasodilators to improve systemic perfusion and simplify ventilator management. Management of any individual patient should be driven by objective analysis of available data and must include efforts to re-evaluate the treatment plan as well as to identify unanticipated problems.

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.

Basal pulmonary vascular resistance and nitric oxide responsiveness late after Fontan-type operation

BACKGROUND

The pulsatile nature of pulmonary blood flow is important for shear stress-mediated release of endothelium-derived nitric oxide (NO) and lowering pulmonary vascular resistance (PVR) by passive recruitment of capillaries. Normal pulsatile flow is lost or markedly attenuated after Fontan-type operations, but to date, there are no data on basal pulmonary vascular resistance and its responsiveness to exogenous NO at late follow-up in these patients.

METHODS AND RESULTS

We measured indexed PVR (PVRI) using Fick principle to calculate pulmonary blood flow, with respiratory mass spectrometry to measure oxygen consumption, in 15 patients (median age, 12 years; range, 7 to 17 years; 12 male, 3 female) at a median of 9 years after a Fontan-type operation (6 atriopulmonary connections, 7 lateral tunnels, 2 extracardiac conduits). The basal PVRI was 2.11+/-0.79 Wood unit (WU) times m2 (mean+/-SD) and showed a significant reduction to 1.61+/-0.48 (P=0.016) after 20 ppm of NO for 10 minutes. The patients with nonpulsatile group in the pulmonary circulation dropped the PVRI from 2.18+/-0.34 to 1.82+/-0.55 (P<0.05) after NO inhalation.

CONCLUSIONS

PVR falls with exogenous NO late after Fontan-type operation. These data suggest pulmonary endothelial dysfunction, related in some part to lack of pulsatility in the pulmonary circulation because of altered flow characteristics. Therapeutic strategies to enhance pulmonary endothelial NO release may have a role in these patients.

A combined stage 1 and 2 repair for hypoplastic left heart syndrome: anaesthetic considerations

Therapy of hypoplastic left heart syndrome (HLHS) consists of the staged Norwood procedure or cardiac transplantation. Stenting the ductus arteriosus and subsequent banding of the pulmonary arteries allows the combination of neoaortic reconstruction with the establishment of a bidirectional cavopulmonary connection (combined stage 1 and 2 procedure) in a later session. We report the anaesthetic management in eight infants ranging from 107 to 195 days undergoing a combined stage 1 and 2 procedure. Nonselective pulmonary vasodilators and nitric oxide were needed in all cases to improve oxygen saturation in the postbypass period. Phosphodiesterase inhibitors and epinephrine were required in all patients for inotropic support during and after weaning off cardiopulmonary bypass. The procedure was successful in seven patients. One patient died intraoperatively because of right heart failure. The physiological changes of this new surgical strategy for palliation of HLHS offers a challenge for the anaesthetist primarily in the early postbypass period.

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.

Essentials of Nitric Oxide for the Pediatric (Cardiac) Anesthesiologist

Short- and long-term survival rates for the operative treat ment of congenital heart disease (CHD) have improved significantly in the past 2 decades. The increasing sophisti cation of the pediatric cardiologist's diagnostic armamen tarium has led to more pervasive use of fetal screening with echocardiography. Early diagnosis and pre-emptive care of the neonate with complex CHD have allowed interventional strategies in the catheterization suite or the operating room to be optimized in both the timing and the quality of pallia tive or corrective procedures. Medications such as prosta glandin E and ventilator strategies using hypoxic and hyper carbic inspired gases exemplify therapies benefitting the contemporary neonate with CHD, often allowing stabiliza tion of the patient before surgery. Surgical care of neonates, infants, and children with CHD has also improved. Insights into maturational differences in myocardial and autonomic function have led to more appropriate myocardial protection strategies and pharmacologic support of the circulation. Recognition of those anomalies in which total correction in the neonate is desirable has stimulated improvements in the technical and cognitive skills of pediatric cardiovascular sur geons and pediatric cardiac anesthesiologists to meet these challenges. The goal of this article is to provide the pediatric anesthesiologist with an overview of inhaled nitric oxide and its relevance to clinical practice.

Comparison of hyperventilation and inhaled nitric oxide for pulmonary hypertension after repair of congenital heart disease

BACKGROUND

Pulmonary hypertension is associated with congenital heart lesions with increased pulmonary blood flow. Acute increases in pulmonary vascular resistance (PVR) occur in the postoperative period after repair of these defects. These increases in PVR can be ablated by inducing an alkalosis with hyperventilation (HV) or bicarbonate therapy. Studies have shown that these patients also respond to inhaled nitric oxide (iNO), but uncertainty exists over the relative merits and undesirable effects of HV and iNO.

HYPOTHESIS

Alkalosis and iNO are equally effective in reducing PVR and pulmonary artery pressure (PAP) in children with pulmonary hypertension after open heart surgery.

SETTING

Critical care unit of a tertiary care pediatric hospital.

DESIGN

Prospective, randomized, crossover design.

PATIENTS

Twelve children with a mean PAP > 25 mm Hg at normal pH after biventricular repair of congenital heart disease.

INTERVENTIONS

Patients were assigned to receive iNO or HV (pH > 7.5) in random order, and the effect on hemodynamics was measured. Each treatment was administered for 30 mins with a 30-min washout period between treatments. Finally, both treatments were administered together to look for a possible additive effect.

MEASUREMENTS AND MAIN RESULTS

Cardiac output and derived hemodynamic parameters using the dye dilution technique. Hyperventilation, achieved by an increase in ventilator rate without a change in mean airway pressure, decreased Pa(CO2) from a mean (SD) of 43.7+/-5.3 to 32.3+/-5.4 mm Hg and increased pH from 7.40+/-0.04 to 7.50+/-0.03. This significantly altered both pulmonary and systemic hemodynamics with a reduction in PAP, PVR, central venous pressure, and cardiac output and an increase in systemic vascular resistance. In comparison, iNO selectively reduced PAP and PVR only. The reduction in PVR was comparable between treatments, although addition of iNO to HV resulted in a small additional reduction in PVR. An additional decrease in PAP was seen when HV was added to iNO, attributable to a reduction in cardiac output rather than a further decrease in PVR.

CONCLUSIONS

Inhaled NO and HV are both effective at lowering PAP and PVR in children with pulmonary hypertension after repair of congenital heart disease. The selective action of iNO on the pulmonary circulation offers advantages over HV because a decrease in cardiac output and an increase in SVR are undesirable in the postoperative period.

Pediatric cardiac intensive care: current state of the art and beyond the millennium

Pediatric cardiac intensive care has emerged as a distinct clinical entity to meet the unique needs of pediatric patients with congenital and acquired heart disease. This new subspecialty demands expertise and experience in the pediatric subspecialties of cardiology, intensive care, cardiac surgery, cardiac anesthesia, neonatology, and others. Ten recent developments will have an impact on pediatric cardiac intensive care for the coming decades: 1) emergence of new patient populations; 2) new clinical methodologies in the treatment of pulmonary hypertension; 3) innovations in techniques of respiratory support; 4) expanding research of single ventricle physiology; 5) advances in the treatment of heart failure; 6) improved noninvasive imaging; 7) new directions in interventional cardiac catheterization; 8) new techniques in pediatric cardiac surgery; 9) use of computer technology and intensive care monitoring; and 10) appreciation for global economics of intensive care. Finally, a multidisciplinary approach with a team esprit de corps remains vital to a successful pediatric cardiac intensive care program.