Acute Effects of Hypoxic Gas Admixtures on Pulmonary Blood Flow and Regional Oxygenation in Children Awaiting Norwood Palliation

Presurgical Use of Hypoxic Mixture for Systemic Perfusion Improvement in Neonates With Complex Congenital Heart Disease: A Systematic Review and Meta-Analysis

Oxygen therapy is essential for the survival of preterm babies and critically ill newborns; however, it has the potential to cause harm through hypoxemia or hyperoxemia. Newborns with complex congenital heart diseases (CHD) suffer from oxygen fluctuations due to the disease and its treatments, altering pre and postnatal development. The objective of this study is to evaluate the evidence for using a hypoxic mixture to decrease pulmonary over-circulation and improve systemic perfusion before surgical interventions in newborns with complex CHD that course with pulmonary over-circulation and systemic hypoperfusion. A search was conducted in PubMed, EMBASE, LILACS, Scielo, Taylor and Francis, SAGE, and Science Direct databases from 2000 to 2022 by two independent authors, including articles with hypoxic mixture treatment in observational studies or trials, with pre-treatment and post-treatment measurements in the same patient, or two groups or more comparisons. Six articles were selected, with a total of 75 patients. The primary outcome was improved systemic circulation and decreased pulmonary over-circulation measured directly with Qp/Qs and indirectly with oxygen saturation and cerebral near-infrared spectroscopy (NIRS). In addition, we performed a meta-analysis for oxygen saturation and cerebral NIRS. Oxygen saturation was the value uniformly reported; three studies reported a significantly lower oxygen saturation after the hypoxic mixture. The cerebral NIRS was measured in 4 studies, with inconsistent results. After using the hypoxic mixture, the Qp/Qs calculation was lower in the two studies but was not statistically significant. The meta-analysis for oxygen saturation showed a fixed effect post-hypoxic therapy of -0.7 (-1.06; -0.35), p < 0.001. The meta-analysis of two studies that measured cerebral NIRS did not show a statistically significant difference at 12 and 24 hours. In conclusion, this is the first systematic review and meta-analysis regarding the pre-operative use of hypoxic gas mixtures for newborns with complex congenital heart disease. Treatment results in lower oxygen saturations, but there is a lack of evidence of improvement in systemic perfusion. The utilization of this therapy is controversial, and better evidence is necessary.

Hypoxic gas therapy in neonatology, considerations in practice

BACKGROUND

Adequate oxygenation is essential in sick newborns. Each disease determines the target of oxygenation. Nevertheless, hyperoxia and hypoxia are related to adverse outcomes. Most studies about this had been made in preterm infants or term babies with pulmonary pathology.

INTRODUCTION

Congenital heart diseases may also require careful oxygenation control and management of oxygen supply.

PROBLEM

Presurgical stabilization of complex heart diseases (CHD) may be difficult, especially after the physiological decrease of pulmonary resistance, which generates pulmonary edema (due to over-circulation) and systemic hypoperfusion. Several strategies have been described to avoid this phenomenon, such as prostaglandin, vasodilators, inotropes, positive airway pressure, and even hypoxic mixture (Inspired fraction of oxygen (FiO2) below 21%).

DISCUSSION

The last therapy is mainly used in single ventricular physiology heart diseases, such as the hypoplasic left heart syndrome (HLHS) or systemic ductus dependent flow CHD (interruption of the aortic arch and coarctation of the aorta). Alveolar oxygen affects pulmonary vascular resistance modifying lung flow. This modification could help the stabilization during the presurgical period of complex CDH. Many centers use hypoxic therapy to avoid hypotension, metabolic acidosis, coronary-cerebral ischemia, and liver, renal and intestinal injury. Despite the theoretical benefits, there are doubts about how tissue oxygen supply would change during hypoxic gas ventilation. It is worrisome that FiO2 < 21% causes a decrease in brain oxygenation, adding neurological injury to the already established because of CHD and other not modifiable factors. Brain monitoring through near-infrared spectroscopy (NIRS) during hypoxic gas therapy is mandatory. Recent studies have shown that hypoxic gas ventilation therapy in patients with HLHS in the preoperative period decreases the ratio between systemic and pulmonary circulation (Qp/Qs) but does not improve regional oxygenation delivery. The use of hypoxic gas ventilation therapy continues to be controversial. It could be an option in some complex CHD, mainly HLHS.

Impact of Medical Interventions and Comorbidities on Norwood Admission for Patients with Hypoplastic Left Heart Syndrome

The purpose of these analyses was to determine how specific comorbidities and medical interventions impact risk of inpatient mortality in those with hypoplastic left heart syndrome undergoing Norwood procedure. The secondary aims were to determine the impact of these on billed charges, postoperative length of stay, and risk of cardiac arrest. Admissions from 2004 to 2015 in the Pediatric Health Information System database with hypoplastic left heart syndrome and Norwood procedure were identified. Admission characteristics, patient interventions, and the presence of comorbidities were captured. A total of 5,138 admissions were identified meeting inclusion criteria. Of these 829 (16.1%) experienced inpatient mortality, and 352 (6.7%) experienced cardiac arrest. The frequency of inpatient mortality did not significantly change over the course of the study era. The frequency of cardiac arrest significantly decreased from 7.4% in 2004 to 4.3% in 2015 (p = 0.04). The frequency of pharmacologic therapies, particularly vasoactive use, decreased as the study period progressed. Regression analyses demonstrated a significant association between cardiac arrest and inpatient mortality with arrhythmias, acute kidney injury, and pulmonary hypertension. Similarly, regression analyses demonstrated a significant association between increase in billed charges and length of stay with year of surgery, presence of heart failure, syndromes, and acute kidney injury. For patients with hypoplastic left heart syndrome undergoing the Norwood procedure, the frequency of pharmacologic therapies and cardiac arrest has decreased over time. There are significant associations between acute kidney injury, arrythmias, and pulmonary hypertension with cardiac arrest and mortality.

Near-Infrared Spectroscopy Monitoring in Pediatric Anesthesiology: A Pro-Con Discussion

Near-infrared spectroscopy (NIRS) has been increasingly used as a non-invasive measurement of cerebral tissue oxygen saturation. The aim of this short review is to discuss the benefits and drawbacks of its use in the pediatric anesthesia population. In the context of cardiac surgery, lower intraoperative NIRS values have shown a modest association with neurodevelopmental outcomes while lower neonatal intensive care unit NIRS values have been correlated with reduced neurodevelopment in children. However, it is still unclear if management aimed at increasing cerebral tissue oxygenation would have any benefit on these outcomes. Without prospective research looking into the effects of intervention given proper thresholds, the true benefit of NIRS use is still up for debate. Even with current research gaps, its use in the clinical setting continues.

The Effect of Hypoxic Gas Therapy Using Nitrogen Before Bilateral Pulmonary Artery Banding on Hemodynamics and Pulmonary Artery Development

This study aimed to identify its influence on pulmonary development and hemodynamics before bidirectional Glenn (BDG) anastomosis. This retrospective study involved 30 consecutive patients with univentricular hearts who underwent bilateral pulmonary artery banding (bil-PAB) and BDG anastomosis between September 2011 and September 2018 at our institution. These patients were classified into the nitrogen (N = 12) and no nitrogen (N = 18) groups according to their use of hypoxic gas therapy. Clinical echocardiographic, operative, and catheter examination data were reviewed. Nakata index was 131 (110-167) in the nitrogen group and 138 (88.4-161.7) in the no nitrogen group (P = 0.8). Pulmonary vascular resistance (PVR) was 1.50 (1.30-2.4) in the nitrogen group and 138 (88.4-161.7) in the no nitrogen group (P = 0.3). There was no statistical difference between the pulmonary development in both groups. In the subgroup of hypoplastic left heart syndrome patients, there was a statistical difference. RVEDV% of normal was 232.5 (215-239) in the nitrogen group and 201 (161-209) in the no nitrogen group (P = 0.03). Pulmonary development was not significantly different when hypoxic gas therapy was performed using nitrogen vs. not using nitrogen. However, RVEDV% of normal might be larger with hypoxic gas therapy using nitrogen. Although there is no obvious systemic atrioventricular valve regurgitation exacerbation with hypoxic gas therapy, it might be useful to prevent a decrease in PVR and may also affect bil-PAB and subclinical increase in systemic atrioventricular valve regurgitation.