Unrecognized coarctation of the aorta (CoA) is a life-threatening component of congenital heart disease (CHD) in which narrowing of the aorta causes obstructed blood flow to the lower half of the body; it can occur in isolation or in combination with other defects. CoA is the type of CHD most likely to be missed by current newborn screening. An evolving coarctation (during closure of the ductus arteriosus) can be challenging to diagnose until often devastating end-organ injury manifests, even in the ICU setting. This study will evaluate currently used tools, such as four extremity blood pressures and pulse oximetry, and the investigators will test new tools - resonance Raman spectroscopy (RRS) and photoplethysmography analysis- to assess the adequacy of oxygen delivery in newborns who are at risk for aortic arch obstruction. The investigators hypothesize that combining an assessment of commonly used non-invasive monitoring tools, new components of these traditional tools, and RRS, will have improved sensitivity in detecting critical impairments to tissue oxygen delivery in newborns with suspected critical aortic arch obstruction.

Coarctation of the aorta (CoA) is a potentially life-threatening form of congenital heart disease (CHD) in which an anatomic narrowing of the aortic arch may cause critical aortic arch obstruction (AAO) following closure of the ductus arteriosus (DA). CoA accounts for 6-8% of all CHD and occurs in about 1 in every 1800 babies born in the United States each year. Despite this prevalence, CoA frequently eludes detection on both prenatal imaging and CHD screening. If undiagnosed, infants may present with catastrophic shock, often leading to mortality or severe morbidities. In many cases, the anatomic appearance of the aortic arch in the fetal or early postnatal period raises suspicion for AAO that can only be confirmed by allowing the DA to become restrictive and closely monitoring for hemodynamic changes. However, the process of monitoring hemodynamics during ductal closure (MHDC, i.e. the 'arch watch') is variable across institutions and can be insensitive to critical deficiencies in oxygen delivery in the setting of decreased blood flow, even in subspecialized ICU environments. Current approaches to monitoring hemodynamic changes in neonates with possible AAO revolve around non-invasive measurements of oxygen saturation (i.e. pulse oximetry, near infrared spectroscopy (NIRS)) and tissue perfusion (i.e. femoral pulse strength, urine output, blood pressure). There are no publications which systematically and concurrently assess these trends during this hemodynamic transition, and as such, there are no agreed upon thresholds to alert clinicians that a developing AAO is causing impaired tissue perfusion/oxygenation. Exploration of traditional measures of tissue oxygenation may prove more sensitive and specific at identifying compromise in newborns with critical AAO. For example, certain pulse oximetry waveform characteristics (photoplethysmography, PPG) have shown differences in healthy newborns versus those with CoA. Resonance Raman spectroscopy (RRS) is another validated non-invasive method that assesses peripheral tissue oxygenation in neonates and has been shown to correlate well with invasive markers of tissue oxygenation. The investigators and others have utilized RRS in healthy neonates and in animals to detect tissue hypoperfusion. To test the hypothesis that a validated MHDC process that combines commonly used non-invasive monitoring tools, new components of these traditional tools, and RRS, will have improved sensitivity in detecting critical impairments to tissue oxygen delivery in newborns with suspected critical AAO, the investigators identified the following aims:

Aim I: To assess the reliability of currently deployed non-invasive markers of tissue oxygenation/perfusion (femoral pulse strength, pre- vs. post- ductal blood pressure and saturation gradient, cerebral/renal NIRS, and urine output) in identifying a critical AAO that will need intervention in the newborn period.

Aim II: To explore the sensitivity of PPG to identify critical AAO requiring intervention in the newborn period.

Aim III: To determine the feasibility of assessing oxygen utilization at the tissue level based on RRS during MHDC and examine its predictive capability in identifying those infants with AAO who will require arch intervention in the newborn period.

Inclusion Criteria:

• Infants with echocardiography-based possible or definite aortic arch obstruction and <1 month postnatal age admitted to the CICU
• Clinical team assent to approach family, (3) parent/guardian informed consent. Inclusion criteria includes infants with concurrent other congenital heart disease, or simple Coarctation of the aorta or arch hypoplasia

Exclusion Criteria:

• Known carrier status for resistant organisms. Resistant organisms are defined as MRSA and VRE.

Infants with prenatal or postnatal echocardiographic findings concerning for or diagnostic of aortic arch obstruction admitted to the BCH CICU.