The purpose of the Oxy-CAHN study is to improve the monitoring capabilities of newborn infants recovering from congenital heart surgery. Currently, we utilize important but unsophisticated measures, such as vital signs and lactate measurements, to monitor these patients. Although they are useful in categorizing patients as well or unwell, these signs currently lack the power quantify a patient's risk for cardiac arrest. More to the point, they are mostly indirect measures of what we really are assessing, which is tissue oxygen delivery.

Our group has significant expertise with devices which quantify the amount of oxygen that a baby consumes every minute. Historically, these values are more commonly used in combination with other measures to assess nutritional and metabolism status. In critically ill patients, however, the volume of oxygen consumed by a patient may be limited by the amount of oxygen their circulation delivers. This may represent a critical relationship, which has been previously described, but not exploited for the purpose of identifying patients with critically low oxygen delivery.

The aims of this study are therefore (1) to demonstrate that oxygen consumption can be safely and precisely measured continuously in newborns undergoing one of two common congenital heart surgeries, (2) to determine whether postoperative circulatory failure is associated with a precedent change in oxygen consumption, and (3) to determine whether the addition of the oxygen-based measurements (including oxygen consumption and venous oxygen saturations) to standardly measured parameters will add power in predicting which patients will experience postoperative circulatory failure.

If successful, this study may improve our capacity to non-invasively and continuously monitor patients following the highest risk congenital heart surgeries, and in the future,to create an algorithm which quantifies a patients risk for having a cardiac arrest. This may permit providers to intervene on these patients earlier, improving the morbidity and mortality associated with congenital heart disease.

Inclusion Criteria:

1. Patients from birth to 6 months of age
2. HLHS AND no prior operations AND planned S1P or HPOR d-TGA/IVS AND planned ASO
3. Written parental informed consent

Exclusion Criteria:

1. Weight < 2 kg

2. Disease specific A. HLHS patients: Infants whose surgical plan includes a neonatal biventricularrepair will be excluded.

   B. d-TGA/IVS patients: Newborns with any additional cardiac defect other than an atrial septal defect will be excluded.

3. Patients on ECMO preoperatively

4. Clinically significant tracheo-esophageal fistula or known preoperative air leak