Investigators are conducting research about oxygen levels in the body and whether it is possible to use a device to measure oxygen in the body's tissues noninvasively, without blood draws or a catheter (a plastic tube placed in a vein). Investigators would like to know how this device compares to standard measurements using blood from a catheter. This may help treat patients who may not be getting enough oxygen to their body.

Investigators will enroll patients in the pediatric intensive care unit who have an indwelling catheter that allows measurement of central venous oxygen saturation. Measurements of central venous oxygen saturation using blood oximetry will be compared with measures of tissue oxygenation at the buccal mucosa using a Raman spectroscopy tissue oximeter. Investigators will also measure the status of the sublingual microcirculation utilizing sidestream dark field microscopy. Basic demographic and clinical variables such as ongoing vasoactive infusions, mechanical ventilation, and laboratory data will also be collected.

Inclusion Criteria:

• Patients admitted to the Pediatric Intensive Care Unit (PICU) or Pediatric Cardiothoracic Unit (PCTU)
• Age >30 days and <18 years -patients with a "high" central venous line (ie internal jugular, subclavian, peripherally inserted central catheter, broviac, port) capable of blood draw and with central venous catheter tip in the superior vena cava

Exclusion Criteria:

• Age <30 days or >18 years
• Known pregnancy or subsequently discovered pregnancy after admission
• Uncorrected cyanotic congenital heart disease

Relative Exclusion Criteria:

• Oral trauma preventing placement of Raman StO2 oximeter probe or microcirculation video device
• Upper extremity trauma preventing placement of BEAM device