Sluggish enrollment.

Thyroid hormones are substances naturally made by the body and are important to many of your body's basic functions such as breathing and brain function. We are investigating whether or not these hormones are at lower levels in critically ill children which could lead to further health problems. We hope to get a better understanding of hormone levels and their effects on critically ill children to better help other children in the future.

We hypothesize that critically ill children that require vasoactive infusions and/or invasive mechanical ventilation have thyroid hormone alterations. We will measure TSH, tT3, fT3, rT3, tT4, fT4, adn tyrosine concentrations in critically ill children with hypotension and/or respiratory failure and correlate thyroid hormone alterations to severity of illness, intensity of therapeutic interventions, and associated morbidity and mortality by using clinical outcomes parameters.

Inclusion Criteria:

• Informed Consent
• Age of less than 12 months and less than or equal to 18
• Patient must weigh greater than 10 kgs.
• Patients must require vasoactive infusions and/or mechanical ventilation.
• Patients must be enrolled within 24 hours of meeting eligibility.

Exclusion Criteria:

• Patient with known or presumed pre-existing thyroid disease will be excluded
• Patients who receive thyroid supplementation will be excluded
• Patients with known or presumed hypothalamic and/or pituitary dysfunction that have thyroid hormone concentration abnormalities not related to an acute illness.
• Patients who are intubated for airway protection only.
• Patients intubated for neuromuscular disease
• Pregnant patients.
• Patients receiving amiodarone supplementation
• Patients who received blood product transfusions equaling more than 1/2 of their blood volume.

Patients who are admitted to the Pediatric Intensive Care Unit at the Children's Hospital of Philadelphia will be approached if they meet inclusion criteria.