Inclusion Criteria:

• * Participant will be a Children's National Health System (CNHS) inpatient or outpatient admitted for at least 24 hours observation as part of the surgical plan of care.
• * Age range will be between 10 and 18.
• * BMI% will be calculated using height and weight and will include the 5th-85th% (normal weight) and greater than or equal to 95th %.( obese weight)
• * ASA physical classification of I, II or III.
• * All racial and ethnic groups will be included

Exclusion Criteria:

• * Any patient that is pregnant or lactating.
• * Renal insufficiency identified by GFR \<60 ml/min/1.73m2 and/or creatinine \> 3 times upper limit of normal values
• * Liver disease identified by : AST, ALT, γ-GT, bilirubin, albumin and AlkP and PT \> 3 times upper limit of normal values
• * Patients with Gilbert-Meulengracht Syndrome
• * Chronic alcohol intake or use of alcohol within last 72 hours
• * Patients who are treated with drugs know to effect CYP2E1(inhibition: dithiocarb and disulfiram. Induction: isoniazid) and UGT (UDP-glucuronyltransferases) (induction: estradiol-containing contraceptives, carbamazepine, phenobarbital, phenytoin, mesuximide, oxcarbazepine, rifampicin, primidone, atazanavir / ritonavir, lopinavir / ritonavir, olanzapine, retigabine , nevaripine, efavirenz, saquinavir, nelfinavir, lamotrigine, felbamate, zonisamide, bupropion. Inhibition: valproic acid)
• * Diabetes mellitus type II patients
• * Smoking
• * Acetaminophen intake up to 24 hours before enrollment.
• * Acetaminophen allergy