IV Acetaminophen as an Analgesic Adjunct

Inclusion Criteria: * Acute (less than 1 week in duration) severe pain necessitating use of intravenous (IV) opioids in the judgement of the treating attending physician Exclusion Criteria: * Use of other opioids or tramadol within past 24 hours: to avoid introducing assembly bias related to recent opioid use, since this may affect baseline levels of pain and need for analgesics. * Prior adverse reaction to hydromorphone, morphine, or acetaminophen. * Chronic pain syndrome: frequently recurrent or daily pain for at least 3 months results in modulation of pain perception which is thought to be due to down-regulation of pain receptors. Examples of chronic pain syndromes include sickle cell anemia, osteoarthritis, fibromyalgia, and peripheral neuropathies. * Alcohol intoxication: the presence of alcohol intoxication as judged by the treating physician may alter pain perception. * Systolic Blood Pressure (SBP) \<100 mm Hg: Opioids can produce peripheral vasodilation that may result in orthostatic hypotension. * Heart Rate (HR) \< 60/min: Opioids can cause bradycardia. * Oxygen saturation \< 95% on room air: For this study, oxygen saturation must be 95% or above on room air in order to be enrolled. * Use of monoamine oxidase (MAO) inhibitors in past 30 days: MAO inhibitors have been reported to intensify the effects of at least one opioid drug causing anxiety, confusion and significant respiratory depression or coma. * Patients using transdermal pain patches