The purpose of this research is to study the effects of intravenous ketamine infusions for the treatment of patients with depressive symptoms in intensive care unit (ICU).

Inclusion Criteria:

• Has been in the Mayo Clinic Florida ICU for the past 1 week.
• PHQ-9 score of 10 or higher.
• One of the following diagnoses: acute myocardial infarction; acute renal failure; chronic obstructive pulmonary disease (COPD); congestive heart failure; end-stage liver disease; patients requiring intra-aortic balloon pump (IABP) therapy or continuous renal replacement therapy (CRRT); post-bone marrow transplant; acute Hypoxemic Respiratory Failure; acute or chronic hypoxemic respiratory failure; pre- or post- lung, liver or heart transplant or surgical overflows (such as abdominal aortic aneurysm, thoracotomy or tracheostomy).

Exclusion Criteria:

• Poor vital sign stability hypoxia: O2 < 95%, hypotension: SBP < 90 hypertension: SBP > 180.
• Heart rate: < 50 or > 120, or Respiratory Rate: < 10 or > 30.
• Altered mental status.
• Patient is unwilling to participate or provide informed consent.
• Any allergy to ketamine or diphenhydramine.
• Patient is female of child-bearing age and unwilling to provide urine or blood for HCG analysis.
• Pregnant or breastfeeding.
• Presence of intracranial mass or vascular lesion.
• Presence of a history of psychosis or hallucinations (as assessed by electronic chart review).
• Weight greater than 115 kg or less than 45kg.
• History of increased intracranial pressure/hypertensive hydrocephalus or increased intraocular pressure.
• Patient is acutely psychotic.
• Provider feels that patient currently or likely will require chemical and/or physical restraints.
• History of prolonged QT-interval.
• Current treatment includes any medication known to affect the N-methyl-D-aspartate receptor system (e.g., lamotrigine, acamprosate, memantine, riluzole, or lithium).
• Patient in withdrawal from substance abuse or who have used hallucinogens (including cannabis) in the last month for any indication, as determined by the clinical interview and urine drug screening.