To evaluate the efficacy of three regimens of sub anesthetic dose of ketamine infusion in relieving chronic refractory pain in patients with complex regional pain syndrome

Ketamine N-methyl-D-aspartate (NMDA) receptor blocker that has recently been studied for its analgesic effect is a phencyclidine or phenyl cyclohexyl piperidine (PCP) derivative that initially became commercially available for human use in 1970 as a rapid-acting intravenous (IV) anesthetic. It is currently classified by the Food and Drug Administration (FDA) as an anesthetic induction agent in doses ranging from 1 to 4.5 mg/kg.

Ketamine has proven to be a desirable drug, despite of its induction dissociative effects and abuse potential. It is favorable due to its short half-life and lack of clinically significant respiratory depression. In addition to its anesthetic effects, ketamine has analgesic, anti-inflammatory, and antidepressant activities.

Inclusion Criteria:

• Patients aged more than 21 years old of both sexes with American Standards Association I ,II.
• Patients diagnosed as ( CRPS) based on Budapest criteria
• The average daily pain intensity required on (NRS) is 7 or more for at least 3 months despite of standard therapy which includes: (pharmacologic therapy as non steroidal anti- inflammatory drugs (NSAIDs), antiepileptic (AEDs), antidepressants), as well as physical therapy and psychiatric care

Exclusion Criteria:

• patients refusal
• Patients with unstable psychological or psychiatric conditions, including : untreated bipolar disorder, post-traumatic stress disorder, major depression , severe personality disorder and psychotic illness.
• Patients have recently undergone major interventional pain procedures, such as nerve blocks or implantable therapies within 3 months of enrollment.
• Patients with known drug dependency or substance use disorder specifically related to ketamine or other psycho-stimulant drugs.
• Patients with previous severe reactions, contraindication or allergy to ketamine.
• Patients with cardiovascular disease (hypertension, arrhythmia), hepatic, renal or other organ impairment.

The data will be available upon a reasonable request from the corresponding author after the end of study for one year.

after the end of study for one year

The data will be available upon a reasonable request from the corresponding author