Three Regimens of Ketamine Infusion in Complex Regional Pain Syndrome

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.