| Category | Examples |
| Medications | Opioids, anti-cholinergics, alpha-2-adrenergic agonists, anti-psychotics, Ca++ channel blockers, cytotoxics, dopaminergics, epidural anesthesia |
| Trauma and orthopedic surgery | Fractures, hip and spine surgery |
| Obstetric and gynecological | Pelvic surgery especially involving spinal anesthesia; cesarian section; vaginal (normal or instrumental) delivery |
| Cardiothoracic surgery or disease | Cardiac surgery including transplantation; myocardial infarction, heart failure, pneumonia |
| Neurological diseases | Parkinsonism, stroke, dementia |
| Retroperitoneal diseases | Malignancy, hemorrhage |
| Metabolic imbalance | K+, Ca++, Mg++ imbalance; hypothyrodism |
| Infection | Herpes zoster |
