Pain MeasurementPainAnalgesiaAnalgesia, EpiduralAnalgesia, ObstetricalAnalgesia, Patient-ControlledPain, PostoperativeAnalgesics, OpioidPain ManagementPain ThresholdChronic PainMorphineBupivacaineAnalgesicsAnesthetics, LocalAcupuncture AnalgesiaFentanylPain, IntractableBack PainLow Back PainLabor PainPain PerceptionAbdominal PainAnesthesia, EpiduralNeck PainMeperidineAcute PainNerve BlockInjections, SpinalSufentanilFacial PainPelvic PainDouble-Blind MethodLabor, ObstetricPain, ReferredAnesthesia, ObstetricalTramadolAnalgesics, Non-NarcoticReproducibility of ResultsAmidesShoulder PainProspective StudiesAnesthesia, Spinal