It is very important to know how much the patient feels pain to evaluate the efficacy of acupuncture or analgesic drugs. There are several methods to evaluate the pain intensity as follows.
A. Measurement of clinical pain
a. Categorical scale
This is a simple descriptive pain scale, grading pain as slight, moderate, severe and agonising.
b. Visual analogue scale (VAS)
Some of the problems of the categorical scale can be overcome by using VAS. VAS is a line of length, with one end labelled no pain and other end the most severe pain. The patient is asked to make a mark along this line signifying the level of pain he is feeling. This is more sensitive than the categorical scale but it necessitates painstaking explanation to the patient.
c. Matching method
Clinical pain is measured by matching the severity of experimental pain. Kast used a machine operated by the patient which applied pressure to the leg. As an experimental pain, tourniquet pain is also used for this purpose.
B. Application of experimental pain
a. An experimental pain is produced by mean of electrical stimulation, radiant heat or chilled water. Then two points on the intensity scale are fixed: the pain threshold and pain tolerance. The former contains much informations about pain sensation, but the latter is more sensitive to analgesic effects.
b. Somatosensory evoked response
It has been noted that somatosensory evoked responses have a good correlation with pain sensation as well as the intensity of stimulation. Though there are some controversies on which component of the somatosensory evoked response is the most useful, it is utilized for the measurement of pain.
c. Signal Detection Theory
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