Surgery and Radiology Section

SENSATION

• Testing for pain is usually done last in the examination to avoid losing cooperation of the patient. The objective of the sensory examination is three fold.
  • Map areas of increased sensation(pain)
  • Map areas of decreased sensation and
  • Ensure that the animal can perceive a noxious stimulus.
• The first two are accomplished by testing for hyperesthesia and the ability to perceive superficial pain, respectively.
• The ability to perceive a noxious stimulus is tested if no reaction occurs to superficial stimuli Always apply the minimum stimulus that elicits a reaction.
• Hyperesthesia is incrased sensitivity to stimulation. Behaviuoral reactions to what should be a non noxious stimulus are interpreted as ‘pain’.
• Testing should be done first from distal to proximal or caudal to cranial.
• Lesions of the nervous system decrease sensation caudal or distal to the lesion, sometimes increase sensation at the lesion site and leave sensation normal proximal to the lesion.
• Therefore, testing from distal to proximal or caudal to cranial goes from decreased sensation through increased sensation to normal sensation.
• The direction can be reversed to more clearly define the boundaries of abnormality.
• The pelvic limbs are palpated first, followed by the vertebral column.
• Beginning with L7 and progressing cranially, the examiner squeezes the transverse process.
• Alternatively one can press each spinous process firmly. The severity of the stimulus is increased from high touch to deep palpation.
• Proper palpation causes no reaction in areas that are painful.
• Animals that are in extreme pain may react regardless of where they are palpated.
• Localization of the source of pain may be more accurate if the animal is sedated before examination.
• Increased muscle tension may be noticed when the painful area is palpated even under light anesthesia.
• Place one hand on the abdomen as you palpate the vertebral column to detect splinting of the abdominal muscles when pain is experienced.
• During palpation of the animal, areas of increased sensitivity are noted.
• Testing for superficial pain or eliciting the cutaneous (panniculus) reflex is best done with a small hemostat. Gently grasp a fold of skin, then pinch.
• Needles may be applied, but they are less reliable and may cause injury.
• The examiner tests the skin just lateral to the midline, then repeats on a line lateral to the site of the first evaluation. The opposite side is tested similarly. Three responses may be observed.
• A behavioural response, a reflex withdrawal of a limb, or a twitch of the skin (the cutaneous or panniculus reflex).
• A behavioral response such as a display of anxiety, an attempt to escape, a turning of the head, or a vocalization indicates perception of superficial pain.
• Withdrawal of a limb is a reflex and only indicates an intact reflex.
• The cutaneous reflex is a contraction of the cutaneous trunci muscle causing a twitch of the skin along the dorsal and lateral areas of the trunk.
• A significant response at any step indicates the presence of sensation and more severe stimuli are not needed once sensation has been established.
• If a dog turns and snaps when its toe is touched, no need exists to squeeze the toe with a hemostat.
• The caudal margins of normal superficial pain can be determined bilaterally.
• spinal cord or nerve root lesions produce an area of hyperesthesia or a transition from decreased to normal sensation in a pattern conforming to the dermatomal distribution of the nerves.
• Testing of cutaneous sensation of the neck is unreliable for localizing cervical lesions.
• Manipulation of the head and the neck and deep palpation of the cervical vertebral are more useful for localizing pain in this area.
• A noxious stimulus that elicits any behavioural response is adequate for determining the presence of deep pain.
• When a response is difficult to elicit, a hemostat is used to squeeze a digit. Withdrawal of the limb is  a behavioural response.