06. Pain

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Pain [ 3 , 4 , 57 ] is a painful and unpleasant sensation perceived by the body in response to a painful stimulus. Usually it is a warning signal from the body to indicate a threat to physical integrity.

The pain may also designate sufferings of sentimental (eg due to death), we will not treat this type of pain here.

Even if it is an unpleasant experience, the pain circuits play a vital role in our survival [ 48 , 187 ], since it is this feeling which forces us to act against our will to escape a potential danger.

Pain is the number one symptom in most diseases [ 208 , 209 ]. Its clinical description is of major interest to reach an accurate diagnosis and subsequently an adequate remedy. However, the pain can be so excessive and intolerable it becomes an evil in itself. Several therapeutic strategies can and should be developed to avoid the patient to suffer.

1. Pathophysiology of pain:

1.1. The periphery to the CNS:

The nociceptive [ 107 ] (painful) results from a painful stimulus to the nerve endings of skin structures [ 69 ], muscle, joint or visceral. This message is then conveyed by afferent nerve pathways to the CNS [ 1 , 4 ].

Polymodal nociceptors (activated by mechanical stimuli, thermal and chemical) and unmyelinated C-fibers play a major role in the detection, encoding the intensity and transmission of cutaneous pain. These are unmyelinated C fibers with a diameter less than 1 micron [ 3 ] and a speed below 2 m / s slow conduction. Other types of fibers are also involved in the conduction of nociceptive signals, for example A-delta fibers (myelinated bit) [ 57 ].

After their passage through the peripheral nerves, nociceptive afferent fibers join the central nervous system [ 41 ] in the posterior roots of the spinal cord or in the brainstem to the cranial nerves.

Substance P (main neurotransmitter in pain) and glutamate excite neurons in the dorsal horn of the spinal cord [ 1 , 38 , 107 ]. The nociceptive impulses then follows the spinothalamic pathway (extra-lemniscal) [ 145 specific] of thermal nociception.

1.2. Modulation of nociceptive messages:

Once the pain signals transmitted from the periphery to the CNS, it will be modulated by various controls [ 35 ].

Afferent fibers (A alpha and beta) that transmit tactile messages will inhibit nociception at spinal level. This explains our attitude to reach the place where you got hurt right after the accident. These phenomena can be inhibitory pre-synaptic or post-synaptic (system of the door, gate-control [ 39 ]).

In the brainstem neurons exist that are responsible for inhibiting descending pathways [ 38 , 107 ] (e.g., those in the periaqueductal gray substance [ 3 ]). These neurons lead by blocking nociceptive pathways analgesia at the area that hurts.

2. The different types of pain [ 69 ]:

2.1 Depending on the mechanism of pain:

2.1.1. Nociceptive pain:

This is the classic model of reception, transmission and perception of pain by the above mechanisms.

2.1.2. Neuropathic pain [ 207 ]:

Says pain not caused tissue damage, but due to an interruption of nociceptive pathways leading to disruption of the transmission system.

2.1.3. Psychogenic pain [ 207 ]:

Expresses pain with no organic explanation.

2.1.4. Referred pain [ 3 , 209 ]:

The fibers of the spinothalamic pathway sometimes receive afferent converging both of the skin and of certain viscera. Upon receipt of a nociceptive impulses, the brain assigns the source of stimulus to the skin which is also the most stressed.

This is the case for example when a myocardial infarction which is the left hand and the mandible that hurt although there is no damage to their level.

2.2 The evolution of pain:

  • Acute pain [ 48 ].
  • Chronic pain [ 69 ].

3. Pain assessment:

3.1. Simple verbal scale (EVS) [ 210 ]:

We verbally asks the patient to evaluate her pain by 4-5 categories which result in a score, 0: no pain, 1: Low 2: Medium 3: Intense 4: Extremely intense.

3.2. Digital Scale (EN) [ 208 ]:

This allows the patient noted pain knowing that the minimum score is 0 and the maximum score is 10 intolerable.

3.3. Analog [visual scale (VAS) 91 , 179 ]:

This is a strip which has a line side and a subjective across a strip of 100 mm. The patient will draw a line or advance the cursor depending on the intensity of pain from (no pain) to (worst pain imaginable). The caregiver will match the rating on the back to move the cursor of the slider.

3.4. Other so-called multidimensional methods [ 208 ]:

This category includes several types of questionnaires and behavioral scales.

It is not necessary to emphasize the subjectivity of the above means in the assessment of pain, are elements of guidance and monitoring developments.

4. Analgesic treatments:

Therapeutic measures should primarily target the source of pain, but must also relate to the relief of the patient [ 69 ]. The World Health Organization (WHO) has classified the different analgesic substances into three levels according to their activity. It is recommended that you follow this step by step strategy in the management of pain [ 91 ].

4.1. Level 1:

The paracetamol and the nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, noramidopyrine (or metamizole) ... If considered low or moderate pain by a physician, these medications must be prescribed first.

They act principally by inhibiting cyclooxygenase, a head of a cascade of chemical reactions that enzyme, among others, pain.

The most common side effects of these drugs are mostly stomach, but other serious problems may occur in case of overdose.

4.2. Level 2:

Weak opioids analgesics [ 211 ] derivatives (lightweight) of opium and morphine as codeine, dihydrocodeine, dextropropoxyphene and tramadol ...

Codeine and dextropropoxyphene are often associated with analgesics Level 1 as their modes of action are different and complementary, their action is synergistic. This type of substance acts on the CNS to specific receptors responsible for the abolition of pain.

The main side effects include constipation, drowsiness, nausea, vomiting, or difficulty breathing. This type of compounds exposed to physical dependence.

4.3. Level 3:

Strong opioid analgesics, morphine [ 48 , 211 ] and its derivatives. These drugs have the same characteristics and the same mode of action as the previous ones, but are more powerful. They are used in cases of severe pain or refractory to analgesics level 2. They have the same side as weak opioids analgesic effects and can cause the same addiction.