Anaesthesia

1. Pain

1. Pain It has been said that the most humane application of chemistry is for the purpose of achieving anaesthesia. Although the benefits to the patient (derived from th e increasing skill, knowledge and experience of the anaesthetists) can be felt in many fields of medical practice, e.g. cardio-pulmonary resuscitation, care of the unconscious patient, Intensive Therapy Unit s (I.T.U.), etc., it is mainly i n the operating theatres that th e major part of the anaesthetists' work and commitments are carried out. And here the main objectiv e o f anaesthesi a i s t o rende r surgica l intervention s (operation s an d painful an d unpleasant investigations ) safe and free from pain . Pain, for most people, is an unpleasant sensation. Its intensity can vary from mil d to unbearable. It is caused by various stimuli, surgery being one of the strongest. It is detected b y non-myelinate d o r poorl y myelinate d nerv e fibres whic h ramif y i n th e superficial, deep or visceral tissues. These sensory fibres react to a variety of excessive stimuli, which can be thermal, mechanical, chemical, electrical or other . There is, as yet, no universal agreement whether these 'pain endings' are specific or non-specific, nor as to the exact causative factors. Some think there is a pain producing substance (probabl y a polypeptide), others implicat e change s o f temperatur e a t which alteration s o f tissue protein begi n t o tak e place , yet other s conside r tha t th e level of 'anxiety' is one of the determining factors in the onset of pain. Be it as it may, propagation o f painful stimul i takes place in fibres as shown i n Chart 1. 1 an d con SOMATIC ฀FIBRE S฀ (Myelinated)฀A฀ VISCERAL฀FIBRE S฀B฀ (Myelinated฀and฀ autonomic฀ preganglionic)฀ SOMATIC฀FIBRE S฀C฀ (Unmyelinated)฀ ALPHA฀ BETA฀ GAMMA฀ DELTA฀ EPSILON฀ Diameter฀Speed ฀of฀ of฀fibres฀conduction ฀(M/SEC )฀ 20u 2n CO ฀ O฀ LU฀ X฀^฀ Q.฀5 =฀ >-฀o฀ ฀f฀ Gate฀X~"~"" \฀ Control฀f ฀T ฀J฀ System฀\^^y฀ ^฀ V฀ Motivational-Affective฀ System฀ (Central฀Intensit y฀ Monitor)฀ ^฀ >฀ f฀ Sensory-Discriminative฀ System฀ (Spatio-Temporal฀Analysis )฀ {฀ Intro฀ \฀ Action฀ System฀ (Motor฀ Mechanisms)฀ /฀ duct฀ion฀ Fig.฀1. 2฀Th e฀manne r฀i n฀which฀variou s฀level s฀may฀modif y฀moto r฀(an d฀other )฀response s฀t o฀painfu l฀ stimuli.฀ (A) Non- (1) (2) (3) (4) (5) (6) (B) Surg : (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) surgical methods to relieve pain: Physiotheraphy. Chemotherapy (opiates , analgesics, local analgesics, etc.). Psychotherapy. Hypnosis. Electric shock treatment . Acupuncture. ical methods, including: Neurectomy. Sympathectomy. Various percutaneous cervica l cordotomies. (These consist of surgical section o f the anterolateral quadran t o f the spinal cor d carrie d ou t unde r direct vision. If bilateral pain is to be relieved, a laminectomy of one or two vertebrae is performed an d two spinal cor d section s are made at differen t levels. One is at the upper portion of the wound on the side, the other at the lower portio n o f the woun d o n the other. Post-operativ e difficultie s fro m oedema, haematoma or disfunction ma y be thereby reduced. ) Thoracic cordotomy . Commisural myelotomy . Various tractotomies . Mesencephalotomy. Frontal lobotomy and some other neurosurgical procedures . Pituitary injectio n o f alcohol (recentl y introduce d fo r destruction o f the pituitary gland to relieve pain in patients suffering fro m an y carcinoma an d also in those who have hormone dependent tumours) . Audiofrequency curren t heat coagulation (the probe temperature must not rise abov e 80 ° for mor e tha n 4 0 sees.) fo r relie f o f pai n arisin g a t the posterior facet joints (intervertebral or zygoapophyseal). Pain 9 (11) Electrica l stimulation of peripheral nerves, dorsal column, head of caudat e nucleus an d magnocellula r portio n o f medial geniculat e body , an d septa l area (Lipton, 1979) . Endogenous Analgesics The variation in our perception of pain in different circumstance s has led to suggestions that th e brain itsel f may be capable of producing an endogenou s analgesic . I t has been shown , under battl e condition s in wars, that pai n perceptio n ma y b e tem porarily...