CHAPTER II. SHOCK AND ANÆSTHESIA. Under this short and convenient title, the author proposes to discuss all the changes observable in the patient’s condition, the causation of which can be traced to the procedure of the surgeon. The use of the term _shock_ was at one time, and by some teachers still is, restricted to a definite clinical condition. The patient was described as lying pallid and almost pulseless, with dilated pupils, cold sweating skin, and gasping, irregular respirations. In the view more generally taken to-day, that is but the extreme and final manifestation of a syndrome, which any patient who suffers trauma (whether inflicted accidentally or by the surgeon) exhibits in a greater or less degree, and from which general anæsthesia protects a patient to a very limited extent only. Professor Crile, to whose work we owe so much of our knowledge on this subject, has said, “In general anæsthesia, part of the brain only is asleep.” Though consciousness is abolished, many parts of the brain are quite capable of responding to _centripetal impulses_ passed to the brain through sensory nerves injured by the knife. A full account of the changes demonstrated by Crile in some of the cells of the grey matter of the brain as a result of such stimuli, and of the interpretation put upon these by their discoverer, is not suitable for a text-book of anæsthesia. It is sufficient to say that such changes have been discovered, and that their occurrence as a result of trauma is not prevented by inhalational anæsthesia. Such changes, though of the utmost interest scientifically, cannot be demonstrated clinically, and it is to alterations of _blood pressure_ and of _respiration_ that we must look for clinical evidence of the effects of _shock stimuli_. [Illustration: FIG. 1.--Shock--Blood pressure of a dog undergoing laminectomy under general anæsthesia (Grey and Parsons.) (_Reproduced by kind permission of the Authors._)] With every incision by the surgeon, sensory nerve twigs are of necessity injured. The fibres found in sensory nerves are, it will be remembered, either pressor, or depressor--that is, stimulation of them, causes either an increase or decrease of the blood pressure, the depth and frequency of respiration being usually affected in the same direction as the B.P. That such changes do commonly occur is easily recognised by clinical observation. The veriest beginner in anæsthesia soon learns to expect a deeper, quicker respiration and a stronger pulse as soon as the operation has begun. These changes have been studied experimentally upon animals and upon the human subject by the use of the sphygmomanometer: Fig. 1, drawn from Grey & Parson’s Arris and Gale Lectures of 1912, shows a tracing from a dog undergoing laminectomy under general anæsthesia, and gives a good idea of the early evidences of shock. * * * * *