1 General Consideration of Clinical Problems and Methods

Introduction

In the investigation of any animal disease prob­lem, the veterinarian must, of necessity, under­take a careful and thorough clinical examination with the object of recognizing the nature of the affection, so that effective treatment and, where practicable, control measures are adopted. The situation is rendered complex by the necessity to deal with a variety of species of domestic animals and birds, with, in more recent years, the addition of a variety of exotic animal pets and fish. It is hoped that, with the passing of time, increasing specialization on the part of practising veterina­rians will resolve some of the apparent problems thus presented. In general, however, the same principles may be applied in all cases to deal with the diverse difficulties that clinical diagnosis presents. It must be emphasized at the outset that performing a clinical examination involves a great deal more than directing attention to the patient; consideration must also be given to the past and the immediate circumstances of the animal, and to the environment. Not infre­quently careful consideration of all these facets of a disease situation leads to the emergence of information, otherwise likely to have been over­looked, which significantly assists the diagnosis. All the relevant observations accruing from such a planned investigation should be carefully recorded for final analysis. The tyro clinician is well advised to adopt the habit of recording clinical data as the soundest basis for expanding the individual's experience and expertise.

The application of clinical methods in a sys­tematic manner enables the veterinarian, on the basis of a sound knowledge of anatomy, physiology, pathology and animal behaviour (ethology), to recognize ailing, as distinct from healthy, ani­mals. Obviously an important requisite is com­plete familiarity with the state of health in all species. The presence of disease is revealed by certain changes in the structure of an organ or tissue 'and/or its function, as well as in the be­haviour of the whole living organism. Such changes, which may be quantitative, qualitative or both, are described as the clinical signs of disease, and the process of deducing from them the nature of the disease that is present is des­cribed as 'making a diagnosis'.

It is not always possible to make an exact diagnosis, that is to establish not only the site, but also the cause and nature of the abnormality, but a special effort should be made to establish at least the aetiological diagnosis, i.e. to deter­mine the cause of the disease, for without this knowledge treatment cannot be other than em­pirical. If the disease is not recognizable with certainty, the diagnosis is said to be tentative. If a particularly prominent clinical sign is present, but the site and cause of the primary abnormality are unknown, a so-called symptomatic diagnosis may have to suffice, e.g. jaundice, which is not a disease but only a clinical sign of a variety of diseased conditions, including obstruction of bile ducts, certain protozoan infections of the blood and, among others, some of those diseases which cause toxic damage to the liver. When­ever possible the diagnosis should be based on a rational consideration of all the evidence avail­able from the three facets of any disease situa­tion; such a reasoned conclusion will enable the most useful and worthwhile aids to diagnosis to be selected. It must be said, however, that in veterinary medicine all too many diagnoses are made on the basis of previous experience; the method breaks down when the clinical pattern of a disease changes to an unusual one or a new disease is seen for the first time.

'Giving a prognosis' means expressing an opinion as to the probable duration and outcome of the disease. The owner is interested, chiefly, in the prognosis; that is to say, he wishes to know whether an early recovery is to be expected, whether the animal will be restored to its original usefulness, and so on. For the veterinarian, however, the diagnosis is of primary importance because only this knowledge will enable him to give the required prognosis and, when necessary, to provide treatment or institute control or prophylactic measures.

There are very few individual clinical signs on the existence of which a diagnosis can be accur­ately based. These are known as pathognomonic signs (e.g. positive venous pulse in tricuspid in­sufficiency; rusty-brown watery nasal discharge in the exudative stage of infectious equine pneumonia; prolapse of the membrana nictitans in tetanus in the horse). If only pathognomonic clinical signs had to be considered, the technique of clinical diagnosis could easily be mastered. However, since the majority of clinical signs may arise from a variety of causes, diagnosis demands, in every individual case, the application of precise knowledge and intellectual effort, along with practical experience, in a rational way.

It will be clear from what has already been said that the study of clinical signs as such (clinical propaedeutics) is a necessary prelimi­nary to the study of diagnosis. The student must therefore make himself familiar with the appear­ance of the various clinical signs in each species, the methods of demonstrating or eliciting them where necessary, their possible origin and their significance.

Methods used in the Detection of Clinical Signs

The clinical examination is performed by means of the senses of sight, touch, hearing and smell, and is comprised of two major parts: (a) the general and particular examination in­cluding the initial inspection and (b) the physical examination.

The preliminary general inspection, which is carried out some distance away from the animal, should never be omitted, and might best be undertaken during the period devoted to obtain­ing the history of the case and taking note of the environment. The outer surface of the body and the external orifices are also examined with the unaided eye at a somewhat later stage of the pro-ceedings. The interior of hollow viscera, not otherwise visible from the exterior, can be examined (endoscopy) with the aid of instru­ments with built-in illumination, collectively known as endoscopes. Radiological apparatus also enables certain of the internal structures of the body to be visualized.

The techniques used in the physical examina­tion are as follows:

Palpation

This includes direct palpation which consists of handling the tissues by means of the fingers, for which one or both hands may be employed, and indirect palpation with a probe. The object of palpation is to detect the presence of pain in a tissue by noting increased sensitivity. Other im­portant pathological changes that may be detec­ted in an organ or tissue by this means include variation in size, shape, consistency and tem­perature. The conditions identified by palpation may be defined by terms such as the following: resilient, when a structure quickly resumes its normal shape after the application of pressure has ceased; doughy, when pressure causes pit­ting as in oedema; firm, when the resistance to pressure is similar to that of the normal liver; hard, when the structure possesses bone-like consistency; fluctuating, when a wave-like movement is produced in a structure by the application of alternate pressure (see p. 78); or emphysematous, when the structure is swollen and yields on pressure with the production of a crepitating or crackling sound.

Percussion

This is a physical method of examination in which, by means of striking a part of the body, it is possible to obtain information about the con­dition of the surrounding tissues and, more par­ticularly, the deeper lying parts. The value of the method arises from the vibrations imparted at the point of impact producing audible sounds, which vary when reflected back, because of the difference in density of the tissues. Percussion is used mainly for the examination of the thorax (lungs, heart), but it is also employed in relation to diseases of the abdominal cavity, paranasal sinuses, in subcutaneous emphysema, etc.

The traditional method of carrying out per­cussion in large animals is by means of a circular or oval, ivory or hardwood plate (a pleximeter) and a hammer with a firm rubber end (a per­cussion hammer or plexor)—hammer-pleximeter percussion. The fingers may be used instead of a pleximeter disc.

In small animals, percussion is performed by using both hands, the middle finger of one hand acting as a pleximeter and the flexed middle finger of the other hand as a hammer (finger-finger percussion). If desired the finger may be used to strike a pleximeter or a hammer to strike the finger. The use of the fingers is always preferable in animals of any size as they produce little or no additional sound. When the finger, or a pleximeter, is placed over the area being struck the procedure is termed mediate percussion; striking the part directly with the fingertips, which is the method most commonly employed, is termed immediate percussion.

The diagnostic value of percussion in large animals is rather limited because the internal organs are too large, and the overlying tissues (muscles, subcutaneous fat) in many instances too thick, to recognize the limits of the organs or abnormal areas, unless the clinician is highly experienced. The presence of subcutaneous fat in the pig, and the wool coat in the sheep, makes the application of percussion impracticable in these species.

General rules to be observed while applying percussion:

1. The pleximeter, or finger when serving the same purpose in the mediate method, must be pressed firmly against the body surface, so that no air space exists between the pleximeter and skin.

2. The hand using the hammer must be at a higher level than the hand holding the plexi­meter. The handle of the hammer must not be held too firmly, but must rest loosely between the thumb and first two fingers, in order to deliver a swinging blow. The movement should come from the wrist, and not from the elbow or shoulder. When the finger acts as a striker the hands should be held in the same relative position and the movement should involve the wrist.

3. The blows should fall perpendicularly on to the pleximeter, or directly on to the part of the body being examined, because blows delivered

from any other angle will evoke a response which may lead to misinterpretation.

4. The whole of the area requiring examination should be percussed in a systematic manner, and not only in isolated places, otherwise localized pathological changes in the structure of under­lying tissues or organs may not be detected.

5. When the mediate method is employed the pleximeter should be struck only when it is stationary. It is then moved a distance equal to its own width, blows of equal force being de­livered at each point.

6. The force of the blows should be no heavier than is necessary; the lighter they are, within reason, the easier it is to distinguish differences in resonance.

Strong percussion is used in the examination of deeply situated structures, and weak percus­sion for those more superficially situated. Very gentle percussion (threshold percussion), when applicable, yields particularly accurate infor­mation.

Modified forms of percussion include ballottement and fluid percussion. In the former an interrupted, firm push-stroke is applied to an appropriate part of the body with the object of evoking motion in the underlying organ and causing it to rebound on to the fingertips. Iden­tifying the presence of the fetus in advanced pregnancy in the ox is achieved by this technique. The latter enables free fluid in a body cavity to be recognized by percussing the surface of the body on one side, and detecting the fluid wave produced by palpation of the opposite side.

These rules are intended only for general guidance. Percussion requires much practice, and its value depends on experience, and when instruments are used, familiarity with a particu­lar one is most important. Other general factors, for which allowance must be made in the inter­pretation of the results of percussion, are the thickness of the body wall and the amount of air or gas in the underlying viscus; in the area of the thorax, percussion over a rib must not be compared with percussion on an intercostal space.

The quality of the sounds produced by per­cussion are classified as: resonant, which is characteristic of the sound emitted by air containing organs, such as the lungs; tympanic, the sound produced by striking a hollow organ containing gas under pressure, e.g. tympanitic rumen or caecum; dull, emitted by a solid organ like the liver or heart.

Auscultation

Auscultation means listening to the sounds produced by the functional activity of an organ located within a part of the body, in order to assess its condition. The method is used chiefly in the examination of the lungs, trachea, heart and certain parts of the alimentary tract.

Auscultation may be performed by either the direct or the indirect method. The indirect method, employing a suitable stethoscope (Fig. 1a), is the more preferable and, with adequate experience, will ensure more uniform results than the direct method. In veterinary practice, the flexible binaural stethoscope is the one most commonly employed. It consists of a chest-piece connected by fairly thick-walled, flexible rubber tubing (plastic tubing allows the entry of extraneous environmental sounds, and some loss of functional sounds) to two ear-pieces. The chest-piece, which is acoustically designed, is shaped like an open bell and should have a rubber rim, the purpose of which is to eliminate friction between the chest-piece and the hair of the animal's coat. For large animals, a chest-piece about 2-5 cm or so in diameter is satisfac­tory, but for cats, puppies and small dogs, the size of chest-piece used for human infants is preferable. The phonendoscope (Fig. 1в) re­sembles the stethoscope in general appearance, but its chest-piece, which may be up to 5 cm in diameter, is surmounted by a hard plastic dia­phragm which is placed in contact with the surface of the body. Since the skin is thickly covered with hair in most animals, the resultant frictional sounds seriously interfere with aus­cultation. There is provision, with the more elaborate phonendoscopes, for fitting on an additional diaphragm with a screw-in pedestal mount, which enables the clinician to identify functional sounds arising from restricted areas, such as the heart valves in large animals. For all general purposes, however, a stethoscope of the type described is to be preferred in veterinary clinical work. A detailed description of the normal and abnormal sounds heard during auscultation of the various organs will be given later in the appropriate parts of the text.

Direct auscultation is performed by placing the ear in contact with the body surface over the organ to be examined. The disadvantages of the method are obvious and include difficulty in maintaining contact in restless animals, friction sounds which arise from opposing movements between the clinician and the coat of the animal, difficulty in excluding extraneous sounds arising from the immediate environment of the animal, the coat of the animal may be wet, soiled with dirt, faeces or skin secretions, or the skin may harbour ectoparasites such as ticks, fleas, lice, mange mites, ringworm fungi or bacteria poten­tially pathogenic to man.

Methods of Restraint

Since animals often resist many of the clinical examination procedures, it may be necessary to employ some suitable means of restraint, in order to be able to carry out the examination safely and without danger to the clinician or his assistants. The methods available may be clas­sified as physical restraint when various instru­ments are employed (Fig. 2) or chemical restraint when drugs inducing varying degrees of sedation or immobilization are administered.

In the horse, a twitch is applied to the upper or lower lip or to the ear (Fig. 3); a loop of strong cord or soft rope is applied to the appro­priate part and twisted up tightly enough to cause just sufficient pain to distract the animal's attention away from the part of the body being examined. It is sometimes useful to cover the eyes with the hands or to place a sack over the head as a hood or blind.

In the ox, both horns are held or tied to a strong post, or the nasal septum is gripped between the thumb and one finger (Fig. 4) or with 'bull-dogs' (Fig. 5); leg twitches are also employed. In the horse and ox, in order to obtain protection against kicks from the hind-foot, the forefoot is held up in the flexed position on the side on which the clinician is standing. In the cow an udder kinch (see Fig. 181, p. 257) may be used for the same purpose. The pig is restrained by means of a wire or rope twitch (see Fig. 188, p. 264), or a pair of blunt tongs applied to the upper jaw or snout, or by con­fining it in a corner with a small gate or hurdle. Small animals are restrained by placing them on a table in the upright, lateral or dorsal position. In most instances the owner will assist in hand­ling his pet animal for this purpose. In the dog a tape muzzle (Fig. 6) or a leather muzzle (Fig. 7) is used. For handling parrots or other birds, or animals apt to bite, thick leather gloves are worn.

Sometimes the animal is so refractory, because of fear or pain, that even with the aid of physical restraint examination is unsafe or impracticable. Use must then be made of special aids such as stocks or a crush (Fig. 8), hobbling and casting or the administration of sedative, tranquillizing, narcotic or immobilizing drugs (chemical re­straint). Drugs that are useful for this purpose include those with ataractic or tranquillizing properties and include acepromazine, acetylpromazine, chlorpromazine, promazine and trimeprazine; members of this group can be used in most species of animals. Chloral hydrate is used mainly in large animals; its effect varies from sedation to narcosis depending upon the amount given. Morphine also induces narcosis after an initial phase of excitement, which varies in intensity according to the species; because of its excitatory action it is very rarely used for restraint purposes. Of the more recently intro­duced sedative drugs, azaperone is of especial value in the pig and xylazine in cattle. The mor­phine derivative, etorphine, is capable of pro­ducing profound narcosis and is used when immobilization is desirable. Muscle relaxants such as succinylcholine have been employed for the latter purpose.

Morphine and its derivatives pethidine and etorphine are unsuitable for cats; short-acting anaesthetics of the barbiturate group or the phenothiazine psychotherapeutic drugs are often used in this species.

Needless to say, physical or chemical restraint should, whenever possible, not be applied prior to such preliminary procedures as general observation of the patient, taking the pulse and temperature and noting the character of the respirations. It is important to perform all the physical manipulations in a quiet and gentle manner in order to avoid disturbing the patient.