Examination of the chest
As with all areas of the body, examine the chest thoroughly, observing and recording any abnormalities:
Observe the breathing pattern and place a hand on the chest during breathing to check for crackles, broken ribs, etc.
External wounds: Check for swellings, bite wounds, claw wounds, bullet wounds, puncture wounds, etc. Small puncture wounds on the chest wall must be explored carefully to determine whether they penetrate into the thoracic cavity in which case there is a significant risk of intra-thoracic infection and collapse and/or damage to lungs.
Detection of pulse: The rhythmical throbbing of arteries as blood is propelled through them by the beating heart is known as a pulse. The easiest places to feel a peripheral pulse in a tiger are the femoral artery in its groin or the coccygeal artery on the ventral surface of the tail. (The pulse is easiest to palpate in the proximal part of the tail). A pulse can also be detected on the medio-dorsal aspect of the metatarsus in the hind foot (dorsal pedal artery – see pic below). The pulse should be taken at the same time the heart is auscultated to check they are synchronised, and to assess for arrhythmia’s.
Listen to the heart: It is essential to auscultate (listen) to the heart using a good quality stethoscope. This is easiest to do in a quiet environment although in the field that may be difficult. At least ask those around to keep quiet while the examination is performed.
The apex heartbeat can be most easily heard on the left hand side of the tiger in the 6th intercostal space (i.e the gap between the 6th and 7th ribs) – approximately just caudal to where a flexed elbow would touch the chest wall. If a large tiger is lying on its right side it may be necessary to listen to the apex beat from the right. A normal heart generates two distinct sounds when auscultated – S1 and S2 – sounds often described as “lub” and “dub”. The listener should hear “lub” followed by “dub” each time the heart beats. S1 is a low frequency sound occurring at the beginning of systole (contraction of the heart) and is caused by the closure of the atrioventricular (or A-V) valves in the heart between the large ventricle chambers and the smaller atrial chambers (mitral and tricuspid valves). Clinically, S1 corresponds to the pulse. S2 represents closure of the semilunar (aortic and pulmonary) valves. Abnormal heart sounds (or murmurs) can be caused by several factors including incompetence of valves and structural abnormalities in the heart. The interpretation of abnormal heart sounds is outside the scope of this resource and requires the input of an experienced veterinarian. NB: Some anaesthetic agents (especially anaesthetic combinations including medetomidine) can also cause cardiac murmurs which are generally of little clinical significance.
Experienced veterinarians will often wish to listen carefully to the heart sounds over the various cardiac valves to detect abnormal function and even structure. However, due to the large size of the tiger’s chest this can be challenging. At a basic level it is sufficient to record a heart rate and listen for any arrythmias (irregularities in beat pattern) or murmurs (abnormal sounds).
Listen to all areas of the lungs: All areas of both lungs and the trachea should be auscultated (see pictures below). Again this should be performed in a quiet environment. Normal lung sounds in a tiger will be fairly quiet with soft breath sounds throughout. Listen for abnormal sounds – gurgling, rasping etc – see table below.
|Abnormal sound||Location||Cause of sound||Common diseases|
|Wheeze (high pitched whistling)||Upper or lower airways||Air moving through narrowed or collapsed airways.||Bronchitis, pneumonia, respiratory tract infection, pulmonary oedema, anaphylaxis|
|Rhonchi (low pitched rattling/snoring)||Upper airways||Large airway secretions causing obstruction to air flow.||Bronchitis, pneumonia|
|Rales (small clicking, bubbling, crackling or rattling sounds)||Lung - lower airways||Air passing through fluid, pus or mucous in lower airways||Pulmonary oedema, pneumonia.|
|Stridor (high pitched harsh, grating sound)||Upper airways during inspiration especially||Air turbulence, obstruction||Mass in upper airways, foreign bodies|
|Stertor (snoring sound)||Nasal cavity, nasopharynx||Airway narrowing/ obstruction||Nasal foreign body/ mass|
Blood pressure measurement (indirect): Although measurement of indirect blood pressure (BP) is a valuable tool, it is rarely essential in the field. The tiger should be placed on its side and an inflatable cuff used to occlude an artery. A doppler probe is then placed over the artery distal to the cuff. Recommended sites for the doppler probe include:
- Palmar arterial arch on the ventral proximal metacarpal region
- Plantar arterial arch on the ventral proximal metatarsal region
- Median caudal artery on the ventral aspect of the tail
Coupling gel should be applied to the doppler probe and it should be taped in position so that the sound of blood flow can be detected. The cuff should then be positioned on the limb (avoiding joints) or tail proximal to the probe. There should be enough room to insert a small finger between the cuff and the tiger. The cuff is inflated to a pressure that occludes the blood flow so that the sound of blood flow stops. The pressure this occurs at is the systolic pressure. The cuff is then slowly deflated until the sound of blood flow is heard again. This is the diastolic pressure. Normal systolic blood pressure in anaesthetised tigers is 122-218 mmHg and normal diastolic pressure 85-159mmHg, but these are only guide values.
A number of reasonably-priced, automatic, indirect blood pressure measuring devices are available for human use, and these can be a simple solution to measuring indirect BP in tigers.
MORE ADVANCED DIAGNOSTIC TECHNIQUES:
Some advanced diagnostic techniques such as radiography, electrocardiography (ECG) and echocardiography (Echo) are undoubtedly valuable in investigating structures in the chest. However, these are specialist disciplines requiring expensive equipment and considerably veterinary skill and experience to conduct and interpret. Other advanced techniques require veterinary expertise, but can be performed with relatively simple equipment.
Endotracheal wash is a technique which involves the instillation of sterile saline into the upper airways (lower trachea and bronchi) and aspiration of the saline to allow analysis. If a lung infection is suspected this technique can be used to obtain a sample for cytology and culture of any pathogenic organisms. The culture results are then used to guide treatment. The tiger should be intubated with a sterile endotracheal tube. A long sterile urinary catheter (e.g. a male dog catheter 4-6 Fr. The length of the catheter should be checked against the endotracheal tube before the procedure and the packaging of the catheter marked at the point where the catheter will extend 2-3mm beyond the end of the endotracheal tube) is advanced down the endotracheal tube to the pre-marked length. To avoid contamination the catheter should be inserted by feeding it through the sterile packaging. 0.25ml/kg warmed sterile saline should then be injected through the catheter and immediately aspirated back. The injection of saline and aspiration should be repeated 2-3 times as required, a process helped by using a 3-way tap attached to the free end of the catheter. Some of the harvested fluid should be placed in a sterile plain tube for culture and some also placed in an EDTA tube for cytology.
Bronchoalveolar lavage is a more invasive technique involving instillation of sterile saline into the lower airways followed by its aspiration for analysis. This has the advantage of obtaining samples from much deeper in the lung, but carries a slightly higher risk of complications. This technique should not be attempted by the inexperienced.
Radiography is an advanced imaging technique using X-rays or similar ionizing radiation to view the internal form of an object. Diagnostic radiography does have a role in detecting diseases of the heart and lungs in tigers, but for adults a powerful machine is required. The technique is better suited to examine injuries of the lower limbs in large tigers, although it can be used to investigate all areas of smaller individuals. There are significant health and safety issues to be addressed by operators of xray equipment, and interpretation of the images is a specialist task. Battery operated units suitable for use in the field are available at a price.
Electrocardiography: An electrocardiogram, or ECG, is a simple test that can be used to check a heart’s rhythm and electrical activity. Sensors are attached to the skin and used to detect the electrical signals generated by the heart each time it beats. ECGs can provide evidence of anatomical changes within the heart, arrhythmias and pericardial and pleural disease. To be diagnostically useful an ECG is best conducted and interpreted by an experienced veterinarian.
Echocardiography (or cardiac ultrasonography) is an extremely useful technique to investigate the structure and function of the heart, although the equipment is expensive and requires specialist training to use effectively. Echocardiography can be used to investigate the anatomy of the heart chambers, valves, large blood vessels and the pericardial sac around the heart. The function of the heart can also be assessed by imaging blood flow characteristics through the organ. For adult tigers a 3.5MHz convex probe is recommended. A detailed description of the equipment and its use will not be given here, but there are a range of relevant textbooks that can be consulted – eg Schartz and Johnson 2008.