To use clinical signs and differentiate different lung conditions.

Before we set out to discuss all of these, I am going to point out some key pointers for certain conditions.

Succussion splash: Gastric dilatation or Hydopneumothorax.

Localized  paradoxical breathing: Rib fractures with flail rib.

Pulsus paradoxus: Severe obstructive lung disease (COPD/Asthma) or Cardiac tamponade.

Now the principles which will simplify lung signs.

1. Sound passes best through a solid.

2. Sound gets impaired if there are different mediums that it has to go through.

3. When sound passes through liquid, the high frequency sounds pass through better. This leads to egophony - or the A to E sound (as it is known as in the US)

Auscultation: Which lobe over which part of the chest? Right middle lobe is best heard in right axilla; lingula in left axilla; upper lobes heard anterior to the middle and lower lobes heard posterior to it. The only EXCEPTion is the uppermost posterior 1/4th of the chest where again - a part of the upper lobe is heard. This helps localize pathologic processes that follow anatomic boundaries (e.g. pneumonia). Some disease processes (e.g. pulmonary edema, bronchoconstriction) are diffuse, producing abnormal findings in multiple fields.

1. The stethoscope's ear pieces should be directed forwards into the ear. Adjust the head of the scope so that the diaphragm is active. If you're not sure, scratch lightly on the diaphragm, which should produce a noise. If not, twist the head and try again. Gently rub the head of the stethoscope on your shirt so that it is not too cold for the patient's skin.
2. The upper aspect of the posterior fields (i.e. towards the top of the patient's back) are examined first. Listen over one spot and then move the stethoscope to the same position on the opposite side and repeat. This helps compare with the other. The entire posterior chest can be covered by listening in roughly 4 places on each side.
3. The lingula and right middle lobes can be examined while you are still standing behind the patient.
4. Then, move around to the front and listen to the anterior fields in the same fashion. This is generally done while the patient is still sitting upright. Asking female patients to lie down will allow their breasts to fall away laterally, which may make this part of the examination easier.

A few additional things worth noting.

1. Don't get in the habit of performing auscultation through clothing.
2. Ask the patient to take slow, deep breaths through their mouths while you are performing your exam. This forces the patient to move greater volumes of air with each breath, increasing the duration, intensity, and thus detectability of any abnormal breath sounds that might be present.
3. Sometimes it's helpful to have the patient cough a few times prior to beginning auscultation. This clears airway secretions and opens small atelectatic (i.e. collapsed) areas at the lung bases. Before one makes a diagnosis of crackles at the bases, one must have a patient do this to make sure that this does not clear with coughing.
4. If the patient cannot sit up (e.g. in cases of neurologic disease, post-operative states, etc.), auscultation can be performed while the patient is lying on their side. Get help if the patient is unable to move on their own. In cases where even this cannot be accomplished, a minimal examination can be performed by listening laterally/posteriorly as the patient remains supine.
5. Requesting that the patient exhale forcibly will occasionally help to accentuate abnormal breath sounds (in particular, wheezing) that might not be heard when they are breathing at normal flow rates.

What can you expect to hear? A few basic sounds to listen for:

1. A healthy individual breathing through their mouth at normal tidal volumes produces a soft inspiratory sound as air rushes into the lungs, with little noise produced on expiration. There is a long inspiration, then a gap and then a short expiratory phase. These are referred to as vesicular breath sounds.
2. Wheezes are whistling-type noises produced during expiration (and sometimes inspiration - if a patient has these, one must suspect a fixed defect in the airway like tracheal stenosis or a foreign body) when air is forced through airways narrowed by bronchoconstriction, secretions, and/or associated mucosal edema. As this most commonly occurs in association with diffuse processes that affect all lobes of the lung (e.g. asthma and emphysema) it is frequently audible in all fields. In cases of significant bronchoconstriction, the expiratory phase of respiration (relative to inspiration) becomes noticeably prolonged. Clinicians refer to this as an increased I to E ratio. Normal is approximatley 1:2 (i.e. expiration twice as long as inspiration) though actual timed measurements are neither practical nor reliable. Focus instead on simple observation, noting whether E seems >> I. The greater the difference, the worse the obstruction. Occasionally, focal wheezing can occur when airway narrowing if restricted to a single anatomic area, as might occur with an obstructing tumor or bronchoconstriction induced by pneumonia. Wheezing heard only on inspiration is referred to as stridor and is associated with mechanical obstruction at the level of the trachea/upper airway. This may be best appreciated by placing your stethescope directly on the trachea.
3. Rales (a.k.a. crackles) are scratchy sounds that occur in association with processes that cause fluid to accumulate within the alveolar and interstitial spaces. The sound is similar to that produced by rubbing strands of hair together close to your ear. Pulmonary edema is probably the most common cause, at least in the older adult population, and results in symmetric findings. This tends to occur first in the most dependent portions of the lower lobes and extend from the bases towards the apices as disease progresses. Pneumonia, on the other hand, can result in discrete areas of alveolar filling, and therefore produce crackles restricted to a specific region of the lung. Very distinct, diffuse, dry-sounding crackles, similar to the noise produced when separating pieces of velcro, are caused by pulmonary fibrosis, a relatively uncommon condition.
4. Dense consolidation of the lung parenchyma, as can occur with pneumonia, results in the transmission of large airway noises (i.e. those normally heard on auscultation over the trachea… known as tubular or bronchial breath sounds) to the periphery. In this setting, the consolidated lung acts as a terrific conducting medium, transferring central sounds directly to the edges. It's very similar to the noise produced when breathing through a snorkel. Furthermore, if you direct the patient to say the letter 'eee' it is detected during auscultation over the involved lobe as a nasal-sounding 'aaa'. These 'eee' to 'aaa' changes are referred to as egophony. The first time you detect it, you'll think that the patient is actually saying 'aaa'… have them repeat it several times to assure yourself that they are really following your directions!
5. Secretions that form/collect in larger airways, as might occur with bronchitis or other mucous creating process, can produce a gurgling-type noise, similar to the sound produced when you suck the last bits of a milk shake through a straw. These noises are referred to as ronchi.
6. Auscultation over a pleural effusion will produce a very muffled sound. If, however, you listen carefully to the region on top of the effusion, you may hear sounds suggestive of consolidation, originating from lung which is compressed by the fluid pushing up from below. Asymmetric effusions are probably easier to detect as they will produce different findings on examination of either side of the chest.
7. Auscultation of patients with severe, stable emphysema will produce very little sound. These patients suffer from significant lung destruction and air trapping, resulting in their breathing at small tidal volumes that generate almost no noise. Wheezing occurs when there is a superimposed acute inflammatory process (see above).

Most of the above techniques are complimentary. Dullness detected on percussion, for example, may represent either lung consolidation or a pleural effusion. Auscultation over the same region should help to distinguish between these possibilities, as consolidation generates bronchial breath sounds while an effusion is associated with a relative absence of sound. Similarly, fremitus will be increased over consolidation and decreased over an effusion. As such, it may be necessary to repeat certain aspects of the exam, using one finding to confirm the significance of another. Few findings are pathognomonic. They have their greatest meaning when used together to paint the most informative picture.