Answer :USMLE step 2 Mcq 78: A 70 year old white woman was admitted fr treatment of an acute non-Q wave myocardial infarction




Correct Answer: A

The correct answer is a) increased resonance on percussion The signs given should alert you to the presence of a pneumothorax. The CXR in this case reveals two signs of pneumothorax: a visible pleural line with absent lung markings peripherally and a deep sulcus sign. The "deep sulcus" is due to the anterior pneumothorax accentuating the costophronic angle. What is lung resonance ? The lung is filled with air (99% of lung is air), hence, percussion of it gives a resonance. This step helps identify areas of lung devoid of air. How do you measure lung resonance ? Keep the middle finger firmly over the chest wall along intercostal space and tap chest over distal interphalangeal joint with middle finger of the opposite hand. The movement of tapping should come from the wrist. Tap 2-3 times in a row. Do not leave the percussing finger on , otherwise you will dampen the sound. Listen and feel the resonance. Percuss the chest all around. Stand back, have the patient cross arms to shoulder. This maneuver will wing the scapula and expose the posterior thorax. Percuss starting from top to bottom of thorax on either side. Compare the resonance by percussing the corresponding spaces alternately. Stand on one side and with your flat of hand, tap the chest from top to bottom and from side to side to compare. Then, have the patient keep their hands over head and percuss axilla. Then move to the front and percuss anterior chest clavicles and supraclavicular space. Normal resonance Appreciate the dullness of the left anterior chest due to heart and right lower chest due to liver. Note the hyper-resonance of the left lower anterior chest due to air filled stomach. Normally, the rest of the lung fields are resonant. What causes ncreased resonance ? Decreased or increased resonance is abnormal. Increased resonances can be noted either due to lung distention as seen in asthma, emphysema, bullous disease or due to Pneumothorax. Decreased resonance is noted with pleural effusion and all other lung diseases. Experienced physicians are able to discriminate between dullness of pleural effusion from a consolidation or a mass lesion of lung. The dullness is flat and the finger is painful to percussion with pleural effusion. Example: Suppose there is dullness half way up the right hemithorax, it certainly rules out the consideration of pneumothorax. We have to decide whether it is pleural effusion or mass lesion. Physical Findings of Pneumothorax without Tension ,

       1. Mediastinum stays in middle since there is no positive pressure in the pleural space. The mediastinum and diaphragm are not displaced.

       2. Chest Expansion is dramatically decreased on the side of pneumothorax.

       3. There will be hyper-resonance on the side of pneumothorax due to the presence of air in pleural space. Loss of cardiac or hepatic dullness can be noted if there is sufficient air to overlay these structures.

     4. Breath Sounds are dramatically decreased secondary to decreased ventilation on the side of pneumothorax.

      5. Voice Transmission is decreased.

      6. There will not be any adventitious sounds.

      7. Hemi thorax will be enlarged on the side of pneumothorax due to loss of negative pressure in pleural space.

     8. Effort of Ventilation is increased in the acute stage, as recognized by respiratory rate and use of accessory muscles. After the acute event, patient can return to a state of comfort without a significant increased effort at breathing.

    9. Effect on function: Hypoxemia is mild and may not be recognized clinically. If you have stereophonic stethoscope you can appreciate the decreased breath sounds and poor voice transmission on the side of pneumothorax by simultaneous auscultation of both sides Pneumothorax with Tension The following are features unique to tension pneumothorax:

          1. Mediastinum gets pushed to opposite side.

          2. Diaphragm gets pushed downward resulting in decreased diaphragmatic excursion. In extreme cases it becomes concave upwards resulting in paradoxical movement with respiration.

         3. Intercostal bulge can be noticed due to increased pleural pressure.

         4. You may hear amphoric type of bronchial breathing. The bronchial tree is patent in the atelectatic lung. Bronchial breathing from the atelectatic lung is transmitted by tense air. This gives the metallic quality to bronchial breath sound.

        5. Voice Transmission is also increased with a characteristic metallic quality.

       6. Coin Sound: Transmission of coin tapping sound is increased on the side of tension pneumothorax. You need two half dollar silver coins to demonstrate this. Have one of your colleagues place one coin in back and tap it with the other while you listen in front. Compare the sound with the normal side. You will hear increased transmission of sound on the side of tension pneumothorax with a metallic tone to it.

       7. Neck Veins are distended and non-pulsatile. There is impediment to venous return because of increased pleural pressure. This results in small rapid pulse and falling blood pressure.

       8. Effort of Ventilation: A significant increased effort is noted with severe shortness of breath and use of accessory muscles of respiration.

       9. Effect on Function: Central cyanosis becomes evident. 


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