CR: PBL 4 (Pneumothorax)

Question 1

Describe the physiology of inspiration

Answer 1

Diaphragm contracts –> abdominal contents move down and ribcage moves up and out–> decreases thoracic pressure –> air moves in

Question 2

Describe the physiology of expiration

Answer 2

Diaphragm relaxes (dome) and ribcage moves in and down –> increased thoracic pressure –> air moves out

Question 3

Which muscles are used in deep inspiration?

Answer 3

Accessory muscles: external intercostals and sternocleidomastoids contract to pull ribcage up and out

Question 4

Which muscles are used in forced expiration?

Answer 4

Internal intercostals and abdominal muscles pull ribs in and down

Question 5

What is a ‘pneumothorax’?

Answer 5

When there is air trapped between the lung and the chest wall

Question 6

Name some risk factors/causes of pneumothorax

Answer 6

Men 4x more likely than women, under 40s, smokers, underlying respiratory disorder, chest trauma

Question 7

How may pneumothorax be diagnosed on lung auscultation?

Answer 7

Breath sounds diminished/absent on affected side partly due to the air in the pleural space dampening the sound

Question 8

How may pneumothorax be diagnose by chest x-ray?

Answer 8

Larger amount of black is likely to be pneumothorax (As air breached pleural cavity), collapsed lung (sometimes) may deviate the mediastinum and size of pneumothorax can be determined from distance between chest wall and lung

Question 9

When might a CT scan be conducted to check for a pneumothorax?

Answer 9

In trauma patients who cannot stand as X-ray will miss 1/3 of pneumothorax in those who can’t stand

Question 10

When might an ultrasound be conducted to check for a pneumothorax?

Answer 10

Rapid size quantification in emergency trauma situations

Question 11

Name the 4 different types of pneumothorax

Answer 11

Primary spontaneous, secondary spontaneous, traumatic and tension pneumothorax

Question 12

Describe primary spontaneous pneumothorax

Answer 12

No apparent reason for development thought to be due to tiny tear in lung apex (at blebs - bleb wall not as strong) –> air trapped between lung and chest wall

Question 13

Describe secondary spontaneous pneumothorax

Answer 13

Develops as a complication of an existing lung disease especially with COPD

Question 14

What conditions increase the risk of pneumothorax?

Answer 14

Pneumonia, TB, cystic fibrosis, lung cancer

Question 15

Describe traumatic pneumothorax

Answer 15

Blunt trauma/penetration of chest wall, most commonly due to penetration of sharp, bony points at new rib fracture

Question 16

What is a tension pneumothorax?

Answer 16

Involves progressive air build-up in pleural space –> deviates mediastinum to other side and obstructs venous return to the heart –> significant impairment of respiration and circulation

Question 17

How does the body respond to pneumothorax?

Answer 17

Air pressure in lung and pleura equalises, small tear will heal in a few days and then trapped air is gradually reabsorbed into the blood stream and lung gradually expands back to it’s original size

Question 18

Define pleural pressure

Answer 18

Pressure within the pleural fluid between the lung and the chest wall

Question 19

Define transpulmonary pressure

Answer 19

Difference between the alveolar pressure and the pleural pressure in the lungs (PL= Pa-Pl)

Question 20

Define alveolar pressure

Answer 20

Pressure in the alveoli of the lungs

Question 21

What is alveolar pressure ordinarily?

Answer 21

Zero

Question 22

What is the treatment for pneumothorax?

Answer 22

Largely no treatment is used, x-ray may be taken to ensure repair OR aspiration of the trapped air

Question 23

Why shouldn’t you fly with a pneumothorax?

Answer 23

The pressure drop at altitude means the volume of gas rises and therefore a greater volume of gas may enter the pleural cavity –> tension pneumothorax

Question 24

What happens to a normal thorax at the end of expiration?

Answer 24

Stretched lung recoils inwardly and chest wall recoils outwardly causing a negative pleural pressure

Question 25

What happens in a pneumothorax at the end of expiration?

Answer 25

Pleural pressure will equal atmospheric –> transpulmonary pressure is zero –> and elastic recoil causes lung collapse

Question 26

Describe the role of pressure differences in ventilation

Answer 26

Inspiratory muscles contract –> thoracic cavity expands –> pleural pressure becomes more negative –> transpulmonary pressure increases –> lungs inflate, increasing alveolar diameter –> alveolar pressure becomes subatmospheric –> air flows into lungs until pressure equilibriates

Question 27

What is tachycardia?

Answer 27

Abnormally rapid heart rate (greater than 100bpm)

Question 28

What is tachypnea?

Answer 28

Abnormally rapid breathing (greater than 20 breaths/min)

Question 29

Describe the pressure differences on inspiration in a pneumothorax

Answer 29

Inspiratory muscles contract –> thoracic cavity expans –> pleural pressure remains zero (in contact with atmosphere) –> tranaspulmonary pressure is zero –> lungs don’t inflate so alveolar diameter doesn’t increase –> no pressure gradient –> on recoil this causes lung collapse

Question 30

What is the intrapleural cavity?

Answer 30

Space between parietal and visceral membranes with serous fluid inbetween

Question 31

How is intrapleural pressure generated?

Answer 31

At the end of expiration the elastic recoil of the lungs (inward) and chest wall (outward) cause the generation of a negative/subatmospheric pressure in the intrapleural space

Question 32

What happens to the intrapleural pressure during a traumatic pneumothorax

Answer 32

Becomes equal to or greater than atmospheric pressure (ordinarily is negative)

Question 33

Describe the symptoms of a pneumothorax

Answer 33

Sudden sharp pain in chest and back, shortness of breath, tachycardia, tachypnea, repeated dry coughing, reduced breath sounds

Question 34

What structures are involved in inspiration?

Answer 34

Diaphragm supported by external intercostal muscles

Question 35

Why does smoking or COPD increase the likelihood of pneumothorax?

Answer 35

Potentially makes the wall of any ‘bleb’ weaker and therefore is more likely to tear

Question 36

How may pneumothorax be diagnosed on percussion?

Answer 36

Percussion of chest may be hyper-resonant (booming drum)

Question 37

What is the treatment of tension pneumothorax?

Answer 37

Relieving air pressure immediately (puncture)

Question 38

When one lung collapses, what prevents the other lung from collapsing?

Answer 38

The mediastinal membrane