Flashcards in CR: PBL 4 (Pneumothorax) Deck (38):
Describe the physiology of inspiration
Diaphragm contracts --> abdominal contents move down and ribcage moves up and out--> decreases thoracic pressure --> air moves in
Describe the physiology of expiration
Diaphragm relaxes (dome) and ribcage moves in and down --> increased thoracic pressure --> air moves out
Which muscles are used in deep inspiration?
Accessory muscles: external intercostals and sternocleidomastoids contract to pull ribcage up and out
Which muscles are used in forced expiration?
Internal intercostals and abdominal muscles pull ribs in and down
What is a 'pneumothorax'?
When there is air trapped between the lung and the chest wall
Name some risk factors/causes of pneumothorax
Men 4x more likely than women, under 40s, smokers, underlying respiratory disorder, chest trauma
How may pneumothorax be diagnosed on lung auscultation?
Breath sounds diminished/absent on affected side partly due to the air in the pleural space dampening the sound
How may pneumothorax be diagnose by chest x-ray?
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
When might a CT scan be conducted to check for a pneumothorax?
In trauma patients who cannot stand as X-ray will miss 1/3 of pneumothorax in those who can't stand
When might an ultrasound be conducted to check for a pneumothorax?
Rapid size quantification in emergency trauma situations
Name the 4 different types of pneumothorax
Primary spontaneous, secondary spontaneous, traumatic and tension pneumothorax
Describe primary spontaneous pneumothorax
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
Describe secondary spontaneous pneumothorax
Develops as a complication of an existing lung disease especially with COPD
What conditions increase the risk of pneumothorax?
Pneumonia, TB, cystic fibrosis, lung cancer
Describe traumatic pneumothorax
Blunt trauma/penetration of chest wall, most commonly due to penetration of sharp, bony points at new rib fracture
What is a tension pneumothorax?
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
How does the body respond to pneumothorax?
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
Define pleural pressure
Pressure within the pleural fluid between the lung and the chest wall
Define transpulmonary pressure
Difference between the alveolar pressure and the pleural pressure in the lungs (PL= Pa-Pl)
Define alveolar pressure
Pressure in the alveoli of the lungs
What is alveolar pressure ordinarily?
What is the treatment for pneumothorax?
Largely no treatment is used, x-ray may be taken to ensure repair OR aspiration of the trapped air
Why shouldn't you fly with a pneumothorax?
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
What happens to a normal thorax at the end of expiration?
Stretched lung recoils inwardly and chest wall recoils outwardly causing a negative pleural pressure
What happens in a pneumothorax at the end of expiration?
Pleural pressure will equal atmospheric --> transpulmonary pressure is zero --> and elastic recoil causes lung collapse
Describe the role of pressure differences in ventilation
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
What is tachycardia?
Abnormally rapid heart rate (greater than 100bpm)
What is tachypnea?
Abnormally rapid breathing (greater than 20 breaths/min)
Describe the pressure differences on inspiration in a pneumothorax
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
What is the intrapleural cavity?
Space between parietal and visceral membranes with serous fluid inbetween
How is intrapleural pressure generated?
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
What happens to the intrapleural pressure during a traumatic pneumothorax
Becomes equal to or greater than atmospheric pressure (ordinarily is negative)
Describe the symptoms of a pneumothorax
Sudden sharp pain in chest and back, shortness of breath, tachycardia, tachypnea, repeated dry coughing, reduced breath sounds
What structures are involved in inspiration?
Diaphragm supported by external intercostal muscles
Why does smoking or COPD increase the likelihood of pneumothorax?
Potentially makes the wall of any 'bleb' weaker and therefore is more likely to tear
How may pneumothorax be diagnosed on percussion?
Percussion of chest may be hyper-resonant (booming drum)
What is the treatment of tension pneumothorax?
Relieving air pressure immediately (puncture)