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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)


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

The mediastinal membrane