Clinical information
A 47 year old male was admitted to ICU following a high speed MVA. On arrival in ED, he had a GCS of 7 and was intubated for airway protection. Apart from his reduced conscious level, he appeared to have no other injuries. Trauma radiographs, including a chest x-ray and plain x-ray of his pelvis, were unremarkable. CT scanning of his brain and C-spine identified a small frontal contusion, but no cervical spine injury. He was admitted to ICU for ongoing care.
On admission to ICU, he had a routine chest x-ray.
Questions
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What are the most striking abnormalities on this chest radiograph?
Answer
- Left sided deep sulcus sign, consistent with the presence of a left sided pneumothorax
- Right subclavicular venous catheter that deviates cephalad up the right internal jugular vein
- The ETT tip does not appear to be optimally placed and may need advancement further into the trachea
- The nasogastric tube tip is adequately below the level of the diaphragm
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[su_spoiler title=”Question 2″]
What is the pathological explanation for the appearance of a possible pneumothorax and what could be the causes in this case?
Answer
- The presence of air in the pleural space (i.e. a pneumothorax) enhances the contrast between the lung and the diaphragm and chest wall, such that the costophrenic rescess becomes more apparent, showing up as a “deep sulcus sign” on the CXR.
- Causes in this case:
- Traumatic pneumothorax at the time of the MVA/MVC; e.g. rib fracture [The rib fracture may not be visible on the CXR], forceful expiration against a closed glottis
- Iatrogenic – high airway pressure during or after intubation; e.g. overventilation ? volutrauma / barotrauma, inadequate neuromuscular blockade ? coughing ? barotrauma
- Iatrogenic – traumatic / repeated attempts to insert the nasogastric tube
- Iatrogenic – during insertion of the subclavian catheter (Less likely as it has been sited on the contralateral side [but still worth mentioning as it displays an open mind and a ranking of probability]).
- Underlying lung disease; e.g. asthma, pleural bleb, canabis use [Maybe that’s why he crashed in the first place], bronchiectasis, alpha-1 AT deficiency [Beginning to stretch it a bit, but still valid as long as it is not top of your list]
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[su_spoiler title=”Question 3a”]
How would you clinically confirm your radiographic suspicion of a pneumothorax?
Answer
Can be difficult in the ICU environment, with low sensitivity and specificity:
- Reduced chest wall movement with ventilation on the side of the pneumothorax
- Increased / hyper-resonance on the side of the pneumothorax
- Decreased breath sounds on the side of the pneumothorax
- Look for features of clinical tension – may be confounded in the setting of trauma due to hypovolaemia from other injuries
- Also look for evidence of injury on that side of the chest, such as bruising, rib tenderness, subcutaneous emphysema
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[su_spoiler title=”Question 3b”]
How might you confirm your radiographic suspicion of a pneumothorax from the ventilator parameters?
Answer
SIMV
- Rising FiO2 requirements [This is better than stating falling SpO2 or SaO2, as these are not ventilator parameters per se, which is what has been asked, and increasing the FiO2 is generally the response to a falling SpO2]
- Rising mean airway pressure, especially in volume control mode. An increasing end-expiratory airway pressure is also recorded. Pressure volume loop may start to demonstrate a “bird’s beak” appearance [See the “Respiratory monitoring” study notes in the Fellowship exam section].
- Falling Vt, especially in pressure control mode
- Falling Vte (expiratory tidal volume) – though the breath to breath change is likely to be very small and unlikely to trigger any alarms until quite late
PSV
- Similar changes as SIMV pressure control mode, but may also demonstrate increasing resp rate, as the patient is breathing spontaneously
- Ventilator dysynchrony [Patient fighting the ventilator due to increasing respiratory distress as the pneumothorax progresses]
For a review of these features with some case studies, there is an article from all the way back in 1975 on this topic: ANESTHESIA AND ANALGESIA, Vol. 54, No. 6, Nov.-Dec. 1975, pg 730-735
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[su_spoiler title=”Question 4″]
Outline how bedside ultrasound might be used to confirm or refute the diagnosis?
Answer
In B-mode (real-time 2D), sonographic presence of “lung slide”, “A-lines” and “B-lines” suggest normal lung proximity to the chest wall at that probe position. The presence of these features needs to be demonstrated at several locations across the chest wall to exclude a pneumothorax. The presence of “lung point” suggests a pneumothorax
In M-mode, the replacement of the normal “seashore” appearance with intermittent touching of lung tissue against the chest wall with inspiration, suggests a small pneumothorax. With a larger pneumothorax, the lung will no longer touch against the chest wall.
The ICU Sonography website, at http://www.criticalecho.com/content/tutorial-9-lung-ultrasound, has a good tutorial on lung ultrasound, with plenty of still images and recorded cine-loops. The site is run by a couple of FJFICM intensivists from the Christian Medical College Hospital in Vellore, Tamil Nadu and is well worth a visit.
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