Tasty Morsels of Critical Care 054 | Chest injuries

13 Dec

Welcome back to the tasty morsels of critical care podcast.

This time round we’re going to have a look at some chest wall injuries you should know about. The main reference here is Oh’s manual chapter 79.

The vast majority of what we see here is going to be simple pneumothoraces and the elderly patient with some rib fractures and contusions or a developing pneumonia. That kind of thing is our bread and butter. This post will focus on some of the more esoteric injuries which of course occur with disproportionate frequency in fellowship examinations.

There are a fairly small number of immediately life threatening injuries we need to recognise and the list could include:

  • tension PTX
  • open/sucking PTX
  • massive haemothorax
  • pericardial tamponade

Massive haemothorax is typically defined as >1500mls immediately or more than 200ml/hr is certainly a concern that should prompt a surgeon to have a look inside. While not mentioned in Oh, the main concern with these is a sort of “damned if you do, damned if you don’t” scenario. When presented with a massive haemothorax and hypotension, it is not always immediately clear what the primary physiology causing the hypotension is. For example a large haemothorax with tension physiology will kink the SVC and obstruct the IVC leading to hypotension due to low preload to the heart. They may also be hypotensive form frank hypovolaemia because all the blood is in the pleural cavity instead of the blood vessels. The bit you can’t account for is how much this tension phenomenon is actually providing some kind of tamponade effect and keeping the remaining intravascular volume in the vasculature. The concern here is that when you decompress the haemothorax the patient is no less hypovolaemic than they were before. The blood is now in the chest drain rather than the pleural space. This hasn’t really fixed the hypovolaemia but has relieved the tension phenomenon obstructing the preload to the heart. Unfortunately it may have also unleashed the remaining circulating volume to enter the pleural cavity and swiftly out through the plastic conduit you’ve placed and into the chest drain.

All this is a very long and convoluted way to say that it’s complicated. I think we will always end up draining that massive haemothorax but it would be wise to have someone capable of dealing with major bleeding inside the chest, immediately on hand.

Speaking of thoracotomies, what follows is a list of interventions that might be potentially useful to do once the chest is open.

  • drain pericardial tamponade, this is 1st, 2nd and 3rd for me in terms of importance and utility.
  • control intrathoracic bleeding – which is a nice coverall term for all the various bits blood could be squirting out of
  • control of massive broncho venous embolism. In this scenario a pulmonary vein is lacerated and air is being entrained into the left side of the heart. This is bad form as one might imagine so it would be wise to clamp it
  • control of massive bronchopleural fistula. Maybe a lung has been avulsed proximally and you can see the ET tube through the bronchus. All the Vt is disappearing into the pleural space and you should something to stop it
  • temporary blocking of the aorta. Commonly done in an attempt to preserve the circulating volume to the heart and brain. You might better achieve this without opening the chest with a REBOA or a SAAP catheter but that’s a whole different kettle of fish
  • internal cardiac massage.

In terms of aortic injuries these are often fatal pre-hospital but if you do find one they’ll typically be at the junction of the fixed and tethered aorta and the slightly more mobile arch. This junction occurs at the isthmus¬† just distal to the take off of the left subclavian. Your cardiac surgeons will likely decide but this may be an open repair or some kind of TEVAR type stenting if they survive long enough.

As mentioned briefly above, tracheobronchial injuries can be a real challenge. The classic region of injury in blunt trauma is at the take off point of the right main possibly because of the steep angle from the trachea. Expect to see a PTX and some mediastinal emphysema. In itself, that might not be a big issue but the real clincher to the diagnosis is the massive PTX and emphysema that occurs when they get intubated and transition to positive pressure ventilation. The flexible bronch is your friend here and allows you to confirm diagnosis as a quick look down the tube will let you see mediastinum and pleura through the bronchus.

Systemic air embolism is more typical in penetrating than blunt injuries and again the problems really begin when you move to positive pressure ventilation. In this instance we’re talking about pulm vein or maybe SVC injury. In negative pressure ventilation the pressure in the pleural space is lower than in the vasculature so blood will flow into the pleural space which is a problem in itself, however this pressure gradient will ensure air is not entering the circulation. Once intubated and in positive pressure ventilation then the gradient reverses and air can enter the vasculature with disastrous haemodynamic and even neurologic consequences if it enters the left sided circulation. A few rescue moves might be to selectively intubate the good lung, get them spontaneously breathing by reversing the rocuronium and get them on 100% O2 in the hope of switching out the non absorbable nitrogen for oxygen.¬† Thoracotomy is likely the next step but again a decision for the surgeons.

There are of course other chest injuries out there but I suspect that’s plenty of exam worthy minutiae for today.

Reading

Oh’s Manual Chapter 79

 

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