VAT Pleurodesis
Anaesthesia for VAT Pleurodesis
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A 20-year-old male is booked for video assisted thorascopic (VAT) pleurodesis of his right lung for recurrent pneumothorax.
Can you comment on the pre-operative CXR?
[An A4 photocopy of a frontal CXR is on the wall]
This is a frontal CXR and the most obvious findings are a right-sided apical chest drain with what looks like an persisting small pneumothorax and I’d say there was some left lower lobe collapse as well.
What sort of people get pneumothoraces? What are the general causes of pneumothoraces?
Trauma, patients with bullous lung disease, and tall thin usually Marfinoid males get spontaneous pneumothoraces. Ummm and patients who are positive pressure ventilated for whatever reason, either in the ICU or under anaesthesia.
Trauma from what?
Usually penetrating trauma, but also blunt trauma to the chest wall or to the lower airways, the lower trachea. I should also include iatrogenic causes, trauma from central lines.
Never forget us – anaesthetists.
Now the surgeon says he wants to do this VATS pleurodesis. Have you done one of those?
Ahh, no, but I understand the principles of anaesthesia for this procedure.
So tell us the principles of anaesthesia for that procedure.
So the main issues are that you have a pneumothorax and you don’t want to create a tension pneumothorax with positive pressure ventilation. There is also the potential issue of inability to ventilate because you have an air leak going from the pleura to externally if using positive pressure ventilation. So the principles are that I would like to use a spontaneously breathing anaesthetic with lung isolation. Often the surgeon will want to have the chest drain removed before the anaesthetic so they can prep the area properly.
So how will you achieve that if you want to have a spontaneously breathing anaesthetic and you want to put a tube down presumably? How will you put a tube down in a spontaneously breathing patient?
Well I wouldn’t paralyse them, I’d have them spontaneously breathing on sevoflurane and oxygen. I would topicalise the airway using lignocaine spray and when the patient was deep enough using respiratory signs and eye signs and with an end tidal sevoflurane that I consider to be high enough then I would perform laryngoscopy and intubate the patient with a double lumen tube.
What would you think was a high enough end tidal sevoflurane level?
It depends very much on the age of the patient. With a young patient like this 20 year old I would want at least 1 ½ MAC of sevoflurane with slow diaphragmatic respiration and convergent small pupils.
Now you want to isolate the lung and you’ve mentioned a double lumen tube. Are there alternatives to a double lumen tube you can use to achieve that?
Yes you can use a normal single lumen tube with a bronchial blocker, you can use a combi tube or you can railroad a single lumen tube down usually the right main bronchus.
What is a combi tube?
A combi tube is a normal looking ETT with a bronchial blocker built it. It goes down the external wall of the ETT rather than within the tube.
That sounds pretty good. Why wouldn’t you use one of those?
I’ve never used one of them. I understand they can be very difficult to use.
You can use a double lumen tube? – I always find them pretty difficult!
They’re all difficult but my first choice would be to use a double lumen tube.
In principle what are the advantages of using DLT’s over bronchial blockers, single lumen tubes or combi tubes?
The advantage of DLT’s is that you tend to get better lung isolation, and with experience it is usually quicker to isolate one lung from another, so with a soiled lung it is advantageous. The advantage of a single lumen tube with a bronchial blocker is that if you have a patient with a difficult airway you can quickly intubate them, or if they are an aspiration risk you can usually more quickly intubate them, or if you have an ICU patient who is very unwell and is not going to tolerate a tube change you can just put down a bronchial blocker. The advantage of the combi tube is similar to an ordinary ETT except that the system is all in one piece.
Examiner leans under table slowly and produces a plastic double lumen tube and gives it to me.
Just tell me about what you have in your hand and what the principles are.
This is a PVC right-sided tube, I’m used to using a Roberts-Shaw tube, but that’s OK.
What is the difference between a RS tube and that one?
A RS ETT is made of red rubber and it has a bigger right upper lobe bronchus lumen and the shape is different as well, it is shaped more like the actual bronchus.
Are they re-usable?
No they are disposable they are just red rubber. So this PVC tube has got a stylette so you can push it in more easily. It has an anterior convexity and a lateral convexity. You place it with anterior convexity forward through the cords and once it is through the cords you rotate it so that the second convexity is anterior and then you railroad it. This is the bronchial cuff which goes into the R main bronchus and lines up with the R upper lobe here. This is the tracheal cuff and I would inflate this first. I would listen over the tracheal lumen while ventilating and inflate the bronchial cuff until the leak disappears then I would stop inflating this cuff. You can use a bronchoscope to make sure that the R upper lobe lines up with upper lobe lumen because this is potentially not aligned and can cause hypoxia and collapse of the R upper lobe.
How far from the carina should the R upper lobe opening be?
The R main bronchus is usually about 2 ½ cm though it is variable. Most anaesthetists would look down with a bronchoscope and make sure that you can see the tip of the balloon sticking through the R main bronchus so that it is not in the carina and is not too far down the right.
What is the black line there? (Line just above bronchial cuff)
I’m not sure.
How do you determine in an individual patient what size DLT to insert?
For the Robert Shaw I would just use a large for a male and a medium for a female and a small for a very small female or very small male. These are described in terms of French. 41 is equivalent to a large in a RS, for a male, 39 for a female, and 37 for a small patient.
It goes down to a 28 Fr.
That’s very small. I’ve never used that.
You put one of these down for this guy and we get underway, and are about 10 minutes into the procedure when the sats fall to 87%. What do you do about that?
Scan the monitors and make sure the picture is consistent with what my monitors are telling me. But I would assume there is hypoxia because that is the safest assumption to make. The principles of dealing with a DLT if you have hypoxia are if you’ve got sats of 87% then that is quite hypoxic. So I would ask the surgeon to stop what they are doing. I would first re-inflate both lungs and turn on 100% oxygen until I had saturations I was happy with and I would be happy with 95%, though 100% would be ideal on 100% oxygen. Then I would use some mechanisms to try to prevent the hypoxia from recurring. The first thing I would do would be to apply some CPAP of about 5 cm of water to the non dependent lung. The next strategy would be to apply some PEEP to the dependent lung of about 5 – 10 cm. The third strategy is to provide some intermittent inflation of both lungs and in very severe cases where neither of those things worked you could clamp the pulmonary artery
Tell me what you are trying to achieve with upper lung CPAP and down lung PEEP
You are basically just trying to reduce the shunt, because that’s the problem. You have intrapulmonary shunt because you have perfused lung, which isn’t ventilated. If you ventilate the top lung a little bit with some CPAP you can reduce the shunt.
What does it actually do? Does it distend alveoli that 5cm of PEEP?
Well it can a little bit, it’s not going to inflate the lung completely. That’s the idea you want the surgeon to be able to proceed. But you will reduce the shunt to some extent because you’ll get less hypoxic vasoconstriction to the top lung and some of the blood going to the top lung will be oxygenated to some extent
And the PEEP?
It’s a similar principle. The reason you don’t want to put PEEP on before you put CPAP to the top lung is because you can divert some of the blood from the bottom lung back to the top lung causing the shunt to be worse.
OK are there some people where the PEEP won’t help at all in the dependent lung?
Patients with severe obstructive lung disease who already have their own auto PEEP. It may not make a difference to them.
Good, that’s the answer. All right. Next dilemma. There’s always another one. You’ve fixed that problem. 10 minutes later the high-pressure alarm on the ventilator goes off while you are still ventilating the lower lung. What could be causing that? A sudden doubling of pressure.
So my approach to that is to break it up into the machine, the ETT including the airway, and then distal to the airway. So I would exclude the ventilator by hand ventilating first and confirming high airway pressures, turn onto 100% O2 again, if I was still concerned I would disconnect the machine and use a self inflating bag. I would check the tube and make sure it was in the right position by looking at the measurement at the teeth to make sure it has not migrated down the bronchus, and I would stick a catheter down to make sure it was not occluded by anything.
Why might it be occluded?
There could be a foreign body, sputum, it could be kinked or sitting up against the wall of the bronchus. And then I would consider things outside the lung, things like heart failure and pulmonary oedema, pneumothorax, tension pneumothorax, and I’d treat those as I needed.
If that occurred in combination with a steep fall in blood pressure to 75, what would you then think.
Tension pneumothorax would be my first worry.
Yeah it could be, but it’s not the only possibility.
The surgeons pushing on something in the chest, acute heart failure and pulmonary oedema.
Yeah… The combination of hypotension and high inspiratory pressures?
Anaphylaxis?
Yes.
Time.