Occlusive dressing effects

Following up on the recent topic about pneumothorax, I was wondering what effect exactly the SEChestOcclusiveDressing has. I had been testing this sequence (in Pulse 3.0, in Java) with the soldier patient (intended to model a gunshot wound to the chest):

  1. SETensionPneumothorax, open, right side, severity 0.7
    SEHemorrhage, external, skin, rate 15 mL/min
    SEHemorrhage, external, muscle, rate 35 mL/min
    SEHemorrhage, external, RightPulmonaryArteries, rate 1 mL/min
    SEHemorrhage, external, RightPulmonaryCapillaries, rate 1 mL/min
    SEHemorrhage, external, RightPulmonaryVeins, rate 1 mL/min
  2. By 2 minutes, the patient has deteriorated significantly (tachycardia, tachypnea, hypoxia). So then I mimic performing a needle decompression and applying bandages to stop the bleeding:
  3. SENeedleDecompression, right side
    SEHemorrhage, external, skin, rate 0 mL/min
    SEHemorrhage, external, muscle, rate 0 mL/min
    (I’m not addressing the Pulmonary bleeding here because I’m under the impression that requires surgery.)
  4. Patient vitals rapidly return to normal, except for tachycardia (presumably because the lost fluid has not been replaced). At this point, the patient appears to remain stable for a long time (I ran for 60 sim minutes, and while the patient developed a low-grade fever about 22 mins in, the hypoxia did not come back).

After reading the topic linked above, I’m confused why this worked, because I never did a SEChestOcclusiveDressing action. Perhaps if I waited longer the patient would destabilize again? Or maybe I’m not modeling the dressing correctly, and setting the hemorrhage rates to 0 is screwing something up?

Additionally, I’m curious as to the relationship between SEChestOcclusiveDressing and hemorrhage. If I understand correctly, a real occlusive dressing would contain the bleeding, but I don’t know how that would work in pulse (how would it know which hemorrhages to reduce?). So I’m assuming it does not do this?

After reading the topic linked above, I’m confused why this worked, because I never did a SEChestOcclusiveDressing action. Perhaps if I waited longer the patient would destabilize again? Or maybe I’m not modeling the dressing correctly, and setting the hemorrhage rates to 0 is screwing something up?

TL;DR: Chest occlusive dressing does very little to change the simulated patient’s outcome unless it’s applied before the lung fully collapses.

First, a little explanation of how the model works. The image below shows the circuit elements that are used for tension pneumothorax, chest occlusive dressing, and needle decompression. Normally, all three resistances in the red boxes have a super high resistance to prevent any airflow. When the pneumothorax action is called, the leak resistances are reduced to allow airflow and a valve/diode only allows flow into the pleural space (causing lung collapse). For open pneumothorax, a chest occlusive dressing increases that resistance back to a super high value to prevent airflow on that path again. Then needle decompression reduces the needle resistance to allow airflow in both directions (no valve/diode) to allow air to escape.

I ran some tests using the SETensionPneumothorax values you provided, while ignoring the SEHemorrhages. I also see that using an occlusive dressing doesn’t have much effect at all. I think this makes sense intuitively with how the model works. The needle allows air to escape and reverses the collapsed lung, even if it still flows in simultaneously from the pneumothorax.

I’m pretty sure the only time it would make a significant difference is if the dressing is applied before the maximum amount of air is trapped in the pleural space (say, 1 min into the 0.7 severity pnuemothorax, instead of 2 min). This would stop the lung from collapsing fully and prevent the patient’s condition from worsening before performing needle decompression.

Additionally, I’m curious as to the relationship between SEChestOcclusiveDressing and hemorrhage. If I understand correctly, a real occlusive dressing would contain the bleeding, but I don’t know how that would work in pulse (how would it know which hemorrhages to reduce?). So I’m assuming it does not do this?

There is no direct relationship between SEChestOcclusiveDressing and SEHemorrhage. You would need to explicitly reduce SEHemorrhage values.

Thanks for that detailed explanation! I think where my model is falling short is that I never remove the needle – realistically I should do that, and then I bet the lung would re-collapse without the occlusive dressing.

Yes. Great point! If you remove the needle without the dressing (closing the pneumothorax), you would basically be right back to where you started.

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