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Lynxesandlarynxes t1_jc5tzqh wrote

  • Facilitating mechanical ventilation (MV) typically requires an artificial airway e.g. endotracheal tube, tracheostomy. Inserting these is not without risk, both short- and long-term. A first hurdle.
  • The respiratory tree from nose - to - bronchi is crucial immune defence, helps humidify and warm inspired air and helps clear mucous from your lungs. With MV the presence of said artificial airways bypasses these beneficial mechanisms.
  • MV is essentially backwards. When you inspire naturally your diaphragm contracts to (in short) create negative pressure in your chest, drawing air into your lungs. When you're done inspiring the elastic recoil of your chest etc. pushes air out. This is called 'negative pressure' ventilation. MV is 'positive pressure' ventilation - it blows the lungs up like a balloon with each mechanical inspiration, then they deflate elastically during expiration. This creates issues whereby the alveoli can be subjected to an unnaturally high pressure (barotrauma) and sometimes also volumes of air (volutrauma). Neither are good and have a host of possible short-term (pneumothorax, ALI) and long-term (CLI) sequelae.
  • Ventilator-associated pneumonia. Normally you swallow or spit out your saliva and other upper respiratory tract secretions. When you've an artificial airway in place, these secretions accumulate at the point of the airway's cuff (a small balloon that helps stop it moving). These accumulated secretions contains normally harmless oral bacteria, but over time they'll develop a biofilm, bypass the cuff and enter the lungs causing a pneumonia.

There are other reasons, though I have to go to work now!

Source: Anaesthetist/intensivist


SerialStateLineXer t1_jc66n69 wrote

Would a negative-pressure ventilator like an iron lung solve some of these problems, and if so, is there active research into developing more lightweight alternatives? What about diaphragmatic stimulation?


BadAmbassadors t1_jc74dhb wrote

There are smaller negative pressure ventilator options like the Cuirass from Hayak medical. This is essentially a barrel-like chamber you wear over your abdomen which creates a vacuum allowing ventilation support. You breathe into a 'negative space' and thus gain support. It has advantages and drawbacks.

I have used this with two patients with Motor Neuron Disease both of which could not cope with positive pressure ventilation via a face mask (NIV) and it worked well, that is to say they had symptomatic relief.

This treatment was done at the patient's home overnight and during the day as their disease progressed. The Cuirass shell itself is cumbersome and the ventilator is large and noisy so this isn't a great option (but the only one we had considering the decision not to have a trach). The only reason it was successful is because both these patients and their families were highly committed and willing to put up with the difficulties of using the device. It's certainly not for everyone.

I asked myself the same question about whether this technology was developing and would improve but I think that as the majority of patients cope with NIV there is no impetus to throw money at negative pressure. Indeed negative pressure ventilation via Cuirass is a less recent development than NIV and I think it's unlikely to improve because NIV is so 'easy'.

Speaking as a specialist nurse in home ventilation so happy to be corrected/expanded upon

Edit: with respect to ventilating neuromuscular patients it very much depends on the condition. I have many patients with Duchene's Muscular Dystrophy who have been on NIV for well over a decade and are coping really well. These patients seem to me more likely to die from their cardiac issues than respiratory when managed well on a ventilator.


_night_flight_ t1_jc68rtd wrote

What about those old-fashioned iron lung machines from decades ago, didn't people live with those for years?


Indemnity4 t1_jcj0kgm wrote

Iron lungs are huge! You need a dedicated room.

Iron lungs still exist, but use massively declined after the 1960s. They are too cumbersome and restrict movement, compared to a significantly smaller and mobile positive pressure unit.

The stat was something like only 10 units still existed in USA in the 2010's. There were only two people in 2020's.

Only real use now is novel development post-Covid for patients who need limited assistance and can't tolerate a ventilator. An example may be a person who only needs the negative pressure unit at night.