Thursday, April 24, 2014
Breathing on a breathing machine is not like you or I breathe. One time, when I was doing an ICU rotation, they allowed us to put the end of ventilator tubing inside our mouth and attempt to breathe as the machine delivered a breath. All of us spat that thing right out.
We breathe via negative pressure. We activate our diaphragm and when it contracts it pulls air in via negative pressure. A ventilator delivers a breath via positive pressure-- by basically shoving air into your lungs.
Although at times a patient needs a ventilater-- just being on a vent adds a whole other set of potential complications which is why some of these other "bridge" strategies have become more popular (like CPAP and BiPAP) which are positive pressure but delivered via mask. It is not uncommon for patients to wear these at home.
One of the problems with ventilators is getting it to deliver breaths when the patient breathes. This allows patients to be more comfortable without requiring a lot of sedation. Ventilator manufactorers began developing different modes of ventilation to achieve this goal.
What was available to patients up until now was synch mode but it basically waited until a patient triggered a breath and then would force the breath in after that. The patient and the vent were more coordinated but still not perfectly synchronized.
What's new is a system called NAVA (Neurally Adjusted Ventilator Assistance) which uses a cathether passed down the esophogus to sense when electrial impulses are travelling down the phrenic nerve (which is what stimulates the diaphragm to contract) and delivers a breath at that time-- which is much closer to the timing of when a patient would naturally breathe.
I know-- perhaps this is just exciting for medical nerds like me but keep this technology in mind if you're writing an ICU scene in a big-metro hospital. They are likely using this technology already.