Driving pressure vs. resistance during mechanical ventilaton

[abeluchin]

We are taught in fellowship and by many publications that barotrauma is a factor for VILI in neonates. As a general rule, I use many pointers in management of a ELBW infant during mehanical ventilation to prevent VILI, inluding optimizing lung volume, volume-target ventilation and permissive hypercapnea. I use HFOV as a rescue option when pt develop worsening respiratory acidosis despite implementing the criteria above, or worsening lung compliance as indicated by requiring increase driving pressure on the vent to meet target tidal volumes. I also use the HFOV in air leak syndrome, pulmonary hypoplasia with pulmonary hypertension, among other indications. I do not generally use HFOV as a primary vent in small preemies, but some centers do.

My question to you is: initial settings on CMV (with PIP over 25) in babies < 1kg during volume-target ventilation are generally accepted as too high and potentially a cause for barotrauma. One caviat to this general rule is that during volume-target ventilation, TV is control and barotrauma plays a less important role in development of VILI. Another point is that when a 2.5 ETT is used to ventilate a 800g baby or smaller the resistance of the airway increases signicantly and babies usually require higher driving pressure to overcome this resistance and meet the target tidal volume. These small ETT are usually easily obstructed by mucus plugs in the airway making the resistance to increase even further.

Base on the above assumptions, I do not generally switched babies with small ETT 2.5mm, from volume-target CMV to HFOV to follow the principle of gentler ventilation when the PIP is high or increasing, unless I see obvious deterioration in compliance associated with a inter-current condition such as PDA or sepsis. In fact, I do tend to ignore the PIP when a small ETT (2.5mm) is used as long as I am able to achieve sustained lung inflation without secondary respiratory acidosis or hypoxia, and of course I cannot replace the ETT to a bigger or fresher one.

How do you approach this problem on your daily practice?

Thanks

Edited March 15, 2012 by abeluchin

[kpsanghvi]

Just to add - If we ventilate on Pressure Control modes (with AC or SIMV) to maintain normal gases one needs lower PIPs but the moment one switches over to volume guarantee the PIP goes higher. So are you actually causing more barotrauma (higher PIP) and more volutrauma (higher tidal volume) in the VG mode then in the Pressure control modes. So is volume targetting causing more harm or should we target at lwer tidal volumes. This has been my experience with the Draegger Babylog 8000+ for the past 5 years. Would love to have know your experiences and opinions

[abeluchin]

Thanks Dr. Sanghvi for you input.

In my practice, when I go from a pressure-limited mode such as AC or SIMV to a volume-target mode such as volume guarantee in the Babylog 8000+, I looked at the previous 15 to 10 minutes average tidal volume and set my target volume around that one, usually keeping it in the physiologic range of 4-6ml/kg. I do not generally see an increase in driving PIP to deliver that set volume. I would assume if your tidal volume is set blindly at 5/kg, your driving pressure could be higher or lower than in your pressure mode, depending on the lung compliance and airway resistance.

Again, I think that based on most recent publications VG mode is associated with less biotrauma that pressure modes, giving that you control the most important variable associated with VILI (VOLUME).

THANKS

[yalsaba]

You should set TV to the least which maintains accepted blood gases. If this requires high PIP, try to increase IT or flow rate which increase the delivered TV