Sunday, October 21, 2012

Rebuttal to APC a False Sense of Security



Image 1: Laparoscopic surgery.
In a previous post "Adaptive Pressure Control Ventilation during Anesthesia: a False Sense of Security", I argue that the anesthesia provider should use this mode with caution and described how the mode reacts during changes in pulmonary mechanics. 

After reading the post one could assume that I'm against using this mode of ventilation.

However, I believe this mode has many advantages. 


My main two arguments in the previous post  where:

1. Tidal Volume Consistency. 

2. Latency of Tidal Volume Adaptation. 



video


Pressure-Control ventilation is routinely used during laparoscopic procedures, to prevent  the rapid changes in peak inspiratory pressure (17 to 109% )  associated with inflation of the abdomen. The PIP remains constant however the delivered tidal volume is inconsistent.

The above video demonstrates the rapid change in delivered tidal volume after deflation of the abdomen. The operator has to immediately decrease the pressure control setting to maintain the desired tidal volume. 

I believe the key advantage of APC is that it will automatically titrate the pressure control to maintain the set/'target' tidal volume. 
If using pressure control and the operator was busy (e.g. starting a line, preparing medications, assessing the airway, etc). The patient would continue to receive very high (potentially dangerous) tidal volumes after the abdomen was deflated. 

Latency Time Deflation


The above video demonstrates the latency time of tidal volume adaptation after the deflation of the abdomen associated with APC ventilation. In this scenario the latency time is very short ~ 7-8 breaths or ~ 48 seconds. 

So is latency time really a issue? 

I do not believe it is.

The patient would only receive a larger tidal volume for a short amount of time, similar to  a few sigh breaths. 

Latency Time Inflation


The above video demonstrates the lag time of tidal volume adaptation after the inflation of the abdomen, associated with APC ventilation. 

I previously argued that the lower  tidal volume may result in atelectasis or a derecruited state.

Conversely, is a lower tidal volume really going to make a huge difference? 

First, lower tidal volumes is becoming more common practice due to the fact that higher volumes are associated with ventilator induced lung injury. 

Second, from reviewing the video one will notice that the lag time is very short ~5-6 breaths or ~ 30 seconds. This having little effect on mean airway pressure and end expiratory lung volume. 

 In the original post I just wanted to make practitioners aware of the limitations of APC ventilation. Even with these few limitations I believe that utilizing APC is safe and useful during laparoscopic procedures.