Liquid Ventilation?

[RTDugger]

There is a high degree of difficulty of ventilating patients using liquid ventilation. Like many people have stated, CO2 removal is difficult due to the low partial pressure of it to begin with (at one atmosphere, there is 760mmHg, the partial pressure for most "healthy" people is between 35-45mmHg, which is only about 5% of the partial pressure of the atmosphere, or the air we breathe). Despite the fact that there is still only 0.03% CO2 in the atmosphere, elmination of CO2 from the perflourocarbon is difficult.

Without a rapid ability to eliminate CO2 from the liquid, CO2 has an "obtunding" effect when it increases to as little as PCO2 50mmHg in the circulatory system, which if it cannot be properly eliminated from the liquid, is rather easy to achieve.

Like another member stated, liquid ventilation (mainly partial liquid ventilation) is primarily used on patients with severe lung injury. They do this because liquid lowers the surface tension of the alveoli and the opening pressures are greatly decreased. This in turn is used to decrease the amount of damage that might occur during mechanical ventilation.

There has been better success ventilating patients using partial liquid ventilation apparently because you keep the alveolar opening pressures low while you can still ventilate using conventional methods, increasing the transfer or CO2 and O2 d/t the increased contact time between the oxygen and the liquid.

As for it ever being used in diving? I have never heard of it being used in diving and from what I know of it, it doesn't seem like it will be used anytime soon. The prospect is certainly interesting (liquid is incompressable but you would also need a very expensive closed system) but it seems like more of a dream then anything.

 

[Tassie_Rohan]

Thanks for that RTDugger - I was wondering what the advantage was. I can see where it would help with physical lung damage, but what are its effect on gas exchange and how is it used in DCI treatment?


Also - can they make a liquid ventilator out of beer?

 

[RTDugger]

I have no idea how (or why) it would be used for decompression illness (if thats what you mean by DCI), thats where hyperbaric chambers are for.

The main concern (and difficulty) was for gas exchange. It's well nkown the effects of adding liquids in the lungs to decrease lung damage....especially in babies, hence surfactant treatment for pre-term and IRDS (infant resp. destress syndrome). Apparently oxygen exchange worked well enough but like mentioned earlier, CO2 exchange is the main concern.

Also, the increased density of the liquid to ventilate with (if we were to use the supposed full ventilation system a la the Abyss) is a major concern.

As per Wikipedia:

"At these pressures, most fluorocarbon liquids require about 70 mL/kg minute-ventilation volumes of liquid (about 5 L/min for a 70 kg adult) to remove enough CO2 for normal resting metabolism. This is a great deal of fluid to move, particularly as it is about 1.8 times as dense as water; any activity on the diver's part which increases CO2 production would increase this figure, which is at the limits of realistic flow rates in liquid breathing. It seems unlikely that a person would move 10 liters/min of fluorocarbon liquid without assistance from a mechanical ventilator, so "free breathing" may be unlikely."

Just to give you an idea of the difficulty of this. The normal tidal volume for an average male is about 350-400 mls/breath, times 12 breaths/minute. This means that every minute the average male breathes 4.5-5.0 litres of air.

As cited from Wikipedia:
1.2 kg/m^3 - density of air
9.982 kg/m^3 - density of water at 20 degrees celcius ~8.3x denser then air
17.96 kg/m^3 - density of perflourocarbon ~15x denser then air

This means that ventilating perflourocarbon for liquid ventilation is 15 times harder then breathing air. With an increased work of breathing, you increase the comsumption of O2 and increase the output of CO2, meaning that even if you COULD manage to do it and you had to do the work yourself, that the liiquid you are breathing would need to have a high concentration of O2 (which I wouldn't imagine would be too difficult), but also be able to expel CO2 much more efficiently then it already is.

From what I remember from my calculations in school, by decreasing the diameter of a tube by 1/2, you increase the resistance by 4. So, if you effectivly decrease the diameter of a tube to 1/4 of it's original size, you have effectivly increased the resistance by 16.

To apply it to our terms: Since the human trachea's diameter is between 1.2-~2cm (citing Wikipedia) and the average size of our endotracheal tubes in my ICU, to get the general feel of what it would be like to breathe perflourocarbon liquid for ventilation manually (as in the Abyss, Ed Harris does it all by his own efforts), it would be like breathing through a 3-5mm tube, or a tube smaller then a straw. *ouch*


All I know past this is that liquid ventilation has only ever been used in clinical studies and not passed that. Studying in school I only fround trials that has been done a few years prior.

It's either too costly (the perflourocarbon or it's associated equipment) or inefficient to be used frequently these days.

http://en.wikipedia.org/wiki/Liquid_breathing

Here's a good deal of information from the Wikipedia website, I recommend checking out the diving section of it.