James...
      It takes more air than you think to kill someone, or cause a bad outcome. I am talking about small small amounts.. less than half a milliliter. I am also talking about its presence in a pressure line (a fluid path to a transducer). Some pressure lines have a calibrated leak past a transducer to keep the line flowing at a slow slow rate, say 3 milliliters an hour. Part of our troubleshooting procedure for invasive pressure lines involves checking for air and loose connections if the waveform is "dampened".
 
The biggest problem with patient care is IF a large enough amount of air (say.. 10-15 milliliters in an adult) is injected all at once, it can end up collecting in the right atrium, and interrupt blood flow through the heart.. this tends to be a sudden, and invariably fatal event. Very small amounts (in adults) are absorbed by the blood without bad effects. That being said, NO, we dont go around intentionally injecting air.. but sometimes small amounts end up going in.  So.. to sum it up.. It takes a LOT of air to kill someone, but it only takes a LITTLE bit (in invasive pressure lines) to affect the readings. And treating bad values can be just as dangerous.

Dave

James Maher wrote:

In the medical field, I would think that air in the lines would do more than "affect the readings",... it could kill the patient.

Isn't that why doctors always fill the syringe and then point the needle up and squirt out some liquid to ensure that all the air is out.

Air bubbles in the blood stream can kill.

Air bubbles in the oil are not so deadly.

Jim Maher

 

David Staten <Dastaten@earthlink.net> wrote:

snip

I was basing my question about the purge bit based on my healthcare experience... In the ICU and some OR settings catheters/lines are directly placed into arteries, brain spaces, large veins and pressure readings are transduced in order to manage treatment. Air in the lines affects the readings.. but then I realized the air affects the CHANGES of pulsatile flow.. it dampens it... like the pressure wave with your heartbeat. In a constant-pressure situation (or at least "non-pulsatile" pressures.. in which the character of the pressure waveforms dont matter) I guess you are right.. pressure is pressure.. and the reason we are measuring it shouldnt matter on the presence or absense of air.
 
Dave

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