Annals of Emergency Medicine - The Gas That Just Won’t Pass

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Nurses Edition Commentary

Mizuho Morrison, DO

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Basia H., M.D. -

I had a similar case in the last year. A young man from a group home with several hours of abdominal distension and mottled legs.

He arrived awake and talking with normal vital signs except for tachycardia. His abdomen was massively distended and rigid, legs dusky with no pulses below the waist. Xray showed severely dilated loops of bowel, no obvious free air. The foley would not pass. NGT was placed with only clear fluid returning. Off to CT where the pt had a respiratory arrest on the table, resuscitation was unsuccessful.

Unknown to us during the resuscitation were the CT findings: Massively dilated stomach and bowel diffusely, massive free air, complete compression of the aorta just below the diaphragm. The tip of the NGT was in the lower esophagus. As the pt had multiple passes through the CT scanner the images showed the evolution of air dissecting into the mediastinum then both sides of the chest causing bilateral pneumothoraxes. Towards the end of his brief code subcutaneous air could be felt in the chest and neck and these tissues became tense and swollen to the point that it was difficult for the techs to perform CPR and his mouth could not be opened.

Autopsy was non diagnostic and only reported a post mortem perforation of the stomach.

This was the most grotesque case I have had in 20 years in Emergency Medicine and it near broke me. I cannot fathom a process that would cause the rapid build up of air under such pressure with no way to escape the GI track, causing this scenario.

I was not familiar with the concept of tension pneumoperitoneum or needle decompression of the abdomen. I'm glad you covered this case on EM:RAP so others are more prepared should this monstrous case comes along.

Paul J. -

Wow, thanks for sharing that. Medicine is so humbling and I appreciate you sharing your story with us! Such a rapid decompensation.

Timothy R. W. -

A couple of comments on the presentation. The current recommendation for most accurate IAP measurement is an infusion of 10 cc of fluid, not 25 cc. You can visit the experts web site on this - for more data on that topic. Though this 10 cc infusion is likely academic in young adults, it is not so except in children nor in elderly men with very thick, stiff bladders where the extra fluid infused will result in measuring the bladder wall compliance rather than the passive pressure within the abdomen. Since all you need to accurately measure pressure is a hydrostatic coupling of the tip of the Foley within the bladder to the outside transducer, a smaller volume than 25 cc is totally adequate and avoids any risk of exceeding the bladder compliance threshold.

Secondly, if you choose to use the later suggestion of lifting the Foley up to measure pressure be very cognizant of the distal drain tubing position. You MUST drain all urine and have no loops within the tube or you will get a falsely elevated pressure (the urine/fluid that runs distally into the loop creates a negative pressure and "sucks" the proximal fluid column upwards). Also, 10 cc might not be enough fluid using this method as it can only back flow up to the volume you infuse and if the pressure is pretty high, 10 cc might not fill the tube to a height consistent with the pressure. Ideally you vent the tube to ambient air pressure just as you do for an accurate LP pressure. Basically there are so many possibilities of error using this method that unless you are insightful into all the potentials for error, you should not use this way of measuring IAP.

Which leads to a final point that we all should know about Foley catheters, but I was unaware of until I began research in this area 20 years into my practice. You should never have any loop in the drain tube as the urine within this loop forms a miniscus of fluid on each side - the difference in height resulting in a positive pressure in the proximal air column and preventing urine from draining. This tube pressure can also be transmitted into your IAP arterial line measurement if you fail to remove the drain tube loops. Furthermore this loop and positive pressure it induces result is the patients bladder filling up because it cannot drain against even a small pressure (which is why the nurse lifts the tube up and down several times to get actual UOP, an increase CAUTI risk), irregular urine output measurement, discomfort and the feeling of needing to urinate, possible reflux up into the ureters, higher risk of CAUTI, etc. So, as the device instruction state - lay the tube straight along the bed and off the end with no loops at all if you want the best comfort and least risk to your patient.

Paul J. -

Excellent clinical pearls and points, and well explained! Thanks for sharing and dropping tons of clinical gold! For those of you who'd like some fun background reading and references:
The point of obtaining an accurate IAP reading, as one can imagine, is critical. The old practice "standard" (just years ago) of measuring IAP via the Foley involved instilling anywhere from 50mL-250mL into the bladder. De Waele et al in 2006 (PMID: 16477411) decided to investigate and published a study of 20 patients where they instilled saline in 10mL increments and basically found that, the more you instill, the higher the IAP (in other words, falsely high IAPs/worse specificity: Fig 1 displays the results very nicely). 10mL was concluded to be more accurate compared to the old practice standard of instilling 50mL or more. Malbrain et al in 2006 (PMID: 16934130) published a study of 30 patients where they instilled saline in 25mL increments and reached a similar conclusion. The 2013 WSACS consensus definitions (PMID: 23673399) then came out recommending: "The reference standard for intermittent IAP measurements is via the bladder with a maximal instillation volume of 25 mL of sterile saline."
More importantly, though, TRW points out arguably the most common source of error when measuring IAP: the Foley. Malbrain in 2004 published a great review worth reading, of several IAP measurement techniques along with pearls/pitfalls, many of which TRW points out (PMID: 14730376). Awesome discussion!

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