Fluid buildup in the single limb circuit

[BobBarker]

Took over a free flap case that had been going since 730am at 5. Just finished the trach. Patient SpO2 at 95%, FI50, ETCO2 45. Pressure control R16, PEEP 5, set pressure 30. Only pulling 500cc TV. Got an ABG. Ph 7.32, PCO2 49, PO2 70. Turned my peep to 7. Pressure limit and kickoff set at 40 started going off. Also turned up my FI to 70%. Turned up my rate and down my set pressure to think for a moment. Made sure the patient was paralyzed. Could hear some sloshing. Disconnected the circuit and dumped 20-40cc's of fluid out of the expiratory limb onto a blue towel. Reconnected the circuit and the pt immediately started pulling much, much larger TVs (850s) and the sat went up quickly to 99%. Dialed the pressure back to 25 and the pt still is pulling TVs greater than 700. ETCO2 dropping appropriately. Back pressure in the exp limb limiting full expiration? Asked my attending and he was no help.

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[IlDestriero]

Took over a free flap case that had been going since 730am at 5. Just finished the trach. Patient SpO2 at 95%, FI50, ETCO2 45. Pressure control R16, PEEP 5, set pressure 30. Only pulling 500cc TV. Got an ABG. Ph 7.32, PCO2 49, PO2 70. Turned my peep to 7. Pressure limit and kickoff set at 40 started going off. Also turned up my FI to 70%. Turned up my rate and down my set pressure to think for a moment. Made sure the patient was paralyzed. Could hear some sloshing. Disconnected the circuit and dumped 20-40cc's of fluid out of the expiratory limb onto a blue towel. Reconnected the circuit and the pt immediately started pulling much, much larger TVs (850s) and the sat went up quickly to 99%. Dialed the pressure back to 25 and the pt still is pulling TVs greater than 700. ETCO2 dropping appropriately. Back pressure in the exp limb limiting full expiration? Asked my attending and he was no help.

What's the question? I used to put a 27g needle in the circuit to drain the expiratory limb of the humidified circuit for the long cardiac cases. Worked great, insignificant leak and much easier than periodic draining.

 

[BobBarker]

Why did the fluid build up effect my delivered TV? The fluid is in the expiratory outer area of the circuit so I don't understand how it could effect my delivered TV.

 

[JSBMD]

Fluid was adding peep to the patient. Once you have that, you can't be sure what the real peep is, regardless of setting. Good news is the patient probably had less atelectasis than they would otherwise have had.

Good job in diagnosing this problem. How long do you think this had been going on? Hours is my guess. Out of curiosity, did you relieve a resident or CRNA? Sounds like they were reading a good book or magazine.

 

[JSBMD]

By the way, scary aspect here is mishandling the circuit can easily dump that water right into the patient's lungs. FYI to newbies.

 

[BobBarker]

Crna.

 

[pgg]

Fluid was adding peep to the patient.

That's it, right there.

In effect, with all that extra PEEP, you were ventilating the patient at the top end of his vital capacity, which hurt V/Q matching and resulted in the observed very high A-a gradient (pO2 of 70 despite FiO2 of 70%). Kind of like breath stacking a COPD'er. Poor compliance, higher pressures, smaller volumes.

 

[cchoukal]

That's it, right there.

In effect, with all that extra PEEP, you were ventilating the patient at the top end of his vital capacity, which hurt V/Q matching and resulted in the observed very high A-a gradient (pO2 of 70 despite FiO2 of 70%). Kind of like breath stacking a COPD'er. Poor compliance, higher pressures, smaller volumes.

This sounds right, but I'd be surprised you wouldn't diagnose this by looking at the pressure waveform (or having the high peep alarm go off) before you'd even inspect the circuit to find the water.

 

[pgg]

This sounds right, but I'd be surprised you wouldn't diagnose this by looking at the pressure waveform (or having the high peep alarm go off) before you'd even inspect the circuit to find the water.

Yeah good point but I wonder how accurate that pressure sensor would be with a column of water between it and the patient. It might not read what the patient feels.

Maybe tomorrow I'll pour some water in the circuit, stick the mask on my face, turn the ventilator on, and see what happens.

 

[deleted59964]

out of interest - how were the hemodynamics - did they improve after you drained the circuit?

 

[narcusprince]

Another point not mentioned is the resistence of the tubing is greater once you have fluid within tubing hence the lumen of the tubing is smaller. A quick formula I use in the OR is PkP=Vt/C + Resistence x Flow rate. So in PC mode your compliance and resistence determine tidal volumes. If your resistence increases your tidal volumes decrease. What you could also have done which I do all the time is determine whether its a Resistence or flow rate issue versus Tidal volume compliance issue. You can determine this by looking at the plateu pressures most new anesthesia machines can give you an inspiratory hold. During this hold flow rate is zero, hence the high pk pressures high plateau pressures = compliance vs tidal volume issues, high peak pressures low plateu pressures = Resistence vs flow rate issue. Good post.

 

[BobBarker]

The hemodynamics were fine before and after. I finished the case around 0330 and periodically had to drain fluid off. It even was accumulating in the inspiratory limb. The only place it didnt accumulate was in the tubing connecting the bag.

 

[Idiopathic]

id be inclined to think the fluid is not so much of an issue as is auto-peep, especially in PC ventilation. alarms usually go off in my head when it takes me 30 of PC to generate Vt of 500, probably whoever started the case had the RR too high and wasnt allowing for an appropriate E time, necessitating periodic increases in PC to keep minute ventilation stable. This technique was failing when you arrived. The fluid is probably unrelated to the ventilation problem

 

[pgg]

The fluid is probably unrelated to the ventilation problem

Except ventilation dramatically improved after removing the fluid. Doesn't sound like he changed anything else.

 

[Idiopathic]

Except ventilation dramatically improved after removing the fluid. Doesn't sound like he changed anything else.

he disconnected the circuit, relieving the autopeep...the fluid came out, but i think its unlikely that fluid in the expiratory limb of a relatively compliant circuit would have been the major contributor

 

[Idiopathic]

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