ARDS patient, dialysis

[zzyzx]

I had a patient with severe ARDS who had been anuric for 24 hours. She was in a respiratory acidosis, with a PaCO2 of 75 and a bicarb of 18. Her pH was 7.20.

The fellow ordered CRRT, but the next day the attending d/c it saying that the pt didn't need CRRT because this was a respiratory acidosis.

This didn't make sense to me. First of all, even though the pt's electrolytes were stable, shouldn't anurea itself be an indication for immediately starting dialysis? (She was hypotensive, so she needed CRRT). Also, the bicarb wasn't compensating for the respiratory acidosis. I agreed with the fellow's reasoning which was that by starting dialysis to compensate for the respiratory acidosis we could use lower lung volumes, which would benefit the pt's ARDS. All that made sense to me, but the attending disagreed. I didn't hear his reasoning, but what do you guys think?

[ClauICURN]

Why was the patient hypotensive? Was this a MODS patient, volume down?

Was the patient paralyzed? How much sedation was the patient on and what was the patient RR or vent rate?

And no, the patient being anuric for 24 hours is not an indication for immediately starting dialysis. What was the renal function like? Did the patient not respond to other methods to diurese such as albumin/lasix etc?

[zzyzx]

The patient was perhaps hypotensive due to sepsis, though she could also have been volume down. She initially came in for chronic pancreatitis, then developed a GI bleed, then came to the ICU because she went into respiratory distress after she got blood transfusions. At first they suspected cardiogenic pulmonary edema and diuresed her, but then suspected TRALI.

Her creatinine was still WNL.

I don't remember the vent settings, but of course she was on a lung-protective strategy (A/C PC) due to the severe ARDS. The idea behind the dialysis was to reduce the acidosis and thereby allow easier vent settings (less volume). No she was not paralyzed, but she was heavily sedated with fentanyl and propofol.

[Chisca, RN]

Early verses late initiation of CRRT is a continuing controversy among nephrologists with studies to back both approaches. At this point it is physician preference with evidence to support both opinions.

[Banana nut, BSN, RN, EMT-B]

I'm not an RN yet but I have a few thoughts, and I want to learn stuff. My question is: if the Pt. is volume down the first thing to go is the kidney, could perhaps fluid volume resuscitation allow for an increase in renal perfusion, thus increasing urine output?

Could giving bicarb iv lower her PaCO2/increase her PH without being as invasive as CRRT? If her Creat/BUN is not sky high and and she has no Hx of kidney disease why assume that this is RTA/intrarenal issue? it sounds prerenal to me? What was her MAP and SVV?

I'm sure I could keep asking questions but ill stop while i'm ahead....or behind either or.

Thank you

[Lev, MSN, RN, NP]

The kidneys produce bicarb and the patient's bicarb level was low at 18 so it was undercompensating. Perhaps by improving the function of the kidneys, they can start playing a part in acid base unbalance to correct the acidosis. Was the patient on a bicarb drip?

[ClauICURN]

OK I think there's a few different things we should consider. OP states that the renal function appeared normal with BUN/creat in range. The patient is in severe respiratory acidosis, which cannot be expected to be compensated by the kidneys to any meaningful extent. The kidneys would take a long time to be able to compensate for such respiratory acidosis, if at all. The reason I asked about sedation and rate on the vent is that the pCO2 could in theory be lowered some with higher rates on the vent if the patient is so sedated that they are not triggering breaths. Even if the patient is in ARDS and you want to go for low tidal volumes, there is still some room there to increase the volumes a bit and it would all depend on how bad the ARDS was and the pressures the patient was doing. There are two things that affect your CO2 on a vented patient, and those are tidal volumes and rate and dialysis is not going to solve this particular problem.

The second line of thinking has to do with the patient volume status. It is possible that this patient was in severe multiple organ failure/septic shock and was not making urine due to the fact that there was very little perfusion to the kidneys or as compensation for the patient fluid status. How much fluid was this patient getting, was the patient on vasopressors?

As for dialysis, it is not clear from the information given that this patient had an indication for it. I know there is some debate regarding how soon to start RRT, but generally the indication for any type of dialysis would be related to an acute fall in GFR or that the patient has/is at risk for developing solute imbalance or volume overload, as in acute pulmonary edema resistant to diuretics, hyperkalemia and metabolic acidosis that are refractory to medical management, or removal of toxic substances that can be dialyzed such as salicylates. Yes, the patient's bicarb is slightly on the lower end but usually a bicarb of 18 does not warrant a bicarb drip, especially since it could make the respiratory acidosis worse. I feel that the main problem with this patient had to do with vent management.

[Lev, MSN, RN, NP]

What was her creatinine? You write WNL, but if the she is anuric, it is impossible that her creatinine is WNL.

[MunoRN, RN]

While you can compensate to some degree for respiratory failure with kidney function or manipulated kidney function in the end you can't get rid of CO2 with even artificial kidney function, to remove CO2 you need extracorporeal carbon dioxide removal (ECCO2R) which is the other half of ECMO. In theory, this should improve outcomes from ARDS since it reduces the workload of the lungs, they've even tried just inducing apnea ECCO2R/ECMO but unfortunately this hasn't yet shown an a clear improvement in outcomes from ARDS.

[BSN16]

OK I think there's a few different things we should consider. OP states that the renal function appeared normal with BUN/creat in range. The patient is in severe respiratory acidosis, which cannot be expected to be compensated by the kidneys to any meaningful extent. The kidneys would take a long time to be able to compensate for such respiratory acidosis, if at all. The reason I asked about sedation and rate on the vent is that the pCO2 could in theory be lowered some with higher rates on the vent if the patient is so sedated that they are not triggering breaths. Even if the patient is in ARDS and you want to go for low tidal volumes, there is still some room there to increase the volumes a bit and it would all depend on how bad the ARDS was and the pressures the patient was doing. There are two things that affect your CO2 on a vented patient, and those are tidal volumes and rate and dialysis is not going to solve this particular problem.

The second line of thinking has to do with the patient volume status. It is possible that this patient was in severe multiple organ failure/septic shock and was not making urine due to the fact that there was very little perfusion to the kidneys or as compensation for the patient fluid status. How much fluid was this patient getting, was the patient on vasopressors?

As for dialysis, it is not clear from the information given that this patient had an indication for it. I know there is some debate regarding how soon to start RRT, but generally the indication for any type of dialysis would be related to an acute fall in GFR or that the patient has/is at risk for developing solute imbalance or volume overload, as in acute pulmonary edema resistant to diuretics, hyperkalemia and metabolic acidosis that are refractory to medical management, or removal of toxic substances that can be dialyzed such as salicylates. Yes, the patient's bicarb is slightly on the lower end but usually a bicarb of 18 does not warrant a bicarb drip, especially since it could make the respiratory acidosis worse. I feel that the main problem with this patient had to do with vent management.

I completely agree. anuria its self is not an indication for CRRT. Sounds like a resp problem to me. However many aspects are missing from this. Such as...the patient was hypotensive to begin with which probably caused an AKI, but....how is the patient now? Are they hemodynamically stable? Pressures? fluid volume status? etc...

[Banana nut, BSN, RN, EMT-B]

OK I think there's a few different things we should consider. OP states that the renal function appeared normal with BUN/creat in range. The patient is in severe respiratory acidosis, which cannot be expected to be compensated by the kidneys to any meaningful extent. The kidneys would take a long time to be able to compensate for such respiratory acidosis, if at all. The reason I asked about sedation and rate on the vent is that the pCO2 could in theory be lowered some with higher rates on the vent if the patient is so sedated that they are not triggering breaths. Even if the patient is in ARDS and you want to go for low tidal volumes, there is still some room there to increase the volumes a bit and it would all depend on how bad the ARDS was and the pressures the patient was doing. There are two things that affect your CO2 on a vented patient, and those are tidal volumes and rate and dialysis is not going to solve this particular problem.

The second line of thinking has to do with the patient volume status. It is possible that this patient was in severe multiple organ failure/septic shock and was not making urine due to the fact that there was very little perfusion to the kidneys or as compensation for the patient fluid status. How much fluid was this patient getting, was the patient on vasopressors?

As for dialysis, it is not clear from the information given that this patient had an indication for it. I know there is some debate regarding how soon to start RRT, but generally the indication for any type of dialysis would be related to an acute fall in GFR or that the patient has/is at risk for developing solute imbalance or volume overload, as in acute pulmonary edema resistant to diuretics, hyperkalemia and metabolic acidosis that are refractory to medical management, or removal of toxic substances that can be dialyzed such as salicylates. Yes, the patient's bicarb is slightly on the lower end but usually a bicarb of 18 does not warrant a bicarb drip, especially since it could make the respiratory acidosis worse. I feel that the main problem with this patient had to do with vent management.

This was such a great insight to your critical thinking process. Thank you for this post. Reading through gave me a more clear understanding as to what we are keeping in mind when caring for a pt. with this issue.

[zzyzx]

Ok, got it. Thanks for all the responses. I realize now that the dialysis could not have made a significant impact on reducing the respiratory acidosis. Makes sense.

At one point after she was intubated, I had a chance to bag her for a little while. Wow, I never realized just how poor the compliance is on a ARDS patient. I thought you could only have such poor compliance with an obstruction or a pneumo. That made me really understand just how damaged these patients are!