How does dialysis resolve metabolic acidosis?

[iaskdumbquestions]

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The administration of bicarb is controversial, but usually nephrology will recommend it. In refractory acidosis we put people on dialysis or RRT. How exactly do these modalities resolve acidosis? Is it only if the imbalance is due to renal failure? What about sepsis / multi-organ failure in which the acidosis is driven by lactate and you cannot treat it rapidly enough and the patient is becoming more and more acidotic - dialysis is indicated here as well? Thank you for helping me to understand this.

 

[jdh71]

The administration of bicarb is controversial, but usually nephrology will recommend it. In refractory acidosis we put people on dialysis or RRT. How exactly do these modalities resolve acidosis? Is it only if the imbalance is due to renal failure? What about sepsis / multi-organ failure in which the acidosis is driven by lactate and you cannot treat it rapidly enough and the patient is becoming more and more acidotic - dialysis is indicated here as well? Thank you for helping me to understand this.

Giving bicarb isn't "controversial" - it simply doesn't help everyone survive enough to get a signal in the studies where it was looked at - so we don't just give it to everyone and anyone. It probably does help often enough, but there is too much noise and confounders in the ICU to really tease out or make good conclusions about really anything there. Bicarb infusions are usually high volume relatively speaking and it's probably the extra volume leading to equivocal outcomes in many of the studies. Regardless, sometimes it makes sense, and I tend to consider use when I have single digit CO2 on the panel, and I definitely use when pH is <7.0

Dialysis simply buffers the acidic fluid going into the machine and puts the fluid back into the body with a more physiological pH

They do not resolve acidosis per se, they make the physiological milieu more consistent with life than not. You resolve the acidosis by fixing what its causing it, the DKA, the shock, the acute renal failure, etc.

And yes RRT is often used in septic shock simply because of acidosis, EVEN IF urine is still being made. "A" is one of the "AEIOU"'s of dialysis indication, yeah?

 

[Chemist0157]

The administration of bicarb is controversial, but usually nephrology will recommend it. In refractory acidosis we put people on dialysis or RRT. How exactly do these modalities resolve acidosis? Is it only if the imbalance is due to renal failure? What about sepsis / multi-organ failure in which the acidosis is driven by lactate and you cannot treat it rapidly enough and the patient is becoming more and more acidotic - dialysis is indicated here as well? Thank you for helping me to understand this.

There's a right and wrong way to use bicarbonate fluid. It tends to be overused. It is not without risk (overcorrection, volume overload, hypocalcemia, etc). If bicarb gtt is being considered, a pH should be checked. I would not start it just because HCO3 is low on a metabolic panel. It is generally a temporizing measure unless AKI is expected to improve with volume repletion from a prerenal cause.

RRT will not necessarily resolve an acidosis. It depends on the underlying cause and other factors such as presence of ongoing production. Dialysis will buffer with HCO3 fluid from the dialysate as well as removal of acids driving an anion gap metabolic acidosis (urea, lactic acid). The acuity of kidney disease would matter. Acidosis in chronic kidney disease progresses from a non-anion metabolic gap acidosis from poor acid excretion initially and then later AGMA from accumulation of urea. Acidosis in AKI tends to both. For the most part, RRT is supportive care with the hope being that the underlying cause can be addressed. Take necrotic tissue for example. If that is something that can addressed in the OR, RRT makes sense. If the patient is on multiple pressors, still hypotensive, worsening lactic acidosis, poor surgical candidate, RRT is a bridge to nowhere, and I do not recommend it. It is not infrequent that such a patient would still have persistent acidosis despite CVVHDF.

 

[iaskdumbquestions]

Thank you both for your answers, they're very helpful and I have a better grasp of it now.