Bicarbonate in sepsis/acidosis

Dear all, this week’s question:

Is there a role for bicarbonate in the management of the septic patient?

Does bicarbonate have a place in other types of metabolic derangement?


A

Have to be honest I always feel a bit sheepish about giving bicarbonate as rightly or wrongly I’m a believer in the Stewart Approach (or “quantative” approach) as I think it helps explain the complex acid base disturbances we see in critical care more completely than the traditional Henderson Hassleback view.

In the Stewart view it’s water dissociation that provides the hypothetically limitless supply of H+ ions that register as a the low pH on our blood gas analysers. So factors that influence the rate of water dissociation (namely the strong ion difference, albumin and CO2) are the culprits and should therefore be the targets for treatment. Any effect a bicarbonate solution has on the pH (ie [H+]) is just as likely to be due to whatever else is in that solution (like sodium which happens to be a strong ion).

It would be interesting to hear a renal physician’s view though as I know they use it a lot……

B

I echo A‘s reply.

I subscribe to the Stewart approach so give Bicarbonate as a means of giving un-opposed Na+ ions thereby correcting a strong ion difference acidosis eg hyperchloraemia. If you subscribe to this then it is actually a treatment for a SID acidosis rather than a papering over the cracks therapy to elevate pH.

It does presuppose the patient can blow off the CO2 or you can ventilate it off.

If we had potassium acetate then that is a way of giving supplementary K ions and treating a SID acidosis as again the acetate is metabolized and your giving in-opposed cations.

C

I’ve always subscribed to the idea that once you get below a certain pH you can get into a vicious cycle of acidosis -> haemodynamic compromise -> hypoperfusion -> acidosis, which might gather fatal momentum during your (usually slow) correction of the underlying cause. So I’ve usually only considered bicarb in patients who were not only severely acidotic (pick a number, say pH <7.1) but also haemodynamically compromised, and able to increase their minute ventilation to cope with the extra CO2, and with monitoring of the ionised calcium.

There’s no evidence to show that bicarb improves haemodynamics in this way, but unless anyone knows otherwise I don’t think there have been any studies that have controlled all the above factors, so we’re left with doing what seems to make sense. (Review at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4391479/)

I’ve also used it for acute renal failure with hyperkalaemia refractory to other treatment, while arranging for RRT. One such patient had a potassium of 7.5 despite insulin/dex, and a pH of 6.9, and was anuric for six hours despite fluid resuscitation. Gave a dose of bicarb and by the time he got to the ICU about two hours later (no bed) his potassium and pH were normal, he started peeing shortly after, and my vascath never got used. No miracle drug, but it saved him being filtered.

D

From a renal perspective we tend to use a lot of bicarb in our CKD patients as there is some evidence it slows progression to ESKD. It is also useful for those who have CKD stage 4/5 who are prone to hyperkalaemia and have a degree of acidosis (usually started when their bicarb level is below 20). This can sometimes allow you to continue their ACE inhibition and again slow their progression. 

I tend to like using 1.26% bicarb as an alternative crystalloid in patients with AKI who are dry, acidotic and hyperkalaemic. As the last post mentioned this can sometimes help in not having to dialyse people for hyperkalaemia, but more often than not provides you a bit more time to arrange the timely procedure that is arranging ‘acute’ dialysis. I can’t say I am a fan of stronger bicarb solutions and retained from an AKI perspective think you should be priming the filter rather than correcting the numbers with some bicarb.

Obviously it’s main strength is its use as baking powder, without which I would not be able to enjoy my blueberry muffin with my costa coffee in a morning! 

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