This topic contains 3 replies, has 3 voices, and was last updated by 
-
Posts
-
can you give us an easier way to figure/calculate the acidosis/alkalosis
This is usually a tough topic, but I’ve tried to provide a methodical way of approaching the questions. What specifically are you struggling with?
Hi I was looking through to see if there was one main area to post corrections in case someone mentioned it already..but here are the minor ones in acid bad disorders:
pg273- Posthypocapnea causes non gap metabolic acidosis and posthypercapnea causes metabolic alkalosis due to serum bicarb decrease and increase by renal compensation during prolonged resp alkalosis and acidosis respectively. This happens usually over a period of few days after correction of hypo/hypercapnea before kidneys go back to the normal reabsorption.
Pg 276- decrease in bicarb could be 2 per 10 CO2 decrease or 5 per 10 of CO2 decrease….(study guide says increase)
Ahh… you’re right, and THANK YOU for bringing it to our attention.. For the first one it looks like I fell into the terminology trap, which can get confusing. For the second one, it was a copy/paste error from topic above it.
Here goes….
HypOcapnea means there is low CO2 in the blood, and this occurs due to HypERventilation. Therefore you get a RESP ALKALOSIS and a compensatory nongap metabolic ACIDOSIS.
HypERcapnea means there is high CO2 in the blood, and this occurs due to hypOventilation. Therefore you get a RESP ACIDOSIS and a compensatory metabolic ALKALOSIS.
Revised versions of both topics are below
NON-ANION GAP METABOLIC ACIDOSIS
Non-anion gap metabolic acidosis conditions include Ureterostomy, Small bowel fistula, Extra chloride, DIARRHEA (most common cause), Carbonic anhydrase inhibitors (acetazolamide), Adrenal insufficiency, Renal Tubular Acidosis, and Parenteral nutrition/Pancreatic fistula/PosthypOcapnea. Look for HYPERCHLOREMIA and a LOW BICARB. Here are a few mechanisms to keep in mind:
* Extra chloride: Too much saline causes a hyperchloremic non-gap metabolic acidosis
* Diarrhea: Acidosis occurs from bicarbonate loss.
* RTA: Mechanism varies.
* Carbonic Anhydrase Inhibitor: Promotes renal bicarbonate loss.
PEARL: -CAPNEA refers to how much CO2 is in the blood and is NOT referring to how fast someone is breathing. So, hypOcapnea means there is low CO2 in the blood, and this occurs due to HypERventilation. Therefore you get a RESPIRATORY ALKALOSIS and a compensatory nongap metabolic ACIDOSIS. HypERcapnea means there is high CO2 in the blood, and this occurs due to hypOventilation. Therefore you get a RESPIRATORY ACIDOSIS and a compensatory metabolic ALKALOSIS. Make sure you look carefully at the terminology in the question stem or vignette.
MNEMONIC: “Acid-azolamide”
MNEMONIC: NON-GAP CRAP! Several stool related issues cause a non-gap acidosis (diarrhea, small bowel fistula, ostomies).
MNEMONIC: USED CARP (Ureterostomy, Small bowel fistula, Extra chloride, DIARRHEA, Acetazolamide/Adrenal insufficiency, Renal Tubular Acidosis, and Parenteral nutrition/Pancreatic fistula/Poshypercapnea.
MNEMONIC: If you do not know your normal values for routine chemistries, a non-gap acidosis can be tricky. If you just calculate the gap and see that it’s normal, you could get in trouble. You should look closer at the chloride and bicarbonate levels. So, what I’m saying is that the chemistry looks good on the outside (i.e. gap looks good), but it’s actually falling apart on the inside (low bicarb and high chloride), LIKE A USED CARp!
MNEMONIC: Building on the one above mnemonic, a USED CARp can only travel on smooth roads WITHOUT GAPS/potholes!
===
RESPIRATORY ALKALOSIS
A respiratory alkalosis can be caused by basically anything that causes tachypnea. Sometimes this is due to hypoxia. The list includes, but is not limited to, early asthma, pneumonia, one of the aspirin phases, high altitude, fever and anxiety/hyperventilation.
PEARL: If given an ABG and you note a respiratory alkalosis, ALWAYS calculate for compensation. You do this by looking at the decrease in PCO2 from the baseline of 40, and checking to see if the compensatory decrease in bicarbonate (compensatory metabolic acidosis via bicarb excretion) is appropriate. If the bicarbonate level is even lower, then you have an additional primary metabolic acidosis. If it’s higher than expected, then there is an additional primary metabolic alkalosis. Keep in mind that the compensatory decrease in bicarbonate could be 2 per CO2 decrease of 10, or 5 per CO2 decrease of 10. That depends on whether or not you are dealing with an acute or a chronic respiratory alkalosis.
You must be logged in to reply to this topic.