Thanks to Robert for presenting a great case of a patient with history of alcohol use presenting with severe hypokalemia and metabolic alkalosis! We had a terrific discussion of acid-base disorders, as well as the differential and workup of metabolic alkalosis!

Pearls below!!

Acid-Base evaluation:

- What is the
__primary disorder__?- Primary acidosis if pH <7.4, alkalosis if >7.4

- Is it
__metabolic__or__respiratory__?- If acidosis, high CO2 implies respiratory, low bicarb implies metabolic
- If elevated anion gap, a metabolic acidosis is present (but may not be primary)

- If alkalosis, low CO2 implies respiratory, high bicarb implies metabolic

- If acidosis, high CO2 implies respiratory, low bicarb implies metabolic
- Is there a 2
^{nd}disorder too?__Compensation__formulas:- Metabolic acidosis
- Expected pCO2 = 1.5 x bicarb + 8 +/- 2 (Winter’s formula)

- Metabolic alkalosis
- Expected pCO2 = 0.7 x bicarb + 20 +/- 5

- There are also compensation formulas for acute and chronic respiratory acid-base disorders: http://www.anaesthesiamcq.com/AcidBaseBook/ab9_3.php
- If calculated value does not match expected value, there is a 2
^{nd}disorder.

- If calculated value does not match expected value, there is a 2

- Metabolic acidosis
- Is
__anion gap__elevated (*corrected for albumin)? Calculate the “__delta gap__” or “__delta ratio__.”- Normal anion gap = 12, Normal HCO3 = 24
__Delta gap__= (AG – 12) – (24 – HCO3)- If Delta gap >6, superimposed metabolic alkalosis
- If Delta gap <-6, superimposed non-gap metabolic acidosis

__Delta ratio__= (AG – 12)/(24 – HCO3)- If Delta ratio >1, superimposed metabolic alkalosis
- If Delta ratio <1, superimposed non-gap metabolic acidosis

The differential diagnosis for **metabolic alkalosis** isn’t too bad!

- Think:
**H+ loss**, too much**bicarb**,**shift**, or**contraction**! **Common**: Vomiting/NG suction! Diuretics! Post-hypercapnic! HypoK! Contraction!- See table for more detail

One or more of the following is required (in absence of ESRD) to maintain metabolic alkalosis:

- Volume depletion
- Hypochloremia
- Hypokalemia
- Increased sodium delivery and absorption in the distal nephron

Send a **urine chloride**!

- Urine Cl <25 = saline responsive (e.g. vomiting, diuretics, contraction)
- Give volume!

- Urine Cl >40 = saline unresponsive (mostly renal/electrolyte causes!)
- Treat underlying cause!

- If saline unresponsive, what is BP?
- If normal/low BP, consider severe hypoK or Bartter’s!
- If elevated BP, consider hyperaldosteronism/hypercortisolism!

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