Evaluation of Acid Base Disorders Flashcards by Kayla Schenheit

What is rule 1 in evaluating Acid Base Disorders?

Look at pH using Arterial Blood Gases!

-Whichever side of 7.40 is the primary abnormality (acidosis or alkalosis –> body never fully compensates)

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What is normal pH?

7.40

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What does a pH below 7.40 indicate?

Acidosis

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What does a pH above 7.40 indicate?

Alkalosis

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What is rule 2 in evaluating Acid Base Disorders?

Calculate the ion gap!

-If elevated, you need to explain it

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What two things will include an anion gap?

Primary metabolic acidosis

- Mixed acid base problem (w/ ion gap)

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What if pH is normal and you have an anion gap?

You have anion gap acidosis!!

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What is rule 3 in evaluating Acid Base Disorders?

If there is an elevated anion gap, calculate the osmol gap

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How do you calculate the osmol gap? What should it be?

Measured osmolarity - Calculated osms

–> Should be

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How do you calculate osmolarity for the osmol gap?

2 (Na) + Glucose/18 + BUN/2.8 = calculated osms (usually 285 or so)

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What is the normal anion gap?

About 12

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In what clinical scenarios will you find osmol gaps?

Ingestions - like ethylene glycol, methanol, etc.

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What is rule 4 in evaluating Acid Base Disorders?

Delta gap!!
Calculate the excess anion gap (calculated minus 12) and add to measured bicarb –> should equal normal bicarb level (24-26)

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What if the delta gap is low?

There is also a non-anion gap acidosis.

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What if the delta gap is high?

There is an underlying metabolic alkalosis

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What other thing should you know about delta gap?

Normally, a change in gap of 1 will drop HCO3- by an equal amount –> if it doesn’t add up right, there is a second ongoing process

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What is rule 5 in evaluating Acid Base Disorders?

Interpret using the clinical picture

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If ABG is normal, but you have an elevated ion gap. . .

. . .you have a mixed metabolic alkalosis and anion gap metabolic acidosis

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Mixed Metabolic Acidosis and Respiratory Alkalosis leads to. .

. . .PCO2 lower than predicted for the acidosis

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Mixed Metabolic Alkalosis and Respiratory Acidosis leads to . . .

. . .bicarb (HCO3-) higher than predicted for acidosis

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Mixed metabolic and respiratory alkalosis . . .

. . .get a higher HCO3- and lower PCO2 than predicted

What is the primary disturbance in Metabolic Acidosis?

Retention of acid –> reflected by decrease of HCO3-

What is the compensatory response in Metabolic Acidosis?

Increased ventilation and decreased PaCO2

What are four mechanisms by which metabolic acidosis can be produced?

Overproduction of acid
Loss of alkali stores
Failure of renal mech. to synthesize base
Failure of renal mech. to excrete acid

What do labs show with High Anion Gap Metabolic Acidosis?

What should you ALWAYS calculate with High Anion Gap Acidosis?

Osmol and delta gap!

What does MUDPILES ddx stand for? What condition does it relate to?

``` M - Methanol U - Uremia D - DKA/AKA P - Paraldahyde I - Iron or INH (Isoniazid - TB treatment) L - Lactic acid E - Ethylene Glycol (and ethanol) S - Salicylates ```

What does methanol cause?

- Creates osm gap (methanols osm forces/3 = methanol level) | - See in alcoholics using other volatiles to get intoxicated

What do you see in uremia?

High anion gap acidosis | -Generally over 5, BUN over 60, gap rarely over 20

What do you see in DKA/AKA?

(diabetic or alcoholic ketoacidosis) - Acidosis is due to ketone production - Alcohol increase the osm gap

What do you see in Lactic Acid High Anion gap Acidosis?

See with sepsis, hypotension, CO or cyanide poisoning, measure level

What do you see with Ethylene Glycol (and ethanol)?

- See ODs, antifreeze or windshield washer - Causes renal failure, oxalate urine crystals - Creates Osm gap, each mosm gap = 6mg% of ethylene glycol - Dialysis, alcohol or medical rx are treatments

What do you see with Salicylates?

These can cause almost any acid base disorder (except metabolic acidosis) - Multiple presentations, can cause coagulopathy, seizures - Also tend to see a primary resp. alkalosis or acidosis with this

What mechanism often causes Normal Anion Gap Acidosis (Hyperchloremic Metabolic Acidosis)?

Due to loss of HCO3- from kidney or GI is most common. | -See equal rise in Cl- for loss of HCO3-

What lab values do you see in Normal Anion Gap Metabolic Acidosis?

``` Low bicarb (HCO3-) High Cl- Low pH (acidosis) ```

What clinical presentations are associated with Normal Anion Gap Metabolic Acidosis?

HARDUP

What does HARDUP stand for?

H - Post hyperventilation, hyperalimentation A - Acid ingestion (Carbonic Anhydrase Inhibitor, HCl) R - RTA (renal tubular acidosis) D - Diarrhea U - Ureteral and ileal diversion P - Pancreatic fistulas

What is the primary disturbance in Metabolic Alkalosis?

Increased plasma bicarbonate (HCO3-)

What is the compensatory mechanisms for Metabolic Alkalosis?

Hypoventilating (we have limited ability to do this!)

What are Cl- responsive Metabolic Alkalosis?

Urine Cl-

What is Cl- unresponsive Metabolic Alkalosis?

Due to high Aldo! --> causes inc. H+, K+ excretion --> inc. Na+, NaHCO3 reabsorption

What conditions cause Cl- unresponsive Metabolic Alkalosis?

- Cushings - Hyperaldo. including Barter's - Secondary hyperaldo. (CHF, CRF) - Bicarb. ingestion

What is the primary disturbance in respiratory acidosis?

Increase in arterial CO2

What is the compensation for Respiratory Acidosis?

Elevating bicarb. by metabolic mechanisms

What is acute and chronic compensation for respiratory Acidosis?

``` Acute = HCO3- rises 1 mEq for each rise of 10 of pCO2 Chronic = HCO3- increases 3 for each rise of 10 of pCO2 ```

What do you see for lab values in respiratory acidosis?

High CO2 Low pH High HCO3-

What conditions cause respiratory acidosis?

- Airway obstruction - Lung (COPD, Asthma, pneumothorax, infection, etc.) - CNS (Sedative/Hypnotics, drugs- heroin overdose, tremor) - Neuromuscular weakness (ALS, G-B syndrome)

What is the primary disturbance in respiratory alkalosis?

Decrease in arterial CO2

What is the compensation for respiratory alkalosis?

Decreasing HCO3-

What is acute and chronic compensation for respiratory alkalosis?

``` Acute = HCO3- falls by 2 mEq for each drop of 10 of pCO2 Chronic = HCO3- falls by 4 mEq for each drop of 10 of pCO2 ```

What conditions cause respiratory alkalosis?

- Anxiety - Aspirin and other drugs; cocaine, progesterone - Any cause of tachypnea: sepsis, fever, PE, Pneumonia, hypoxia - Alcohol or narcotic withdrawal - Many others