Kleinschmidt- Acid Base Differential Diagnosis Flashcards
What should you first consider when evaluating AB disorders?
Look at pH using ABG- whichever side of 7.40 is the primary abnormality (acidosis or alkalosis, the body never fully compensates)
When evaluating AB disorders, what should you do once you’ve figured out the pH?
Calculate the anion gap,
What does an elevated anion gap indicate?
primary metabolic acidosis or a mixed acid base problem that includes a anion gap
When evaluating AB disorders, what should you do next if there IS an elevated anion gap?
Calculate a osmol gap
How do you calculate an osmol gap?
Measured osmolarity- calculated osms should be < or = 10
2 (Na) + Glucose/18 + BUN/2.8= calculated osms (usually 285 or so)
What might you find by calculating an osmol gap?
Ingestions such as ethylene glycol, methanol, etc
Once you’ve calculated the elevated anion gap and the osmol gap what should you do next?
Calculate the excess anion gap (calculated minus 12) and add to measured bicarb, it should equal a normal bicarb level (24-26)
What does it mean if the excess anion gap is low? high?
LOW means there is also a non anion gap acidosis
If it is HIGH there is an underlying metabolic alkalosis.
Normally a change of gap of 1 will drop the HCO3‾ by equal amount. What is going on if it doesn’t add up right?
There is a SECOND ongoing process.
This process is also called the “delta gap” by some.
If ABG is normal but you have an elevated anion gap you may have a….
mixed metabolic alkalosis and anion gap metabolic acidosis
What leads to leads to PCO2 lower than predicted for the acidosis?
Mixed Metabolic Acidosis and Respiratory Alkalosis
What leads to HCO3‾ higher than predicted for the acidosis?
Mixed Metabolic Alkalosis and Respiratory Acidosis
What causes a higher HCO3‾ and lower PCO2 than predicted?
Mixed metabolic and resp alkalosis
What is the primary disturbance behind metabolic acidosis and the compensatory response? What are the sources of these disturbances?
Primary disturbance is retention of acid, this is reflected by a decrease of HCO3‾.
Compensatory response is to increase ventilation and decrease the PaCO2 on ABG.
Either is caused by an overproduction of acid or loss of alkali stores, or failure of renal
mechanisms to synthesize base or excrete acid.
What is indicative of high anion gap acidosis?
- ph <7.35, low HCO3‾ on ABG or chemistry tests
- AG over 15
- Compensation is to get rid of CO2
- pCO2= (1.5 x HCO3‾) + 8 (+/-2)
- or PCO2= last 2 digits pH
If a pt has high anion gap acidosis what should you always calculate?
osmol and delta gap
What is the differential diagnosis for Metabolic acidosis?
MUDPILES! M=Methanol U=Uremia D= DKA and AKA (diabetic and alcoholic ketoacidosis) P= Paraldahyde I= Iron or INH L= Lactic Acid E=Ethylene Glycol (and ethanol) S= Salicylates
How does methanol cause metabolic acidosis? What population is this commonly observed in?
Creates osm gap (methanols osm forces/3= methanol level)
See in alcoholics using other volatiles to get intoxicated
What is commonly observed in uremia induced metabolic acidosis?
Create generally over 5, BUN over 60. Gap rarely over 20
How do DKA and AKA cause metabolic acidosis?
Acidosis is due to ketone production.
Alcohol increases osm gap
Lactic Acid induced Metabolic Acidosis is commonly observed with what conditions?
sepsis, hypotension, CO or cyanide poisoning, measure level
When is Ethylene glycol induced metabolic acidosis observed? What does it do? How do you treat it?
See in OD’s, 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 are the multiple presentations for salicylate induced metabolic acidosis? What do you also tend to see with this?
coagulopathy, seizures
Also tend to see a primary resp alkalosis or acidosis with this
What is another name for Normal Anion Gap Acidosis? What causes it?
Hypercholeremic Metabolic Acidosis
Due to LOSS of HCO3 from kidney or GI
See EQUAL rise of Cl for loss of HCO3
H- post hyperventilation, hyperalimentation A- Acid ingestion (CAI, HCl) R- RTA (especially in diabetes) D- Diarrhea (MCC) U-Ureteral and ileal diversion P- Pancreatic fistulas
What is the primary disturbance and compensatory mechanism in Metabolic Alkalosis?
Increased plasma HCO3
Hypoventilating (limited ability)
Bicarb and pH are ELEVATED–> compensate by hypoventilating which is LIMITED
What causes chloride responsive metabolic alkalosis?
Responds to SALINE INFUSION!
Vomiting Diuretics-> too aggressive--> increase bicarb NG suction--> suck acid out of stomach Diarrhea causing dehydration, Cl wasting Villous adenoma
What does low urine Cl denote?
Kidney is holding on to NaCl
What causes chloride unresponsive metabolic alkalosis?
High Aldosteronse >
increased H and K excretion in EXCHANGE for reabsorbing Na as NaHCO3
Cusings
Hperaldosteronism (Barters)
Secondary Hyperaldosteronism (CHF, CRF)
Bicarb ingestion
What is the primary disturbance and compensatory response in respiratory acidosis?
Increase in ARTERIAL CO2
ELEVATE HCO3 BY METABOLIC MECHANISMS
*compensation has acute and chronic components
What is acute compensation in respiratory acidosis?
HCO3 rises 1 mEq or each rise of 10 of pCO2
What is chronic compensation in respiratory acidosis?
HCO3 increases 3 for each rise of 10 pCO2
What causes respiratory acidosis?
Airway obstruction
LUNG- COPD, Asthma, PTX, Infection
CNS- Sedative/hypnotics, drugs, tomor
Neuromuscular weakness
What is the primary disturbance and compensatory response in respiratory alkalosis?
DECREASE IN ARTERIAL CO2
DECREASING HCO3
*Has acute and chronic compenets
What is the difference between acute and chronic compensation in respiratory alkalosis?
HCO3 falls by:
2 mEq (acute) 4 mEq (chronic)
for each drop of 10 pCO2
What causes respiratory alkalosis?
ANXIETY> blow off CO2 > raise pH
ASPIRIN and other drugs: cocaine, progesterone
Causes of TACHYPNEA- sepsis, fever, PE, pneumonia, hypoxia
ALCOHOL or narcotic w/drawal
