Acid/Base disorders Flashcards
What are ABG’s used for
monitoring oxygenation, ventilation, acid base balance
quantifying level of carboxyhemoglobin and methhemoglobin
How do you draw an ABG
from artery (MC radial)
mix with anticoag (heparin)
put on ice
take to the lab ASAP, results w/in 5-15 min
What are the ABG’s
pH 7.35-7.45 pO2: 80-100 O2 sat: >95 pCO2: 35-45 HCO3: 22-26
pO2 is used to determine
how well a patient is oxygenated (better than an O2 sat), NOT for determining acid-base conditions
What is our body’s normal physiology
body maintains homeostasis with strict control of hydrogen ions
buffer systems keep pH in normal range
acidosis/alkalosis are disorders
acidemia and alkalemia are pH of blood
What are respiratory and metabolic problems
Resp acidosis: pCO2 >45
Resp alkalosis: pCO2 <35
Met acidosis: HCO3 <22
Met alkalosis: HCO3 >26
Acid base disorders indicate
underlying disease process- so Tx underlying disease!
You can have up to 3 AB d/o- we have to figure out the primary one and treat it
(but you can only have ONE respiratory AB d/o)
What is the compensatory process
body will compensate for an AB d/o with the opposite
Respiratory compensation for metabolic d/o= fast
metabolic compensation for resp d/o= days-weeks
What causes metabolic acidosis
high anion gap: MUDPILES (methanol, uremia, DKA, propylene glycol, iron, lactate, ethanol, salicylate/starvation)
non-high anion gap: diarrhea (you lose more bicarb), RTA, Acetazolamide, spironalactone, Hyperchloremia
How do you treat metabolic acidosis
Sodium bicarb (band aid)
allow for respiratory compensation (hyperventilation, low CO2)
treat underlying cause
What is renal tubular acidosis
defects in H+ secretion and urinary acidification
Metabolic acidosis + NORMAL anion gap
What are the 2 types of renal tubular acidosis
Type 1: failure to excrete H+
Type 2: failure to reabsorb filtered HCO3
Explain Type 1 RTA (distal)
AI disease and hypercalciuria (or genetic) cause H+ to not be excreted
Tx: correct metabolic acidosis (sodium bicarb), give potassium citrate if persistent hypokalemia
Explain Type 2 RTA (proximal)
Defect in proximal bicarb reabsorption, or other defects in proximal tubule that inhibit reabsorption of phosphate, glucose, uric acid, and amino acids
-Fanconi syndrome: generalized proximal tubular dysfunction caused by multiple myeloma or acetazolamide
How do you treat Type 2 RTA
correct academia
Vitamin D and phosphate
+/- thiazide
With metabolic Alkalosis, what do you need to check
Urine chloride
If Metabolic alkalosis + Urine chloride <25 (responsive to alkalosis) it is caused by
Vomiting (you lose more acid)
Diuretics (contraction alkalosis)
CF
**Tx with FLUIDS!
If Metabolic alkalosis + urine chloride >25 (not responsive to alkslosis) it is caused by
Cushing’s, high aldosterone, low potassium, citrate toxicity
chronic diuretics
renin secreting tumor
*Tx underlying cause, +/- potassium
What happens in respiratory acidosis
you cant ventilate well (hypoventilation) so you build up CO2 (>45)
What are causes of respiratory acidosis
Acute airway obstruction (FB, laryngospasm)
Lung Dz: PNA, PE, COPD, PE
CNS depression: narcotics, trauma, OSA
NM d/o: Guillan barre, MG, brain stem/S.C. injury
How do you treat respiratory acidosis
Tx underlying cause
BiPAP (resp support) if acute
chronic is more stable an dmay not need Tx
What are Sx of respiratory alkalosis
(hyperventilation, pCO2 <35)
Light headed, palpitations, tachypnea, paresthesias
What can cause respiratory alkalosis
Hyperventilaiton (anxiety) sepsis compensation pain salicylate OD (mudpiles!) pregnancy high altitude hypoxemia hepatic encephalopathy
How do you treat respiratory alkalosis
treat underlying cause
What is compensation
if pH is close to normal, pt is compensating
if highly abnormal pH, patient is not compensating
What is an anion gap
anions that cant be measured on BMP- albumin, phosphate, sulfate, etc
Na- (Cl+HCO3)= 8-12 mmOl normally
What does anion gap >20 mean
primary metabolic acidosis (regardless of what other ABG’s say!)
body doesn’t generate large anion gaps as compensation, so there must be an underlying metabolic acidosis
Explain mixed acid base disorders
you can have up to 3 at a time, but only 1 respiratory d/o at a time
Take home points
normal pH does NOT mean no acid base disorder low bicarb (metabolic acidosis) is usually pathologic- investigate it
What does MUDPILES stand for
Methanol Uremia DKA Propylene glycol Iron Lactate Ethanol Salicylate OD/starvation
They all cause high anion gap metabolic acidosis!
