Acid Base Disorders Flashcards
Is pH and pCo2 calculated or measured?
Measured using electrodes in an analyzer
Is HCO3 and BE calculated or measured?
Calculated from measured pH and pco2
What knowledge do you need to determine acid-base status?
patient history, pH, pco2, HCO3
What does calculating base excess do?
quantifies a metabolic disorder
What is purpose of anion gap?
helps determine the metabolic source. (MUDPILES and FUSEDCARS)
What does the “base” mean in base excess?
Sum of weak acid anions in plasma (hemoglobin, plasma proteins, phosphate, and bicarbonate)
What is the same as base excess?
Strong ion difference (SID)
How do you calculate base excess?
BE = calculated HCO3 - 24mEq/L (normal HCO3)
What are our standard conditions?
37 degrees C, pH 7.40, Pco2 40
What is our base excess at standard conditions?
0mmol/L !
What can base excess be a useful predictor for?
severity of critical illness associated with hypovolemic shock and consequent metabolic acidosis
What is normal base excess?
-2 to 2
3 possible mixed acid-base disorder scenarios
- pH 7.4 where respiratory and metabolic have opposite effects
- pH <7.35 and both derangements contribute to acidosis
- pH >7.45 and both derangements contribute to alkalosis
Respiratory acidosis
pH <7.40, paco2 > 45 (ROME)
Respiratory alkalosis
pH >7.4 paco2 <35 (ROME)
Metabolic acidosis
pH <7.4 HCO3 <22 (ROME)
Metabolic alkalosis
pH >7.4 HCO3 >26 (ROME)
If both HCO3 and Paco2 are not outside their normal ranges is the disorder compensated, partially compensated, or uncompensated?
uncompensated!
If both HCO3 and paco2 are both outside their normal ranges and pH is not in normal range changed in the same direction are they compensated, partially compensated or uncompensated?
partially compensated!
if both HCO3 and paco2 are outside their normal ranges and changed in the same direction and pH was in normal range is the disorder compensated, partially compensated, or uncompensated?
fully compensated!
if HCO3 and PaCO2 change in opposite directions outside their normal ranges and pH is 7.4 what does that indicate?
Mixed disorder!
How do you calculate anion gap?
AG =. Na - Cl - HCO3
What acid base disorder would you increase RR/Vt on the vent?
respiratory acidosis
What acid base disorder would giving Naloxone (Narcan) benefit?
respiratory acidosis
Which acid base disorder would you give bronchodilators?
respiratory acidosis d/t bronchoconstriction (asthma, COPD exacerbation)
Which acid base disorder would you give Dantrolene?
metabolic acidosis d/t malignant hyperthermia
Which acid base disorder would you give NaHCO3?
metabolic acidosis
aerobic metabolism produces what kind of acids?
volatile acids (carbonic acid)
anerobic metabolism produces what kind of acids?
nonvolatile acids (lactic acid, hydrogen phosphate)
physiological effects of acidemia
myocardial and smooth muscle depression
- reduction of contractility (decrease Co and BP- vasodilation)
- reduced peripheral vascular resistance
- less responsive to endogenous catecholamines
- threshold for vfib decreased
- coronary dilate, pulmonary constrict!
tissue hypoxia: despite rightward shift of Hgb affinity for O2
progressive hyperkalemia
- .6 mEq for .1 pH
- K+ out, H+ in
- risk for dysrhythmias
cns depression: increased CBF and intracranial HTN (CO2 narcosis)
what makes up majority of anion gap?
albumin (4mg/dL)
physiological effects of alkalemia
K+ in, H+ out (hypokalemia)
increases number of binding sites on plasma proteins for Ca2+ which decreases Ca2+ (circulatory depression and neuromuscular irritability)
decreases CBF (vasoconstriction)
increases SVR
precipitate coronary vasospasm
increase bronchial smooth muscle tone (bronchoconstriction)
decrease pulmonary vascular resistance (vasodilation)
anesthetic considerations for respiratory alkalosis
prolong the duration of opioid induced respiratory depression, general ischemia can occur with reduction in CBF especially if hypotensive
how long does max respiratory compensation for metabolic disorder to occur?
12-24 hours
how long does max renal compensation for respiratory disorder to occur?
3-5 days
