ABG Flashcards
venous blood gas
Differences in pH and PCO2 are relatively small
In general the pH is 0.03-0.04 units lower than arterial
In general the PCO2 is 7 or 8mmHg higher than artery
-less accurate and less preferred than arterial
Hend. Hasselbach
pH= 6.1 + log (HCO3/0.03*PCO2)
questions
Acidic or Basic? 7.35-7.45 Who’s to blame? look at CO2
Is that all?
Normal CO2
35-45
to evaluate acid-base disturbance, need
simultaneous measurements of electrolytes, albumin, arterial blood gas
ABG directly measures
pH and Pco2
if the pH is acidic
And the CO2 is elevated (acidic)—blame the lungs (respiratory)
But if the CO2 is decreased (basic)—blame the body (metabolic)
The body can have a basic single acid base disturbance…or…
the more frequent double acid base disturbance, or the complex triple acid base disturbance
for ever multiple of 10 the co2 is elevated or decreased (from normal: 40) the pH should change by..
0.08 times (from 7.40) that multiple
Example: pH of 7.24 with a CO2 of 60
*single A-B disturbance
it is physically impossible to have a…
respiratory acidosis w/ resp. alkalosis but CAN have an anion gap metab. acidosis w/ metab. alkalosis
measurement of cations/anions in plasma
[Na] + Unmeasured cations = HCO3 + Cl + Unmeasured anions
anion gap =
Na – (HCO3 + Cl)
Normal Anion gap is from 12 +/- 4
major unmeasured cations
Ca (2 mEq/L), Mg (2 mEq/L), gamma-globulins, and K (4 mEq/L)
major unmeasured anions
albumin (2 mEq/L per g/dL), PO4 (2 mEq/L), sulfate (1 mEq/L), lactate (1–2 mEq/L), and other organic anions (3–4 mEq/L).
anion gap: misleading data from..
hypoalbuminemia (for every 1g change in albumin, the AG should have a 2meq change (inc. if albumin low, dec. if high)
hyper or hyponatremia
certain antibiotics
causes of increased anion gap: metabolic anion
Diabetic, alcoholic, starvation ketoacidosis lactic acidosis (Type A (tissue ischemia), Type B (altered cell metabolism), D-Lactic acidosis) CKD 5-oxoproline acidosis from acetaminophen toxicity
causes of inc. anion gap: drug or chemical anion
Salicylate intoxication Sodium carbenicillin therapy Methanol (formic acid) Ethylene glycol (oxalic acid) Cyanide Isoniazid Propofol Propylene glycol Valproic acid Paraldehyde
causes of anion gap: metabolic acidosis (MUDPILES)
Methanol Uremia DKA (and etOH, starvation ketoacidosis) Paracetamol (acetaminophen) (Paraldehyde) Iron, Isoniazide, Inborn errors of metabolism Lactic acidosis Ethanol, Ethylene Glycol Salicylate/ASA
lactic acidosis
from pyruvate in anaerobic glycolysis, normal 1mEq
-Metab of lactate mostly: liver gluconeogenesis (30% by kidneys)
Type A (hypoxic): dec. perfusion (shock, CO poisoning)
Type B (metab/toxins): DM, KD, leukemia, lymphoma, salicylates, metformin, INH, propofol, etc.
DKA
acetoacetate/B-hydroxybutyrate cause INC. metab. gap, also have comb. lactic acidosis from tissue HYPOperfusion and inc. anaerobic metab.
DKA may dev. this during recovery phase
hyperchloremic non-anion gap metab. acidosis from saline resuscitation
*important to monitor anion gap–>when to turn off insulin drip (guides tx)
alcoholic ketoacidosis
lots of variation:
- primarily: Beta hydroxybutyrate and acetoacetate excess
- Lactic acidosis since alcohol increases production of lactate especially when accompanied by thiamine deficiency (if v. high >6 consider pancreatitis, sepsis, post-seizure (concomitant)
- metab. alkalosis from vomiting and vol. contraction
- resp. alkalosis from w/drawal and pain
decreased anion gap
Hypoalbuminemia (decreased unmeasured anion)
Plasma cell dyscrasias
Monoclonal protein (cationic paraprotein) (accompanied by chloride and bicarbonate)
Bromide intoxication
normal anion gap acidosis
loss of HCO3 renal loss of HCO2 renal tubular dysfunction hypoaldosteronism Chloride retention admin. of HCl equiv or NH4Cl argining and lysine in parenteral nutrition
normal anion gap acidosis: loss of HCO3
Diarrhea
Ureteral diversion
Proximal colostomy
Ileostomy (pancreatic fluid loss
normal anion gap acidosis: renal loss of HCO3
Proximal Renal tubular acidosis
Carbonic anhydrase inhibitors
normal anion gap acidosis: renal tubular dysfunction
ATN
Chronic tubulointerstitial disease
Distal RTA type 1
Distal RTA type 4
normal anion gap acidosis: hypoaldosteronism
Addison’s disease
K+ sparing diuretic
strong ion difference, what if >30?
[SID] = [Na+] + [K+] + [Ca2+] + [MG2+] - [CL-] - [Other Strong Anions]
*Na and Cl are biggest contributors (calculate: Na-Cl)
if >30: metabolic alkalosis
contraction alkalosis
decreasing volume increases SID (inc. Na+ relative to Cl-)
causes of respiratory alkalosis
see slide- think of what makes you breathe rapidly
causes of respiratory acidosis
see slide- consider airway obstruction, laryngospasm, mucus plug, anesthesia, resp. depression (meds), high carb diet, sedatives
typical patterns seen in disease states
Combined Metabolic Acidosis and Respiratory Acidosis (Cardiogenic Shock- not breathing as much and hyper perfusion)
Combined Metabolic Acidosis and Respiratory Alkalosis (Sepsis, Salicylate poisoning)
Respiratory Acidosis with metabolic alkalosis (Chronic COPD-body compensating for resp. acidosis w/ the metab. alk)
