ABGs and Acid-Base Flashcards
What is an ABG?
frequently used to detect and monitor indices of:
Oxygenation
Ventilation
Acid-base balance
also quantify levels of carboxyhemoglobin and methemoglobin
What can you also get quickly with an ABG?
H/H and lytes
How do we get ABGs?
blood drawn from an artery- usually radial
collected with an anticoagulant (heparin), put on ICE and take it to lab
quick! ~5 min
What’s on an ABG?
ph pO2 O2 sat PCO2 35-45mmHg HCO3 22-26 mmol/L
What is pO2 used for?
determining how well the pt is oxygenating
more reliable than pulse ox
Role of Acids and Bases
both work as a buffer system
Body maintains precise control of hydrogen ions to maintain homeostasis
Acidemia? Alkalemia?
Ph <7.35
ph > 7.45
A primary respiratory problem involves….
primary metabolic problem involves…
pCO2
HCO3
If both pCO2 and HCO3 are HIGH …
respiratory acidosis or metabolic alkalosis
If both pCO2 and HCO3 are LOW …
respiratory alkalosis OR metabolic acidosis
If pCO2 and HCO3 are moving in opposite directions, there is a
mixed disorder present
Compensatory process in acid-base disorder
body tries to compensate for an acid-base disorder by using respiratory or metabolic processes that attempt to return a patient’s pH to normal
Causes Metabolic Acidosis?
high anion gap metabolic acidosis
- MUDPILES
non anion gap metabolic acidosis: GI bicarb loss, renal bicarb loss, hypercholeremia due to saline resuscitation
MUDPILES?
Causes for metabolic acidosis with high anion gap:
Methanol Uremia DKA Propylene Glycol Iron/Isoniazid Lactate (lactic acidosis) Ethanol/ethylene glycol Salicylates/starvation
Tx for metabolic acidosis?
treat underlying cause!!
+/- sodium bicarb to temporarily help
allow for norm. respiratory compensation
What is renal tubular acidosis (RTA)?
RTA is a family of syndromes of metabolic acidosis from defects in tubular H+ secretion and urinary acidification.
Relatively uncommon
metabolic acidosis and NORM anion gap
What are the 2 types of RTA?
Failure to reabsorb filtered HCO3 (Type 2)
Failure to excrete H+ (Type 1)
Describe type 1 RTA, tx?
(distal)
Most often caused by autoimmune disease and hypercalciuria. Can also be genetic.
correct metabolic acidosis
potassium citrate if persistent hypokalemia
Describe type 2 RTA, tx?
Isolated defect in proximal bicarb reabsorption or in association with other defects in the proximal tubular function that impair reabsorption of other solutes
Correct acidemia
May need Vit D and phosphate supplements
+/- Thiazide diuretics
Tx of metabolic alkalosis if urine chloride <25?
if >25?
give fluids!
tx underlying cause, may need K
Describe respiratory acidosis
not able to ventilate well enough, leading to an accumulation of CO2
Causes of respiratory acidosis?
acute airway obstruction
lung disease i.e. COPD, pna
CNS depression i.e. drugs (narcotics), CNS event
Neuromuscular disorder i.e. MG, GBS
Tx for respiratory acidosis?
tx underlying cause
res. support - BIPAP
- determine if acute or chronic
What is respiratory alkalosis
excressive elimination of CO2 from lungs
CO2 <35
sxs: lighheadness, palpitation, tachypnea, +/- paresthesias
What are some causes of respiratory alkalosis?
hyperventilation, anxiety
compensatory in sepsis
pain
CNS, etc.
How do you determine primary acid-base disorder?
look at PH!!
How can you tell if pt is compensating?
If ph is close to normal
How do you calculate anion gap?
Na -(Cl + HCO3)
normal: 8-12mmol/L
Anytime you have a very high anion gap greater than …… there automatically has to be a primary metabolic acidosis,
20
Does a normal Ph mean that you don’t have an acid base disorder?
NO
could be compensated
low bicarb is usually…
pathologic
make sure you investigate it
Causes of metabolic alkalosis w/ urine chloride < 25
GI losses (vomiting)
Diuretics (“contraction alkalosis”)
Cystic fibrosis
Causes of metabolic alkalosis w/ urine chloride > 25
Barter's Cushing's Hyperaldosteronism K depletion Citrate toxicity Chronic diuretics Renin secreting tumor
