Clin Lab: ABGs (done) Flashcards
What is ABG used for?
assess O2 status & acid/base balance
Where is the blood drawn from for ABG test?
radial artery
Absolute contraindications for ABG test.
- poor blood flow to the hand (via Allen test)
- known vascular dz in the extremity
Relative contraindications for ABG
- bleeding disorder or on blood thinner
- low platelet count
Procedure for ABG test
- Allen test
- Wrist positioning
- Needle insertion (self fills)
- 5 min pressure after removal
Measurement components of an ABG
- PaO2
- SaO2
- pH
- PCO2
- HCO3
Normal PaO2
80-100 mmHg
(some say 75-100)
Normal SaO2
94-100%
Normal pH
7.35 - 7.45
Normal PaCO2
35 - 45
Normal HCO3-
22 - 26
Acid-Base problems occur when there is…
too much or too little acid in relation to base
What happens once pH has large shifts?
- proteins start to change shapes
- enzymes start to denature
What two components of an ABG are important, but not part of acid/base balance?
PaO2 & SaO2
3 main regulators of pH
- Buffer Systems - primary
2A. Lungs
2B. Kidneys
What is the main driver of the principle buffer system?
bicarbonate
What are the other parts of the principle buffer system?
- hemoglobin
- phosphate
- proteins
Role of hemoglobin.
- can absorb or release acids
Role of phosphate
- holding on or giving off H+
What info does the Henderson Hesslebach equation give us?
what the expected pH is going to be. (7.40)
What is the ratio for bicarbonate & carbonic acid?
20:1
Principles of acid/base regulation. Normal status (equation)
H+ + HCO3- <–> H2CO3 <-CA-> CO2 + H20
What is pKa?
acid dissociation constant specific to each acid
What is the biggest determiner of pH in our body?
bicarbonate balance
If HCO3- goes up to 40, what would the H2CO3 be?
2
If the HCO3- goes down to 10, what would the H2CO3 be?
.5
If buffer systems are not sufficient, what two system respond?
Lungs & kidneys
What short term fix kicks in if the buffer system isn’t sufficient?
the lungs
How do the lungs combat acid/base imbalances?
change levels of CO2 by increasing/decreasing rate of resp
What does increasing resp rate do to the acid/base balance?
- more CO2 exhaled = decr CO2 in blood
- Equilibrium shifts to right, reducing H+
What does decreasing resp rate do to the acid/base balance?
- less CO2 exhaled = inc CO2 in the blood
Equilibrium shifts to left, increasing H+
How long does it take the lungs to respond to acid/base imbalance?
minutes
How do the kidneys participate in acid/base regulation?
regulate HCO3-
What do the kidneys do if pH is acidic?
reabsorb more HCO3- and excrete more H+
What do the kidneys do if the pH is alkaline?
- excrete more HCO3- & reabsorb more H+
How long does it take the kidneys to respond to acid/base imbalance?
3-5 days
If pH is too acidic, what do the kidneys do?
excrete H+ & reabsorb bicarb
If pH is too basic, what do the kidneys do?
excrete bicarb & reabsorb H+
What two possible main issues to cause acidosis?
- resp acidosis
- metabolic acidosis
What is the cause to result in resp acidosis?
- rate of ventilation of CO2 is decr (lungs aren’t working)
What is the cause to result in metabolic acidosis?
- ^ production of acid
- ^ loss of bicarb
What two possible main issues to cause alkalosis?
- resp alkalosis
- metabolic alkalosis
What is the cause to result in resp alkalosis?
- rate of ventilation ^^
What is the cause to result in metabolic alkalosis?
- ^^ bicarb
- ^^ loss of acid
A person who only has one type of acid-base disorder is considered…
simple
What is it called when a pt. has more than one acid-base disorder at a time?
mixed
Can you have 4 acid-base disorders?
NO
Can you have resp acidosis & resp alkalosis?
NO
Can you have resp acidosis, metabolic acidosis, & metabolic alkalosis at the same time?
YES
Describe pCO2 & pH in Resp acidosis
^ pCO2 & v pH
What can cause Resp acidosis? (w/examples)
- decreased ventilation
(obstruction, pneumo, pleural effusion, emphysema, COPD, stroke) - decreased perfusion
(PE, cardiac arrest)
NM condition
S/S of resp acidosis
- HA
- Tachycardia
- CNS depression
- Cardiac arrhythmia
- Obtunded
Therapy for resp acidosis?
- CPAP, BiPAP
- pneumonectomy
Acute (no compensation) presents as…
- CNS depression - drug OD, acute stroke
- Acute airway obstruction
- Severe pneumonia & pulm edema
Chronic (compensation) presents as…
- chronic lung disease
- chronic NM disorder
- chronic resp center depression
- obesity
Describe pCO2 & pH in resp alkalosis.
v pCO2 & ^ pH
Causes of resp alkalosis (w/ examples)
- hyperventilation
(anxiety, stress, fear, CNS disease, drug uses, pregnancy, sepsis, liver dz, hypoxemia, low O2
S/S of resp alkalosis
- Lightheadedness
- CNS irritability
- Cardiac arrhythmias
Therapy for resp Alkalosis
- anti-anxiety meds
- O2 if b/c of hypoxia
- CO2 rebreathing
Describe an aspirin OD
leads to hyperventilation early on–> resp alkalosis
aspirin continues to absorb –> leads to metabolic acidosis
How does sepsis cause resp alkalosis?
usually from fever
fever will incr resp rate, & lead to akalosis
Describe HCO3 & pH for Metabolic acidosis
v HCO3 & v pH
Causes of Metabolic acidosis
- acid production (poisoning, abnormal metabolism, shock/low perfusion)
- loss of base (diarrhea, pancreatic fistula)
S/S of metabolic acidosis
(HAC)
- HA
- CNS depression
- altered mental status
Therapy for Metabolic acidosis
- correct underlysing causes
- improve tissue oxygenation (lactic acid)
- consider giving NaHCO3 if pH < 7
Major cations in the blood?
Na+ & K+
Major anions in blood
Cl-, HCO3-, phosphate (PO4-)
Define an anion gap.
the difference b/t measured anions & measured cations
Normal anion gap range
8 - 16
In anion gap: there will always be more ___ things than ___ things.
positive; negative
What causes a decreased anion gap & should we be worried?
-hypoalbuminemia or incr in unmeasured cation
NO
Which type of anion gap are we most worried about? & what causes it?
increased gap =
retention of 1 or more unmeasured anions (weak base from acid accumulation)
Take home message–> incr gap = too much acid
Which type of acid/base disorder deals w/ anion gaps?
metabolic acidosis
Reasons for high anion gap metabolic acidosis (MUDPILES)
- methanol/metformin
- Uremia (high BUN)
- DM ketoacidosis
- Paraldehyde/phenformin
- Iron/Isoniazid
- Lactate
- Ethylene glycol (antifreeze)
- Salicylates (aspirin)
HAGMA anion gap value
> 20
Go study slide 30 in ABG lecture
Okay
Acronym for reasons of high anion gap metabolic acidosis
- M - Methanol/metformin
- U - Uremia (high BUN)
- D - Diabetic ketoacidosis
- P - Paraldehyde/phenformin
- I - Iron/Isoniazid
- L - Lactate
- E - Ethylene glycol (antifreeze)
- S - Salicylates (aspirin)
Describe HCO3- & pH for metabolic alkalosis.
- ^ HCO3- & ^ pH
Causes for metabolic alkalosis
- base accumulation (excessive antacids, blood transfusion)
- loss of acid (vomiting, gastric suction (NG tube), diuretic use
S/S of metabolic alkalosis
- CNS irritability
- eventual CNA depression
Therapy for Metabolic alkalosis
- revere underlying causes (antacids, low Cl-, low K+, vomiting)
- almost NEVER give HCl
Which acid-base disorder has to do w/ the release of aldosterone?
metabolic alkalosis
Describe Chloride responsive
Low Urine Cl- Level
- vomiting, nasogastric suction
- laxative abuse
- diuretic use
CAN FIX W/ FLUIDS (NaCl)
except w/ diuretic induced alkalosis has a result of CHF
Describe chloride resistant
(something rare)
Normal or High Urine Cl- Level
- excess mineralocorticoid activity (Cushing’s syndrome, Conn’s syndrome, exogenous steriods, licorice ingestion, incr renin states)
- excess alkali admin
Is normal or high Urine Cl- levels responsive or unresponsive
unresponsive: tx underlying cause
Describe uncompensated.
pH is off
PCO2 or HCO3- is off & one is WNL
Describe partially compensated.
pH, PCO2 & HCO3 are off
Describe fully compensated.
PCO2 & HCO3 are off
pH is NORMAL
