Flashcards in Arterial Blood Gas (ABGs) Deck (33)
What sites of placement do we use to insert arterial lines?
Brachial artery (watch out for embolis)
Dorsalis pedis (foot) artery
What are the main components of an ABG analysis?
BE (base excess)
AG (anion gap)
Electrolytes (Na+, K+, Ca++, Cl-)
What is the normal range of blood pH?
What are 3 indicators on an ABG reading that may indicate general acidosis?
Blood pH < 7.35
PaCO2 > 45
HCO3 < 22
BE < -3
What are 3 indicators on an ABG reading that may indicate general alkalosis?
Blood pH > 7.45
PaCO2 < 35
HCO3 > 26
BE > +3
What is the respiratory buffer response and how long does it take to kick in?
Blood pH changes in response to varying levels of H2CO3; body responds by either hypoventilating (compensation for alkalemia) or hyperventilating (compensation for acidemia) --> so PaCO2 will be affected by this response.
This response occurs within 1-3 minutes of blood pH shift in normal physiology.
What is the difference between acidemia and acidotic?
AcidEMIA refers to an acid state of blood.
Acidotic refers to a generally acidic state of the patient.
What is the renal buffer response and how long does it take to kick in?
The kidney can retain or excrete HCO3 (bicarbonate). It will do either in response to changes in blood pH - for example, if blood pH decreases, kidneys will retain HCO3.
This buffer system takes hours to days to correct the imbalance so cannot be relied on clinically - we must help pt compensate.
What is the difference between respiratory and metabolic acidosis/alkalosis?
Are they mutually exclusive?
Respiratory acidosis = pCO2 > 45
Metabolic acidosis = HCO3 < 22
Respiratory alkalosis = pCO3 < 35
Metabolic alkalosis = HCO3 > 26
No, patient can have both respiratory and metabolic acidosis.
What are some causes of respiratory acidosis?
Pleural disease (think pleural space of lungs)
Musculoskeletal disorders (that may affect lung function)
Compensation for metabolic alkalosis
What is base excess?
Indicates the amount of excess or insufficient level of bicarbonate -2 to +2mEq/L
H+ value that corresponds with pH of 7.4? 7.3? 7.5?
7.4 = 40, 7.3 = 50, 7.5 = 30
What is the respiratory buffer response?
The blood pH changes according to the level of H2CO3 present, triggering the lungs to increase or decrease the rate and depth of ventilation.
This response occurs within 1-3 minutes.
How does the body compensate for chronic respiratory acidosis?
Renally via synthesis and retention of HCO3.
Also by excreting more Cl to balance charges (causing hypochloremia).
How does the body respond to acute and chronic respiratory alkalosis?
Acute - decreases HCO3 2mEq/L for every 10mmHg decrease PCO2
Chronic - decreases HCO3 4mEq/L for every 10mmHg decrease in PCO2
A 1mEq/L decrease in HCO3 causes how much of a change in PCO2?
Decreases PCO2 by 1.2mmHg
Causes of Metabolic Gap Acidosis?
MUDPILES - Methanol, Uremia, DKA, Paraldehyde, INH, Lactic acidosis, Ethylene glycol, Salicylate
Also non-gap metabolic acidosis - hyperalimentaiton, acetazolamide, RTA, diarrhea, pancreatic fistula
Stepwise Approach to ABG
1. Acidemic or alkalemic?
2. Respiratory or metabolic?
3. Assess PaO2. Below 80mmHg = hypoxemia. For respiratory, is it acute or chronic?
4. For metabolic acidosis, is anion gap present?
5. Assess normal compensation by respiratory system for a metabolic disturbance.
How do you tell if hypoxemia is acute?
If the change in PaCO2 is associated with a change in pH
If pH is acidotic, but the PaCO2 decreases, what does this indicate?
The lungs are compensating for a metabolic acidosis by blowing off excess CO2.
If pH and HCO3 are moving in opposite directions, what does this indicate?
The kidneys are compensating for a respiratory disorder by holding or releasing HCO3
What are some possible causes of respiratory acidosis?
-Compensation for metabolic alkalosis
What is the effect of respiratory alkalosis on chloride electrolyte levels?
Cl- will increase to balance charges
What are some possible causes of respiratory alkalosis?
-Anxiety that decreases lung compliance
-Salicylate and progesterone drug usage
How does the body compensate in chronic respiratory alkalosis?
Decreased bicarb (acid) reabsorption and ammonium excretion to normalize pH
How long does it take for complete activation of respiratory compensation (alkalosis) for metabolic acidosis?
Causes of non-gap metabolic acidosis?
-Hyperalimentation (overconsumption of food, can be through tube)
-RTA (renal tubular acidosis)
Causes of metabolic alkalosis?
In multiple ABG readings, your patient's pH is decreasing along with his PaCO2. Is this a primary respiratory or metabolic problem?
a primary metabolic problem