Diagnostics: ABG Flashcards
Arterial Blood Gas testing is used to determine…
pH, PaCO2, PaO2
What is an Allen’s test used to assess?
Whether blood flow is patent in both the radial and ulnar arteries
Normal pH? Acidotic pH? Alkalotic pH?
Acidic – Below 7.35
Normal – 7.4
Alkalemia – Above 7.45
Normal PaCO2. Differences in PaCO2 indicate…
40.
Ventilatory Problems
Normal PaO2. Differences in PaO2 indicate…
100
Oxygenation problems
For teaching purposes, the HH equation can be shortened to…
pH = (HCO3/PaCO2)
Four kinds of primary acid-base disorders?
Metabolic/Respiratory Alkalosis/Acidosis
Explain compensation
Changes in bicarb or PaCO2 that result from the primary event.
Important rule about compensation
You NEVER over compensate
Explain Respiratory Alkalosis
A primary disorder caused by lowering PaCO2
Kidney helps control by getting rid of bicarb
Caused by Anxiety/Hyperventilation
Explain Respiratory Acidosis
Elevation of PaCO2, resulting in decreased pH
Kidneys retain bicarb to compensate
Heroin OD/Not breathing, Breathing high CO2 air
Explain Metabolic Acidosis
Loss of HCO3
Compensation by hyperventilation
Causes vary with anion gap
Explain Metabolic Alkalosis
Retention of too much HCO2
Slowed breathing rate
Contraction alkalosis, diuretics, steroids, gastric suctioning, VOMITING
Also – Cl resistant – hyperaldosterone
How to calculate Anion Gap
Na - (Cl + CO2)
The CO2 is mostly Bicarb
Normal Anion Gap value?
10-12 mEq/L
Causes of increased anion gap metabolic acidosis?
MUDPILES
Methanol, Uremia, Diabetic Ketoacidosis, Paraldehyde, Infection, Lactic Acidosis, Ethylene Glycol, Salicyclates.
Causes of normal anion gap metabolic acidosis
HARDUP
(Hyperchloraemia, Acetazolamide, Addison’s disease, Renal tubular acidosis, Diarrhea/Vomiting, Ureteroenterostomies, Pancreatoenterostomies)
Expanded list of respiratory acidosis causes…
CNS Depression (Drug OD) Chest Bellows Dysfunction (Guillian Barre, myasthenia) Lung Disease (COPD, Severe Asthma, Severe Pulm. Edema)
Expanded list of respiratory alkalosis causes..
Hypoxemia
Anxiety
Sepsis
Acute Pulm. Insult (Pneumonia, Mild Asthma Attack, Early pulm edema, pulm embolism)
In ACUTE respiratory situations, a pH drop of .08 correlated with a PaCO2 rise of…
10
In CHRONIC respiratory situations, a pH drop of 0.03 is correlated with a PaCO2 rise of…
10
Enough time for the kidneys to compensate by retaining bicarb
Co2 travels between the tissues and the lungs as…
bicarb
What is the Haldane effect?
Oxygenation of Hb promotes dissociation of H+, shifting equilibrium toward CO2 formation
What is…
FiO2, PaO2, SpO2, SaO2, Pi02
FiO2 = Fraction of inspired oxygen in the air (ex. 21%) PaO2 = Arterial oxygen conc. (dissolved) SpO2 = Bound Oxygen % via finger probe SaO2 = Bound Oxygen % measured directly PiO2 = Pressure of inspired oxygen in the trachea
First step in understanding a patient’s oxygenation failures?
A-a gradient
What is an A-a gradient?
What does it mean when its high?
Alveolar Oxygen - Arterial Oxygen
Elevated with gas diffusion is impaired
Expected normal A-a gradient?
(Patient’s Age/4) + 4
What kinds of hypoxia have a normal A-a gradient?
Pure Hypoventilation
Altitude
How do you calculate A-a gradient without Arterial Oxygen numbers?
PiO2 -(PaCO2/R) - PaO2
R= Ration of Co2 produced to O2 consumed (.8)
PiO2 for folks around sea level
150
To qualify the degree of diffusion impairment or hypoxemia, you need to know what two (other than A-a gradient) relationships?
SpO2:PaO2
PaO2:FiO2
Oxygen Dissociation Curve Mneumonic
CADET, FACE RIGHT
Co2, Acidosis, 2,3 DPG, Exercise, Temperature
PaO2 should be about __x FiO2
Normal PaO2:FiO2?
5X
475
As severity of diffusion impairment increases, what happens to PaO2:FiO2 ratio?
The ratio decreases
Problem with the sigmoidal nature of the oxygen dissociation curve?
Because the slope is so shallow at saturations above 90, large diffusion defects can happen without notice
What to use A-a gradient vs. P:F ratio?
A-a gradient – Works best on room air
P:F – Works best with supplemental oxygen
What is indicated by a decreased V/Q?
Areas in the lung that are better perfused then ventilated
What is indicated by increased V/Q?
Areas that are better ventilated then perfused
V/Q mismatching occurs when?
In normal lungs based on lung zones
V/Q in the upper vs. lower lobes?
Upper – 3
Lower – 0.6
With exercise, how does lung perfusion change in the lungs?
Vasodilation of apical capillaries
V/Q approaches 1
Causes of increase in V/Q
Pulmonary Embolism
Trachea
Causes of decreased V/Q
Emphyzema (non-functioning alveoli)
Fibrosis (Poor diffusion of air)
Secretions/Edema (Blocks diffusion of air)
What is a shunt? What are the two types?
Venous blood mixes with arterial blood, bypassing circulation.
Extrapulmonary and Intrapulmonary
Examples of extrapulmonary shunts
Tetralogy of Fallot, PFO
Examples of intrapulmonary shunts
Blood transported thru lung w/out gas exchange.
Atelectasis, Pneumonia, Hepatopulmonary syndrome, AVM
