6) Principles Of PFT & ABG Testing Flashcards
Hypercarbia
Respiratory failure from too much CO2
Hypoxemia
Not enough O2 in the blood
Hypoxia
Not enough O2 at the tissue level
What can lead to hypoxia?
Hypoxemia
Chemoreceptors
Sense O2 content of blood
Partial Pressure
O2 dissolved in blood plasma
Respiratory Acidosis
Can’t get blow off CO2 so blood becomes acidic
Respiratory Alkalosis
Blow off too much CO2 so blood becomes basic
What is the physiologic mechanism of breathing?
1) Chemoreceptors in the carotid & aorta respond to changes in blood chem
2) Signals are sent to the medulla as PaO2 & PaCO2 change
3) Medulla sends signals to respiratory muscles to contract
4) Diaphragm contracts & thorax expands
5) Transpulmonary pressure changes
6) Air moves from AW into alveoli
Normal Vital Capacity
4.8L
Normal Inspiratory Capacity
~3.5L
Normal Functional Residual Capacity
~2.4L
Flow
Primary measure of AW volume/obstruction over time
PFT Flow Measures
Peak expiratory flow rate; % of FVC exhaled in 1 sec
What % of FEV1 & FEF should PFT be?
- FEV1=75-80%
* FEF=25-75%
Peak Flow Measurement
Measures max air flow during forced expiration
Who are peak flow measurements done on & why?
Pt’s w/asthma to monitor AW tone to detect the onset of an attack so drugs can be properly adjusted
Body Plethysmography
Approximates body’s blood gases if pt can’t exhale
Pattern for obstructive disorders
Decr flow & incr volume
Pattern for restrictive disorders
Incr flow & decr vol
Diffusion Capacity
Amount of air that diffuses through the lungs in 1 breath
What is the range for diffusion capacity?
25-30mL CO/min/mmHg
When will diffusion capacity be low?
W/alveolar capillary membrane destruction
When will diffusion capacity be high?
Emphysema
Indications for PFT
- Measure lung vol, capacities, & flow for baseline & normal values
- Quantify level of lung dysfunction
- Measure pt tx response
- Pre-op screening
- Disability eval
O2 will diffuse from alveoli into blood when the PaO2 is in what range?
80-100torr
CO2 in blood will diffuse into alveoli when the PaCO2 is in what range?
35-45torr
Examples ventilatory & oxygenation abns:
- Ventilatory=Obstructive & Restrictive
* Oxygenative=Duffusion Deficit & Shunt (Atelectasis, ARDS)
Tidal Volume
Air taken in 1 normal breath
Normal Tidal Volume
~500mL
Inspiratory Reserve Volume
Max amount of air that can be taken in after a normal inhale
Normal inspiratory reserve volume
3L
Expiratory Reserve Volume
Amount of air that can let out after a normal exhale
Normal expiratory reserve volume
1.2L
Residual Volume
Air left in lungs after a max exhale (1.2L)
What is a capacity test?
Looks at 2+ volumes
Define total lung capacity
Amount of air in lungs after a max inhale
Examples of restrictive diseases
Kyphoscoliosis
Idiopathic PF
Sarcoidosis
Morbid Obesity
ABG’s are done to determine:
- Adequacy of ventilations
- Adequacy of oxygenation
- Metabolic status
Where are ABG’s usually drawn from & why?
Brachial or radial arteries bc they’re easy to palpate & aren’t near any major vessels
What is an Allen’s Test?
Pinch off ulnar & radial arteries & release ulnar to check pt’s collateral circulation
*<15sec is good
Normal pH range
7.35-7.45
Normal PCO2 range
35-45torr
Normal PO2 range
80-100torr
Normal HCO3 range
22-26meq
Normal base excess range
-2 to +2
Normal SpO2 range
95-100%
Values for mild hypoxemia
PO2 of 67-75torr on room air
Values for moderate hypoxemia
PO2 of 50-65torr
Values for severe hypoxemia
PO2 <50torr
Values for hyperoxia
PO2 >100-120torr
What values put a pt in respiratory alkalosis?
PCO2 <35torr
What values put a pt in metabolic acidosis?
HCO3 <22meq
What values put a pt in respiratory acidosis?
PCO2 >45torr
What values put a pt in metabolic alkalosis?
HCO3 >26meq