PFT Quiz number 3 Flashcards
Why do we need specialized tests?
-Patient has symptoms but a normal PFT but has respiratory symptoms.
-Hyperresponsiveness in the airways.
-Uncertain results of bronchodilator testing.
Bronchoprovocation Challenge
(Bronchial Challenge)
-Used to identify and characterize hyperresponsiveness in the airways.
- The less amount of time it takes to evoke a negative response, the more hyperreactive the airway.
Direct Stimulus vs. Indirect Stimulus
Direct stimulus-Acts directly on the parasympathetic smooth muscle.
Indirect stimulus-Release of endogenous mediators (chemical agent).
Agents used in the Methacholine challenge
Direct Stimulus Indirect Stimulus
-Methacholine -Mannitol
-Histamine -Adenosine
-Prostaglandins
Methacholine and Histamine
Increases parasympathetic response in bronchial smooth muscle.
Eucapnic Voluntary Hyperventilation
Uses cold air or room temp gases to cause heat and water loss from the airways.
Methacholine challenge
-Methacholine is inhaled in increasing doses 0.016 to 16 mg/mL
-Stimulates a parasympathetic response in bronchial smooth muscle
-Used for patients who cannot tolerate repeated spirometry testing.
-When the FEV1 is reduced by 20%, it is considered a positive test. AKA PC20 or Provocative Concentration.
-The test is considered negative if the dose of methacholine reaches 16 mg/mL without a 20% reduction in the FEV1.
Will ALL patients experience a change in airway with increasing concentrations?
Yes. The lower the dose needed to stimulate a response, the more hyperresponsive the patient is.
Testing Criteria
The patient must be asymptomatic.
Withholding Medications
Antihistamines (72-96 hours)
Performing the test
-Baseline spirometry is performed to ensure FEV1 is greater than 60%.
-Highest doses for either test is 16 mg/mL
-FEV1 is measured after each increase in concentration.
Dosimeter
-Dosing starts at 0.625 and is increased x4 for each step up until you reach the max dose of 16 mg/ml.
-Can be prepared in advance and stored in fridge, must be room temp at the time of use.
-Delivers a consistent volume of drug with a fixed volume of aerosol on each breath.
-Pt takes 5 breaths of 1st concentration.
-Spirometry is repeated 30 to 90 seconds after each dose.
-Test is repeated until FEV1 decreases 20% or until the maximum concentration of Methacholine is reached.
-At any time, the FEV1 decreases by 20%, the test is complete.
-After the test, a bronchodilator is given to reverse bronchospasms.
2-minute tidal breathing
-A filter is used on expiratory limb.
-Output needs to be 0.13 ml/min
-Dosage starts at 0.031 and increases x2 for each step up to the max of 16.0.
-Can be prepared ahead of time but room temp when used.
-A filter is used on expiratory limb.
-Bronchodilator is used to reverse bronchospasm.
Reporting the results
-If a decrease in FEV1 occurs after the first dose, report: PC20 less than first dose. (Less than the lowest concentration given).
-If there is no decrease after the last dose, report PC20 is greater than 16 mg/mL (greater than the maximum dose 16 mg/mL)
PC20 related to Asthma
A decrease in FEV1 of 20% at low doses of methacholine indicates a high probability of asthma.
A decrease of less than 20% of FEV1 at highest does of asthma indicate that asthma is highly unlikely.
Steroids
Never withhold steroids.
Histamine challenge
-Stimulates bronchoconstriction directly.
-As long as the patient does not have a decrease in FEV1 of greater than or equal to 20% with the diluent, the test continues.
-Patient breathes in 5 breaths at first concentration.
-Dosing starts at 0.03 mg/ml and doubled until max dose of 10.00 mg/ml is reached.
Common effects of histamine
Bronchospasm can be blocked by histamine.
Exercise challenge
-Bronchospasm usually occurs during or immediately after exercise.
-Usually related to heat and water loss in the airways.
-Do not repeat testing for at least 4 hours.
Pre-test prep
-History and physical
-EKG
-No bronchodilators prior to the test.
-FEV1 should be no less than 65% of predicted.
-No vigorous exercise for 4 hours prior to the test.
-No Resp, infections 3 to 6 weeks prior to the test.
Excercise Testing
-Workload should be at 80% to 90 % of max HR for 4 to 6 mins.
-During the test, EKG HR, BP and saturations are monitored.
Positive Exercise Challenge Test
-A decrease of 10% to 15% in the FEV1 is consistent with airway hyperreactivity.
-In a healthy patient, the FEV1 will increase, not decrease.
Eucapnic Voluntary Hyperventilation Testing
-Provokes bronchospasms
-CO2 is added to prevent hyperventilation and maintain the pH.
-Creating a CO2 narcosis
Cold Air Method
-CO2 is added to prevent hyperventilation and maintain the pH.
Results
In a healthy patient, eucapnic voluntary hyperventilation will cause bronchodilation not a bronchospasm.
-A greater than or equal to 10% decrease in FEV1 indicates a hyper reactive airway.
ENo test (Exhaled NO)
-Measures inflammation in the lungs.
Before the test
-No smoking for 1 hour.
-No eating for 1 hour.
-No drinking for 1 hour.
-Must have at least 2 acceptable tests within 20% of each other, then average them.
What do Exhaled NO numbers mean?
If the levels are elevated above the norms, suspect eosinophilic inflammation alveolitis.
Why use NO?
Changes in NO happen quicker than PFT’s.
ABG’s
Considered most basic test of lung function.
-pH
-PCO2 is inversely related to pH.
-Oxygen tension (PO2)- influence by the altitude and temperature.
Henderson-Hasselbach equation
-PaCO2 (by separating the hydrogen and bicarbonate)
-Diffused through a Polarographic electrode AKA: Clark electrode
Body Temperature
-As the body temperature increases the CO2 increases and inversely the pH decreases.
-The body’s response to an increased CO2 level is to take deeper breaths or more breaths to compensate.
-When this happens, the Pao2 increases as well.
-Venous samples are not useful in assessing oxygenation.
