Spirometry quality control & predicted values Flashcards
Define calibration
Calibration: comparing the measurements of 2 instruments, one with a known magnitude (standard device), against another in which you correct or rectify.
Define verification
Verification: is checking an instrument & ensuring that any error of measurement is within limits, spirometer is verified by injecting a known volume, a 3L syringe is used to do so
Verification is acceptable if in range from –3%->+3%
Why calibrate the spirometer?
If accuracy is not checked then errors would not be detected this could lead to incorrect interpretation of data.
Spirometry results can only be correctly interpreted if the results are accurate, this is why spirometry is performed to ATRP standards, to ensure spirometry results are reliable
Describe the stages in the verification process for correct calibration
Use a 3L syringe, syringe needs to be checked yearly
Range needs to be within +/-3% of the true value
Calibration should be verified every morning before clinic & after every 4 hours of use
A calibration log should be maintained
Recheck the room temperature to see if its changed by greater than 5’c
What if the spirometer fails to pass checks?
If the calibration fails to pass checks, then the spirometer must not be used & must be returned to manufacturer to be recalibrated. It cannot be used for testing until correctly calibrated
Describe calibration at different flows
Some spirometers need to be calibrated at different flow rates
Low, medium & high flow rates are generated by applying different pressures to the calibration syringe
How to perform physiological (biological) control of the spirometer
Spirometer should be verified via physiological control, involves testing a healthy controlled person, includes 2 ARTP standards
To do so complete 10 consecutive with 10 days spirometry tests and should be reproducible & acceptable, these should be performed via the same operator at a similar time of day
Add the 10 FEV1, 10RVC & 10 PEF together & divide by 10 to get an average
Work out 5% each side to get normal variability & create an acceptable operating range
Check your own results against the range of weekly & log results
What should the calibration log book include?
The equipment calibrated
Make & model
The serial number
Date & time of calibration
Temperature of the room
The operator during testing
Syringe used
If the spirometer passes calibration check
Define predicted values
Predicted values refer to the estimated normal lung function measurements for an individual based on specific factors such as age, gender, height. Predicted values are used as a benchmark to assess whether a person’s measured spirometry results (like FEV1, FVC, and the FEV1/FVC ratio) fall within the expected range for their age and physical characteristics
Values are calculated using reference equation
Describe the reference equation
the reference equation is a mathematical formula used to estimate normal or expected lung function values based on a person’s characteristics, such as age, gender, height
FEV1(L)= (4.30xHeight)- (0.029xage)-2.49
=ANS in litres
Using the reference equation, a healthcare provider can calculate the predicted normal values and then compare them with the patient’s actual spirometry results. If values fall significantly below the predicted normal range, further diagnostic evaluation is often needed.
Define repeatability
Refers to the variation in measurement using repeat measurements under identical conditions
Define reproducibility
The variations in measurements when there are different conditions
Describe quality control
Equipment is working/not damaged
Environment e.g., room temperature
RProcedures and protocols, following standard guidelines to reduce variability
Patient, patient receive full explanation
Physiologist, competency checks, do they need to do it supervised, are they peer reviewed and have a national qualification
Explain the purpose of repeatability criteria
3 technically acceptable results selected, max of 8 efforts
Chosen FVC & FEV1 should not differ from next base values for FVC & FEV1 by more than 150ml
In patients with FVC of <1.00L, should be no greater than 100ml
Report highest FVC & FEV1 , these can come from any one of three efforts meeting the criteria
The ratio is calculated from 2 numbers perhaps from different tests
Describe acceptable criteria
Aim is to achieve best result possible
Patients may be able to fulfill acceptable criteria, but results may still be used with clinical discretion. Lack of fulfillment should be documented and taken into consideration when interpreting results
The patient needs to continuously observed to ensure test is carried out correctly, they should be encouraged throughout test to ensure they are breathing as hard and fast as possible, until they are empty.
How do we know if the trace was satisfactory?
- if there was no leaks
- no obstruction to mouthpiece
- no coughing
- good effort & compliance
- maximal inspiration
Give examples of what could cause an error in spirometry
- a slow start (poor FEV1)
- coughing
-bronchoconstriction
-obstruction to mouthpiece
Describe how the lungs develop from embryonic development to fully developed
Lungs begin to develop on day 28 of embryonic development within gestation.
Alveoli begin to develop from 24 weeks onwards & lung surfactant between 22-24 weeks
Number of alveoli increase throughout childhood, lungs increase in size
Lungs are fully developed at 20yrs of age
What are the factors affecting lung volume
Age
Sex
Ethnicity
Height
What are the affects of ageing in the lungs
Loss of elasticity
Reduction in collagen & elastin
Decrease in muscle tone
Exposure to pollution
Impaired nutrient supply
Reduction cell membrane permeability
Rigidity in chest wall
Describe the influence of height on lung volume
taller people have larger thoracic cavities so can accommodate larger lungs, this enables greater lung volumes, total lung capacity tends to be greater in taller people, as their lungs are physically bigger to match their body size
Describe the influence of sex on lung volume
Children have similar lung volumes until puberty. Males have broader shoulders, increased trunk size & chest dimensions, have a greater lung volume than females. Men generally have more muscle mass and stronger respiratory muscles, which contributes to greater lung volumes and efficiency in breathing.
Describe the influence of ethnicity on lung volume
Caucasians tend to have greater lung volume than other ethnic groups due to larger average body sizes. Lung volume can be influenced by environmental, genetic or lifestyle factors.
What are predicted values?
Predicted reference values are standardized benchmarks used in medical and physiological assessments to compare an individual’s test results (such as lung function or growth measurements) to the expected range for a person of the same age, sex, height, weight, and sometimes ethnicity. Values are collected from healthy individuals e.g., non-smokers
These are calculated for each patient based on their height, age, birth, sex & ethnicity
How do we create a predicted value?
Draw a representative group from the general population, ideally being healthy e.g., non-smokers
Exclude those with respiratory disease
Complete a physical examination
Chest ray / X-ray
What are the limitations of the reference value equation
Reference values need to be adjusted for other ethnicities than just using Caucasian reference values
Values for those over 70yrs should be extrapolated
There should be greater and more reliable reference values for the transition from a child to an adult
How to calculate test result
we calculate the test result as a percentage of the predicted value
(test value/predicted value) x100
Describe the use of the absolute FEV1/FVC%
The absolute FEV1/FVC% is a measurement used in respiratory medicine to assess lung function. It refers to the ratio of the Forced Expiratory Volume in one second (FEV1) to the Forced Vital Capacity (FVC), expressed as a percentage.
The FEV1/FVC ratio is crucial for diagnosing and monitoring obstructive lung diseases like asthma and chronic obstructive pulmonary disease (COPD). In healthy individuals, the ratio is typically around 70–80% in adults. A lower percentage suggests airflow limitation or obstruction in the lungs
What should be used instead of the absolute FEV1/FVC%
The true lower limit of normal can be calculated (LLM)
This is determined statistically
The normal range is calculated, this is a measure of the range from the lower limit of normal to the upper limit of normal.
How do we create a normal range?
Is a predicted value which is +/-1.64 SD
LLN at –1.64 and ULN at +1.64
It includes 90% of the population
How do we calculate the upper & lower limits?
Equation:
FEV1(L)=4.30x(height)
-0.029x(age)-2.49
e.g., 32yr male, 1.68m tall
FEV1(L)=(4.30x1.68)-(0.029x32)-2.49
=3.80L (predicted value)
to calculate range use residual SD
LLN=predicted value- (1.64xRSD)
=3.80-(1.64x0.51)
=2.96L (litres)
therefore normal range is 2.96-4.64
Describe the z score
A way the test results can be expressed in terms of how many standard deviations it is from the predicted value, also known as the standard residual score
SR score=(value-predicted)/SD
Describe if the z score is zero, positive or negative
At 0 then the test value is the same as the predicted value
If the z score is positive then the test score is higher than the predicted value
If the z score is negative than the test value score is lower than the predicted value
test value is in normal range when z score is between -1.65/+1.64
