The effect of bronchospasm on the patient’s expiratory flow rate 

As the airway smooth muscle constricts, it tightens and the lumen diameter decreases.

Raw [airway resistance to air flow] increases so that the exhaled flow rates decrease. The gas moves slower.

The peak flow meter will measure the fastest exhaled flow rate, so that the increased Raw can be seen as a decreased PEFR reading

The PEFR will measure this velocity which is recorded in Liter/minute or L/second.

Methods used to assess this reduction in airflow.

The RCP can:  

·         Measure this reduction with various instruments--- but we will discuss only one of them right now. The PEFR.
 

·         Hear this reduction

·         By auscultation of the chest in which the expiratory sounds will whistle--- or WHEEZE

·         By auscultation of the chest in which the expiratory time is prolonged so that the I: E ratio changes.

·         See these changes in the patient’s condition

·         In changes of his work of breathing and changes in his vital signs

·         Persons with shortness of breath [SOB] may not be able to speak more than one or two syllables without catching their breath--- Breathlessness.

 

What is a peak flow meter?  

The PEFR meter is a device into which the patient exhales as hard and fast as he can.

The peak flow meter is a form of pneumotachometer. “Air-speed-meter” As airways close off, the speed of the air decreases and the meter will record this.  As bronchospasm increases, the PEFR number decreases.

Indications , contraindications and the hazards of PEFR measurements at the bedside.

Persons who will be assessed via the peak flow meter will be persons for whom the level of their bronchospasm must be tracked and assessed. This will include the following:

·         Asthma

·         Emphysema or other COPD

·         Persons who are getting medication to combat bronchospasm brought on by bronchopneumonia and viral pneumonias such as the flu.

·         Frequently the patient getting drugs to combat bronchospasm [bronchodilator] will get a PEFR before and after their treatment to assess the effectiveness of the bronchodilator

·         Occasionally, one may get a patient in whom there is no audible wheezing, just a cough. When this person gets a bronchodilator the cough disappears & the patient feels better without any change in breath sounds. This is called coughing asthma and it can be detected with changes in the PEFR before and after the bronchodilator

·         On the other hand, some folks who don't display the s/s of Bronchospasm will be ordered on bronchodilators. They can be detected by PEFR because the values are normal before and after. This documentation can be used to ask for discontinuance of the therapy.  

 

Contraindications

There will be times when your patient’s chest is so tight that to attempt the PEFR is detrimental. The newly admitted asthmatic patient is an example of this. He will have a high degree of s/s of increased WOB and respiratory distress.

The PEFR should be offered but if the patient is too stressed to perform so be it.

It is impossible to get a child under the age of 5 years to do this procedure. As a matter of fact, the tables of normal values only go down to the age of a five-year-old

Persons who are confused, very sedated or retarded may not be able to follow directions

Hazards of the Peak Flow Meter

·         Can trigger more Bronchospasm

·         Can trigger coughing

·         A Person on supplementary 02 can become hypoxic if he is removed from his 02 and asked to do work as stressful as this.

·         Cross contamination: if you are using the same PEFR device on several persons you must use bacteria filters or one-way valves with cardboard mouthpieces.

·         It is suggested that one buys the cheaper types of dedicated peak flow meters, so that each patient gets one that he can take home and use to assess his wheezing after discharge

·         If you have a really sick patient who cannot perform reproducible numbers, it would be better for the patient to skip this assessment & get the medication.  Later, the patient might be able to perform a post treatment PEFR and that inability would be diagnostic in-of-itself

The peak flow meter is the most popular bedside pulmonary function study done, because the measuring tools can be made of simple cheap construction, so that the patient can buy one and take it home.

What is the significance of reproducible results?  

Reproducible Results

The peak flow meter is the least dependable of the pulmonary function studies because it is so effort dependent. The patient can alter the results with poor effort.

In an effort to make sure the patient’s effort is optimal, there is a need to have reproducible data. The RCP must repeat the test again to see if the results are statically reproducible [within 5% +/- of each other.]

A reproducible study is one in which both the PEFR are within 5% of one another.

Calculate the reproducible results:  

EXAMPLE: Mr. Peters has the following PEFR results:
· 385
· 393
· 415

We are supposed to report his highest score but is it really 415?

There are several ways to discover reproducibility, but this is the quickest:

Take the highest measurement and multiply it by .95% then see if the second highest number falls between the first number and 95% of the first number.

415 x .95 = 394

The 2nd highest number [393] does NOT fall between 415-394 so 415 is not reproducible.

We do the same to the second highest number and see if the third number falls into range.
393 x .95 = 373
The 3rd number [385] falls between 373-393, so 393 is the number you report as the highest PEFR.

Using the graph provided [usually found in the peak flow instructions] find the normal PEFR for a person based on his sex, height and age.  

Select the graph based on the patient’s sex.
Find the patient’s age and then move to their height.
Where the two intersect is this patient’s normal value for PEFR

If the PEFR is in 2 or 3 digits the measurement is in lpm.
If the PEFR is in one digit, the measurement is l/sec.

Occasionally, you may have to convert from lpm to l/sec; to do this divide the lpm by 60...To convert from l/sec to lpm multiply by 60

Peak Flow - Normal Values

Measure the peak flow and compare it to the predicted value [normal value]  

Now that you have values you can trust, you are ready to calculate the percent predicted. [% Predicted] The % predicted is just grading the lung.

The normal values for PEFR are based on the patient’s age, sex and height. Your PEFR meter instructions will contain normal values for you patient in a booklet with the meter. You will take the number you got and divide it by the normal setting. The figure you will get will be in a decimal, which can be converted into a percent.

EXAMPLE
Your patient’s best PEFR is 300 LPM and your patient’s predicted PEFR is 600.

% Predicted = actual PEFR/predicted PEFR
% Predicted = 300 lpm/600 lpm
% Predicted = .5 or the patient’s PEFR is 50% of predicted

Measure the peak flow in such a way that your results are statistically valid because they are reproducible.