Peak Flow

On the Peak Flow Current Add screen, select the Device Type - either Wright or EN13826 (the patient must be 75 years or younger). The calculation of predicted peak flow depends on which is selected. Enter the peak flow Value(L/min). Select the Result Qualifier as relevant: None, Very High, High, Normal, Low, Very Low, Abnormal, Potential Abnormal, Outside referral range. The default ReadTerm is 3395 Peak exp. flow rate: PEFR/PFR but there are several picklist options.

Peak Flow Current displays the calculations for the Predicted Peak Flow and Previous Best Ever and Percentage Best Ever for adults only.

When Vision 3 upgrade was introduced, existing Peak Flow entries (Current, Predicted, Best Ever, Before and After Nebulising) were replaced with a single Current Peak Flow, which also displays and calculates Predicted and Best Ever (Previous and Percentage of). Note that there was no conversion of existing Peak Flow Current records as part of the Vision 3 upgrade process. Previously, Vision held Peak Flow recordings in five separate entities: Peak Flow Current, Peak Flow Predicted, Peak Flow Best Ever, PF Last Attack Before Nebulising, PF Last Attack After Nebulising.

PF Last Attack continues as before.

Because both Predicted and Best Ever values can be calculated at run time from the patient's data, these become redundant. So Peak Flow Predicted and Peak Flow Best Ever can be found in the Superceded Records at the bottom of the navigation pane. The Add form is no longer available, but it will still be possible to edit existing records.

Peak Flow Best Ever:

339D Best ever peak flow rate (Read code default)

339X Percentage of best ever peak expiratory flow rate

Peak Flow Current

3395 Peak exp.flow rate:PEFR/PFR (Read code default)

339E More than 80% of predicted peak flow rate

339F 60-80% of predicted peak flow rate

339G Less than 60% of predicted peak flow rate

339W Worst peak flow rate

339g Serial peak expiratory flow rate

339n Serial peak expiratory flow rate abnormal

339o Peak expiratory flow rate measured using EN 13826 device

Note - 339A Peak flow rate before bronchodilation, and 339B Peak flow rate after bronchodilation, have been removed from picklist.

Peak Flow Predicted

339C Expected peak flow rate (Read code default)

339H Predicted peak flow

339I Expected peak flow rate x 50%

339J Optimal peak flow rate

339K Expected peak flow rate x 30%

339L Expected peak flow rate x 80%

339V Recorded/predicted peak expiratory flow rate ratio (new code in range)

339Y Percentage of peak expiratory flow rate variability (new code in range)

See also the list of Read codes in FEV1 and Lung Function

Peak Flow Current screen

When the Peak Flow Current Add form displays, the Predicted and Best Ever values are calculated according to the patient data and the information displayed as read-only on the form:

It depends on the choice of Device Type - either Wright or EN13826 (and the patient must be 75 years or younger).

The Best Ever value is calculated by reading all Peak Flow Current and Peak Flow Best Ever records on or before the event date and storing the highest value. If Best Ever is blank, there are no previous peak flow records.

Percentage of Best Ever is calculated from the Current and Best Ever, for example, if Current PK is 480 and Best Ever 500, Percentage of Best Ever is 96%.

Calculated values will only input values stored with units of L/min.

The Predicted peak flow is calculated as soon as you select the Device type.

For adults, the Predicted value is calculated using the patient's height and age, according to the following equations:

PF_FEMALE = (((Height * 3.72) + 2.24) - (Age * 0.03)) * 60

PF_MALE = (((Height * 5.48) + 1.58) - (Age * 0.041)) *60

Where Height is the last recorded height prior to the event date and Age is the patient’s age in years at the event date.

On saving the form the calculated values are stored, and appended by any notes entered by the GP.

Note that Predicted Peak Flow will not be calculated in children under 16 from DLM 260

On editing an existing Peak Flow Current record, the calculated values, if they exist, are stripped from the notes field and discarded. New values are calculated and displayed as per the Add form and stored on pressing OK. Note that these values are calculated only from records with an event date less than or equal to the event date of the record and using the patient’s age at that event date.

Should the GP subsequently edit data such as the height, used to perform a calculation on a Peak Flow Current record, the stored calculation results will be invalid. Any such invalidated records will not be automatically updated. All subsequent additions of Peak Flow will automatically take into account the changed data and existing records may be edited in order to reflect the changes and the GP may choose to revalidate subsequent records simply by editing them.

Note - The Current Peak Flow compared with the Best Ever may need clinical interpretation. Because the Best Ever Peak Flow is now a derived rather than a recorded field, a word of caution - if the patient's best ever was recorded 20 years, percentage calculations are still made against this, and performance does drop naturally over time (note that there is no limit to the number of years the records look back to for the Best Ever calculation).

Predicted peak flow does increase from childhood to adulthood and then declines with advancing years. For example, a chronic asthmatic may never have had a "good" peak flow (for their age and size), even if the current peak flow is "low" (for non-asthmatics), it may be reasonable or good for them, and the comparison with Best Ever for that patient aids that understanding. For a non-asthmatic, who has grown significantly or aged considerably, then the comparison with a Best Ever taken a long time ago may not be so relevant.