Friday, 24 August 2007

Peak Flow In Asthma

I have recently been teaching doctors about the use of Peak Flow Meters for use in Asthma.

It appears that most physicians here rely on listening for resolution of wheeze when deciding on whether asthma is improving.

Although this is a relatively good measure, it does not provide the physician with any means of equating what is normal or the extent of improvement or worsening of the patient's respiratory condition.

Some Japanese physicians use peak flow meters, but there is no consistent use from what I have observed thus far.

Peak Flow Meters (PFM) are commonly used in the UK and USA to grade the severity of asthma as they are a guide to the extent of air trapping in the lungs. Hence, the more severe the asthma, the worse the peak flow reading.

The are normal predicted values for both males and females in Japan and these peak flow values are slightly less than for caucasian patients.

By taking a Peak Flow reading in an asthma attack, and comparing to the predicted normal value for a patient of particular age, sex and height, a percentage from normal can be calculated.

This percentage value can then guide the physician on how severe the asthma attack is and with treatment, it can show if there is any improvement in the Peak Flow percentage and also whether the improvement is sustained as a result of the treatment.

Peak Flow measurements should be done before asthma treatment is commenced and after the treatment to see the extent of the improvement.

The British Thoracic Society in the UK has excellent guidelines from 2003 which can easily be accessed for free on the internet and they give the emergency / internal medicine physicians firm guidance on how to assess, treat and whether to admit the patient or send them home.

As an example, the use of a PFM helped with the care of a patient in the UK with an infective exacerbation of asthma. The patient was seen in the outpatient clinic and given beta-stimulant therapy but with recurrence of wheezing soon after the initial therapy. However, the patient wanted to go home and a decision needed to be taken as to whether it is was safe. Hence, PFM was used and showed that the peak flow was 66% of predicted which was sustained several hours after repeated therapy in the clinic. The patient appeared to be improving and in accordance with the UK guidelines it was considered acceptable to allow the patient home despite PEFF being less than 75% of predicted as there was a sustained improvement. However, on returning to a booked appointment in the outpatient clinic 48 hours later, the asthma was still a problem and the peak flow was measured again, and it showed to be less than 50% which precipitated a hospital admission for more intense therapy.

Without such use of the PFM, the doctor would have had no other way to convince the patient that admission for more intense therapy was absolutely necessary. With inpatient hospital nebulisation therapy, iv steroids and ipratropium (no aminophylline !!!) the patient made a good improvement and the asthma stabilised as evidenced by improvements in the PEFF measurements.

Hence, if you have not used a PFM then you should be. The guidelines on use of PFMs have been available for many years and are well established and are incorporated into the UK asthma guidelines. Please see my blogs on asthma from april and march 2007.

Please consider..........

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