Peak expiratory flow rate does not predict exacerbation of asthma

Question Does measuring peak expiratory flow rate predict asthma exacerbations?

Synopsis This non-randomised controlled study was conducted in an interesting setting: 36 pharmacies spread over a geographical area to study the effect of care provided by pharmacists to patients with asthma. Randomised by pharmacy, patients received either a peak flow meter with instructions from the pharmacist on how to use it, a peak flow meter with written instructions, or usual care (no peak flow monitor given). The 660 patients were evaluated at enrolment and at 6 and 12 months using the McMaster asthma-specific quality of life questionnaire and measured peak expiratory flow rate (PEFR). Patients also were telephoned monthly to obtain their PEFR measurement and information about any recent emergency department visits and hospitalisations. During the follow up, 13% of the patients experienced at least one exacerbation of asthma. A PEFR of less than 50% of predicted at baseline predicted an exacerbation over the following 12 months, but change in PEFR was not a better independent predictor than quality of life scores. By contrast, the quality of life scores were independently predictive of an exacerbation at both four months (hazard ratio 0.63; 95% confidence interval 0.46 to 0.87) and 12 months (hazard ratio 0.66; 0.54 to 0.82).

Bottom line Routine measurement of peak expiratory flow rate does not predict subsequent exacerbations of asthma. Therefore, routine measuring of lung function in this way is not useful. A peak flow meter has a role in asthma management, but spot checking in the office, other than to evaluate technique, is not helpful.

Level of evidence 1b (see www.infopoems.com/levels.html). Individual inception cohort study with > 80% follow up; or a clinical rule not validated on a second set of patients.