A peak flow meter is used to monitor the flow rate of an asthma patient over time. So it should be used regularly, even several times daily, depending on the severity of the asthma symptoms.

Peak flow meters are useful because they can give quantitative evidence about the state of the patient’s lungs. A person cannot always accurately guess how well they are by how they ‘feel’. Judging how easily they can breathe is also tricky, and misleading. A peak flow meter measures the amount of air expelled in one breath, and the force with which it is exhaled. No matter how good a patient is feeling, their peak flow will show if there is something wrong in their lungs.

Peak flow meters are also used to judge how well an asthma medication is working. If peak flow improves after taking the medication, that’s evidence that the inflammation is being reduced. If it doesn’t, it tells the patient that they should consult their doctor about changing their asthma treatment.

Peak flow meters can also allow the patient to find out what triggers their asthma attacks. Also, if they are feeling particularly unwell, a peak flow check will let them know whether an attack is imminent and if they need to go to the emergency room.