To properly treat asthma it is important to classify a patient's current severity to determine the appropriate therapy choices.
Therefore a stepwise approach is used. Asthma is classified as either mild intermittent or persistent.
Persistent asthma is further classified as mild, moderate or severe. Regardless of the classification there may be periodic exacerbations ranging from mild to severe which can make therapy quite challenging and requires the patient, patient's family and physician to watch closely for any changes.
Even a mild intermittent asthmatic can have severe life threatening episodes. These episodes may be separated by months or years with no symptoms at all. A patient's asthma classification certainly can and probably will change (in either direction) over time so just one symptom characteristic of a given classification level is enough to raise a patient into that severity class thereby providing the best control possible. Due to the overlapping nature of the categories if the classification seems a bit fuzzy, the patient should be staged in the highest class for which any characteristics are seen.
LUNG FUNCTION TESTING
Before beginning a discussion of the classification of asthma it is important to understand the common tests that are used to determine a patient's level of pulmonary function. It is very helpful to perform at least a basic pulmonary function test and not base a diagnosis of the severity (type) of asthma only on the signs and symptoms presented. The most common office test is spirometry which measures the maximal volume of air forced on exhalation from the point of maximum inhalation (forced vital capacity (FVC) and the volume of air exhaled during the first second of the FVC (FEV1). A patient can also use a peak flow meter at home to check the peak expiratory flow (PEF) variation between morning and in the afternoon (after using a short acting beta-agonist inhaler) to get the PEV variability. To determine the predicted PEF get a peak flow reading in the afternoon when the patient feels as close to normal as possible (even if a couple of puffs of a short acting beta-agonist are needed). These two PEV markers will be referred to in the subsequent sections.
Many asthma patients fall into the mild intermittent category. This group of patients may be symptom free for extended periods of time or may have short exacerbations on a fairly frequent basis. To be classified as mild intermittent a patient will have symptoms such as wheezing or shortness of breath no more than twice per week and nighttime symptoms no more than twice per month. The symptomatic exacerbations may last from a few hours to a maximum of a few days (although the severity may vary from one episode to the next). Between episodes there will be no symptoms and lung function tests will be normal. In this group lung function tests will show a PEF that is at least 80% of the predicted (best afternoon) value and have a variability of less than 20% (between morning and afternoon). This type of asthma patient usually will not require medication on a daily basis and can use a short acting rescue inhaler such as albuterol if needed for symptomatic control. A rule of thumb is that if the rescue inhaler is used more often than twice per week or if a canister lasts less than a month then there may be need for some type of controller medication. An occasional flare-up can be treated with a short course of steroids such as prednisone. A special class of asthmatics should be mentioned here, these are those with exercise induced asthma. A patient with exercise induced asthma typically will only be symptomatic during times of physical stress and usually can be controlled by pretreating with a short acting inhaler such as albuterol or even cromolyn. A diagnosis of exercise induced asthma although often easy to control should not be taken lightly for without pretreatment to prevent symptoms an attack could become a medical emergency.
This class of asthma presents with patients who have symptoms more often than twice per week but less than once per day. Mild persistent asthmatics often have nighttime symptoms more often than twice per month but less than once per week. Lung function testing would show a PEF of greater than 80% of the predicted value which is similar to mild intermittent but with the difference of more variability in the 20 to 30% range. Most mild persistent asthmatics can be best treated with inhaled corticosteroids with a rescue inhaler used only on an as needed basis. Other treatment options exist but will not be covered here. This is the class of asthmatic that seems to often be mismedicated because although a rescue inhaler will often keep many patients essentially symptom free it will do nothing to decrease the inflammation that is a component for even the mild persistent asthmatic. This point should be reinforced: you do not treat persistent asthmatics with a short acting inhaler as monotherapy and the rule of thumb should be considered and a patient considered not under suitable control if they exceed one inhaler per month.
Prior to treatment the moderate persistent asthmatic typically has daily symptoms with exacerbations at least twice per week on average. These flare-ups affect normal daily activity and often last for a number of days. Nighttime symptoms are seen more often than once per week. Lung function tests will show a PEF in the range of 60 to 80% of the predicted value with a variability of greater than 30%. Like the mild persistent asthmatic there are many moderate persistent asthmatics that are not being treated correctly. A short acting rescue inhaled used as monotherapy for an asthmatic at this level is simply bad medicine. It must be remembered that any one of the classifying symptoms is enough to place a patient in a given level so for example if a patient has nighttime symptoms more than once a week (one of the features of this class) then they should be considered to be moderate persistent even with out any of the other features. Remember if uncertain where to stage a given patient the physician should move in the direction of higher rather than lower classification. The moderate persistent asthmatic is usually best treated with a low to medium dose inhaled corticosteroid in combination with a long acting beta-agonist. Other treatment options exist but this is the best for most moderate persistent patients. Once again it needs to be reinforced that excessive use of short acting inhalers on a regular basis is a sign of poor control and the need for reevaluation of the treatment plan!
This is the highest classification of asthma patient. The severe persistent asthmatic is always symptomatic with the ability for only limited physical activity. Both daytime and nighttime exacerbations are frequent and can last for extended periods. Lung function testing will show a PEF of 60% or less of predicted value with a variability of greater than 30%. The severe persistent asthmatic is usually best treated with a high dose inhaled corticosteroid combined with a long acting beta-agonist. To achieve long term control oral corticosteroids are often needed with the goal of achieving control with the lowest daily dose possible thereby reducing systemic side effects.
This article has focused on the importance of correctly determining the type (category) of asthma that a patient has thereby providing their physician the information needed to deliver optimal therapy. The levels can certainly change (either up or down) over time because asthma categories are not static.