Asthma-8

Diagnosis

Asthma is defined simply as reversible airway obstruction. Reversibility occurs either spontaneously or with treatment. The basic measurement is peak flow rates and the following diagnostic criteria are used by the British Thoracic Society.

• ≥20% difference on at least three days in a week for at least two weeks;
• ≥20% improvement of peak flow following treatment, for example:
  

(a) ... 10 minutes of inhaled β-agonist (e.g., salbutamol);
(b) ... six week of inhaled corticosteroid (e.g., beclometasone);
(c) ... 14 days of 30mg prednisolone.

• ≥20% decrease in peak flow following exposure to a trigger (e.g., exercise).

In many cases, a physician can diagnose asthma on the basis of typical findings in a patient's clinical history and examination. Asthma is strongly suspected if a patient suffers from eczema or other allergic conditions—suggesting a general atopic constitution—or has a family history of asthma. While measurement of airway function is possible for adults, most new cases are diagnosed in children who are unable to perform such tests. Diagnosis in children is based on a careful compilation and analysis of the patient's medical history and subsequent improvement with an inhaled bronchodilator medication. In adults, diagnosis can be made with a peak flow meter (which tests airway restriction), looking at both the diurnal variation and any reversibility following inhaled bronchodilator medication.

Testing peak flow at rest (or baseline) and after exercise can be helpful, especially in young asthmatics who may experience only exercise-induced asthma. If the diagnosis is in doubt, a more formal lung function test may be conducted. Once a diagnosis of asthma is made, a patient can use peak flow meter testing to monitor the severity of the disease.

Monitoring asthma with a peak flow meter on an ongoing basis assists with self monitoring of asthma. Peak flow readings can be charted on graph paper charts together with a record of symptoms or use peak flow charting software. This allows patients to track their peak flow readings and pass information back to their doctor or nurse.

In the Emergency Department doctors may use a capnography which measures the amount of exhaled carbon dioxide, along with pulse oximetry which shows the amount of oxygen dissolved in the blood, to determine the severity of an asthma attack as well as the response to treatment.

More recently, exhaled nitric oxide has been studied as a breath test indicative of airway inflammation in asthma.

All text is available under the GNU free documentation lisence
http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

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