Asthma is a chronic lung disease characterized by inflamed and narrowed airways. When the inflamed airways of asthma patients react strongly to certain inhaled substances, commonly referred to as an asthma attack, the outcome is a hyper-reactive airway that results in acute bronchospasm, reducing the flow of air into the lungs. Swelling and excess mucus can also constrict the airways.

Asthma symptoms include wheezing, tightness in the chest, shortness of breath and coughing. More than 22 million Americans, including roughly 6 million children, have asthma. Risk factors include allergies and a family history of asthma. Asthma is the most common chronic disease among children, and asthma affects nearly 235 million people of all ages worldwide. In 2011, asthma resulted in 1.8 million emergency department visits and was the primary diagnosis in 25 percent of pediatric emergency department visits.

Common diagnostic tests for asthma include allergy tests and pulmonary function tests, such as spirometry and methacholine challenge tests. Treatments include quick-relief medicines, such as albuterol, and long-term control drugs, such as inhaled corticosteroids. Both reduce airway inflammation and alleviate symptoms.

Quantitative waveform capnography can serve as an accurate, noninvasive parameter to help EMS providers recognize bronchospasm in initial assessments and to gauge the effectiveness of therapy.

Capnography and Asthma

Asthma attacks can mimic other respiratory conditions. Not all asthma attacks cause wheezing, but wheezing and diminished breathing can be caused by multiple conditions, including asthma, COPD and pneumonia. Some asthma patients, particularly children, present with forceful, persistent coughing rather than wheezing. Accurate diagnosis of the cause of respiratory distress is critical, but it can be difficult when the patient is a child without the words to describe what’s happening or an adult who has difficulty speaking.

When added to a thorough history and physical exam, waveform capnography is a valuable assessment tool to determine the severity of an asthma patient’s respiratory distress, to guide treatment decisions in the prehospital environment and to monitor the patient’s response to those treatments.

Learn more about Asthma:

EMS1.com: EMS assessment and treatment of asthma: 5 things to know

Asthma attacks are one of most common EMS responses, and the symptoms often mimic those of other respiratory conditions. Waveform capnography is a valuable tool to differentiate an asthma attack from other causes of respiratory distress and choose the most appropriate treatment.

The waveform represents air movement throughout the respiratory cycle and is rectangular for normal respiration. Bronchoconstriction causes air to be released unevenly from the alveoli, which makes the capnography waveform appear rounded, similar to a shark’s fin. The more severe the bronchoconstriction, the more pronounced the shark fin and length of the waveform. This can be seen even if the patient has diminished breath sounds and is not wheezing.

EMS1.com: Use capnography as a primary assessment tool for asthma and COPD exacerbation

The primary goal in EMS treatment of asthma is to reverse bronchospasm with bronchodilators, with a secondary goal of reducing inflammation, typically with corticosteroids. Assessment of acute bronchospasm in the field, however, is often complicated by the austere nature of the EMS work environment. In the prehospital environment, where EMS providers rarely have access to spirometry and measurement of arterial blood gases, quantitative waveform capnography can prove useful in both initial assessment and in gauging the effectiveness of therapy in the asthma patient.

Asthma and Allergy Foundation of America: AAFA provides a wealth of information for patients and providers.

AAFA offers free continuing education for health professionals and educational programs to help providers teach patients to manage asthma, with materials available for download in English and Spanish.

Iranian Journal of Allergy, Asthma and Immunology: Frequency analysis of capnogram signals to differentiate asthmatic and non-asthmatic conditions using radial basis function neural networks

This paper presents a method of differentiating asthmatic and non-asthmatic patients using frequency analysis of capnogram signals: Non-asthmatic capnograms have one component in their power spectral density estimation, in contrast to two components in asthmatic capnograms. This study explores the significant difference between the magnitude of the first component for both asthmatic and non-asthmatic capnograms. The researchers concluded that this method “could further assist the health care professionals and medical practitioners involved in respiratory care, as it would be possible to monitor severity of asthma automatically and instantaneously with minimum human errors.”

2009 IEEE International Conference on Signal and Image Processing Applications: Analysis of capnography for asthmatic patient

This paper seeks to differentiate the asthmatic and non-asthmatic capnogram, finding that slope ratio (SR) and the Hjorth Parameters (HP2-Mobility) are the best among the 13 investigated parameters in differentiating the two groups.