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{{Asthma}} | {{Asthma}} | ||
'''Editor(s)-in-Chief:''' [[C. Michael Gibson, M.S., M.D.]] [mailto:charlesmichaelgibson@gmail.com] Phone:617-632-7753; [[Philip Marcus, M.D., M.P.H.]] [mailto:pmarcus192@aol.com]; {{AOEIC}} {{LG}} | |||
'''Editor(s)-in-Chief:''' [[C. Michael Gibson, M.S., M.D.]] [mailto: | |||
==Overview== | ==Overview== | ||
Asthma is defined as | Asthma is defined as reversible airway obstruction that occurs both, spontaneously without intervention or even with treatment. Measurement of [[peak expiratory flow rate|peak flow rates]] and [[spirometry]] are two valuable methods to assess pulmonary function. While measurement of airway function is possible in adults, most new cases that are diagnosed constitute the pediatric age group, who are unable to perform such tests. Diagnosis in children is based on a careful compilation and analysis of the individual's [[medical history]] and demonstration of symptomatic improvement with the administration of [[bronchodilator|inhaled bronchodilator]]. In adults, diagnosis can be made with a [[peak flow meter]] that assess any airway restriction, [[Circadian rhythm|diurnal variation]] and any reversibility following inhaled [[bronchodilator]]. Young asthmatics may experience only [[exercise-induced asthma]]; hence, testing [[peak expiratory flow rate|peak flow]] at rest and after [[exercise]] may be beneficial. If in doubt, [[spirometry]] may be conducted to ascertain the diagnosis. Once the diagnosis is established, [[peak flow meter|peak flow meter testing]] may be conducted to monitor the severity and progression of the disease. [[Capnography]] may be used in the emergency situations, to measure the amount of [[carbon dioxide|exhaled carbon dioxide]] and if used in conjunction with [[pulse oximetry]] may be possible to estimate the amount of [[oxygen]] dissolved in the blood, in order to determine the severity of an asthma attack as well as the predict the response to therapy.<ref name="pmid16187465">Corbo J, Bijur P, Lahn M, Gallagher EJ (2005) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=16187465 Concordance between capnography and arterial blood gas measurements of carbon dioxide in acute asthma.] ''Ann Emerg Med'' 46 (4):323-7. PMID: [http://pubmed.gov/16187465 16187465]</ref> | ||
==Pulmonary Function Test== | |||
==Spirometry== | ===Spirometry=== | ||
*The preliminary investigation of choice to establish diagnosis of asthma is the assessment of lung function using | *The preliminary investigation of choice to establish diagnosis of asthma is the assessment of lung function using [[spirometry]] that includes measurement of forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). [[spirometry|Baseline spirometry]] provides a fairly accurate assessment of the disease severity, degree of airway obstruction and also helps to differentiate between obstructive or restrictive patterns of airway disease.<ref name="pmid8298772">Enright PL, Lebowitz MD, Cockroft DW (1994) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=8298772 Physiologic measures: pulmonary function tests. Asthma outcome.] ''Am J Respir Crit Care Med'' 149 (2 Pt 2):S9-18; discussion S19-20. PMID: [http://pubmed.gov/8298772 8298772]</ref> | ||
*The classic spirometry findings consistent with airway obstruction include a reduced [[Spirometry#Explanation of common test values in FVC tests|FEV1]] and a subsequent reduction in the [[Spirometry#Explanation of common test values in FVC tests|FEV1:FVC ratio]]. However, a normal to increased FEV1:FVC ratio would rule out the presence of an airway obstruction. | *The classic spirometry findings consistent with airway obstruction include a reduced [[Spirometry#Explanation of common test values in FVC tests|FEV1]] and a subsequent reduction in the [[Spirometry#Explanation of common test values in FVC tests|FEV1:FVC ratio]]. However, a normal to increased FEV1:FVC ratio would rule out the presence of an airway obstruction. | ||
*The hallmark of asthma is the reversibility of airway obstruction that can be demonstrated with the initial spirometry by measuring the lung volumes before and after the administration of a [[bronchodilator#Short-acting β2-agonists|short-acting bronchodilator]]. A 12% or greater increase in [[Spirometry#Explanation of common test values in FVC tests|forced expiratory volume in 1 second (FEV1)]] is strongly suggestive of asthma. | |||
*Single-breath counting is a measurement of how far an individual can count in a normal speaking voice after a maximal effort inhalation and serves as a convenient method to measure pulmonary function in children.<ref name="pmid20825771">Ali SS, O'Connell C, Kass L, Graff G (2011) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=20825771 Single-breath counting: a pilot study of a novel technique for measuring pulmonary function in children.] ''Am J Emerg Med'' 29 (1):33-6. [http://dx.doi.org/10.1016/j.ajem.2009.07.006 DOI:10.1016/j.ajem.2009.07.006] PMID: [http://pubmed.gov/20825771 20825771]</ref> | |||
===Peak Expiratory Flow Rate=== | |||
*Peak expiratory flow rate (PEFR) is a measurement of an individual's maximum ability to expel air from the lungs. | |||
*A significant reduction in the peak expiratory flow rate from normal predicted value is suggestive but not diagnostically conclusive of asthma. However, the reversibility of peak flow rate following the administration of a [[Bronchodilator#Short-acting β2-agonists|short-acting bronchodilator]] may favor the diagnosis of asthma. | |||
*A serial monitoring of peak expiratory flow rate helps to monitor the patient's response to therapy, evaluate the severity of symptoms and estimate the frequency of exacerbations. | |||
*The PEFR is an effort dependent measurement that is recorded using a [[peak flow meter]] which is a small hand-held device and helps to define the patient's normal peak flow rate. | |||
*Based on the American Lung Association, peak flow readings are classified into three zones of measurement namely: green, yellow, and red. | |||
:*The green zone means 80 to 100 percent of the usual or normal peak flow readings are clear. A peak flow reading in the green zone indicates that the asthma is deemed under "good" control. | |||
:*The yellow zone means 50 to 80 percent of the usual or normal peak flow readings indicate caution. It may indicate narrowing of respiratory airways and hence an additional medication may be required. | |||
:*The red zone means less than 50 percent of the usual or normal peak flow readings indicate a medical emergency. It signifies severe airway obstruction that may warrant immediate medical attention. | |||
*''Limitations of PEFR:'' <ref name="pmid1952453"> (1991) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=1952453 Lung function testing: selection of reference values and interpretative strategies. American Thoracic Society.] ''Am Rev Respir Dis'' 144 (5):1202-18. PMID: [http://pubmed.gov/1952453 1952453]</ref><ref name="pmid1350971">Smith HR, Irvin CG, Cherniack RM (1992) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=1350971 The utility of spirometry in the diagnosis of reversible airways obstruction.] ''Chest'' 101 (6):1577-81. PMID: [http://pubmed.gov/1350971 1350971]</ref><ref name="pmid8298772">Enright PL, Lebowitz MD, Cockroft DW (1994) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=8298772 Physiologic measures: pulmonary function tests. Asthma outcome.] ''Am J Respir Crit Care Med'' 149 (2 Pt 2):S9-18; discussion S19-20. PMID: [http://pubmed.gov/8298772 8298772]</ref><ref name="pmid7663792"> (1995) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=7663792 Standardization of Spirometry, 1994 Update. American Thoracic Society.] ''Am J Respir Crit Care Med'' 152 (3):1107-36. PMID: [http://pubmed.gov/7663792 7663792]</ref> | |||
:*Reduced PEFR may be observed in both [[Chronic obstructive pulmonary disease|obstructive]] and [[Restrictive lung disease|restrictive]] airway disease and is not specific for asthma. | |||
:*PEFR does not differentiate asthmatic wheeze from [[Wheeze differential diagnosis#Complete Differential Diagnosis of the Causes of Wheeze|other causes of wheeze]]. A predominant inspiratory monophonic wheeze is suggestive of [[Vocal cord paresis|vocal cord dysfunction]], while a polyphonic expiratory wheeze is more consistent with asthma. | |||
:*PEFR is effort dependent and the validity of the measurement solely depends on the individual's effort and technique employed. | |||
:*PEFR readings are not consistent and varies with different instruments. | |||
===Diagnostic Criteria Based on The British Thoracic Society<ref name="pmid17446617">Pinnock H, Shah R (2007) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=17446617 Asthma.] ''BMJ'' 334 (7598):847-50. [http://dx.doi.org/10.1136/bmj.39140.634896.BE DOI:10.1136/bmj.39140.634896.BE] PMID: [http://pubmed.gov/17446617 17446617]</ref>=== | |||
==Diagnostic Criteria Based | |||
*≥20% difference on at least three days in a week for at least two weeks; | *≥20% difference on at least three days in a week for at least two weeks; | ||
*≥20% improvement of [[peak expiratory flow rate|peak flow]] following treatment. For example: | *≥20% improvement of [[peak expiratory flow rate|peak flow]] following treatment. For example: | ||
:*10-minutes of inhaled beta-agonist such as [[salbutamol]] | :*10-minutes of inhaled beta-agonist such as [[salbutamol]] | ||
:*6-week of inhaled [[corticosteroid]] such as [[Beclometasone dipropionate|beclometasone]] | :*6-week of inhaled [[corticosteroid]] such as [[Beclometasone dipropionate|beclometasone]] | ||
:*14-days of [[prednisolone|30mg prednisolone]]. | :*14-days of [[prednisolone|30mg prednisolone]]. | ||
*≥20% decrease in [[peak expiratory flow rate|peak flow]] following exposure to a [[Asthma risk factors|trigger]] such as [[Exercise induced asthma|exercise]]. | *≥20% decrease in [[peak expiratory flow rate|peak flow]] following exposure to a [[Asthma risk factors|trigger]] such as [[Exercise induced asthma|exercise]]. | ||
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==References== | ==References== | ||
{{reflist|2}} | {{reflist|2}} | ||
{{WH}} | |||
{{WS}} | |||
[[Category:Disease]] | [[Category:Disease]] | ||
[[Category:Overview complete]] | |||
[[Category:Template complete]] | |||
[[Category:Pulmonology]] | [[Category:Pulmonology]] | ||
[[Category:Immunology]] | |||
[[Category:Emergency medicine]] | [[Category:Emergency medicine]] | ||
[[Category:Intensive care medicine]] | [[Category:Intensive care medicine]] | ||
[[Category:Allergology]] | |||
[[Category:Asthma]] | |||
[[Category:Up-To-Date]] | |||
[[Category:Up-To-Date pulmonology]] | |||
[[Category:Mature chapter]] | |||
Latest revision as of 20:30, 29 July 2020
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Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-632-7753; Philip Marcus, M.D., M.P.H. [2]; Associate Editor(s)-In-Chief: Lakshmi Gopalakrishnan, M.B.B.S. [3]
Overview
Asthma is defined as reversible airway obstruction that occurs both, spontaneously without intervention or even with treatment. Measurement of peak flow rates and spirometry are two valuable methods to assess pulmonary function. While measurement of airway function is possible in adults, most new cases that are diagnosed constitute the pediatric age group, who are unable to perform such tests. Diagnosis in children is based on a careful compilation and analysis of the individual's medical history and demonstration of symptomatic improvement with the administration of inhaled bronchodilator. In adults, diagnosis can be made with a peak flow meter that assess any airway restriction, diurnal variation and any reversibility following inhaled bronchodilator. Young asthmatics may experience only exercise-induced asthma; hence, testing peak flow at rest and after exercise may be beneficial. If in doubt, spirometry may be conducted to ascertain the diagnosis. Once the diagnosis is established, peak flow meter testing may be conducted to monitor the severity and progression of the disease. Capnography may be used in the emergency situations, to measure the amount of exhaled carbon dioxide and if used in conjunction with pulse oximetry may be possible to estimate the amount of oxygen dissolved in the blood, in order to determine the severity of an asthma attack as well as the predict the response to therapy.[1]
Pulmonary Function Test
Spirometry
- The preliminary investigation of choice to establish diagnosis of asthma is the assessment of lung function using spirometry that includes measurement of forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). Baseline spirometry provides a fairly accurate assessment of the disease severity, degree of airway obstruction and also helps to differentiate between obstructive or restrictive patterns of airway disease.[2]
- The classic spirometry findings consistent with airway obstruction include a reduced FEV1 and a subsequent reduction in the FEV1:FVC ratio. However, a normal to increased FEV1:FVC ratio would rule out the presence of an airway obstruction.
- The hallmark of asthma is the reversibility of airway obstruction that can be demonstrated with the initial spirometry by measuring the lung volumes before and after the administration of a short-acting bronchodilator. A 12% or greater increase in forced expiratory volume in 1 second (FEV1) is strongly suggestive of asthma.
- Single-breath counting is a measurement of how far an individual can count in a normal speaking voice after a maximal effort inhalation and serves as a convenient method to measure pulmonary function in children.[3]
Peak Expiratory Flow Rate
- Peak expiratory flow rate (PEFR) is a measurement of an individual's maximum ability to expel air from the lungs.
- A significant reduction in the peak expiratory flow rate from normal predicted value is suggestive but not diagnostically conclusive of asthma. However, the reversibility of peak flow rate following the administration of a short-acting bronchodilator may favor the diagnosis of asthma.
- A serial monitoring of peak expiratory flow rate helps to monitor the patient's response to therapy, evaluate the severity of symptoms and estimate the frequency of exacerbations.
- The PEFR is an effort dependent measurement that is recorded using a peak flow meter which is a small hand-held device and helps to define the patient's normal peak flow rate.
- Based on the American Lung Association, peak flow readings are classified into three zones of measurement namely: green, yellow, and red.
- The green zone means 80 to 100 percent of the usual or normal peak flow readings are clear. A peak flow reading in the green zone indicates that the asthma is deemed under "good" control.
- The yellow zone means 50 to 80 percent of the usual or normal peak flow readings indicate caution. It may indicate narrowing of respiratory airways and hence an additional medication may be required.
- The red zone means less than 50 percent of the usual or normal peak flow readings indicate a medical emergency. It signifies severe airway obstruction that may warrant immediate medical attention.
- Reduced PEFR may be observed in both obstructive and restrictive airway disease and is not specific for asthma.
- PEFR does not differentiate asthmatic wheeze from other causes of wheeze. A predominant inspiratory monophonic wheeze is suggestive of vocal cord dysfunction, while a polyphonic expiratory wheeze is more consistent with asthma.
- PEFR is effort dependent and the validity of the measurement solely depends on the individual's effort and technique employed.
- PEFR readings are not consistent and varies with different instruments.
Diagnostic Criteria Based on The British Thoracic Society[7]
- ≥20% difference on at least three days in a week for at least two weeks;
- ≥20% improvement of peak flow following treatment. For example:
- 10-minutes of inhaled beta-agonist such as salbutamol
- 6-week of inhaled corticosteroid such as beclometasone
- 14-days of 30mg prednisolone.
References
- ↑ Corbo J, Bijur P, Lahn M, Gallagher EJ (2005) Concordance between capnography and arterial blood gas measurements of carbon dioxide in acute asthma. Ann Emerg Med 46 (4):323-7. PMID: 16187465
- ↑ 2.0 2.1 Enright PL, Lebowitz MD, Cockroft DW (1994) Physiologic measures: pulmonary function tests. Asthma outcome. Am J Respir Crit Care Med 149 (2 Pt 2):S9-18; discussion S19-20. PMID: 8298772
- ↑ Ali SS, O'Connell C, Kass L, Graff G (2011) Single-breath counting: a pilot study of a novel technique for measuring pulmonary function in children. Am J Emerg Med 29 (1):33-6. DOI:10.1016/j.ajem.2009.07.006 PMID: 20825771
- ↑ (1991) Lung function testing: selection of reference values and interpretative strategies. American Thoracic Society. Am Rev Respir Dis 144 (5):1202-18. PMID: 1952453
- ↑ Smith HR, Irvin CG, Cherniack RM (1992) The utility of spirometry in the diagnosis of reversible airways obstruction. Chest 101 (6):1577-81. PMID: 1350971
- ↑ (1995) Standardization of Spirometry, 1994 Update. American Thoracic Society. Am J Respir Crit Care Med 152 (3):1107-36. PMID: 7663792
- ↑ Pinnock H, Shah R (2007) Asthma. BMJ 334 (7598):847-50. DOI:10.1136/bmj.39140.634896.BE PMID: 17446617