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| ==Epidemiology==
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| Approximately 10% of the US population is affected by asthma and an increased prevalence of 60% is observed in all age groups, with status asthmaticus requiring the highest rates of hospitalization.<ref name="pmid18955910">Gorelick M, Scribano PV, Stevens MW, Schultz T, Shults J (2008) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=18955910 Predicting need for hospitalization in acute pediatric asthma.] ''Pediatr Emerg Care'' 24 (11):735-44. [http://dx.doi.org/10.1097/PEC.0b013e31818c268f DOI:10.1097/PEC.0b013e31818c268f] PMID: [http://pubmed.gov/18955910 18955910]</ref>
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| ==Predisposing factors==
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| *Increase use of [[bronchodilator]] despite resistance,
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| *Frequent exacerbations despite the use of [[corticosteroids]],
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| *Despite adhering to therapy, a [[Asthma pulmonary function test#Peak Expiratory Flow Rate|peak flow rate]] of less than 10% from baseline,
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| *Frequent hospitalization for acute attacks,
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| *History of [[syncope]] or [[seizure]] during an acute asthmatic attack,
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| *[[Asthma laboratory tests#Pulse Oximetry|Oxygen saturation]] lower than 92% despite supplemental oxygen,
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| *Airway obstruction is significantly reduced, resulting in severe impairment of air motion that leads to a '''silent chest''' with the absence of [[wheeze]] suggestive of an [[respiratory failure|imminent respiratory arrest]].
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| ==Diagnosis==
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| ===History and Symptoms===
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| *[[dyspnea|Rapidly progressive dyspnea]]
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| *[[cough|Non-productive cough]]
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| *[[sweating|Profuse sweating]]
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| *[[Cyanosis|Central cyanosis]]
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| *[[Loss of consciousness]] and/or [[seizure]] secondary to [[hypoxia|severe hypoxia]] may be observed
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| *Inability to speak more than one or two words may be observed with severe airway obstruction
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| ===Physical Examination===
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| ====Vital Signs====
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| *[[Tachypnea|Increased respiratory rate]] greater than 30 cycles per minute
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| *[[Tachycardia|Increased heart rate]]
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| *[[Pulsus paradoxus]] (fall in [[Systolic blood pressure|SBP]] greater than 20-40 mmHg during inspiration)
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| ====General Physical Examination====
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| *Sit upright with arms extended to support the upper chest ('''tripod position''') that assists the use of accessory muscles of respiration
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| *[[Asthma pulmonary function test#Peak Expiratory Flow Rate|Peak flow rate]] measurement is a simple bedside method to assess the severity of airway obstruction. A '''red zone''' indicates less than 50% of the usual or normal peak flow reading signifying a severe airway obstruction.
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| ====Respiratory Examination====
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| =====Inspection=====
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| *Use of accessory muscles of respiration such as [[sternocleidomastoid]], [[scalene]] and intercostal muscles, correlates with the disease severity
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| *Intercostal retractions
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| *Paradoxical thoraco-abdominal breathing
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| =====Auscultation=====
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| *High-pitch prolong polyphonic expiratory [[wheeze]]
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| *Bilateral crackles
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| *Air entry may or may not be reduced depending on the disease severity
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| *Absence of [[wheeze]] and [[breath sounds]] secondary to severe airway obstruction may represent a '''silent chest''' which is an ominous sign of imminent [[respiratory failure]].
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| ====Cardiovascular Examination====
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| Progressive untreated airway obstruction and increased work of breathing eventually leads to worsening [[hypoxemia]], [[hypercarbia]] and increased [[air trapping]] with compromised [[stroke volume]] that results in [[bradycardia]], [[hypotension]], [[hypoventilation]] and subsequent [[cardiorespiratory arrest]].
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| ====Neurological Examination====
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| *Level of consciousness ranges from lethargy, agitation to even [[loss of consciousness]] or [[seizure]], secondary to severe airway obstruction, [[hypoxia]] and carbon-di-oxide retention.
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| *Unable to speak in full sentences
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| ===Laboratory Tests===
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| *Measurement of oxygen saturation by [[Asthma laboratory tests#Pulse Oximetry|pulse oximetry]] may be useful to identify patients with acute severe asthma who may rapidly progress to [[respiratory failure]] and thereby require more intensive therapy.<ref name="pmid1121560">Overall JE (1975) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=1121560 Rating session. Video taped interviews and BPRS ratings.] ''Psychopharmacol Bull'' 11 (1):15. PMID: [http://pubmed.gov/1121560 1121560]</ref>
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| *[[Arterial blood gas]] may reveal [[respiratory alkalosis]] that is consistent with the [[hypoxemia]] and/or [[hypercarbia]] secondary to significant [[hypoventilation]].
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| *[[Asthma laboratory tests|CBC count]] may demonstrate an increase in [[white blood cell|peripheral WBCs]] secondary to the use of [[steroids]] and [[Bronchodilators|β-agonists]].
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| ===Pulmonary Function Test===
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| [[Spirometry#Explanation of common test values in FVC tests|FEV1]] '''lower than 60% predicted''' is strongly suggestive of severe airway obstruction.
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| ===ECG===
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| The presence of [[supraventricular tachycardia]] on ECG should raise a suspicion of [[Bronchodilator#Theophylline|theophylline toxicity]].
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| ===Imaging Modalities===
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| [[Asthma CT|High-resolution CT]] may reveal several structural changes related to small-airway disease including [[Bronchiectasis|cylindrical bronchiectasis]], bronchial wall thickening, and [[air trapping]].<ref name="pmid1094668">Robards VL, Lubin EN, Medlock TR (1975) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=1094668 Renal transplantation and placement of ileal stoma.] ''Urology'' 5 (6):787-9. PMID: [http://pubmed.gov/1094668 1094668]</ref>
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| ==Stating based on Arterial Blood Gas Analysis==
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| ====Stage 1====
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| *[[Hyperventilation]] with normal PO<sub>2</sub>
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| *No [[hypoxemia]]
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| *Patients may benefit from nebulized [[ipratropium]] used adjunctive to [[Bronchodilator|β2-agonist]] therapy
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| ====Stage 2====
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| *[[Hyperventilation]] with [[hypoxemia]] (low PO<sub>2</sub> and PCO<sub>2</sub>)
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| *Patients may require [[corticosteroids]] in addition to [[bronchodilator]] therapy
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| ====Stage 3====
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| *[[CO2 retention]] due to respiratory muscle fatigue
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| *Markedly elevated PCO2 levels are an indicator for mechanical ventilation
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| *Aggressive [[Bronchodilator|β2-agonist]] therapy along with parenteral [[steroids]] and/or [[Bronchodilator#Theophylline|theophylline]] is indicated
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| ====Stage 4====
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| *Severe [[hypoxia]] with markedly elevated PCO<sub>2</sub>
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| *[[FEV1]] lower than 20% predicted is suggestive of an impending [[respiratory failure|respiratory arrest]] that may require [[intubation]] and [[mechanical ventilation]]
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| *Metered-dose inhalation of [[Bronchodilator|β2-agonist]] and [[Bronchodilator#Anticholinergics|anticholinergics]] are recommended. Administration of parenteral [[steroids]] and/or [[Bronchodilator#Theophylline|theophylline]] has also shown to be beneficial.
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| ==Treatment==
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| *Initial severity assessment is evaluated using [[Asthma laboratory tests#Arterial Blood Gas|arterial blood gas]] and [[Asthma pulmonary function test|pulmonary function test]] and aggressive therapy is initiated to prevent progression to [[respiratory failure]]
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| *'''Supplemental [[oxygen]]''' via nasal canula or [[face mask]] is recommended to alleviate severe [[hypoxia]]. Oxygen saturation is maintained above 92% and is monitored using [[Asthma laboratory tests#Pulse Oximetry|pulse Oximetry]]
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| *Mainstay drugs for the management include '''nebulized [[Bronchodilator|β2-agonists]]''' such as [[albuterol]], [[salbutamol]] or [[terbutaline]], '''parenteral [[steroids]]''' such as [[hydrocortisone]] or [[prednisolone]] and '''[[Bronchodilator#Theophylline|theophylline]]'''
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| *[[Bronchodilator#Anticholinergics|Anti-cholinergics]] such as '''[[ipratropium bromide]]''' may be indicated in patients who are unable to tolerate inhaled [[Bronchodilator|β2-agonists]].
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| *In patients non-responsive to nebulized [[bronchodilator]], '''IV-[[aminophylline]]''' or '''oral-[[Leukotriene antagonist|leukotriene inhibitor]]''' may be used.<ref name="pmid1934839">Press S, Lipkind RS (1991) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=1934839 A treatment protocol of the acute asthma patient in a pediatric emergency department.] ''Clin Pediatr (Phila)'' 30 (10):573-7. PMID: [http://pubmed.gov/1934839 1934839]</ref>
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| *'''Helium with oxygen mixture''' has shown to reduce airway resistance and thereby reduce the work of breathing and also improve [[bronchodilator]] efficacy.
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| *Use of [[Magnesium sulfide|magnesium sulphate]] administered either IV or nebulized in addition to [[Bronchodilator|β2-agonists]] remains controversial.<ref name="pmid11097697">Scarfone RJ, Loiselle JM, Joffe MD, Mull CC, Stiller S, Thompson K et al. (2000) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=11097697 A randomized trial of magnesium in the emergency department treatment of children with asthma.] ''Ann Emerg Med'' 36 (6):572-8. [http://dx.doi.org/10.1067/mem.2000.111060 DOI:10.1067/mem.2000.111060] PMID: [http://pubmed.gov/11097697 11097697]</ref><ref name="pmid12023699">Bessmertny O, DiGregorio RV, Cohen H, Becker E, Looney D, Golden J et al. (2002) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=12023699 A randomized clinical trial of nebulized magnesium sulfate in addition to albuterol in the treatment of acute mild-to-moderate asthma exacerbations in adults.] ''Ann Emerg Med'' 39 (6):585-91. PMID: [http://pubmed.gov/12023699 12023699]</ref><ref name="pmid12501154">Glover ML, Machado C, Totapally BR (2002) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=12501154 Magnesium sulfate administered via continuous intravenous infusion in pediatric patients with refractory wheezing.] ''J Crit Care'' 17 (4):255-8. [http://dx.doi.org/10.1053/jcrc.2002.36759 DOI:10.1053/jcrc.2002.36759] PMID: [http://pubmed.gov/12501154 12501154]</ref><ref name="pmid15846687">Blitz M, Blitz S, Beasely R, Diner BM, Hughes R, Knopp JA et al. (2005) [http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=15846687 Inhaled magnesium sulfate in the treatment of acute asthma.] ''Cochrane Database Syst Rev'' (2):CD003898. [http://dx.doi.org/10.1002/14651858.CD003898.pub2 DOI:10.1002/14651858.CD003898.pub2] PMID: [http://pubmed.gov/15846687 15846687]</ref>
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| *'''Non-invasive ventilation''' using [[Positive airway pressure|C-PAP]] or tight-fitting [[Medical ventilator|face mask]] may be used to reduce the work of breathing without intubation. | | *'''Non-invasive ventilation''' using [[Positive airway pressure|C-PAP]] or tight-fitting [[Medical ventilator|face mask]] may be used to reduce the work of breathing without intubation. |