PEFR 

                                                                   
 age |       male (height in cm)    |     female (height in cm)  
 (y) | 150  160  170  180  190  200 |  150  160  170  180  190  200
 15  | 510  520  540  550  560  570 |  440  450  460  460  470  480
 20  | 550  570  580  600  610  620 |  460  470  480  490  500  500
 25  | 580  590  610  630  640  650 |  470  480  490  500  510  520
 30  | 590  610  630  640  650  670 |  470  480  490  500  510  520
 35  | 590  610  630  650  660  670 |  470  480  490  500  510  520
 40  | 590  610  630  640  660  670 |  470  480  490  500  510  510
 45  | 590  600  620  640  650  660 |  460  470  480  490  500  510
 50  | 580  590  610  630  640  650 |  450  460  470  480  490  500
 55  | 560  580  600  610  620  640 |  440  450  460  470  480  480
 60  | 550  560  580  590  610  620 |  430  440  450  460  460  470
 65  | 530  550  560  570  590  600 |  410  420  430  440  450  460
 70  | 510  530  540  560  570  580 |  400  410  420  430  440  440
Calculations as per Nunn & Gregg 1989 [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1836460/pdf/bmj00228-0026.pdf]
(see BTS/SNC guidelines 2008);
Table calculations: see attached R script:
pefr <- function(age,height,male){ if(male) exp(0.544*log(age)-0.0151*age-74.7/height+5.48)
  else exp(0.376*log(age)-0.0120*age-58.8/height+5.63) }

Diagnosis

• Clinical features that icr the probability of asthma
• >1 of: wheeze, breathlessness, chest tightness, cough, esp if
• worse at night and in early morning
• in response to exercise, allergen exposure, cold air
• after taking aspirin or beta-blockers
• Hx/FHx of atopic disorder
• widespread wheeze on auscultation
• otherwise unexplained low FEV1 or PEF (historical or serial readings)
• otherwise unexplained eosinophilia
• Clinical features that dcr the probability of asthma
• prominent dizziness, light-headedness, peripheral tingling
• chron productive cough in the absence of wheeze or breathlessness
• repeatedly normal physical examination of chest when symptomatic
• voice disturbance
• symptoms with cold only
• significant smoking Hx (>20 pack yrs)
• cardiac disease
• normal PEF or spirometry when symptomatic;
• If likely asthma: explore possible causes, also occupational
• confirmation of airflow obstruction varying over short periods of time; spirometry preferable to PEF
• based on Hx and confirmed airflow obstruction:
• if hi prob of asthma: treatment trial; otherwise further / alternative Ix

Differential diagnosis of asthma in adults

• without airflow obstruction (FEV1/FVC>=0.7)
• chron cough syndromes
• hyperventilation syndr
• vocal cord dysfx
• rhinitis
• gastro-oesophageal reflux
• heart failure
• pulmonary fibrosis
• with airflow obstruction (FEV1/FVC<0.7) [* spirometry may be nml]
• COPD
• bronchiectasis*
• inhaled foreign body*
• obliterative bronchiolitis
• large airway stenosis
• lung cancer*
• sarcoidosis*
• Possible additional Ix in patients with atypical presentation or additional signs (crackles, clubbing, cyanosis, cardiac dis)
• CXR
• full lung fx tests
• eosinophil count
• IgE
• allergen skin prick tests
• Treatment trials, eg
• 200mcg inhaled beclomethasone (or equiv) bd for 6-8wks [or prednisolone 30mg od for 2 weeks]
• FEV1 icr>400mL: strongly suggestive of asthma

Management

• Secondary Non-pharmacological prophylaxis: house dust mite avoidance; food allergen avoidance
• Pharmacological Mx
• Aim: control of asthma (while minimal side effects):
• no daytime symptoms
• no nighttime awakening due to asthma
• no need for rescue medication
• no exacerbations
• no limitations on activity including exercise
• normal lung fx (FEV1 a/o PEF>80% predicted or best)
• Short-acting relievers: inhaled short-acting beta2-agonists, inhaled ipratropium, beta2-agonist tablets/syrup, theophyllines
• Inhaled steroids
• if: exac in last 2yrs, symptomatic or use of inhaled beta2-agonist>x3/wk, waking x1 night/wk
• adult starting dose 400mcg/d
• Long-acting beta2-agonists
• leukotriene receptor antagonists
• theophylline