JC WCS 15: ASTHMA
Prof. Mary Ip
Medicine
Fri 08-11-02
ASTHMA DEFINITION
- Aw disease
- Paroxysmal or persistent symp (dyspnoea, chest tight, wheeze, cough)
- Variable aw obstruc
- Aw H-responsiveness to variety of (+)
ASTHMA CLASSIFICATION
|
|
Atopic
Allergic
Extrinsic |
Non-atopic
Non-allergic
Intrinsic |
|
Atopy |
+ |
- |
|
Age of onset |
Child/ adoles |
Adult |
|
Hx eczema/ allergic rhinitis |
+ |
- |
|
Tx/ Px |
Remission |
No remission
Life-long Tx |
EPIDEMIOL
Ranges 2.5% (China, India, Nepal) 23.5% (Aus, UK)
China: prev w/Western living, 2nd gen Chinese in Aus same prev as Aus (\ env > genetics)
HK: 12-18yo 6.6% (1992) ® 11.2% (1995), 7th dis req LT f'up, 5th cause hospitalisation (w/COPD), Death 1.5/ 100,000 (80-100/ yr; 1/3 15-45yo), Epidemic 1960's + 1990's ( short-acting b -ag)
RISK FACTORS FOR ASTHMA DEV
Predisposing
- Genetics
: multiple genes
- Atopy
: greatest risk factor, XS ability to produce IgE, most child asthmatics are atopic (50-70% adults), allergy ¹ asthma
- Gender
: (a) < 18yo M>F (15:9 / 1,000) (b) 19-60yo F>M (c) >60yo M>F (12:11 / 1,000)
Causal
- Allergens
: Indoor (house dust mite faeces, cockroach, cat/dog, 2-10m mÆ ) > Outdoor (alternaria, slender mould in USA). Not pollen b/c Æ 500m m (yes if frag)
- Occupational agents
: 5-15% intrinsic asthma (eg. plastic, baker flour, duck)
Contributing
- Infection
: early resp viral (developing C = infec ® (+) Th1 ® (-) Th2 (chemokines for asthma dev). RSV = risk (esp. atopic children)
- ETS
: triggers existing + risk dev
- Air pollution: diesel exhaust particles
® sensitis'n to allergens
ASTHMA TRIGGERS
- PA
- Cold air (less in HK)
- Low-level irritants (ETS)
PATHOLOGY
- Aw inflam/ oedema
- Mucus (plug bronchioles)
- Eosinophils to submucosa (epith damage - shed, collagen deposit; vasc perm; aw H-responsiveness)
- SM constrict
PATHOPHYSIOLOGY
- Allergen-Ab reaction (IgE) ® mediators (1) Histamine - early (2) LT, ECF, NCF - late
- Asthma reac'n type [cellular immune response?]
- Immed: onset 10-15m, dur 30-60m
- Late: onset 2-6h, dur 12-24h (H-responsiveness, inflam, eosinophil)
- Biphasic: immed ® spontaneous recover ® late
CLINICAL FEATURES
- Episodes: dyspnoea, wheeze, cough (transient, recur)
-
night/ early morning (cf. COPD)
- Note: DDx cough + wheeze (1) Gen: COPD (2) Local: foreign body, tumour, vocal cord
DX ASTHMA
- Compatible Hx
- Reversibility of obstruction
- FEV1 B4/after inhaled bronchodil
- Af obstruct ® (1) FEV1 < 80% predicted (2) FEV1/FVC < 70%
- +ve response to bronchodil = FEV1 > 12% (200ml)
- If severe asthma, maybe no reversib'y w/b -agonist \ try prednisolone (steroid)
- Variability of af obstruction
- Monitor PEF o'1-2w for var'n [+ve response = diurnal var'n PEF > 15%]
- Non-allergic aw H-responsiveness
- If no aw obstruc'n ® challenge testing (methacholine, histamine) until FEV1 ¯ 20%
ASTHMA ASSESSMENT
- Rule out DDx - eg. CXR
- Assess lung func
- Severity (a) Attack freq (b) PEF% predicted (c) PEF variab'y
- Triggers (\ prevention)
ASTHMA MX (complete control)
- ¯
symp, attack, A&E, hosp
- Prevent: symp,
D lifestyle b/c symp, perm impaired lung func, premature death
- Avoid S/E drugs/ Tx
- Req (1) Drugs (2) Prevent'n (2) Pt educ'n
Pharmacological Tx
- Step-wise
(based on severity)
- Occasional bronchodil
- If need short-acting inhaled b -ag > 1x/d ® low-dose inhaled corticosteroids (rarer: nedocromil, cromoglycate)
- Hi-dose inhaled corticosteroids or low-dose inhaled corticosteroids + salmeterol/ theophyllines
- Hi-dose corticosteroids + either: salmeterol, theophyllines, long-acting b -ag tab, anticholinergics
- All of above + corticosteroid tab
- Relievers
(bronchodil)
- Short-acting b -ag
(eg. Salbutamol/Ventolin, Terbutaline/Bricanyl) - "on demand" dur 4-6h, NOT for regular use (epidemic), S/E: tremor, h'ache, arrhy, non-spec aw H-responsiveness)
- Long-acting b -ag
(eg. Salmeterol, Formoterol) - when low-dose inhaled 'roids (< 800m g/d) no use, regular use (esp. w/low-dose inhaled 'roids)
- Xanthines
(oral) - adjunct to b -ag (esp. nocturnal symp)
- Anticholinergics
(inhaled) - adjunct if sig chronic obstruct'n, not 1st line asthma Tx
- Preventors
(anti-inflam)
- Inhaled 'roids
- efficacious, safe
- Systemic 'roids
(eg. Meclomethasone/Becotide/Becloforte, Budesonide/Pulmicort, Fluticasone/Flixotide) - mod-sev episodes
- Na cromoglycate
- children only (adults useless)
- Nedocromil Na
- adults
- LT-rec antagonist
(PO once/d), mild-mod asthma, 'roid sparing, for aspirin/ exercise-induced/ angioedema, unmask un-Dx Churg-Strauss syndrome (prev mask by 'roids)
|
Inhalation Devices |
|
Age(y) |
|
1st choice |
2nd choice |
|
0-2 |
|
MDI + Spacer w/mask
(Babyhaler, Nebu-chamber, Aerochamber- infant) |
Nebuliser
(PortaNeb) |
|
3-6 |
|
MDI + Spacer
(NebuChamber, Volumatic, Nebuhaler) |
|
|
6-12 |
'Roids |
MDI + Spacer |
Drug powder inhaler
(Turbohaler, Accuhaler, Diskhaler) |
|
|
Bronchodil |
MDI + Spacer or Drug powder |
|
|
>12 |
'Roids |
MDI + Spacer |
Drug powder |
|
|
Bronchodil |
Drug powder |
MDI w/trg |
Non-Pharm Tx
Avoidance
- House dust mite: vinyl cover, hot wash bedding, no carpet/ stuffed toys
- Cat
- Smoking, ETS, irritants
- Immunotherapy/ Hyposensitis'n
a) Controversial - highly-selected Pt w/specialised med unit
- Pt educ'n (Asthma Educ Prg in hosp, Asthma Soc of HK)
- Pt (+ parents)
- Asthma: def'n. triggers, drugs (mech, admin, S/E)
- Self-Mx if acute attacked (eg. A&E: v SOB, anxious, bronchodil no use)
ECF = eosinophilic chemotactic factor
NCF = neutrophilic chemotactic factor
LT = leukotriene