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Asthma
Definition
Pathophysiology
Epidemiology
Diagnosis
Chronic inflamm disorder of airways; variable reversible airway obstruction; bronchial hyperresponsiveness to stimuli
Type I HS reaction; BronchoC, mucus hypersecretion, inflamm and oedema, thickening of BM, incr perm, lung overinflation, mucus plugging, SM
hypertrophy; subepithelial fibrosis; incr physiological dead space, air trapping and airway obstruction, incr airway resistance, incr airway p, VQ
mismatch; cytokines, chemokines, IgE, lymphocytes, mast cells, eosinophils involved
5% adults; 25% children
Reversible airway obstruction with >15% improvement in FEV1 (>400ml in adult), FVC, PEFR with beta-agonist; 20% variation in
PEFR readings over days-wks; abnormal reactivity with methacholine inhalation stimulation
Symptoms
Categories
85% >3hrs at presentation; 15% sudden onset; rapid onset = rapid response = less likely admission = less likely infectious trigger; initial response to
beta-agonists most accurate measure of severity (not severity of presentation)
Triggers: beta-blockers, ACEi, adenosine, aspirin (incr LT’s and bronchial hyperactivity), NSAIDs, sedatives (CI in acute asthma, risk sudden death)
RF’s for severe: prev hyperCO2, ICU admits, ED attendances, compliance, on PO steroids in last 6/12, monotherapy with long acting beta agonist, 3+
classes of meds used, old, smoking, psych, social, co-morbidities, heavy beta-agonist use, >50% decr peak flow
Mild:
short acting beta agonist, low dose inhaler steroid
Mod:
DD includes…
Investigation
>75% PEFR, FEV1
50-75% PEFR, FEV1
>95% SaO2
90-95% SaO2
HR 100-120
talks in phrases; mod-loud wheeze; pulsus paradoxus and central cyanosis possible
.
Severe:
long acting beta agonist, high dose inhaled steroid, >50% decr PEFR
<40-50% PEFR, FEV1
<90% SaO2
HR >120 (>130 if 2-5yrs)
RR >30 (>50 if 2-5yrs)
talks in words; quiet wheeze; pulsus paradoxus (>10-20mmHg) and central cyanosis
paradoxical chest wall movement; altered LOC; deterioration despite max trt
Extremis: ?PEFR/FEV1
<80% SaO2
HR >140 or brady
coma
FB, carcinoid, PE, eosinophilic pneumonias, systemic vasculitis
Bloods: hypoK (inhaled beta agonists decr K by 0.4), hypoP/Mg, hyperG, lactic acidosis, incr WCC (stress, steroids, E; is v common)
ABG: should be resp alkalosis (if not, ?impending hypoventilation); PaCO2 >40-42 / PaO2 <60 = life threatening; concurrent metabolic
.
.
acidosis also bad
Chronic
treatment
(in order)
Acute
treatment
(in order)
Indications: severe - refractory, SaO2 <92%, monitor resp fatigue, monitor response to trt
CXR: barotrauma, atelectasis, pneumonia, hyperinflation, bronchocoeles
Indications: 1st presentation asthma, ?pneumonia / barotrauma, pyrexia >39 not explained by viral illness, focal signs not responding to beta
agonist, chest pain, long term steroids, failure to respond to aggressive trt, severe resp distress
PEFR: easier to measure, cheap, portable, safe; usually 5-10% more than FEV1; if <200ml / 30% predicted, likely pACO2 >40
(max daily PEFR – min daily PEFR) / mean PEFR = diurnal variation = measure of control (20%, poor control; 5% good)
FEV1: gold standard; if <1L / 25% predicted, likely pACO2 >40; FEV1, PEFR, RC, FRC all decr with obstructive disease (can’t get air out)
ECG: R heart strain, ST/T/P changes; normalise with trt
ETCO2: concern if >37-39mmHg; not as sensitive as ABG as air trapping may cause normal ETCO2
Short acting beta agonist: use on >3/7 per wk needs review
Low dose inhaled steroid (beclamethasone, budesonide, fluticasone): reduce mortality and hospital admissions; onset <3hrs; prescribe to all patients
receiving PO steroids on discharge (either commence, or incr usual dose for 2/52); SE: oropharyngeal candidiasis
Long acting beta agonist (eformoterol, salmeterol): DOA 12hrs
Med – high dose inhaled steroid
Incr dose of LABA and steroid
Others: chromolyns (in exercise-induced asthma as prophylaxis), LT receptor antagonists
O2: Effects: reverses hypoxic pul vasoC, reverses bronchoC, protects against decr pO2 from beta agonist
Dose: use in all except mild; humidify to prevent bronchoC from dry gas; high flow O2 has been shown to worsen outcome, so stick to endpoints
below
Endpoint: aim SaO2 >92%
Short acting beta agonist (salbutamol, terbutaline)
Effect: bronchoD, incr ciliary activity, decr mediator release
Onset: 3-5mins, DOA 3hrs
Dose: 8 puffs spacer = 5mg (with optimal technique, 15% reaches lungs) NEB = equivalent effect; use 6 puffs regardless of age Q20minly
NEB: Pros: not temp dependent; doesn’t require patient co-operation; continuous nebs recommended in severe
Cons: delivery depends on RR and TV; only 55% dose nebulised, 33% nebulised, is inhaled; 20% dose overall delivered
IV: Pros: use if can’t do inhaled (eg. Coughing ++) or refractory / life-threatening
Cons: no benefit over INH, more autonomic SE’s
500mcg (10mcg/kg) IV bolus over 2mins  repeat dose at 10mins if not improving
 1-20mcg/kg/min infusion (start at 5-10mcg/kg/min for 1hr in children, then reducing down to 1-2mcg/kg/min)
SE: tremor, headache, lactic acidosis, hypoK, hypoG, cramps, insomnia, tolerance; cause vasoD of poorly aerated areas therefore incr VQ mismatch
Anticholinergics: use in mod-severe asthma, COPD, mod asthma in children; best in combination with beta agonist, otherwise poor effect
Onset: 20mins, peak 2hrs, DOA 6hrs
Dose: Ipratropium: 4 puffs via spacer, or 250mcg neb (add to 2nd neb); Q20minly for 3 doses, then Q4hrly; give Q20minly in severe
SE: dry mouth, cough, blurred vision, glaucoma; no advantage to continuing after 1st 24hrs
Steroids: early use decr hospital admission, relapse rate, beta agonist use
Effects: decr inflamm, secretions, reactivity, mediators; incr beta receptor no, function and sensitivity
Onset: 2-6hrs, DOA 24hrs
Dose: Use IV if severe (PO absorption compromised); 10-14/7 course for adults (shorter if sudden onset, rapid response), 3-5/7 for children;
tapering not required unless on maintenance steroids / >2/52 course
Prednisone 25-50mg (1mg/kg) PO OD
Dexamethasone 4-8mg (0.1mg/kg) IV – IV drug of choice
Hydrocortisone 100-200mg (4mg/kg) IV – has mineralocorticoid effects / SE’s (HTN, hypoK, met alk, Na retention)
MgSO4: severe refractory asthma; decr admission and improve FEV1
Effects: improves lung function; prevents tachyphylaxis to beta agonists, bronchoD, anti inflamm; safe
Dose: 1.2-2g (25-50mg/kg) IV over 20mins one-off dose
monitor levels and for toxic adverse events; inhaled is safe but lack of clear benefit for use
SE: flushing, hypoT, sweating, N, sedation, arreflexia in toxicity
Aminophylline: severe asthma refractory to above; role in children but not adults (unless COPD)
Effects: bronchoD, CNS and cardiac stimulation, incr skeletal muscle contractility, diuretic, incr gastric secretion
Dose: 6mg/kg (ideal body weight) (10mg/kg in children, max 500mg) loading dose IV over 60mins (NOT if on PO; if on PO, get serum level)
 0.5-1mg/kg/hr infusion
Pharmacology: factors increasing clearance = fags, phenytoin, carbamazepine, phenobarb; factors decreasing clearance = pul oedema, hepatic/renal
probs, erythromycin, cipro
Endpoint: goal is level 10-14mg/dL
SE: anxiety, N+V, headache, ectopics, multi-focal atrial tachycardia, seizures
Adrenaline: life threatening refractory to above; imminent cardioresp arrest
Effects: alpha properties help airway oedema, beta cause bronchoD
SE: hypoK, arrhythmia, lactic acidosis
CI: cardiac disease, >40yrs
NIV: may prevent/delay mechanical ventilation, decr WOB, bronchoD, decr airway resistance, decr CV impact of changes in p’s caused by asthma
Dose:
BiPAP (12:6 to start, 12-18:6-12 titrate) best
requires less sedation, doesn’t require paralysis, preservation of airway reflexes, less pneumonia; may need 0.05-0.1mg/kg midaz or 0.5-1mg/kg
ketamine to tolerate
RSI: only intubate if life threatening and max therapy failed; 10-20% mortality if tubed; trial of apnoea if cardiac arrest
Indications: cardiac / resp arrest or pre-arrest, profound decr RR, exhaustion, decr LOC, severe decr pAO2, severe resp acidosis despite trt
Aims: limit PAP, avoid gas trapping
permissive hypercarbia to help this (prevents barotrauma; CI if incr ICP / severely impaired myocardial Fx; risk of cerebral oedema, decr
myocardial contractility, vasoD, pul vasoC, post-arrest; can give NaHCO3 if pH <7.2 and don’t want to change ventilator settings)
Technique:
Give IVF 20ml/kg bolus pre-intubation to minimise risk of hypotension
Induce sitting up, ventilate by hand
Lignocaine 1.5mg/kg 3 mins pre-induction to decr laryngospasm
Ketamine: sympathomimetic and bronchoD
SE: hypersecretion, hypotension/HTN, CI in IHD, HTN and incr ICP
2mg/kg IV induction bolus  2-3mg/kg/hr INF (may prevent need for ETT; intubating agent of choice but no proven benefit
from ongoing treatment)
Propofol: short acting, bronchoD, good if HTN
SE: vasoD, hypotension esp if vol replete
Volatile anaesthetics: may cause bronchoD, helpful in ICU (eg. Isoflurane, halothane)
Sux 2mg/kg
or
roc 1mg/kg
 Vec 0.1mg/kg/hr
Salbutamol via ETT: 1-2ml neb solution diluted to 5ml; continuous nebs using 2-4x dose (as ETT is barrier to delivery)
Hand ventilate  place on volume cycled ventilator once airway p and TV acceptable
 FiO2 1.0 (titrate to O2 goals), RR 6-8 (titrate to lowest tolerable pH), TV 5-8ml/kg (6-10ml/kg in children), I:E 1:5
or more (titrate to airway p’s; may not be possible on oxylog 3000); minimal PEEP, PIP <40-45, target plateau
pressure <20
Heliox: at least 70% (therefore can’t deliver high conc O2 when using); lower density, decr resistance, decr WOB, improve nebulisation, decr resp
distress, incr GE; in severe refractory asthma to avoid ETT
External chest compression: decr air trapping, in extremis, cardiac arrest
Admit if:
ICU if:
Discharge if:
Discharge
advice
Pregnancy
Pre-treatment PEFR <25-30%
SaO2 <92%
Post-treatment PEFR <40% (or -60% if not improving well over few hours)
Child needing spacers <3hrly despite 4-6hr trt in ED
Also consider: social factors, geographical factors, co-morbidities, previous asthma history
Altered LOC; exhaustion; marked decr AE; incr pCO2 despite trt; high RF; failure to improve despite trt; intubation needed; multiple co-morbidities;
need for ongoing intensive trt
Post trt PEFR >60% (-40% if doing well)
ASS 0-2
Adequate social circumstances etc….
Observe for 30-60mins after most recent bronchoD dose
Combined use PO and INH steroids; written action plan (how to recognise Sx, mng of exac, how to gain medical attention, clear FU instructions); close
FU; patient and family education; review preventative treatment; check inhaler technique
Assoc with pre-eclampsia, prem, LBW, CS; worsens in 1/3, improves in 1/3, stays same in 1/3; exac most common in 2nd and 3rd trimesters; PEFR and
FEV1 not changed much; steroids OK in acute; beta agonists and budesonide safe
PaCO2 >35, PaO2 <70 worrying in pregnancy
Cardiac
arrest
Referral
Admission: SaO2 <95%, FEV1 / PEFR <70%, any fetal compromise
Trial of apnoea; external chest compression; volume challenge; adrenaline; treat complications
No GP; newly diagnosed asthma; change in medications; >2 ED attendances in 6/12; >2 admissions in 1yr; non-compliance; >4 courses of PO steroids
per year
Notes from: Dunn, Cameron (adult and paed), TinTin, Starship guidelines