October 2004-09-21
Protocol for management of acute life-threatening asthma on PICU
The following signs are established features of Life-threatening Asthma:
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Disturbance in conscious level (decreased conscious level or agitation)
Silent Chest
Exhaustion
Poor Respiratory Effort
Cyanosis in air (i.e. SaO2 < 85% in air)
PEFR < 33% expected or best
(BTA Guidelines, Thorax 1997)1
General Management
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Administer Oxygen
Oxygen delivery should be adequate to maintain SaO2 above 94%
Provide a calm and reassuring environment.
Allow child to assume most comfortable position. Often sitting upright
reduces distress and improves chest wall movement.
NO routine CXR
the decision to intubate, is made on clinical grounds
Antibiotics are not routinely given.
There is NO place for long acting beta2agonists in severe acute asthma
Most asthmatics are dehydrated due to poor intake of fluids and
increased insensible losses. Hence fluids should be given but care
should be taken to maintain euvolaemic state as hyperhydration may
lead to problems with pulmonary oedema and SIADH.
Monitoring
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ECG monitoring
Close serum electrolyte and blood glucose monitoring. Watch carefully
for hypokalaemia.
BP monitoring
Oxygen saturation monitoring
Note PEFR monitoring will not be tolerated by these patients.
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Asthma therapy
Beta2agonists
Nebulised Salbutamol
Dose
2.5 mg under 5yrs
5mg above 5 yrs
IV Salbutamol bolus
5 micrograms per
kilogram over 5 minutes
IV Salbutamol infusion
1 to 5 micrograms per
kilogram per minute
Notes
Can be repeated as
required. Can give
continuous nebulisation
(up to between 40 and
80mg per hour)
Maximum concentration
200 micrograms per ml.
Dilute if needed in 0.9%
Saline or 5% Dextrose.
Recommended
concentration 10
micrograms per ml. (If
problems with excessive
volume, maximum
concentration 200
micrograms per ml).
Dilute if needed in 0.9%
Saline or 5% Dextrose.
Nebulised therapy
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Administer salbutamol either nebulised or intravenously.
 Salbutamol via MDI is inappropriate in these hypoxic patients
Nebulisation must be driven via oxygen between 6 and 10 l/min O2.
In severe asthma, continuous nebulisation has been shown to be
advantageous over intermittent nebulisation3.
Intravenous Salbutamol
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Intravenous Salbutamol should be used in patients who are
unresponsive to nebulised therapy or in patients who have decreased
tidal volume with near complete airway obstruction.
After an initial loading dose of 5micrograms/kg over 5 minutes, a
continuous infusion of 1 to 5micrograms/kg/min should be set up 1.
Monitor blood electrolytes and glucose carefully. Be especially vigilant
for hypokalaemia.
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Anticholinergics
Nebulised ipratropium
bromide
Initial management
Nebulised ipratropium
bromide
Subsequent management
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Dose
Give 3 doses of 250
micrograms every 20
minutes
250 micrograms every
6 hours
500 micrograms every
6 hours
Notes
Ipatropium can be combined
with salbutamol for
nebulisation
if 5 years age or younger
if above 5 years age
Current evidence suggests that Ipatropium Bromide significantly
improves lung function in acute severe asthma5,6.
Ipratropium Bromide should be nebulised concurrently with salbutamol.
In severe or life-threatening episodes of asthma the greatest benefit is
achieved by giving three doses of 250micrograms of nebulised
Ipratropium Bromide in the first hour of management (i.e. every 20
minutes)5,6
After the first hour, nebulised Ipratropium should be prescribed 6-hourly
(250micrograms if below 5 years and 500micrograms if above 5years).
Steroids
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Hydrocortisone 4mg/kg (max 100mg) 6 hrly iv
Switch to oral prednisolone once the patient is stable.
Aminophylline
Aminophylline has been shown to improve lung function and decrease the
need for ventilation in severe asthma7. It has a place in the management of
children not responding to aggressive beta2agonists and ipratropium therapy.
It is administered intravenously:
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Loading dose 5mg/kg over 20 minutes (Omit if patient takes oral
theophylline)
Maintenance dose1mg/kg/hr (dilute to 1mg/ml in 0.9%Saline or
5%Dextrose). (If above 12 years of age, reduce to 800 micrograms/kg/hr)
Monitor plasma levels and serum electrolytes. Reduce dose in liver disease
and note potential for drug interactions.
DRUG INTERACTIONS – Decreased effect/increased toxicity:
(Decreased theophylline level
Aminoglutethimide, barbiturates, carbamazepine, charcoal, high protein/low
carbohydrate diet, hydantoins, isoniazid, I.V. isoproterenol, ketoconazole,
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loop diuretics, phenobarbital, phenytoin, rifampin, smoking (cigarettes,
marijuana), sulfinpyrazone, sympathomimetics
Increased theophylline level
Allopurinol, beta-blockers, calcium channel blockers, carbamazepine,
cimetidine, ciprofloxacin, heart failure, corticosteroids, disulfiram, ephedrine,
erythromycin, fever/viral illness, hepatic cirrhosis, influenza virus vaccine,
interferon, isoniazid, loop diuretics, macrolides, mexiletine, oral
contraceptives, propranolol, quinolones, thiabendazole, thyroid hormones,
troleandomycin)
IV Magnesium8
Indication:
Intravenous magnesium is indicated in children not responding adequately to
aggressive inhaled beta2agonists, ipratopium therapy and intravenous
bronchodilators. It may be used as a treatment modality to try to avoid the
need for ventilation.
IV Magnesium Sulphate
bolus
Dose
0.2 mmol/ kg over 20
minutes
Notes
Dilute to maximum
concentration 1mmol in
5mls (dilute with 0.9%
Saline or 5% Dextrose).
This use is as a one-off bolus in the early stages. It may be repeated after 12
hours but serum electrolytes and Magnesium levels should be checked first.
Alternatively, an infusion of 0.4 mmol/ kg Magnesium Sulphate can be given
over 6 hours (can repeat this infusion after 24 hours). Again, serum
electrolytes and Magnesium levels should be checked before repeating the
infusion.
Heliox
Unproven benefit in children9.
October 2004-09-21
Intubation and mechanical ventilation should be avoided if at all
possible.
However, it may become necessary at any point from presentation and
indications for intubation and mechanical ventilation are discussed below.
Decision to Intubate
If at all possible, mechanical ventilation should be avoided as this may
increase bronchospasm, increase barotrauma and cause circulatory collapse.
However, absolute indications for intubation include:
 Cardiac Arrest
 Respiratory Arrest
 Severe Hypoxia
 Rapid Deterioration in child’s mental state
 Progressive exhaustion despite maximal treatment is a relative
indication
Note that this decision is not based on arterial blood gas analysis but
rather on clinical parameters.
Induction & Intubation
There is no uniform consensus on ventilation of Asthmatics but the following
points should be remembered.
1) 50% of complications surrounding the mechanical ventilation of asthmatics
occur around intubation.
For this reason experienced senior help should be enlisted.
Possible complications are due to gas trapping and include:
i. worsening hypoxia
ii. hypotension
iii. pneumothorax and surgical emphysema
iv. arrest
v. tube malposition
2) Use Ketamine and consider rapid sequence induction using sedation and
muscle relaxation aswell. (Ketamine acts as a bronchodilator as well as an
induction agent).
3) Consider topical lignocaine to pharynx and larynx to avoid reactive
bronchospasm.
4) Use a Cuffed tube (as high PIP’s are often required).
October 2004-09-21
5) Avoid rapid breaths when ventilating by bag. Slow bagging will give time
for adequate expiration and avoid dynamic hyperinflation.
6) CXR after intubation
Ventilator Settings
Tidal volume
suggested 6 to 8 mls/kg
Rate
well below that expected for age
(Suggest 8-16).
Inspiratory time
suggested 0.9-1.5s
I: E ratio
expiratory time must be longer to avoid dynamic
hyperinflation. Adequate expiration can be
assessed by termination of wheeze (or return to
baseline on flow-time wave or return to plateau on
capnography) before onset of the next breath
(Suggest 1:3 to 1:5)
PEEP
High PEEP should be avoided to avoid dynamic
hyperinflation. Initial PEEP should be set at ~60%
of the initial intrinsic PEEP measured by the
ventilator.
(Suggest 4 cmH2O)
PIP
the PIP needed to achieve adequate tidal volumes
is likely to be very high in asthmatic patients. Most
of this pressure will not be transmitted to the alveoli
and inspiratory plateau pressure may be a more
accurate assessment of the amount of transmitted
pressure.10
(Aim to keep plateau pressure < 30)
Waveform
A high inspiratory flow rate is needed if using
volume ventilation.
A square waveform is usually used
October 2004-09-21
Permissive Hypercapnia
The benefits of hypoventilating these patients when using mechanical
ventilation have long been recognised.11 Lower rates and tidal volumes can
be used to achieve permissive hypercapnia. PaCO2 up to 12 kPa have been
allowed as long as the rise is not too rapid and the pH > 7.1
Contraindications to permissive hypercapnia include:
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Raised Intracranial Pressure
Poor myocardial function
Significant Metabolic acidosis
Possible pregnancy
Note:
 A rise in FIO2 is to be expected when utilising permissive hypercapnia
 PaCO2 should be allowed to rise slowly in increments of 1kPa every hour
 pH should be maintained above 7.1
 Sodium Bicarbonate is seldom indicated in these patients
Sedation and Paralysis
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Avoid Paralysis unless adequate ventilation cannot be achieved at
acceptable inspiratory pressures. The combination of steroids and
paralysis causes an unacceptably high rate of critical care myopathy
and neuropathy.
Check CK levels daily in paralysed patients
Increased sedation is necessary if using permissive hypercapnia.
Sedation should always be adequate enough to avoid patient-ventilator
asynchronicity as this will worsen the hyperinflation.
Refractory Hypoxaemia
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Other simple causes for hypoxia must be ruled out before resorting to
the extraordinary treatment modularities outlined below.
In particular, it is necessary to rule out atelectasis, pneumothorax,
frequent β2agonists and hypovolaemia as causes of hypoxia.
In some patients, simply reducing sedation, reducing the rate of
ventilator breaths and allowing more patient-synchronised pressure
supported breaths (ASB) can improve oxygenation. It is worthwhile
trying this before resorting to extraordinary treatments.
In the absence of other causes, the most likely cause for the hypoxaemia is
the underlying V/Q mismatch of asthma. Possible treatment13,12 strategies
include:
1. Ketamine infusion
iv ketamine 2mg/kg bolus followed by an infusion at 0.2 to 2 mg/kg/hour
2. Magnesium infusion (see above).
October 2004-09-21
3. Inhalational anaesthetics
Isofluorane may be used as a bronchodilator but this requires a full-time
anaesthetist.
4. Broncho-alveolar lavage or use of nebulised DNase has been tried to clear
mucus plugging in extreme cases. Its role is uncertain.
5. ECMO
The use of extra-corporeal membrane oxygenation in asthma is not
certain. Currently, in the UK it used as a last resort
6. Consider proning
Weaning
The following clinical parameters can be used to assess clinical improvement
of the ventilated asthmatic patient:
i. Disappearance of pulsus paradoxsus (i.e. a drop of systolic bp of less
than 10mm Hg in inspiration in a ventilated asthmatic patient is a sign of
improvement). It is important to document daily the exact value of pulsus
paradoxus in asthmatics. (This can be done by selecting arterial line on
the main menu and choosing arterial cursor. The swing on the arterial
line corresponding to inspiration will be obvious if present. Then the
cursor can be moved to measure the peak arterial pressure in inspiration
and expiration. The difference will be the exact value of the pulsus
paradoxus). For example, below, pulsus paradoxus = 16mmHg.
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ii. Good PaO2 in an FiO2 of 40% or less and a PIP of <35cmH20
iii. Minimal atelectasis on CXR
iv. Decreased intrinsic PEEP (as measured by ventilator)
When weaning, it is important to minimise patient – ventilator asynchrony as
this will increase agitation and gas trapping.
This can be achieved by reducing the rate of ventilator breaths and allowing
more patient-synchronised pressure supported breaths (ASB).
BIPAP/ASB or ASB alone are helpful at this stage.
REFERENCES
1.
British Thoracic Society Guidelines on Asthma. Thorax, 1997; 52: S2S8
2.
Brooks et al. Significance of roentgenographic abnormalities in children
hospitalised for asthma. Chest 1982 82: 315-318
3.
Michele et al. A Prospective, randomised study of continuos versus
intermittent nebulised albuterol for severe status asthmaticus in
children. Critical Care Medicine 1993 21: 1479-1486
October 2004-09-21
4.
5.
6.
7.
8.
9.
10.
11.
12.
Werner HA. Status Asthmaticus in Children. Chest 2001 119(6): 19131929
Zorc et al. Ipatropium bromide added to asthma treatment in the
pediatric emergency department. Pediatrics 1999 103: 748-752
Rodrigo GJ and Rodrigo C. The role of anticholinergics in acute asthma
treatment. Chest 2002 121(6) 1977-1987
Yung et al. Randomised Control Trial of aminophylline for severe acute
asthma. Archives of Diseases in Childhood 1998 79: 405-410
Ciorallo et al. Intravenous Magnesium therapy for moderate to severe
pediatric asthma: results of a randomised placebo controlled trial.
Journal of Pediatrics 1996 129: 809-814
Carter et al. Evaluation of heliox in children with acute severe asthma,
a randomised crossover trial. Chest 1996 109: 1256-1261
Leatherman et al. Life threatening asthma. Clinical Chest Medicine
1994 15:453
Dworkin et al. Mechanical ventilation for status asthmaticus in children.
Journal of Pediatrics 1989 114: 545-9
Rice et al. Rapid response to isofluorane anaesthesia in refractory
status asthmaticus. Archives of Diseases in Childhood 1998 78: 395-6
October 2004-09-21
SUMMARY CHART- ACUTE LIFE THREATENING ASTHMA
ALL PATIENTS
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OXYGEN
MONITOR ECG, SaO2
CONTINUOUS NEBULISED
SALBUTAMOL
NEBULISED IPATRIOPIUM
EVERY 20 MINS IN FIRST
HOUR AND 6 HOURLY
THEREAFTER
IV SALBUTAMOL OR IV
AMINOPHYLLINE
INTUBATE AT ANY
STAGE IF:
1. Cardiac Arrest
2. Resp Arrest
3. Severe Hypoxia
4. Rapid deterioration in
mental state
Consider Intubation if
progressive exhaustion
CONSIDER
IV MAGNESIUM
IF INTUBATED
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SENIOR EXPERIENCED HELP ON INTUBATION
RAPID SEQUENCE INDUCTION – CONSIDER KETAMINE,
SUXAMETHONIUM AND MIDAZOLAM
CONSIDER CUFFED TUBE
SLOW BAGGING
CXR POST INTUBATION
IF VENTILATED
 ARTERIAL LINE
 CONSIDER PERMISSIVE HYPERCAPNOEA
 LONG EXPIRATORY TIMES
 LOW PEEP
LAST RESORTS
 Ketamine infusion
 Magnesium infusion
 Broncho-alveolar lavage or DNAse
 Isofluorane
 ECMO