Asthma is a reletively uncommon cause for PICU admission, although there is some evidence it is becoming more frequent. Ventilation is difficult, and it will often take several hours for respiratory acidosis to resolve. It is usually the case that blood gases will be significantly worse than pre-intubation gases.
All patients requiring admission to PICU for asthma will be on IVI Salbutamol, and should have recieved an IV bolus dose over 5 minutes (Age 2 - 18yrs, 15 micrograms/kg - MAX 250micrograms) then continuous IVI of 1 - 2 microgramsg/kg/min (100 micrograms/ml solution). It is unusual, although not unknown, to employ doses above 2mcg/kg/min as this often produces tachycardia and acidosis without much if any additional benefit in ventilation.
Titrate to clinical improvement and HR
In practice we often find that increasing the IVI above 2mcg/kg/min only increases tachycardia and agitation and produces a metabolic acidosis without additionally improving bronchospasm.
Regular monitoring of electrolytes
Intravenous hydrocortisone 4 mg/kg repeated four hourly.
Consider adding IV aminophylline if no improvement with salbutamol
5 mg/kg loading dose should be given over 20 minutes
omit loading dose in those receiving maintenance oral theophyllines
then continuous infusion at 1 mg/kg/hour.
Consider IV magnesium sulphate
10% solution (0.4 ml/kg = 40 mg/kg) over 20-30 min
All patient should be on 100 % maintenance initially
This could be adjusted to maintain the patient euvolaemic
Most patient will require initial fluid bolus
GI prophylaxis with ranitidine until established on full enteral feed
CXR- On the general paediatric ward CXR in acute asthma is not recommended. However children admitted to PICU with acute asthma should have a CXR done to look for complications (e.g. Pneumothorax) or factors contributing to the severity of the attack (e.g. Mycoplasma pneumonia)
There is insufficient evidence to support or refute the role of antibiotics in acute asthma, but the majority of acute asthma attacks are triggered by viral infection. If features suggestive of Mycoplasma pneumoniae infection are present on CXR (i.e. widespread areas of patchy bilateral consolidation the patient should be treated with a macrolide)
Blood gases: not as useful in paediatric practice as in adult practice as the decision to ventilate is usually made on clinical grounds. They need to be monitored once the patient is ventilated.
Electrolytes: should be checked regularly while patient is on frequent salbutamol nebulisers, on IV salbutamol or on IV aminophylline.
Ventilation in asthma
Non-invasive ventilation (mask CPAP or BiPAP)
Mask CPAP or BiPAP can be tried in the asthmatic patient that is getting tired or failing to oxygenate satisfactorily in an attempt to prevent the need for invasive ventilation.
If possible invasive ventilation should be avoided in the management of acute asthma. Such patients are notoriously difficult to ventilate.
Indications for ventilation
- Respiratory arrest
- Failing to oxygenate despite maximum oxygen therapy (oxygen saturations < 90% in 100% oxygen)
Ketamine or inhalation anaesthesia are useful induction agents, as they seem to have a bronchodilator effect
Prolonged use of paralysis also not recommended
Asthmatic patients are difficult to ventilate.
We do not aim for perfect gases but allow high pCO2 as long as the pH is 7.2 or over.
These patients usually need a long expiratory time and are therefore ventilated at a slow rate.
In the past no PEEP was used but current thinking and experience suggest that some PEEP is benficial. Some patients will require HFOV.
Bronchodilators and steroids need to be continued while the child is ventilated.
Bronchodilator therapy should only be weaned when the patient has been stable on current therapy for several hours.
Wean slowly one drug at a time and be prepared to escalate therapy back to previous level if any deterioration occurs during weaning.
The usual order for weaning is IV Salbutamol (decreasing rate)
Stop IV Aminophylline
Nebulised Atrovent (decrease frequency)
Nebulised Salbutamol (decrease frequency)
As the child improves the salbutamol and atrovent mode of delivery can be changed to MDI and spacer