Ventilating Children
This guide is intended for use when the need to ventilate children outside a PICU is required. This is likely during a flu pandemic, but also occurs intermittently when resources are stretched at busy times of the year. It is likely that care will be better facilitated through ongoing communication at the time, but this guideline will allow such communication to be more efficient and effective, at a time when time itself is a valuable resource.
Principles
Children present with different problems to adults, although during a pandemic, the diagnosis is likely to be the same as for adults, i.e. influenza.
Management of single organ respiratory failure should use mechanical ventilation as a last resort, but contrary to usual guidance, the use of non-invasive support (CPAP/BiPAP) may be contraindicated. Anaesthetic induction should be unchanged, but intubation should be carried out with cuffed endotracheal (ET) tubes and closed circuits used wherever possible, but the management of ventilation for those children not taken to the lead centre may be different from current practice:
- Appropriate sedation will need to be ongoing, not simply 'holding'
- Adequate monitoring will be required
- Ventilation strategy will need to be set
- A weaning strategy will be required
- Feeding should be initiated where appropriate
Sedation
Most children requiring mechanical ventilation do not need paralysis, except for transportation (including within the hospital) or for defined procedures. Sedation should be maintained while mechanical ventilation is necessary, for patient comfort and safety. Sedation should be at a level that allows the patient to cough and move to some extent, but should not be sufficient to allow accidental extubation, loss of iv access etc. Safety can be augmented by the appropriate nursing ratio and the use of splints.
Propofol is contraindicated as a sedative for children below 17 years old.
Morphine (start at 20 micrograms/kg/hr) and midazolam (start 100 micrograms/kg/hr) are the current first line choice for PICU and are prescribed according to response. Oral sedatives (e.g. chloral hydrate) may be useful to reduce Infants often need less drug and benzodiazepines are avoided below 3 months old, wherever possible. The youngest infants can sometimes be managed with intermittent oral sedatives only. Other strategies and drugs can be considered e.g. clonidine.
Once ventilatory requirement is reducing, sedation needs to be weaned in parallel with the ventilation, to facilitate extubation in a timely fashion.
Monitoring
In pandemic flu, contamination of non-infected areas should be minimised and blood gas analysis should therefore be undertaken less often or using near patient I-stat analysers where possible. However, ventilation should be monitored effectively and the routine use of end tidal CO2 monitoring is essential. This will give more reliable results than usual, as the ET tubes will be cuffed. Oxygen saturation (SpO2) will be the most useful way to ensure adequate oxygenation. Blood gases will ensure that the ventilation strategy is being followed.
Ventilation Strategy
In single organ respiratory failure, the patient should never be stable'! There should always be a need to increase or reduce ventilation, ensuring optimised risk/benefit from ventilatory support and aiming to provide the least amount of ventilation for the shortest duration.
Ventilation should be similar to that for ARDS prevention and treatment. Tidal volumes of 5-7ml/kg, permissive hypercapnoea and pH >7.25 are reasonable aims. SpO2 88-92% will ensure adequate tissue oxygenation, provided adequate circulatory function.
Inspiratory times are generally shorter in children, but should be 0.5s as a minimum. Rates are generally higher (e.g. 30-1 in infants). In children triggering, care must be taken to avoid inverse ratios; remember that as rate increases, the ventilatory cycle shortens. PEEP should be used. 4cmH2O as a minimum overcomes some of the resistance in the ETT.
Weaning strategy
Ventilation should be kept to a minimum as a general principle. In a pandemic, this principle will need to be rigorously applied. PEEP can be weaned as oxygenation improves, with an aim of extubation at a PEEP of 4cmH2O. Oxygenation index (OI)* may help. Rate and inspiratory pressure wean as dictated by pH (CO2). Although weaning to pressure support mode (or equivalent) is an objective for adults and older children, for some ventilators this will impose an excessive workload for very small children and infants and in practice they can wean to a rate of 10-1. It would be usual to see that they are generating a reasonably normal respiratory drive and rate. Sedative drugs will need to have weaned in parallel to the ventilation. Feeds stop approximately 4 hours before extubation.
*OI: mean airway pressure X FiO2 X 100 / PaO2 (mmHg)
The higher the OI, the worse the oxygenation; 40 may indicate ECMO referral.
Feeding and other support
Enteral feeding should be quickly established in patients with single organ respiratory failure. Feeds should be stopped prior to planned transportation, surgery or before extubation to reduce the risk of aspiration. However, enteral feeding will protect the gut from ulceration and inflammation and maintain nutritional status. Fluid management is also less difficult, with less water retention and electrolyte imbalance.
DVT is not a common problem in children and prophylaxis is usually only required for immobilised patients (e.g. after trauma), or who have other risk factors (e.g. previous thrombosis).
Physiotherapy will be required for all ventilated children, in order to help improve secretion removal and improve lung recruitment.
Fluids should not be given excessively. Normal fluid administration follows the anaesthetic model: 4ml/kg first 10 kg; 2ml/kg next 10 kg; 1ml/kg thereafter. This should be as nasogastric feed in most cases, with drug and infusion fluids subtracted from the calculated daily total. Diuretic treatment is not routine but may be required if excessive fluid accumulation occurs, resulting in overt oedema, as this may lead to an increased oxygen requirement and risk of subsequent ARDS.