Paediatrics: Conventional positive pressure ventilation

Conventional positive pressure ventilation

IPPV via ETT with continuous flow of heated and humidified gas allows the non-paralysed baby to breathe spontaneously. The ventilator is time-cycled, pressure limited (TCPL) where the user sets the positive inspira-tory pressure (PIP), inspiration time (Ti) and ventilator rate. In this mode the tidal volume is determined by the lung compliance. Some ventilators can adjust PIP within a set range to deliver a set tidal volume (volume guarantee). Some ventilators can terminate inspiration when a set volume is reached or when inspiratory flow is declining below a threshold level. Whichever method is chosen the user must be familiar with the operation and limitations of the ventilator.

Indications

•   Worsening respiratory failure, e.g. RDS.

•   Impending or actual respiratory arrest from any cause.

•   Recurrent apnoeas.

•   Massive pulmonary haemorrhage.

•   Severe cardiac failure.

•   Persistent pulmonary hypertension of the newborn.

•   Severe congenital lung malformation, e.g. diaphragmatic hernia.

•   Severe HIE.

•   Anaesthesia.

Ventilation parameters

•   Peak inspiratory pressure (PIP).

•   PEEP.

•   TI and expiratory (TE) time (often expressed as I:E ratio).

•   Inspired O₂% or fraction inspired O₂ (FiO₂).

•   Gas flow (L/min) through ventilator circuit (may not be adjustable).

Monitoring ventilation

•   Review and adjust ventilation settings soon after commencement.

•   Monitor blood gases and adjust ventilation as appropriate. Acceptable limits will depend on the clinical situation, however, as a guide in preterm infants; pH 7.2–7.35, PCO₂ 5–8kPa, PO₂ 6–10kPa, saturation 90–95%, expired tidal volume around 5mL/kg.

•   If PaO₂ is too low—i FiO_2, or ‘rise’mean airway pressure (the latter by either ‘rise’PIP, ‘rise’PEEP, or ‘fall’ TE which will ‘rise’rate as TI stays constant). Do the opposite if PaO₂ is too high.

If PaCO₂ is too high—i alveolar ventilation, i.e. minute volume, by ‘rise’PIP, or ‘fall’ PEEP, or ‘rise’rate. Do the opposite if PaCO₂ is too low.

Acute deterioration during ventilation

May present as systemic collapse, ‘fall fall’ PaO₂, or ii PaCO₂. Ventilate with manual system, e.g. T-Piece (preferably with PEEP), and O₂ as required. Rapid improvement suggests ventilator problem. Otherwise consider ob-structed ETT, displaced ETT, pneumothorax, or non-respiratory disease, e.g. intraventricular haemorrhage (IVH), gut perforation.

Slow deterioration during ventilation

May present as slow deterioration in overall clinical condition, ‘rise’PaCO₂, or ‘fall’ PaO₂. Consider: worsening respiratory disease; partial ETT obstruc-tion; airway circuit leak; non-respiratory disease.

Ventilation weaning

As condition starts to improve aim to wean ventilation. Wean O₂ to low-est needed to maintain adequate PaO₂ (d retinopathy risk). As lung com-pliance improves wean PIP to maintain appropriate expired tidal volume (d risk of pulmonary air leak) in 2cmH₂O steps until 12–14cmH₂O (moni-tor blood gases). Then wean rate by 5 or 10 increments until 10–20breaths/ min. Following extubation it is often helpful in preterm infants to start nasal CPAP 5cmH₂O. Extubation without CPAP may be appropriate after short-term ventilation.