Paediatrics: Conventional positive pressure ventilation

2021-03-05 12:00 AM

IPPV via ETT with a continuous flow of heated and humidified gas allows the non-paralysed baby to breathe spontaneously.

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 inspiratory 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, PCO25–8kPa, PO2 6–10kPa, saturation 90–95%, expired tidal volume around 5mL/kg.
  • If PaO2is too low—i FiO2, 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 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 obstructed 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’ PaO2Consider: worsening respiratory disease; partial ETT obstruction; airway circuit leak; non-respiratory disease.

Ventilation weaning

As condition starts to improve aim to wean ventilation. Wean O2 to lowest needed to maintain adequate PaO2 (d retinopathy risk). As lung compliance improves wean PIP to maintain appropriate expired tidal volume (d risk of pulmonary air leak) in 2cmH2O steps until 12–14cmH2O (monitor 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.