1. In lung conditions, where infants require aggressive ventilation (e.g. severe meconium aspiration syndrome or PPHN), it may appear that the VG method is not effective with constant low tidal volume (VT) alarms. This is frequently due to a reluctance to set the back-up pressure high enough to allow the ventilator to reach target VT. In this case, the options are:

(a) Increase the back-up pressures high enough to allow the target VT to be reached. This is based on the premise that volutrauma – and not barotrauma – causes lung damage [2]. Therefore if the volume is appropriate, the pressure needed to achieve that volume is irrelevant.

(b) As some people remain unhappy using high peak inspiratory pressures, the alternative is to switch to high frequency oscillation.

(c) It is always important with any mode of ventilation to check that the amount of ventilator support required is in line with the clinical situation. If not, other contributory causes of poor ventilation (e.g., blocked endotracheal tube, pneumothorax) should be excluded .

2. Infants can actively tighten their abdominal muscles that can prevent gas entering the lungs during inflation; often termed ‘splinting’ [3]. Forced expiration and splinting cause hypoxemic episodes due to low lung volume and low VT delivery, causing obstruction’ and ‘low VT’ alarms. Fig. 1 shows a recording from a 1000-g baby ventilated with assist control (AC) and VG ventilation at a rate of 50 per min, a set peak inflating pressure (PIP) of 40 cm H2O, and a set VT 5 mL. It illustrates the effect on the inflating pressure when the baby tightens the abdominal muscles enough to temporarily stop inflation. This is preceded by active expiration. During the first ten inflations, the pressure is modulated to maintain the expired VT. During inflations 7, 8 and 9, the expired VT is larger than set VT and so the pressure is reduced. At inflation 10, there is a very small VT, and therefore the pressure is increased by 3 cm H2O for each inflation for the next five untriggered inflations until a VT is produced. This is then followed by triggered inflations at a similar inflating pressure to the start of this recording, with one untriggered inflation in between. A higher Pmax setting may allow the ventilator to increase the PIP and overcome the obstruction more quickly [4].

Fig. 1 Ventilator recordings showing effect of ‘splinting’ in a neonate on Assist Control Volume Guarantee Ventilation.