Comparison of airway pressure-triggered and airflow-triggered ventilation in very immature infants G Dimitriou, A Greenough, B Laubscher and N Yamaguchi Children Nationwide Regional Neonatal Intensive Care Centre, King’s College Hospital, London, UK Dimitriou G, Greenough A, Laubscher B, Yamaguchi N. Comparison of airway pressure-triggered and airflow-triggered ventilation in very immature infants. Acta Pædiatr 1998; 87: 1256–60. Stockholm. ISSN 0803-5253 Failure of patient-triggered ventilation in very immature infants may be due to the use of inappropriate triggering systems. Two types of airflow trigger were therefore compared consecutively to an airway pressure (SLE) triggering system. Each comparison was made in 10 infants, 28 weeks of gestation. Comparison was made of the delivered volume, trigger performance and blood gases using each system for 1 h. Both comparisons showed that the airflow triggering systems performed better: one (Draeger Babylog 8000) had a higher sensitivity ( p  0:01) and the other (Bird VIP airflow trigger), in which inflation was terminated by sensing a reduction in inspiratory flow, had a lower degree of asynchrony ( p  0:01) and a tendency to deliver higher volumes. These results suggest that triggering systems sensing airflow changes may be superior to those sensing airway pressure changes in very immature infants. The use of a mechanism to synchronize the termination of inflation to the end of the patient’s inspiration may offer further advantages.  Patient-triggered ventilation, prematurity A Greenough, Children Nationwide Regional Neonatal Intensive Care Centre, 4th Floor, Ruskin Wing, King’s College Hospital, London SE5 9RS, UK Patient-triggered ventilation (PTV) has been shown to be the superior mode of weaning from ventilator support when compared with weaning by either conventional mechanical ventilation (CMV) (1) or synchronized intermittent man- datory ventilation (SIMV) (2, 3). Unfortunately, a compar- ison of patient-triggered ventilators demonstrated that they all functioned less well in very immature infants with respect to a longer trigger delay (or response time) and lower sensitivity (4). In an immature population, a body surface trigger has advantages over an airway pressure trigger regarding sensitivity, triggering rate and trigger delay, but these advantages are offset by an undesirable tendency; that is, in some infants, triggering occurs not only in inspiration but also in expiration (5). Further research, therefore, is needed to identify the optimum triggering mechanism in very immature infants. As a con- sequence, an alternative triggering method was compared in such a population, namely detection of airflow changes to an airway pressure-triggering system. Patients and methods Immature infants (28 weeks of gestational age) 2 weeks of age, whose respiratory failure had recovered sufficiently to allow weaning and the clinicians, therefore, deemed ready to transfer to PTV, were studied. The infants had all followed the routine weaning protocol of the neo- natal intensive care unit (NICU), i.e. ventilator rate and pressure were reduced to 40 breaths min -1 and less than 18 cmH 2 O respectively. At that stage, sedation is stopped and caffeine (10 mg kg -1 loading dose and then 3 mg kg -1 d -1 maintenance) administered. All infants had been venti- lated on the SLE 2000 (SLE Ltd, South Croydon, UK) on which they initially remained. The ventilatory mode was then changed to PTV, the inspiratory times were kept between 0.3 and 0.4 seconds, back up rates between 30 and 40 breaths min -1 and trigger sensitivity set at max- imum. Infants were examined if they had been stable on PTV with blood gases within a predetermined range [arter- ial oxygen tension (PaO 2 ) 6.7–10.7 kPa, arterial carbon dioxide tension (PaCO 2 ) 4.7–7.4 kPa and pH 7.25–7.40] for at least 2 h. Two consecutive comparisons of two different airflow triggering systems and an airway pressure triggering system were undertaken. In the first (study A), infants were assessed initially on the SLE 2000 (airway pressure trigger which at maximum sensitivity is triggered by a change in airway pressure of 0.5 cmH 2 O) and then the Draeger Babylog 8000 (Draeger Lubeck, Germany) with software 4.0 (dual hot wire anemometer flow sensor), each for 1 h. The Draeger’s flow signal is integrated to obtain volume and at maximum sensitivity a positive pressure inflation is triggered by a spontaneous inspiratory volume of 0.02 ml (flow threshold 0.2 l min -1 ). In the second comparison (study B), infants were exam- ined first on the SLE 2000 and then on the Bird VIP (VIP Bird, Palm Springs, CA, USA) (variable orifice differential Acta Pædiatr 87: 1256–60. 1998  Scandinavian University Press 1998. ISSN 0803-5253