Patient triggered ventilation

Ventilatory management and bronchopulmonary dysplasia in preterm infants

Improvements in antenatal and neonatal care have resulted in increased survival of very preterm infants. However, the incidence of bronchopulmonary dysplasia (BPD) has not changed, probably as a consequence of a demographic shift. The underlying pathophysiology of BPD appears to differ for the current population of preterm infants compared to that described by Northway et al., and management strategies should be targeted to limit ventilator-induced lung injury. Non-invasive respiratory support techniques are currently under evaluation, but results of the trials have thus far failed to show a reduction in BPD. This review will focus upon various ventilation modalities for preventing and managing bronchopulmonary dysplasia.

Newer forms of conventional ventilation for preterm newborns

Although life saving, mechanical ventilation can cause complications such as ventilator-induced lung injury and bronchopulmonary dysplasia in very preterm babies. The ventilator-induced lung injury is multi-factorial. There has been an introduction of a number of newer forms of mechanical ventilation, which are aimed to reduce such complications. These are based on sound physiologic principles and clinicians should familiarize themselves with these advances.

Pressure support ventilation combined with volume guarantee versus synchronized intermittent mandatory ventilation: a pilot crossover trial in premature infants in their weaning phase

OBJECTIVE

To compare pressure support ventilation combined with volume guarantee (PSV-VG) to synchronized intermittent mandatory ventilation (SIMV) regarding safety, course of blood gases, and infant-ventilator interaction in premature infants.

DESIGN

Prospective, two-treatment, crossover pilot study.

SETTING

Tertiary care neonatal unit.

PATIENTS

Twenty-five ventilated premature infants: median (range) gestational age 26.1 wks (23.1-35.7), birth weight 765 g (450-3170), age at study 5 days (2-27), in their weaning phase.

INTERVENTIONS

Infants were studied for three 30-min periods, starting from SIMV, followed by PSV-VG, and back again to SIMV. After concluding the last period, all infants were switched back to PSV-VG. On the next day, infants were studied in the opposite direction. During each period, vital parameters, ventilation parameters, degree of physical activity, duration of rhythmic breathing, and the number of vital signs monitor alarms were recorded.

MEASUREMENTS AND MAIN RESULTS

Nineteen infants (84%) could be successfully ventilated with PSV-VG till the next day. PSV-VG achieved a similar oxygenation level as SIMV but with significantly lower ventilation pressures. Comparable ventilation was achieved, but infants with strong respiratory drive were more liable to hyperventilation episodes during PSV-VG. Although infants breathed more rhythmically during PSV-VG, suggesting better infant-ventilator synchrony, the infants' behavioral state and the fluctuations in blood gases did not differ.

CONCLUSIONS

The potentials of PSV-VG to improve infant-ventilator synchrony and to decrease pressure needed to ventilate premature lungs are promising, even though the changes were small. However, its benefits during acute illness and on the final outcome remain to be proven.

Update on patient-triggered ventilation

Physiologic studies have demonstrated short-term benefits of triggered ventilation over conventional ventilation. The results of the randomized trials are disappointing. Meta-analysis has highlighted that the only significant difference in outcomes on PTV compared with conventional ventilation is a shorter duration of weaning. A few of the trials included infants with meconium aspiration syndrome and congenital pneumonia, but most infants randomized had RDS. In addition, a high proportion of the infants included in the meta-analysis were from two trials in which the SLE 2000 and airway pressure triggering system were mainly used. We cannot confidently conclude that in a population of infants with another respiratory disorder or even in those with RDS supported by an alternative triggering system, a different result might have been achieved. In addition, the benefits of PTV demonstrated in physiologic studies are largely related to achieving synchronized ventilation. In none of the randomized trials was any attempt made to determine if the infants were breathing synchronously with their ventilators. Before dismissing PTV for use in the management of infants with acute respiratory distress, an appropriately designed trial needs to take place. Essential, before any such trial, is identification of optimum method of PTV delivery, which may be disease specific.