1998 OPEN FORUM Abstracts
'Designer' Modes in Neonatal Assisted Ventilation
Dennis Bing, RRT
Inconsistent tidal volume delivery and ventilator-patient asynchrony have been implicated in some hazards of neonatal mechanical ventilation, such as acute and chronic lung injury and intraventricular hemorrhage. While survival from respiratory immaturity has improved, incidence of these hazards remains unacceptably high. Like designer jeans, new modes of assisted ventilation should provide the best "fit" to individual infants and their changing needs. Pressure Support Ventilation with Volume Guarantee (PSV+VG) is a new mode of mechanically assisted ventilation, introduced with the Drager Babylog 8000 plus neonatal ventilator. The concept of PSV+VG is to allow the infant to dictate the type and degree of support from the ventilator. With PSV+VG, the infant determines each component of the breathing pattern:
The start of inspiration
The PSV+VG is a fully synchronous mode, with the beginning of the inspiratory cycle initiated by patient effort. The flow sensor, located at the proximal airway, detects initial inspiratory volume as small as 0.3 mL, and triggers the ventilator into inspiration within 40 msec. The threshold of patient effort detection is automatically compensated for endotracheal tube leaks, which can cause autocycling in some infant ventilators.
Tidal Volume / Inspiratory pressure
Appropriate tidal volume delivery for mechanically ventilated preterm infants with surfactant deficiency ranges from 5 to 7 mL per kg of ideal body weight. PSV+VG determines the pressure needed for delivery of a set Vt based on expired tidal volumes from previous breaths, thus discounting endotracheal leak volume. Peak inspiratory pressure is regulated down, or up to a set maximal level, in response to changes in lung condition.
The end of inspiration
In PSV+VG, as pressure applied to the proximal airway equalizes to the lung, flow decelerates to end the inspiratory cycle. The actual Ti is determined by the infant's lung compliance and resistance and respiratory effort. The infant adjusts the Ti for each breath according to their need.
PSV+VG mode is synchronized with the infant's respiratory effort, so the baby determines breathing frequency. Because Vt is now optimal for all breaths, the infant can maintain minute ventilation at lower respiratory rates, work of breathing and oxygen consumption.
Leak-adapted PSV+VG is a "designer" mode to give control of mechanically assisted ventilation to the infant, to whom it belongs. This allows us, the clinicians, to care for the baby, rather than the machine.
The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.