Comparison between intermittent mandatory and synchronized intermittent mandatory ventilation with pressure in children.

Mechanical ventilation can be life saving in critically ill infants and children, but has important complications. As a consequence, newmodesofmechanical ventilationhavebeen introduced in an attempt to reduce baro/volutrauma. The modes include thosewhich avoid intubation, such as continuouspositive airwayspressure (CPAP),minimize excessive volumes, i.e., volume-targeted ventilation (VTV) and high-frequency oscillation (HFO), and modes which synchronize the infant’s respiratory efforts with ventilator inflations, i.e., patient-triggered ventilation modes. Triggered modes include assist-control ventilation (ACV), when all of the patient’s efforts that exceed a critical trigger level are supported by ventilator inflations, and synchronized intermittent mandatory ventilation (SIMV), when a preset number of the infant’s breaths trigger ventilator inflations. Pressure support ventilation (PSV) is nowalso available. During PSV, as with SIMV and ACV, the initiation of the mechanical inflation is determined by the beginning of patient’s inspiratory effort but, in addition, termination of inflation is also determined by the patient’s inspiratory effort. Exactly when inflation is terminated can be fixed as with the Draeger Babylog ventilator at 15% of peak inspiratory flow or as with the BIRD-VIP and SLE5000 ventilators it can be manually adjusted (termination sensitivity). Increasing termination sensitivity has been shown to decrease the level of asynchrony, but this was associated with a shorter inflation time, which could adversely impinge on gas exchange. There havebeenphysiological, but few randomized, studies assessing the efficacy of PSV compared to other ventilation modes in prematurely born infants. Comparison of SIMV to PSV during four-hour study periods, in 20 infants with a mean gestational age of 29weeks, demonstrated a reduction in respiratory rate and significant increases in tidal andminute volumes when PSV was used. It appears that it is important not to use too lowa level of PSV. Comparisonwas undertaken of two levels of pressure support (3 vs. 6 cm H20) as an adjunct to SIMV during a 50% reduction in the SIMV rate, each stage lasting for 30 minutes. Addition of pressure support (PS) at 6 cm H2O, but not 3 cm H2O, prevented the increased breathing effort seen following a 50% reduction in SIMV rate. There havealsobeencomparisonsof PSVwithvolume targeting (VT) to other forms of ventilatory support, those studies have yielded mixed results. In a crossover pilot study, prematurely born infants in theweaningphase achieved similar oxygenation levels during PSV with VT as with SIMV, but with significantly lower mean airway pressures, suggesting the infants were making a greater contribution to gas exchange during PSVwith VT. Assessment of PSVwith VT compared to SIMVasan initial ventilatorymode inprematurelyborn infants after surfactant treatment for respiratory distress syndrome (RDS) demonstrated that in both groups the peak inspiratory pressure and mean airway pressure (MAP) decreased during the first 24 hours after surfactant administration (p<0.001),