Effort and work of breathing in neonates during assisted patient-triggered ventilation. Flow-cycled versus time-cycled sIPPV in preterm babies with RDS: a breath-to-breath randomised cross-over trial.
OBJECTIVE: This study compares patient-ventilator synchrony, work of breathing and patient effort in neonates during different modes of patient-triggered ventilation. DESIGN: Clinically stable neonates received intermittent mandatory ventilation (IMV), synchronized intermittent mandatory ventilation (SIMV), pressure assist/control ventilation (A/C), and pressure support ventilation (PSV) in a random order for 20 mins. With each mode patient-ventilator synchrony, work of breathing, and patient effort were evaluated. SETTING: Neonatal level III intensive care unit of a university hospital. Measurements and RESULTS: Seven clinically stable neonates (31.4 +/- 2 wks gestation, weighing 1.49 +/- 0.38 kg) were randomly ventilated with the above four modes using a Bird VIP ventilator. Esophageal pressure, airway pressure, and flow were measured using a CP-100 neonatal monitor (Bicore). Data for five consecutive breaths in each mode were analyzed. Patient effort and work of breathing differed significantly among modes of ventilation. The inspiratory pressure time product was least with A/C (0.54 +/- 0.29 cm H(2)O.sec) and increased with PSV (0.60 +/- 0.39 cm H(2)O.sec), SIMV (1.46 +/- 0.55 cm H(2)O.sec), and IMV (2.74 +/- 1.05 cm H(2)O.sec) (p <.05). A similar trend was observed for work of breathing, with work least during A/C (0.07 +/- 0.04 joules per liter [J/L]), followed by PSV (0.17 +/- 0.14 J/L), SIMV (0.33 +/- 0.13 J/L), and IMV (0.41 +/- 0.16 J/L) (p <.05). Marked dyssynchrony between patient-initiated and ventilator-initiated inspiration occurred only during IMV. CONCLUSION: Asynchrony can be avoided by the use of assisted, patient triggered modes of ventilation and, of the available modes, pressure A/C results in the least effort and work of breathing for clinically stable neonates. Few data exist about patient-triggered ventilation techniques in neonatal critical care. Our aim was to compare pressure-limited synchronised intermittent positive pressure (or assist/control) ventilation (sIPPV) in the classical time-cycled (TC-sIPPV) mode against flow-cycled (FC-sIPPV) modality. In this latter, typical sIPPV full respiratory support is provided but both the initiation and the end of inflation are determined by the infant's spontaneous respiratory efforts by using airway flow changes.
                A third-level neonatal intensive care unit.
                Ten preterm babies (<32 weeks' gestation) were randomised to receive 1 h FC-sIPPV followed by 1 h TC-sIPPV or the inverse shift, according to a computer-created randomisation table. Eligible babies had hyaline membrane disease and received 200 mg/kg surfactant at least 6 h before the study period. Respiratory mechanics, ventilatory and vital parameter data were registered real time.
                FC-sIPPV resulted in lower-rate volume ratio, pressure x rate product, mean airway pressure and heart rate; tidal volume and oxygen saturation were higher (all p<0.001). Spontaneous inspiratory time was lower than usually set by the physician and it was directly correlated to birth weight (rho = 0.5, p = 0.001) and gestational age (rho = 0.32, p = 0.001). No differences were noticed in the mechanics and blood gas and vital parameters during the two study phases.
                FC-sIPPV may safely result in a better patient ventilator synchrony. Inspiratory time usually set in neonatal critical care is higher than that decided by the baby during spontaneous effort. This should be considered when establishing time-cycled ventilation.
There is insufficient evidence to determine the safety and efficacy of flow-cycled compared to time-cycled synchronized ventilation in neonates. Large randomized clinical trials using a parallel-group design and reporting on clinically important outcomes are warranted.