Effect of early intervention of high-frequency oscillatory ventilation on the outcome in pediatric acute respiratory distress syndrome.

BACKGROUND: Acute respiratory failure in both pediatric and adult patient populations has been extensively studied with recent emphasis on ventilation strategies that can effect mortality outcome. This research in adults has focused on definitive trials of lung protective strategies that have been proposed following preliminary reports of their potential benefits. High frequency oscillatory ventilation has also been described as a lung protective strategy. For many institutions HFOV is today considered a routine therapy as a "rescue" method in acute pediatric respiratory failure. Because HFOV is considered to be a "rescue" therapy, intervention with HFOV is usually in the later stages of acute respiratory failure and consideration of the time to intervention has not been previously examined.

OBJECTIVE: To evaluate the effect of time to intervention with high-frequency oscillatory ventilation (HFOV) on the survival of children with severe acute hypoxemic respiratory failure who were managed with lung protective strategies on conventional mechanical ventilation (CMV).

METHODS: Twenty-six consecutive patients older 1 month of age with severe hypoxemic respiratory failure and ARDS who at some point in their management were treated with HFOV were evaluated. The mean age was 3.7 years and included three patients treated in the Pediatric Intensive Care Unit (17, 19 and 24 years). Mean weight was 13.8 kg and there were 17 males and 9 females. Nine patients met Extracorporeal Membrane Oxygenation (ECMO) criteria, although only two patients were cannulated. Upon admission to the PICU, patients were initially managed with lung protective strategies using Pressure Controlled Ventilation (PCV) or Pressure Regulated Volume Control (PRVC) modes with limited peak inspiratory pressure, high positive end-expiratory pressure, and permissive hypercapnia. If a Pa-CO2 reached > 75 torr (10.0 kPa) and/or pH < 7.20, tracheal gas insufflation (TGI) was instituted. If FiO2 remained above 0.6 and mean airway pressure (Paw) exceeded 15 cmH2O in order to maintain arterial saturation above 89% or if hypercapnia and/or acidosis on CMV with TGI persisted, the patients were switched to HFOV. An "Optimal Volume Strategy" with HFOV was utilized to recruit alveoli and optimize lung volume. Patients were returned to CMV when their mean airway pressure were between 15 and 20 cmH2O, FiO2 < 0.6, had no evidence of air-leak and/or improved chest X-rays, and did not desaturated during airway suctioning. Patients were offered ECMO if the hypoxemia persisted on HFOV and there were no contraindications to its use. The patients were stratified for analysis by the time to intervention with HFOV. Early intervention was defined as within the first 24 hours of mechanical ventilation (17 patients) and late intervention defined patients beyond 24 hours (9 patients). Demographic data (gender, age, weight, admission PRISM score), time of each mode of ventilation, oxygenation indices and outcomes were recorded for both groups of patients.

MAIN RESULTS: The severity of respiratory failure at the time of HFOV intervention was comparable in both early and late groups (PaCO2/FiO2 83 vs. 79 torr, oxygenation index 27 vs. 33, AaDO2 421 torr (56 kPa) vs. 413 torr (55 kPa)). There were no differences in mean age, weight, admission PRISM score length of HFOV, length of CMV after HFOV (CMV post-HFOV) and the total duration of mechanical ventilation between the groups. We found a statistically significant difference in mortality with 58.8% of the early intervention patients surviving while only 12.5% of the late intervention patients survived. The overall survival rate was 42% (11/26 patients).

CONCLUSION: Early use of HFOV within the first 24 hours of acute hypoxic respiratory failure in pediatric patients is associated with better survival. Use of this therapy should be considered early in the course of treatment of any pediatric patient meeting this definition. (Tab. 2, Fig. 1, Ref. 28.)