Objective: To evaluate the effect of the duration of conventional mechanical ventilation prior to high-frequency oscillation on the effectivity of HFO and patient survival. Study design: Retrospective analysis of the set of patients. Setting: Department of Anesthesiology and Intensive Care; ECMO Center University Children’s Hospital Brno. Patients: 26 patients > 1 month of age with severe hypoxemic respiratory failure and ARDS. Mean age was 44.4 months (three adult patients – 17, 19 and 24 years), mean weight 13.8 kilograms, maximum weight 70 kilograms, 17 boys, 9 girls. 15 patients died. 84,6% per cent of patients suffered from basic medical disease, mean admission PRISM score was 22. Nine patients met ECMO criter ia. In two of them ECMO was not necessary, in 5 ECMO was contraindicated, two patients were treated with ECMO. Four patients ventilated in H FO mode were also treated with NO, in two of them partial liquid ventilation was also implemented. Methods: Patients were ventilated in PCV or PRVC modes with limited peak inspiratory pressures and permissive hypercapnia. Tracheal gas insufflation was instituted if paCO2 > 10.0 kPa and/or pH < 7.20. HFO was started if there was a need for FiO2 > 0,6 and Paw > 15 cmH2O to maintain peripheral blood saturation > 90% or due to persistent hypercapnia and/or acidosis with C MV with TGI. HFO was designed as „High Volume Strategy“ to recruit the alveoli and keep the optimal lung volume. Before switching back to CMV, following criteria had to be met: Paw 15–20 cmH2O, FiO2 < 0.6, no air-leak and/or better chest X-ray, no drop in saturation during airway toilette. Patient was considered to be disconnected when following criteria were met: saturation > 90%, FiO2 < 0.4 Paw < 15 cmH2O, normal pH with respiratory rate (RR) < 30/min and PIP < 35 cmH2O. Patients were divided into two groups with respect to the duration of CMV prior to HFO: early application (CMV pre-HFO Ł 24 hours; 17 patients) and the application (CMV pre-HFO > 24 hours; 9 patients). Following data were collected for each group separately: demographic data (gender, age, weight, admission PRISM score), duration of ventilation (CMV prior to HFO, HFO, CMV after HFO and total duration of ventilation), acid-base status (pH, paO2, paCO2) and indexes – AaDO2, oxygenation index and hypoxemia score (paO2/FiO2). Results: Severity of respiratory failure was comparable in both groups (paO2/FiO2 76.9 vs 75.9 mmHg; OI 31.2 vs. 36; AaDO2 56.3 vs 55 kPa). There are no statistically significant differences in the followed parameters during the observational period. There were no differences in mean age, weight, PRISM score, duration of HFO, duration of CMV after HFO and total duration of mechanical ventilation. We found a statistically significant differences in mortality – in the group with early application 58.8% of patients survived, in spite of 12.5% in the group with late application of HFO. Overall survival rate was 42 per cent (11/26 patients). Conclusion: The duration of mechanical ventilation prior to HFO possess a significant ef fect upon the effectivity of HFO and patient survival. If HFO is implemented early (CMV prior to HFO Ł 24 hours), survival rate is much higher compared to late implementation of HFO (CMV prior to HFO > 24 hours) – 58.8% and 12.5%, respectively.

        Key words: high frequency oscillation (HFO) – early application – late application – respiratory failure – mortality – children