Role of Airway Pressure Release Ventilation in Pediatric ARDS – Our Experience

INTRODUCTION: APRV-TCAV(Habashi) is mechanistic approach in improvement of alveolar recruitment. It causes reduction in alveolar and alveolar duct micro strain and stress raisers, reduction in alveolar Vt. Time is critical component in determining alveolar inflation and deflation during each mechanical breath.(1) PRIMARY OBJECTIVE: To assess the changes in Oxygenation Index (OI) at multiple time points. To analyze the evolution of Tidal Volume (Vt) and Inspiratory Pressure (P high) settings. SECONDARY OBJECTIVE: To compare mortality rates between pulmonary and extrapulmonary ARDS. To assess occurrence of hemodynamic instability after the initiation of APRV. To evaluate relationship between spontaneous breathing and sedation requirements. To monitor air leaks (e.g pneumothorax, pneumomediastinum, subcutaneous emphysema) after APRV initiation. To identify and analyze the factors associated with failure of APRV. MATERIALS AND METHODS: It was a single Centre Retrospective Observational study carried out in PICU at RCH, Bangalore over a period of 25 months. INCLUSION CRITERIA: Children 1-18 years, with ARDS, as defined by the PALICC2 criteria started on APRV mode of mechanical ventilation. EXCLUSION CRITERIA: 1. Preemptive APRV in Dengue: Children with dengue receiving transfusions or in leaking phase, before developing hypoxia. 2. Severe Right Ventricular Dysfunction & Pulmonary Hypertension. 3. Raised Intracranial Pressure, Refractory Shock, Neuromuscular disorder. METHODOLOGY: a In Children with ARDS who were started on APRV- Habashi's TCAV protocol; b P High, T High, T Low, Fio2, Prior conventional setting (If rescue mode) minute ventilation, PaO2, PCo2, Tidal value were entered; c Oxygenation Index and Dead space fraction were calculated; d VIS Score, Sedation used and dose, hemodynamic parameters were noted. e Time Points for Measurement: Baseline, Subsequent Time Points were at 6, 12, 24, 48, and 72 hours post-APRV initiation. STATISTICAL TESTS: Descriptives, chi square tests, repeated variables ANOVA. RESULTS: 48 patients were started on APRV. 62%(30/48) of them had pulmonary ARDS and 37.5% (18/48) had extrapulmonary ARDS. 25%(12/48) had severe ARDS. Among 17 patients in whom APRV was initiated as rescue mode, 12(70%) had pulmonary ARDS. Among them, mean P Plat was 21(18-27), Mean PEEP was 8(7-15)and mean FiO2 was 67.7(60-100%). Patients with Mild to moderate ARDS, TV at initiation of APRV was 6.07 mL/kg (4-8) compared to 4.4 mL/kg (3-6) in severe ARDS. At extubation in Mild to moderate ARDS, TV was 7.5 mL/kg(4.2-12) and in severe ARDS it was 7.06 mL/kg (3.5-12) along with increase in Minute Ventilation. Consistent reduction in P High(21->17) (p0.00) and OI (20 to 9) were noted, which were statistically significant(p<0.000). 7 (18%) were proned. 5(13%) needed HFOV. Sedation requirement decreased over time and spontaneous breathing was allowed by 12 hrs. 13(27%) died, all showed improvement in OI over time. Cause of death were due to non pulmonary reasons(MODS and complications). DISCUSSION: Consistent improvement in Vt and MV with decreasing Phigh suggests lung recruitment over time. Improvement in OI and reduction in dead space fraction also suggest lung recruitment. Reduction in sedation and spontaneous breathing suggest reduction in asynchrony.