This prospective cohort study took place in the Pediatric Intensive Care Unit (PICU) of a tertiary center in Cairo, Egypt. Patients were enrolled from October 2019 to February 2020. Written informed consent was obtained from the parents or guardians of all participants on admission to hospital including the procedures performed during hospitalization. Consent to participate was waived as this study was observational. Ethical approval was obtained from the research ethics board. This study was conducted under the Declaration of Helsinki.
The study subjects were 50 critically ill patients with ALI/ARDS on mechanical ventilation, 24 HFOV, and 26 CMV. The choice of mechanical ventilation mode was according to machine availability at the time of initiation.
Patients’ classification was based mainly on the timing of HFOV and their survival. HFOV patients were initially ventilated by HFOV once diagnosed with ALI, not CMV. Rescue HFOV patients managed by HFOV after the failure of conventional ventilation according to the attending physician assessment.
Early HFOV parameters were mean pressure 10 cm H2O on starting and changed according to oxygen saturation of the patient besides X-ray finding (lung inflation to 9th rib), the frequency was according to age with a range of 6–10 HZ, and the amplitude adjusted according to chest wiggle. According to the applied protocol at the hospital, CMV was assist control with positive end-expiratory pressure (PEEP) 5 cm H2O, peak inspiratory pressure (PIP) 20 cm H2O, and FiO2 40% with target lung recruitment in the form of increasing PEEP and PIP + 2 cm H2O. Rescue HFOV was initiated after the failure of maintaining O2 saturation > 85% and failed lung recruitment. Mean pressure was 5 cm H2O higher than calculated for CMV.
All patients were selected according to AECC Criteria to diagnose ALI/ARDS patients, which includes patients with acute onset, bilateral chest radiographic infiltrates, absence of clinical evidence of left atrial hypertension assessed by bedside echocardiography and impaired oxygenation regardless of positive end-expiratory pressure with a PaO2/FiO2 ratio ≤ 300 mm Hg for ALI and ≤ 200 mmHg for ARDS . According to the Berlin definition, marked lung injury (PaO2/FiO2 ≤ 200) was classified as moderate and severe ARDS, while ALI (PaO2/FiO2 ≤ 300) was classified as mild ARDS .
The exclusion criteria of the population included patients having a history of interstitial lung disease, renal failure, malignancy, inborn errors of metabolism, patients with a cardiac lesion, and if their anthropometric measures were below or above 5th and 95th, respectively. We applied these criteria to limit confounding factors that may affect the outcomes under investigations.
HFOV was performed using SLE5000 (Croydon CR2 6PL UK) according to body weight. All patients were sedated with continuous intravenous infusion of midazolam 1 μg/kg/min and fentanyl 1 μg/kg as an analgesic at the time of applying mechanical ventilation. Prone position, neuromuscular blockers, and inotropes were not used.
All patients enrolled in this study were exposed to detailed medical history, complete clinical examination, scoring of critical illness using Pediatric Logistic Organ Dysfunction (PELOD) score at the time of starting ventilation by a physician who was blinded to the group to which the patient belonged, oxygenation index (OI) measurement defined as (mPAW × FiO2 × 100)/PaO2, ventilatory management, chest X-ray to diagnose ALI/ARDS, assessment of the length of stay in PICU, and the duration of mechanical ventilation in both survivors and non-survivors.
Data were expressed as the mean and standard deviation in normally distributed continuous variables and as median and standard deviation if skewed. T test method was used to compare 2 independent groups’ means. Fisher’s exact test was used to check the difference between categorical variables. P value was always set at 0.05, and all statistical manipulation and analyses were performed using the Statistical Program for Social Science (SPSS Inc., Chicago, IL, USA) Version 16.0 for Windows.