The Instantaneous Effects of High-Frequency Chest Wall Oscillation on Patients With Acute Pneumonic Respiratory Failure Receiving Mechanical Ventilation

Pneumonia may increase bronchial secretion and decrease mucociliary function, thereby causing lung atelectasis. Patients with acute pneumonic respiratory failure receiving mechanical ventilation may therefore have a large amount of pulmonary secretions, thereby worsening bronchial hygiene, oxyhemoglobin saturation and ventilation-perfusion match. Cough function is paramount for expectoration; however, coughing is not practical for patients with endotracheal intubation and sedation. High frequency chest wall oscillation (HFCWO) may dislodge airway secretions as efficiently as conventional chest physical therapy (CCPT). However, pneumonia is not currently an indication for chest physical therapy.

HFCWO compresses and relaxes the chest wall to generate an oscillated volume from the lungs, mimicking a "mini-cough" and producing shear stress at the air-mucus interface which changes the sputum rheology, thereby improving ventilation distribution, gas mixing, and forced expired volume in one second. Most studies that have reported no significant effects have focused on mortality, hospital stay, lung function or BODE (a multidimensional 10-point scale of body mass index, severity of airflow obstruction, dyspnea rated with the modified Medical Research Council, and exercise capacity evaluated with the Six-Minute Walk Distance) score. However, these outcome measurements are not associated with the immediate effects of chest physical therapy and may be affected by other factors such as disease severity.

Using the amount of sputum as the outcome measurement of HFCWO is not strongly recommended. However, immediate cardiopulmonary changes in HFCWO have not been studied in patients receiving mechanical ventilation, although this measurement is more explicit than lung function and BODE score, as they are impractical in these patients. Changes in ventilator settings caused by HFCWO are a concern when the patients receive both treatments simultaneously. The aim of this study was to investigate the effect of HFCWO on pneumonic subjects with acute respiratory failure receiving mechanical ventilation by evaluating immediate cardiopulmonary changes and changes in the initial ventilator settings.

Methods

The investigators conducted this comparative prospective randomized controlled single-blinded study at a university hospital. Adult subjects with pneumonia complicated with acute respiratory failure requiring endotracheal intubation and mechanical ventilation were consecutively recruited from a medical intensive care unit (ICU) (20-bed capacity). Pneumonia was defined as the presence of new or progressive pulmonary infiltrates and two of the following: body temperature > 38.3C or < 36C; white blood cell count > 12,000/mL or < 4,000/mL; purulent tracheal secretions without other signs of infection requiring antimicrobial treatment. Acute respiratory failure was defined as a sudden decrease in PaO2 < 60 mm Hg (or arterial oxyhemoglobin saturation < 90%) with or without PaCO2 > 45 mm Hg.17-19 All of the patients had sufficient sputum production to require the physician to order airway secretion clearance. Disease severity was assessed by Acute Physiology and Chronic Health Evaluation (APACHE) II score. Adverse events were evaluated by the investigators and reported to the institutional review board. The exclusion criteria were pregnancy, pneumothorax, manifest hemoptysis, unstable hemodynamics, increased intracranial pressure, and those undergoing major cardiac, thoracic or abdominal surgery.