BACKGROUND: Endotracheal intubation and prolonged immobilization of patients receiving mechanical ventilation may reduce expectoration function. High frequency chest wall oscillation (HFCWO) may ameliorate airway secretion movement; however, the vigorous oscillation may influence ventilator settings and change instantaneous cardiopulmonary responses. The aim of this study was to investigate these issues. METHODS: Seventy-three patients aged >20 years who were intubated with mechanical ventilation for pneumonic respiratory failure were recruited and randomly classified into two groups (HFCWO group, n=36; and control group who received conventional chest physical therapy (CCPT), n=37). HFCWO was applied with a fixed protocol, while CCPT was conducted using standard protocols. Both groups received sputum suction after the procedure. Changes in ventilator settings and the subjects' responses were measured at pre-set intervals and compared within groups and between groups.

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.

All of the eligible patients had acute pneumonic respiratory failure and received endotracheal intubation and mechanical ventilation, and all signed informed consent forms. The patients were randomly allocated to the study group (HFCWO) or the control group (CCPT), as the efficacy of bronchial hygiene for both HFCWO and CCPT is comparable4. The primary investigators were blinded to which procedure the patients received. The local institutional review board of Chung Shan Medical University Hospital approved this study (No. CS13004). The experimental research was conducted in compliance with the Helsinki Declaration.

To prevent vomiting during or after chest care, all of the subjects underwent the procedure one hour before or two hours after feeding via a nasogastric tube. Inhalation therapy was performed with an aerosolized solution of 6 mL of half saline via the ventilator before HFCWO or CCPT.

HFCWO was performed using a VestTM Airway Clearance System Model 105 (Hill-Rom, St. Paul, Minnesota) connected to a vest via two flexible tubes by trained nurses who were blinded to the purpose of the study. All of the nurses had been well trained in how to perform both HFCWO and CCPT before the study, as these procedures are routinely performed by nurses at the investigators institution. HFCWO was applied to each subject at a frequency of 10-12 Hz and a pulse pressure setting of 1-2 selected from a scale ranging from 1 to 10 (arbitrary units) for 15 minutes. The patients receiving HFCWO were placed in a semi-upright sitting position, and the patients undergoing CCPT received cup-hand percussion with the hands positioned 3 inches from the chest, striking the chest with a waving movement while they were placed in right and left decubitus positions for 5-10 minutes each1. Following HFCWO or CCPT, suction was performed immediately via an endotracheal tube.

Changes to the initial ventilator settings during HFCWO were recorded by the trained nurses by checking the ventilator panel before and at 5, 10 and 15 minutes during HFCWO. The variables included peak airway pressure (Ppeak), positive-end expiratory pressure (PEEP), respiratory rate (RR), fraction of inspired oxygen (FIO2), inspiratory time, and sensitivity settings.

Changes in the patients' cardiopulmonary responses were measured before and at 5, 10 and 15 minutes during oscillation, and at 15 minutes after sputum suction. The measurement protocol for the CCPT group was the same as for the HFCWO group, except no measurements were taken at 5 or 10 minutes during percussion because it was not possible for a single nurse to perform percussion and record measurements at the same time.

Rapid shallow breathing index (RSBI) was calculated as follows:

RSBI = breathing frequency (breaths/minute)/tidal volume (liters) (1) Oxyhemoglobin saturation was measured using a pulse oximeter (SPO2). Data were presented as mean ± standard deviation (SD) or median (interquartile range). For each outcome variable, comparisons were planned a priori. A paired t or unpaired t test was used for within-group or between-group comparisons. For non-normal data, the Mann-Whitney test was used. The chi-square test or Fisher's exact test was used to compare proportions of categorical variables between the two groups. A p value less than 0.05 was considered to be statistically significant. All statistical analyses were performed using SAS software version 9.3 (SAS Institute Inc., Cary, NC) and Microcal Origin version 4.0 (Northampton, MA, USA).

Inclusion Criteria:

• acute pneumonic respiratory failure and received endotracheal intubation and mechanical ventilation,
• having sufficient sputum production to require the physician to order airway secretion clearance

Exclusion Criteria:

• pregnancy
• pneumothorax
• manifest hemoptysis
• unstable hemodynamics
• increased intracranial pressure
• those undergoing major cardiac, thoracic or abdominal surgery