ABSTRACT
BACKGROUND AND OBJECTIVE: Non-invasive ventilation (NIV) improves clinical outcomes in hypercapnic acute exacerbations of COPD (AECOPD), but the optimal model of care remains unknown. METHODS: We conducted a prospective observational non-inferiority study comparing three models of NIV care: general ward (Ward) (1:4 nurse to patient ratio, thrice weekly consultant ward round), a high dependency unit (HDU) (1:2 ratio, twice daily ward round) and an intensive care unit (ICU) (1:1 ratio, twice daily ward round) model in three similar teaching tertiary hospitals. Changes in arterial blood gases (ABG) and clinical outcomes were compared and corrected for differences in AECOPD severity (Blood urea > 9 mmol/L, Altered mental status (Glasgow coma scale (GCS) < 14), Pulse > 109 bpm, age > 65 (BAP-65)) and co-morbidities. An economic analysis was also undertaken. RESULTS: There was no significant difference in age (70 ± 10 years), forced expiratory volume in 1 s (FEV1 ) (0.84 ± 0.35 L), initial pH (7.29 ± 0.08), partial pressure of CO2 in arterial blood (PaCO2 ) (72 ± 22 mm Hg) or BAP-65 scores (2.9 ± 1.01) across the three models. The Ward achieved an increase in pH (0.12 ± 0.07) and a decrease in PaCO2 (12 ± 18 mm Hg) that was equivalent to HDU and ICU. However, the Ward treated more patients (38 vs 28 vs 15, P < 0.001), for a longer duration in the first 24 h (12.3 ± 4.8 vs 7.9 ± 4.1 vs 8.4 ± 5.3 h, P < 0.05) and was more cost-effective per treatment day ($AUD 1231 ± 382 vs 1745 ± 2673 vs 2386 ± 1120, P < 0.05) than HDU and ICU. ICU had a longer hospital stay (9 ± 11 vs 7 ± 7 vs 13 ± 28 days, P < 0.002) compared with the Ward and HDU. There was no significant difference in intubation rate or survival. CONCLUSION: In acute hypercapnic Chronic obstructive pulmonary disease (COPD) patients, the Ward model of NIV care achieved equivalent clinical outcomes, whilst being more cost-effective than HDU or ICU models.
Subject(s)
Hospitals, Teaching , Hypercapnia/therapy , Intensive Care Units , Noninvasive Ventilation , Patients' Rooms , Pulmonary Disease, Chronic Obstructive/therapy , Tertiary Care Centers , Acute Disease , Aged , Aged, 80 and over , Australia , Blood Gas Analysis , Carbon Dioxide/blood , Cost-Benefit Analysis , Female , Forced Expiratory Volume , Humans , Hypercapnia/etiology , Hypercapnia/physiopathology , Intensive Care Units/economics , Length of Stay , Male , Middle Aged , Partial Pressure , Patients' Rooms/economics , Prospective Studies , Pulmonary Disease, Chronic Obstructive/complications , Pulmonary Disease, Chronic Obstructive/physiopathology , Symptom Flare UpABSTRACT
This paper presents theory and experimental data on the resonance frequency of systems consisting of different-sized air bubbles attached to a rigid wall. Effects of the change in resonant frequency with bubble size and distance between the bubbles were studied. It was found that the symmetric mode resonance frequency of the bubble system decreased with increasing r=R(02)/R(01), where R(01) and R(02) are the equilibrium radii of bubbles in the system. Both the symmetric and antisymmetric modes of oscillation were detected in the experiments, with the resonant frequency of the symmetric mode dominant at small bubble separation and the frequency of the antisymmetric mode dominant when the bubbles were farther apart. A linear coupled-oscillator theoretical model was used to describe the oscillations of the bubble system, in which the method of images was used to approximate the effects of the wall. It was found that there was fair to good agreement between the predictions of the coupled-oscillator model with the experimental data.
