ETD Collection

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    Effectiveness of continuous or bilevel positive airway pressure versus standard medical therapy for acute asthma
    (2008-07-09T12:52:43Z) Hanekom, Silmara Guanaes
    ABSTRACT Patients with respiratory failure secondary to acute asthma exacerbation (AAE) frequently present at emergency units. Some patients may develop respiratory muscle fatigue. Current guidelines for the treatment of an AAE center on pharmacological treatment and invasive mechanical ventilation. Noninvasive positive pressure ventilation (NPPV) has an established role in COPD exacerbations. The role it can play in an AAE remains unanswered although it is frequently used in the clinical setting. Aims: The present study proposed to investigate if the early use of NPPV in the forms of continuous positive airway pressure (CPAP) or bilevel positive pressure ventilation (BPPV) together with standard medical therapy in AAE can decrease time of response to therapy compared to standard medical therapy alone. We further tested the effect of BPPV against CPAP. Methods: Asthmatic patients who presented with a severe AAE (PEFR % predicted < 60 %) at the emergency unit were randomized to either standard medical therapy (ST), ST and CPAP or ST and BPPV. Thirty patients fulfilled the inclusion criteria for the study. Groups presented similar baseline characteristics. The mean age for the group was 42.1 ± 12.6 years. Mean baseline PEFR % predicted was 35.2 ± 10.7 % (ST), 30.5 ± 11.7 % (ST + CPAP) and 33.5 ±13.8 % (ST + BPPV). Results: Hourly improvement (Δ) in respiratory rate and sensation of breathlessness was significantly better in the BPPV intervention group. Improvement (Δ) from baseline to end of treatment in respiratory rate and sensation of breathlessness was significant for both CPAP and BPPV (p = 0.0463; p = 0.0132 respectively) compared to ST alone. Lung function was significantly improved in the CPAP intervention group hourly and from baseline to end of treatment (p = 0.0403 for PEFR and p = 0.0293 for PEFR % predicted) compared to ST + BPPV and ST alone. The mean shift (Δ) in PEFR from baseline to 3 hours of treatment was 67.4, 123.5 and 86.8 L/min (p = 0.0445) for ST, ST + CPAP and ST + BPPV respectively. This corresponded to a 38.1, 80.8 and 51.7 % improvement in lung function respectively. Discussion: The effect of BPPV on the reduction of respiratory rate and sensation of breathlessness could be related to the inspiratory assistance provided by BPPV. The significant improvement in lung function in the CPAP group could be related to its intrinsic effect on the airway smooth muscle and / or on the airway smooth muscle load. Conclusion: The present results suggest that adding NPPV to standard treatment for an AAE not only improves clinical signs faster but also improves lung function faster. CPAP seems to have an intrinsic effect on the airway smooth muscle so rendering it more effective in ameliorating lung function.
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    Environmental and host factors associated with persistent lower respiratory tract symptoms or asthma following acute environmental exposure to sulphur dioxide (S02).
    (2007-02-23T12:15:35Z) Baatjies, Roslynn
    Introduction: On the weekend of 16 – 17 December 1995, the community of Macassar was exposed to elevated levels of sulphur dioxide vapours (SO2) caused by a fire on a nearby stockpile for approximately 21.5 hours. It has been estimated that community members were exposed to levels as high as 200 parts per million (ppm) of this gas as some 15 000 tons of the sulphur stockpile ignited. This resulted in a toxic plume of SO2 being blown over the Macassar area by the prevailing wind. The aim of this study was to assess the environmental and host factors associated with persistent lower respiratory symptoms among residents of this community six years after being acutely exposed to elevated exposures of SO2 vapours. Materials and methods: A case-control study was conducted. The cases and controls were selected from adult residents who reported to the Macassar disaster project clinic for a health assessment in order to lodge a medico-legal claim. Survey instruments included a questionnaire, clinical examination and clinical record review by an expert panel. A case was defined as an adult resident who presented to the clinic for an examination with persistent (at year 1 and 6 after the disaster) lower respiratory symptoms. Controls were chosen from clinic attendees without lower respiratory symptoms at year 1 and 6. Environmental exposure was calculated by using the Industrial Source Complex Short Term Model (ISCST 3) to predict time-averaged concentrations at specified receptor locations. Multiple logistic regression was used to investigate the association between lower persistent respiratory symptoms, host and environmental factors (estimated concentration and duration of exposure to SO2). Results: A total of 76 cases and 180 controls were selected. The cases and controls were comparable with respect to age, gender, height and smoking status. The results indicated that a medical history of pulmonary tuberculosis at least one year prior to the fire (OR: 3.5, CI: 1.5-8.4) was significantly associated with having persistent lower respiratory symptoms. Furthermore, subjects with persistent lower respiratory symptoms were nine times more likely to report symptoms of tight chest (OR: 9.9; CI: 5.2-19.1), and twice as likely to report shortness of breath (OR: 2.0; CI: 1.0-4.1) at the time of the fire. None of the exposure metrics (total hours of exposure, cumulative exposure, peak exposure) were significantly associated with persistent lower respiratory symptoms. However, peak SO2 exposure estimated at hour 15 was significantly associated with persistent lower respiratory symptoms (OR: 1.0; CI: 1.0-1.1). Discussion: The results of this study are consistent with previous studies reporting lower respiratory tract symptoms after chemical exposure irrespective of age or smoking status. Furthermore, as in other studies respiratory health status was a significant factor in determining susceptibility to SO2 exposure. Various reports in the literature suggest that exposure > 20 ppm is associated with chronic respiratory symptoms. This however was not demonstrated in this study, using estimates of exposure calculated using the ISCST model suggesting possible exposure misclassification. “Self-selection” bias was an important limitation in this study, since the entire study population was self-referred and as such the study population was not randomly selected. Another limitation is the possibility that there may be potential recall bias operating since the fire incident happened six years ago; however this was considered unlikely as there was nondifferential reporting between cases and control. Self reported symptoms on the questionnaires might have been over-reported due to fear, anxiety and stress or secondary gain related to compensation issues. The lack of association between exposure variables and persistent asthma may have also been due to lack of power (small sample size), although this was thought to be a minor contributory factor. Conclusion: Host-related factors such as a previous history of pulmonary TB and acute asthma-like symptoms at the time of the fire were important predictors of persistent lower respiratory symptoms reported by residents 6 years after acute exposure to SO2 vapours emanating from a sulphur fire.