Age and Ageing Advance Access originally published online on July 5, 2006
Age and Ageing 2006 35(5):543-544; doi:10.1093/ageing/afl050
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The role of selective decontamination of the digestive tract in acute stroke
SIR—The study by Gosney et al. [1] that investigated the role of selective decontamination of the digestive tract (SDD) in acute stroke produced some interesting results. The data regarding the incidence of pneumonia are particularly intriguing. Using the results from Figure 2 in the paper [1], the results summarised in Table 1 can be obtained for all patients, those with a normal swallow and those with an abnormal swallow.
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Using Fisher’s exact two-tailed test, the exact P-value for total patients is 0.0333 (0.0265 for the total patients mentioned in Table 1), whereas the exact P-value for those patients with a normal swallow is 0.462 and for those with an abnormal swallow is 0.127 (0.092 for the patients with abnormal swallow mentioned in Table 1). This would lead to the conclusion that there is no statistically significant difference between the SDD and placebo groups when considering the normal and abnormal swallow groups separately, but when combining them, there is then a statistically significant difference. How could this be? It would seem that the larger number in the normal swallow group who received SDD skew the total group result. Another possibility is that if it is inappropriate to combine the two groups, normal and abnormal swallow, together, because they may be two different disease processes and by doing so biases the total sample. When the numbers of patients who suffered pneumonia are small, this could give rise to a spurious correlation between the use of SDD and preventing pneumonia—also known as Berkson’s fallacy [2].
Another interesting result that was missing from the paper was if the patients whose swallow improved were removed from the abnormal swallow group, would this alter the results and if so how? The writers’ conclusion that SDD gel might be useful in those with an abnormal swallow is warranted, but further larger studies are definitely needed.
Department of Elderly Medicine, St Vincents University Hospital, Elm Park, Dublin, Ireland Email: d.oshea{at}st-vincents.ie
References
- Gosney M, Martin MV, Wright AE. The role of selective decontamination of the digestive tract in acute stroke. Age Aging 2006; 35: 42–7.
[Abstract/Free Full Text] - Li Wan Po A. Dictionary of Evidence-Based Medicine. Abingdon: Radcliffe Medical Press, 1998.
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