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Evidence Watch: Carl Heneghan’s view on evidence that impacts practice


This week’s Evidence Watch highlights preoperative physio, the risk of heart disease in relation to the number of cigarettes smoked per day, use of antipsychotics in hospital and risk of pneumonia, the effect of exercise across 17 countries and the impact of having a large preterm baby.  

Carl Heneghan, Editor in Chief

Does a single preoperative physiotherapy session reduce postoperative pulmonary complications after upper abdominal surgery? Based on this RCT, published in BMJ, the answers seem it is highly likely. [1]

441 adults before elective major open upper abdominal surgery were randomised to receive either an information booklet or 30 minutes of physio education and breathing exercise training. The incidence of pulmonary complications within 14 days was reduced by an absolute 15% (95% CI 7% to 22%) meaning 7 people (95 CI: 5 to 14) need to receive education to prevent one post complication that includes hospital-acquired pneumonia.  If there hasn’t been a trial that replicated this result then, at this effect size, we need one soon.

A Systematic review of 141 cohort studies found that amongst men the relative risk for coronary heart disease was 1.48 for smoking one cigarette per day, and not much more,  2.04 for 20 per day. [2] In women, relative risks were 1.31 and 2.16 for smoking one or 20 cigarettes per day. The advice given is for smokers to aim to quit instead of cutting down, which is sensible advice. However, if you take account of the lung cancer risk (males smoking  >30 cigarettes have ORs of 103.5 for Squamous cell cancers) then cutting down is preferable to high levels of smoking.

It’s worth being aware that antipsychotics are associated with greater odds of aspiration pneumonia. A cohort study found that in a cohort of 146,552 hospitalisations antipsychotics were used in 7.1% hospitalizations. The incidence of aspiration pneumonia was four times more likely in those exposed to antipsychotics (1.2%) compared to the unexposed (0.3%). After adjustment, the association with aspiration pneumonia was less (OR 1.5) but still present.

Guess what? This Lancet analysis in 17 countries tells us that physical activity protects against cardiovascular disease. [4] I thought we knew this so not much for me to say on the subject.

Finally, this cohort study in the BJOG reports that women having large preterm babies are at increased risk of both diabetes and cardiovascular mortality. How, though, this translates into increased clinical vigilance, which the conclusions call for, will be difficult to achieve.


[1] Preoperative physiotherapy for the prevention of respiratory complications after upper abdominal surgery: Pragmatic, double blinded, multicentre randomised controlled trial. Boden I. et al. 2018. BMJ 360, j5916.

[2][ Low cigarette consumption and risk of coronary heart disease and stroke: Meta-analysis of 141 cohort studies in 55 study reports. Hackshaw A., Morris J.K., Boniface S., Tang J.-L., & Milenkovi D. 2018. BMJ360, j5855.

[3] Antipsychotics and the Risk of Aspiration Pneumonia in Individuals Hospitalized for Nonpsychiatric Conditions: A Cohort Study. Herzig S.J. et al. 2017. Journal of the American Geriatrics Society65(12), 2580–2586.

[4] The effect of physical activity on mortality and cardiovascular disease in 130 000 people from 17 high-income, middle-income, and low-income countries: the PURE study. Lear S.A. et al. 2017. The Lancet390(10113), 2643–2654.

[5] Offspring birthweight by gestational age and parental cardiovascular mortality: a population-based cohort study. Morken N.-H., Halland F., DeRoo L.A., Wilcox A.J., & Skjaerven R. 2018. BJOG: An International Journal of Obstetrics and Gynaecology125(3), 336–341.

BMJ Evidence-Based Medicine – original evidence-based research, insights and opinions on what matters for health care.

We select from over 100 journals reliable and useful evidence summarised in BMJ Evidence-Based Medicine.

Read more about BMJ EBM content in the Welcome to BMJ Evidence-Based Medicine Editorial.

Carl Heneghan is Professor of EBM at the University of Oxford, Director of CEBM and Editor in Chief of BMJ EBM

Follow on twitter @carlheneghan

Competing interests

Carl has received expenses and fees for his media work including BBC Inside Health. He holds grant funding from the NIHR, the NIHR School of Primary Care Research, The Wellcome Trust and the WHO. He has also received income from the publication of a series of toolkit books published by Blackwells. CEBM jointly runs the EvidenceLive Conference with the BMJ and the Overdiagnosis Conference with some international partners which are based on a  non-profit model. 

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