Page 199 - Prevention and Treatment of Incisional Hernia- New Techniques and Materials

ITT population that have developed a recurrence between the operation date (T0) and Tx. This will leave us with the problem of what to do with the patients that were “lost to follow-up”. This uncertainty about the status, i.e. recurrence or no recurrence, of the lost to follow-up patients will cause serious bias in the estimation of the calculated recurrence rate. A speci c cohort of patients has no xed recurrence rate because the recurrence rate will increase over time with longer follow-up. The result of a study with a recurrence rate at a speci c point in time during follow-up should include 95% con dence intervals. It is recommended that the statistical analysis of recurrence rates at a speci ed time in a comparative study be performed with the Fisher exact test and logistic regression to include prognostic factors.
A more sensitive method of reporting the outcome is by “time-to-event analysis” as introduced by Kaplan and Meier several decades ago for survival analysis(24). The main reason to favour this approach is that patients lost to follow-up, the dropouts, are accounted for. In abdominal wall surgery, the event studied is most often recurrence and thus “survival rate” can be best described as the “freedom-of-recurrence”. For every patient in the study the time period of follow-up will be de ned by the date of the hernia repair (T0) to the date of recurrence or the date of the last follow-up recorded without recurrence (T1). At T1 the status of the patient will be recorded: recurrence or no recurrence. The di erence between T1 and T0 is the time the patient was at risk of development of a recurrence and was under “surveillance”. During the study period the number of patients at risk will gradually decrease with every patient that has a recurrence or that is lost to follow-up, i.e. censored cases. The outcome of time-to-event data for hernia recurrence is given by a Kaplan-Meier plot of the freedom-of-recurrence and by calculating freedom-of-recurrence rates at predetermined time endpoints. Statistical analysis of time-to-event data is performed using the log rank test or Cox’s regression model if prognostic factors are included. Time-to-event analysis is more powerful than comparing recurrence rates, thus requiring a smaller sample size to test a speci c scienti c hypothesis of an interventional study.
Complications
The consensus group recommends using the Clavien-Dindo classi cation as was proposed previously by the EuraHS working group(25-27). A clear de nition of the di erent complications evaluated and reported must be given, preferably
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Recommendations IH research
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