Why do complications of gastrointestinal disease and procedures come as serial rather than singular events?

Background : It often appears as if complications arising from gastrointestinal disease and interventional procedures come in ‘series’ and ‘cluster’ in individual patients. Aim : The aim of this study was to analyse the clustering of complications in terms of stochastic modelling and Markov chains. Methods : A patient with gastrointestinal disease is simulated to move along either a ‘bad track’ associated with multiple consecutive complications or a ‘good track’ free of complications, the transitions within each track and between the two tracks being governed by probability values. Results : Because the occurrence of a single complication increases the risk of further complications, subjects who encounter their first complication are more likely to experience a second, third or even more complications, before they leave the ‘bad track’ and their personal chain of cascading complications becomes discontinued. The model of a Markov chain explains why the overall number of complications in the total population of patients with digestive disease remains low even if individual patients are expected to encounter more than a single complication. Conclusions : Published complication rates for gastrointestinal procedures underestimate the true risk to the patient, because they do not consider the added vulnerability to cascading complications after the first event.