128 Chapter 6 visual relationship between ILI prevalence and duration of IMV or in the P/F ratio in the first week after surgery. Moreover, given that the length of stay in the ICU is the same between seasons, but the length of stay in the hospital is longer in the ILI season, these complications may occur after ICU discharge. Further studies are needed to investigate the cause of this increased in-hospital mortality, but possible contributing factors suggested in the literature are the differences in behavior, environmental factors, disease frequency, and risk factors as noted, that could influence the overall condition of patients. In conclusion, patients undergoing cardiac surgery during ILI season have an increased risk of in-hospital mortality compared with patients in the baseline season, but we found no evidence that this difference in mortality is caused by direct postoperative pulmonary complications. Further studies are needed to investigate the cause of the observed increase in in-hospital mortality. As we do not have further data, we can only speculate that factors suggested in the literature such as the differences in environmental factors, behavior, disease frequency, and known risk factors that could influence the overall condition of patients could have contributed to changes in mortality risks.
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