To the Editor:
With great interest we have read the article by Joosten et al.1 recently published in Anesthesiology. In their study they investigated the use of colloids versus crystalloids in relation to postoperative complications in major abdominal surgery. They conclude that a colloid-based, goal-directed fluid therapy is associated with fewer postoperative complications than a crystalloid-based approach, possibly as a result of a lower intraoperative fluid balance when colloids are used.
In the last decades many studies have focused on hemodynamic optimization in high-risk surgery with fluids, inotropes, and advanced hemodynamic monitoring.2 As protocol adherence remains an issue in most studies, the use of an automated closed-loop system for fluid administration in the study of Joosten et al. is exceptionally elegant. After reading the article we have one major concern: are the groups really comparable? As the authors point out, despite the randomized setup, the baseline characteristics show that surgery duration and anesthesia duration (and hence duration of mechanical ventilation) are both more than an hour longer in the crystalloid group than in the colloid group. No results of statistical tests are provided to verify that the difference is indeed statistically significant, but it is highly likely. Despite the comparable amount of blood loss, the incidence of high-risk surgery, and the Physiological and Operative Severity Score for Enumeration of Mortality and Morbidity (POSSUM) between the groups, the only right conclusion about the longer surgery time must be that surgery in the crystalloid group was more difficult. It is likely that difficult surgery is associated with more tissue damage and therefore more inflammation. Accordingly, longer surgery is associated with increased markers of inflammation.3 Moreover, the longer duration may still indicate a difference between the groups, an underlying (inflammatory) condition. Thus, an increased state of systemic inflammation in the crystalloid group could have contributed to increased microvascular permeability, resulting in a higher need for fluid administration.4 Longer duration of surgery is also an independent risk factor for anastomotic leakage, which is significantly more present within the crystalloid group.5 Both could explain the results showing an observed better outcome in the colloid group. So unfortunately, in this study it may not be the intervention that makes the difference, it might be the control group.
The authors declare no competing interests.