Discussion
hypoxemia
SECONDARY
In this investigator–initiated, single-center, randomized clinical trial we compared the quality of breathing during postoperative ventilation between closed–loop ventilation using sidestream capnography versus mainstream capnography in elective cardiac surgery subjects. We could not confirm the non–inferiority of INTELLiVENT–ASV using sidestream capnography with respect to the proportion of breaths in the predefined optimal zone of ventilation. There was a statistically significant difference in the incidence of breaths with hypoxemia between the groups––this difference disappeared within the first hour of postoperative ventilation. There were no differences in the other endpoints.This study has several strengths. The trial was performed in a setting where nurses and doctors had extensive experience with the tested closed–loop ventilation mode. The study protocol was straightforward and easy to follow. We used high density, i.e., breath–by–breath ventilator data that was collected directly from the ventilator for the main endpoints. This allowed for an accurate and highly granular comparison of the quality of breathing between the two study groups. The endpoints were predefined and used before [There are several possible explanations for why there were less breaths in the optimal zone in the sidestream group. Sampling delay is a well–known caveat of sidestream capnography, since gas sampling and subsequent transport from the main ventilation circuit to the sensor is required [Interestingly, ventilation using sidestream capnography resulted in a higher median RR and a lower median VOur study increases the understanding of how the tested closed–loop ventilation mode affects ventilator settings and ventilation parameters during postoperative ventilation. Thus far, only two studies directly compared the quality of breathing between closed–loop ventilation and conventional ventilation in postoperative cardiac surgery subjects [This study also has limitations. First, due to the nature of the intervention, caregivers and data collectors could not be blinded for treatment allocation. However, the statistical analysis was performed by an investigator blinded for treatment allocation. Second, this was a single–center trial in a tertiary hospital with extensive experience with closed–loop ventilation. Therefore, it is possible that our findings are not directly generalizable to settings with less experience or less resources. Third, our sample size was not powered to observe differences in secondary clinical endpoints, and all findings should be seen as exploratory. Fourth, as the majority of patients were expected to be extubated within the first 3 hours after start of ventilation in the ICU, we restricted the analysis to the first 3 hours. If the quality of breathing is different at later time points, it could be the subject of a future investigation. Fifth, to increase comparability between patients and homogeneity of the study cohort we adhered to a predefined minimum required time period of postoperative ventilation in the ICU which allowed for an assessment without confounding by duration of ventilation, but this may result in an incomplete reflection of the clinical variability, and with that the quality of breathing with either capnography method. Lastly, as we studied a typical cohort of patients, i.e., one in which ventilation is simple and short–lasting, we cannot give recommendations for use in other patient groups––this applies in particular to patients who benefit from a strict tailoring of the arterial COBased on the results of our study, closed–loop ventilation with sidestream capnography should not be preferred over closed–loop ventilation with mainstream capnography in settings where mainstream capnography is widely available, and in subjects wherein mainstream capnography has little or no disadvantages. However, the results of our study should also be interpreted in the context of the non–inferiority design. Moreover, although the non–inferiority of closed–loop ventilation with sidestream could not be established for the quality of breathing, it is uncertain whether this also translates into clinical endpoints.