Valveless Trocar Systems and Respiratory Mechanics: Need for Revaluation

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We read with great interest the article by Covotta et al1 assessing the effects of a valveless trocar on respiratory mechanics during robotic radical cystectomy. We congratulate the authors for their meticulous study design addressing an important clinical question. The authors found lower end-tidal carbon dioxide levels and lower CO2 elimination rate in the valveless trocar group compared to the standard trocar. However, given the similar insufflation pressure limits in both the groups, one would have expected similar intraperitoneal CO2 fractions leading to similar CO2 resorption and elimination rates. One of the reasons for the unexpected reported results may be because the authors did not take into consideration the possibility of intraperitoneal room air entrainment through the trocars.
In fact, we recently reported that in an experimental setting and a clinical setting, the pneumoperitoneum generated with a valveless system was contaminated with room air in a much larger proportion than with the standard insufflation system. Thus, during laparoscopy performed with the valveless system, the pneumoperitoneal CO2 levels may not be 100% and may be variable.2 Therefore, the pneumoperitoneum generated by both techniques may not be identical with respect to CO2 fractions, which could explain the reported results from Covotta et al.1 On the basis of our observations and given that Covotta et al1 did not assess the composition of the pneumoperitoneum in the 2 study groups, we emphasize the importance of further research in this field.
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