Accuracy of the Set Tidal Volume During Intraoperative Anesthetic Care: An <i>In Vitro</i> Evaluation

Background: Precise adjustment of tidal volume (Vt) and minute ventilation remains a key component of intraoperative care. Control of Vt is regulated by internal pneumotachometers and flow meters, which may be separated from the patient by the anesthesia circuit and the internal circuitry of the anesthesia machine. Given this arrangement, there may be variations in delivered and exhaled (measured) Vt depending on the site of measurement. Methods: The current study used an in vitro model to determine variations in inspired and expired Vt during various volume- and pressure-controlled modes of ventilation using an Avance CS 2 anesthesia machine. Results: During in vitro mechanical ventilation using pressure limited (15 and 20 cm H 2 O) and volume limited (Vt 50, 100, 200, and 300 mL), we saw slight discrepancies between Vt measured using a pneumotachometer placed between the endotracheal tube (ETT) and the anesthesia circuit as compared to those measured internally by the anesthesia machine. Conclusions: Although the differences were statistically significant, the variations were no more than 5-6% at most at the higher Vt with either volume- or pressure-limited ventilation. These differences are unlikely to be clinically significant, thereby demonstrating the accuracy and safety of anesthesia machines from the modern era. Int J Clin Pediatr. 2024;13(3):69-72 doi: https://doi.org/10.14740/ijcp551