Background & Aims: Elimination of carbon dioxide is related to the alveolar ventilation, respiratory rate and tidal volume. The aim of this study  to determine the effect of mechanical ventilation with different tidal volumes and constant minute ventilation on the end tidal Co2  and oxygen saturation during general anesthesia and to seek optimum parameters of mechanical ventilation during general anesthesia.

Materials & Methods: In an analytical study, 38 healthy patients, with the age range of 40-20 years and physical status ASA, I, II candidate to elective lower abdominal or lower extremity surgery under general anesthesia were enrolled. End expiratory carbon dioxide concentration and arterial oxygen saturation in four respiratory rates:  12, 14, 16 and 18 and different tidal volumes with constant minute ventilation were measured.

Results: Mean arterial oxygen saturation in the respiratory rate of 12, 14, 16 and 18, was 97.2 ± 11.5, 95.9 ± 14, 97.3 ± 11.5, 97.4 ± 11.5, respectively, There is no significant difference in mean arterial oxygen saturation in the respiratory rate of 12, 14, 16, 18 no (p =0.94). The Mean end tidal CO2 in the respiratory rate of 12, 14, 16 and 18, was 26 ± 4.9, 25.8 ± 4.9, 25.5 ± 4.3, 25.6 ± 4.5 respectively.  There is no significant difference among Mean end tidal CO2 in the respiratory rate of 12, 14, 16, 18 no (p =0.97)

Conclusion: According these findings, in the respiratory rate of 12-18 bpm, changes in the tidal volume with constant minute ventilation, don’t change ETCO2 and SPO2. This range of respiratory rate can be easily used for ventilation of patients under general anesthesia.

SOURCE: URMIA MED J 2014: 25(9): 825 ISSN: 1027-3727