Comparing the ratio of respiratory dead space volume to tidal volume in supine and prone positions in patients under general anesthesia

Introduction: The prone position in the surgery room provides the surgeon with access to the area of surgery in various types of surgeries. The effects of prone position on respiratory gas exchanges are complex. Methods: This prospective cohort study was performed on 61 patients undergoing general anesthesia in prone and supine positions. Half an hour after intubation, 2 hours after anesthesia and before extubation in recovery, arterial blood gas changes, ETCO2, respiratory dead space volume to tidal volume ratio (VD / VT), and hemoglobin levels in both groups were measured and recorded. Findings: Sixty one patients (29 patients in supine and 32 patients in prone positions) were evaluated. There was no significant relationship between VD/VT ratio during anesthesia between the two groups (P = 0.16). In examining this ratio at different measurement times, the results showed that only in supine group, VD / VT relationship was statistically significant two hours after anesthesia onset and at the end of anesthesia (P=0.01). There were no significant differences in pH, PCO2, PECO2, Ppeak and PaO2 in the two groups at different time points. Hb levels were statistically significant in both groups at different time points; but the difference between the two groups was not significant. Conclusion: The ratio of respiratory dead space volume to tidal volume and oxygenation in the prone position compared to supine position was not changed in patients undergoing general anesthesia with mechanical ventilation. The process of oxygenation changes in the prone position has improved over time.