A comparison of intra cuff pressures in high-flow and low- flow nitrous oxide anesthesia

OBJECTIVES To investigate intra cuff pressure changes in low-flow anesthesia (LFA) and high-flow (HFA) N2O anesthesia during moderate-duration surgical procedures. METHODS We carried out this prospective, randomized, single blind study at Numune Educational and Research Hospital, Ankara, Turkey between January to December 2005. Seventy patients aged between 18-65 years, American Society of Anesthesiologists (ASA) physical status grades I-III, undergoing elective surgery were enrolled in this study. Following a standardized induction, anesthesia was maintained with isoflurane (end-tidal 0.9-1%) at 4 L/minute for the HFA group, or 1 L/minute for the LFA group fresh gas flows. Endotracheal tube cuff (intra cuff) pressures were measured continuously with a pressure manometer, and inspired oxygen and N2O levels were noted every 10 minutes throughout the study. RESULTS There was no significant difference between HFA and LFA groups for initial (first) cuff pressures (mean+/-SD, HFA=20.9+/-4.19, LFA=20.4+/-4.11, cmH2O), and maximum cuff pressures (MCP) (mean+/-SD, HFA=32.3+/-18.74, LFA=33.5+/-8.89, cmH2O) (p>0.05). The time to reach the maximum intra cuff pressure was significantly shorter in the LFA group (77.4+/-20.33 minutes), than the HFA group (89.3+/-23.94 minutes), (p=0.038). Between the tenth and nineteenth minutes, inspired oxygen level was significantly higher in the HFA group (p=0.001), whereas inspired N2O was significantly higher in the LFA group (p=0.001). CONCLUSIONS The intra cuff pressures should be monitored carefully during LFA, since the duration to reach the maximum intra cuff pressures was shorter than that of HFA.