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

OBJECTIVE: 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).

CONCLUSION: 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.