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

ABSTRACT

To investigate intra cuff pressure changes in low-flow anesthesia [LFA] and high-flow [HFA] N2O anesthesia during moderate-duration surgical procedures. 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. 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]. 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