American Society of Anesthesiologists, 2005 Annual Meeting
A795
October 24, 2005
2:00 PM - 3:30 PM
Room C303

Animal Evaluation of a Device To Speed Emergence from Desflurane Anesthesia
Nishant Gopalakrishnan, B.S., Joseph Orr, Ph.D., Derek Sakata, M.D.
Anesthesiology, University of Utah, Salt Lake City, Utah, United States

Introduction: Hyperventilation is often used to quickly remove volatile anesthetic gas from the lungs at the end of anesthesia. However, the resulting hypocapnia decreases respiratory drive as well as cerebral blood flow and can delay emergence from anesthesia. We tested a rebreathing device that uses partial CO₂ rebreathing to maintain slight hypercapnia during hyperventilation. The device also incorporates an anesthetic absorbent to scavenge volatile agents from the rebreathed gas before they are inhaled.

Methods: We compared emergence times with and without the device using desflurane anesthesia in a crossover study of 4 pigs with each pig serving as its own control. The order of emergence was randomized to eliminate the effects of a prior emergence. Prior to emergence, each pig was anesthetized and maintained with 1.4 MAC (13.5%) of desflurane for 2 hours. Tidal volume was adjusted to maintain end-tidal CO₂ at 33 mmHg during maintenance. We recorded the time between when the vaporizer was turned off and when the animal moved multiple limbs. During emergence, fresh gas flow was raised to 6 L/min and hyperventilation was induced by increasing the respiratory rate from 10 to 20 breaths per minute. After emergence, the animals were re-anesthetized with desflurane until the BIS reached the pre-emergence value observed during maintenance.

Results: The average time to movement of multiple limbs was 2 minutes and 37 seconds (52 seconds) when using the rebreathing device. The average emergence time when the device was not used was 5minutes and 49 seconds (2 minutes, 23 seconds). The average difference between the two emergence times was 3 minutes 11 seconds. Figure 1 below shows a plot of the times and standard deviation of the emergence times.

Discussion: This study demonstrates that even though desflurane has very low solubility in blood, using hyperventilation along with rebreathing can still considerably reduce emergence time. The test device was able to speed up emergence by 3.2 minutes (55%) in pigs. Use of the rebreathing device gave more predictable emergence times as indicated by a decrease in standard deviation of emergence time by 1.83 minutes (66%).

Figure 1

Summary: We tested a rebreathing/absorber device that allows simultaneous hyperventilation and mild hypercapnia to speed emergence from volatile anesthesia. After 2 hours at 1.4 MAC of desflurane, the average emergence time in four pigs was less by an average of 3 minutes and 11 seconds (55% reduction).