Human Sevoflurane Studies
Animal Sevoflurane Studies

American Society of Anesthesiologists, 2005 Annual Meeting
A796
October 24, 2005
2:00 PM - 3:30 PM
Room C303

Clinical Evaluation of a Device To Speed Emergence from Sevoflurane Anesthesia
Derek J. Sakata, M.D., Nishant Gopalakrishnan, B.S., Joseph A. Orr, Ph.D., Julia White, R.N., B.S.
Anesthesiology, University of Utah, Salt Lake City, Utah, United States

Introduction: Ideal conditions for rapid emergence from volatile inhaled anesthesia include hyperventilation to quickly remove volatile agent from the lungs, and slight hypercapnia to elevate blood flow to the brain. We evaluated a rebreathing device that allows simultaneous hyperventilation and hypercapnia during emergence.

The device uses an expandable tube placed between the patient and the breathing circuit y-piece to create partial rebreathing. Partial rebreathing allows maintenance of a normal to slightly elevated CO₂ during hyperventilation. To prevent rebreathing of anesthetic gas, the device incorporates a small canister of anesthetic absorbent placed between the endotracheal tube and the rebreathing tube. The combination of a rebreathing tube and an anesthetic absorber allows simultaneous hyperventilation and slight hypercapnia during emergence.

Methods: After IRB approval, 12 ASA class 1 and 2 patients scheduled to receive elective surgery were recruited for the study. Six patients each were randomly assigned to each group (control and experimental). Anesthesia was maintained using 1 MAC of sevoflurane in combination with the anesthetist's choice of type and amount of opioid, along with a continuous infusion of 0.05-0.3 mcg/kg/min of remifentanil.

Emergence was initiated when adhesive wound closure strips were applied. Events were recorded from the time that the sevoflurane vaporizer was turned off. Fresh gas flow was increased to 10 L/min during emergence in both control and experimental groups. Emergence minute ventilation was doubled in the experimental group receiving the test device. Times to eye and mouth opening in response to command and extubation were recorded.

Results: The table below shows the average times to emergence events. Experimental group patients received an average of 3.27 MAC-hours and control subjects received an average of 2.13 MAC-hours of sevoflurane. The figure below shows the average times for each of the emergence events for both groups (see table 1).

Table 1:

Discussion: The differences observed in this data indicate that by using hypercapnic, hyperventilation a considerable decrease in emergence time of 6.95 minutes (54%) can be achieved. Similarly, time to extubation was more predictable when using the device as reflected by the 1-minute decrease in the standard deviation of the emergence time. The data also shows that lower blood and tissue solubility are still relevant given that an earlier test with this device when used with isoflurane showed an emergence time decrease of 10 minutes (see figure 1).

Figure 1:

Summary: We evaluated a rebreathing-absorber device in 12 surgical patients receiving sevoflurane anesthesia. Use of the device decreased time to eye opening by 6.92 minutes, and time to extubation by 6.93 minutes, a timesaving of 54%.

2005 International Anesthesia Research Society, Annual Meeting Abstract
S-226
March 15, 2005
Tuesday, 9:15 a.m. - 10:45 a.m.

Evaluation of a Device in Pigs to Speed Emergence from Sevoflurane Anesthetic
J. Orr, N. Gopalakrishnan, D. Sakata, M. Cluff, D. Westenskow;
Anesthesiology, University of Utah, Salt Lake City, Utah, United States

Introduction: Hyperventilation quickly removes anesthetic gas from the lungs; however, the resulting hypocapnia decreases cerebral blood flow and delays emergence from anesthesia. We tested a device that allows simultaneous hyperventilation and slight hypercapnia during emergence from inhaled anesthesia. It has been previously shown that hyperventilation in the presence of added CO₂ speeds recovery from isoflurane anesthesia. We wanted to determine if hyperventilation in conjunction with increased CO₂ would also be effective when used to remove a lower solubility agent such as sevoflurane. The device is an expandable hose and filter placed between the patient and the Y-piece.

Methods: We compared emergence times from sevoflurane anesthesia with and without the device in 4 pigs. Prior to emergence, each animal was anesthetized at 1.5 MAC of sevoflurane for 2 hours. Time between turning off the vaporizer and return of spontaneous breathing, movement of multiple limbs, and end-tidal sevoflurane less than 0.5 MAC were recorded. Respiratory rate was increased from 10 to 20 breaths per minute and fresh gas flow was raised to 6 L/min during each emergence. The order of testing was randomized to minimize the influence of a prior emergence on subsequent test results.

Results: Average time to spontaneous breathing was 13.2 minutes less using the device. Spontaneous breathing was not observed prior to multiple limb movement in 3 of the animals receiving hyperventilation without the device. Time to movement of multiple limbs was 10.5 minutes less when using the device. The range of emergence times when using the device was 4.4 to 9.6 minutes and 12.8 to 22 minutes without the device. The time to reach end-tidal sevoflurane concentration below 0.5 MAC was 1.3 minutes less when using the device. The figure below shows the time to occurrence for each of the events.

Discussion: Prior studies have shown significant speed-up of emergence using hyperventilation with hypercapnia during reversal of isoflurane anesthetic. These results show that similar benefits are possible when sevoflurane is used.

Reference: 1. British Journal of Anaesthesia 2003; 91:787-92