Human Isoflurane Studies
Animal Isoflurane Studies

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

Clinical Evaluation of a Device to Speed Emergence from Inhaled Anesthesia
D. Sakata, N. Gopalakrishnan, J. Orr, D. Westenskow;
University of Utah, Salt Lake City, UT.
S-225

Introduction: Rapid emergence from a volatile anesthetic is a “trade-off” between hyperventilation to remove volatile anesthetic from the lungs and hypoventilating to maintain normocapnia or slight hypercapnia for elevated blood flow to the brain. We evaluated a device that allows simultaneous hyperventilation and hypercapnia during the reversal process.

Methods: After IRB approval, 18 ASA I patients scheduled to receive anterior cruciate ligament repair surgery were recruited for the study. Patients were randomly assigned to control and experimental groups. All patients received functional femoral nerve blocks. Anesthesia was maintained using 1 MAC of isoflurane and 0.05-0.15 mcg/kg/min of remifentanil.

Emergence was initiated when adhesive wound closure strips were applied. Events were recorded from the time that the isoflurane vaporizer was turned off. Test subjects using the device were hyperventilated by doubling the respiratory rate. Fresh gas flow was increased to 10 L/min in control subjects. The test device was inserted into the breathing circuit of patients in the experimental group. Times to eye and mouth opening in response to command and extubation were recorded.

Results: Using the device, the average time to opening eyes was less by 9.7 minutes (experimental range 4.1 to 11.5 and control range 10.2 to 24.3). Time to respond to an “open your mouth” command was less by 9.5 min (experimental range 4.4 to 11.5 and control range 10.3 to 19.7). Time to extubation was less by 10 minutes (experimental range 5.1 to 12.2 and control range 11.1 to 28.2). For the control, the minute ventilation was kept at an average of 11.7 liters per minute with an average end-tidal carbon dioxide of 29.5 mm of Hg. For the experimental group, the minute ventilation was kept at an average of 14.1 liters per minute with an average end-tidal carbon dioxide of 44.9 mm of Hg.

Discussion: The differences observed in this data set suggest that decreased time to emergence from volatile anesthesia can be effectively achieved by combining hyperventilation with elevated CO₂.

American Society of Anesthesiologists, 2003 Annual Meeting
(winner of the “Excellence in Technology Innovation Award” recognition by the Society for Technology in Anesthesia)
A-576
2003

Evaluation of a Device To Speed Emergence from Inhaled Anesthetic
Derek Sakata, M.D., Joseph Orr, Ph.D., Dwayne Westenskow, Ph.D.
Anesthesiology, University of Utah, Salt Lake City, Utah.

Introduction: Emergence from inhaled anesthesia is more rapid with hyperventilation to remove volatile agent from the lungs and elevated cerebral blood flow to remove anesthetic agent from the brain. Hypercapnia can elevate cerebral blood flow and speed emergence. Hyperventilation, and resulting hypocapnia, leads to decreased cerebral blood flow and decreased clearance of anesthetic from the brain.

We tested a simple device, which rapidly removes inhaled anesthetics from the breathing circuit and also maintains slight hypercapnia during hyperventilation. The device employs an anesthetic absorber filled with activated charcoal placed in the airway to rapidly absorb anesthetic agent and a partial rebreathing volume placed between the Y-piece and the endo-tracheal tube to maintain elevated end tidal CO₂ during hyperventilation. Rebreathing allows hyperventilation while preventing hypocapnia, the absorber scrubs anesthetic vapors to prevent inhalation of anesthetic from the rebreathed volume.

Methods: We compared emergence times from isoflurane anesthesia with and without the rebreathing device in 5 pigs. Prior to emergence, each animal was anesthetized at approximately 2 MAC for at least 6 hours. During emergence, inspired and end-tidal isoflurane concentration, end tidal CO₂, bispectral index (BIS™), and blood pressure were recorded along with time to return of spontaneous breathing, purposeful movement of multiple limbs, and end tidal isoflurane less than 0.5 MAC. The protocol included four emergence time measurements in each animal including a comparison between hyperventilation and rebreathing and a comparison between normal ventilation and rebreathing. The order of testing was randomized to minimize the influence of prior tests on subsequent test results.

Results: The table below shows the average times after the vaporizer was turned off until each of the events were observed. Average time to spontaneous breathing was 6.1 minutes less using the rebreathing device when compared to normal ventilation and 7.0 minutes less when compared to hyperventilation. Spontaneous breathing was not observed prior to purposeful movement in any animal when hyperventilation was used. Time to purposeful movement was 6.9 minutes less when using rebreathing than when normal ventilation was used and 4.0 minutes less when compared to hyperventilation. The time to reach end-tidal agent concentration less than 0.5 MAC was 7.4 minutes less using the rebreathing device compared to normal ventilation and 1.5 minutes less when compared to hyperventilation.

Discussion: To achieve rapid emergence from volatile anesthetic there is a trade-off between hyperventilation for rapid removal of volatile anesthetic from the lungs, and hypoventilation to maintain elevated blood flow to the brain through normocapnia or slight hypercapnia. A rebreathing device appears to allow the clinician to simultaneously achieve both goals during the reversal process.

Anesthesiology 2003; 99: A576