title: Hypercapnia shortens emergence time from inhaled anesthesia in pigs.
abstract: BACKGROUND
  Anesthetic clearance from the lungs and the circle rebreathing system can be maximized using hyperventilation and high fresh gas flows. However, the concomitant clearance of CO2 decreases PAco2, thereby decreasing cerebral blood flow and slowing the clearance of anesthetic from the brain. This study shows that in addition to hyperventilation, hypercapnia (CO2 infusion or rebreathing) is a significant factor in decreasing emergence time from inhaled anesthesia.
  
  
  METHODS
  We anesthetized seven pigs with 2 MACPIG of isoflurane and four with 2 MACPIG of sevoflurane. After 2 h, anesthesia was discontinued, and the animals were hyperventilated. The time to movement of multiple limbs was measured under hypocapnic (end-tidal CO2 = 22 mm Hg) and hypercapnic (end-tidal CO2 = 55 mm Hg) conditions.
  
  
  RESULTS
  The time between turning off the vaporizer and to movement of multiple limbs was faster with hypercapnia during hyperventilation. Emergence time from isoflurane and sevoflurane anesthesia was shortened by an average of 65% with rebreathing or with the use of a CO2 controller (P < 0.05).
  
  
  CONCLUSIONS
  Hypercapnia, along with hyperventilation, may be used clinically to decrease emergence time from inhaled anesthesia. These time savings might reduce drug costs. In addition, higher PAco2 during emergence may enhance respiratory drive and airway protection after tracheal extubation.
authors: Department of Anesthesiology, University of Utah, Salt Lake City, Utah 84132, USA. nishant@abl.med.utah.edu
authors: Nishant A
authors: NA
authors: Gopalakrishnan
authors: Derek J
authors: DJ
authors: Sakata
authors: Joseph A
authors: JA
authors: Orr
authors: Scott
authors: S
authors: McJames
authors: Dwayne R
authors: DR
authors: Westenskow
mesh_terms: D000762:Anesthesia Recovery Period; D000769:Anesthesia, Inhalation / Q000295:instrumentation; D018685:Anesthetics, Inhalation; D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D004867:Equipment Design; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology*; D006985:Hyperventilation / Q000378:metabolism / Q000503:physiopathology; D007530:Isoflurane; D008738:Methyl Ethers; D000077149:Sevoflurane; D013552:Swine; D013997:Time Factors
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D002245:Carbon Dioxide; D000077149:Sevoflurane; D007530:Isoflurane