Hypercapnia shortens emergence time from inhaled anesthesia in pigs.
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.
Gopalakrishnan
Nishant A
NA
Department of Anesthesiology, University of Utah, Salt Lake City, Utah 84132, USA. nishant@abl.med.utah.edu
Sakata
Derek J
DJ
Orr
Joseph A
JA
McJames
Scott
S
Westenskow
Dwayne R
DR
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
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D002245:Carbon Dioxide; D000077149:Sevoflurane; D007530:Isoflurane