Minimum alveolar concentrations of noble gases, nitrogen, and sulfur hexafluoride in rats: helium and neon as nonimmobilizers (nonanesthetics)
We assessed the anesthetic properties of helium and neon at hyperbaric pressures by testing their capacity to decrease anesthetic requirement for desflurane using electrical stimulation of the tail as the anesthetic endpoint (i.e., the minimum alveolar anesthetic concentration [MAC]) in rats. Partial pressures of helium or neon near those predicted to produce anesthesia by the Meyer-Overton hypothesis (approximately 80-90 atm), tended to increase desflurane MAC, and these partial pressures of helium and neon produced convulsions when administered alone. In contrast, the noble gases argon, krypton, and xenon were anesthetic with mean MAC values of (+/- SD) of 27.0 +/- 2.6, 7.31 +/- 0.54, and 1.61 +/- 0.17 atm, respectively. Because the lethal partial pressures of nitrogen and sulfur hexafluoride overlapped their anesthetic partial pressures, MAC values were determined for these gases by additivity studies with desflurane. Nitrogen and sulfur hexafluoride MAC values were estimated to be 110 and 14.6 atm, respectively. Of the gases with anesthetic properties, nitrogen deviated the most from the Meyer-Overton hypothesis.


CONCLUSIONS
It has been thought that the high pressures of helium and neon that might be needed to produce anesthesia antagonize their anesthetic properties (pressure reversal of anesthesia). We propose an alternative explanation: like other compounds with a low affinity to water, helium and neon are intrinsically without anesthetic effect.
Veteran's Administration Hospital, and Department of Anesthesia, University of California-San Francisco, 94143-0464, USA.
D D
DD
Koblin
Z
Z
Fang
E I
EI
Eger
M J
MJ
Laster
D
D
Gong
P
P
Ionescu
M J
MJ
Halsey
J R
JR
Trudell
D000777:Anesthetics / Q000009:adverse effects / Q000378:metabolism; D018685:Anesthetics, Inhalation; D000818:Animals; D001128:Argon; D000077335:Desflurane; D006371:Helium / Q000009:adverse effects; D007530:Isoflurane / Q000031:analogs & derivatives; D007726:Krypton; D008297:Male; D009356:Neon / Q000009:adverse effects; D009584:Nitrogen / Q000378:metabolism; D005741:Noble Gases / Q000009:adverse effects / Q000378:metabolism; D010313:Partial Pressure; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013459:Sulfur Hexafluoride / Q000378:metabolism; D014978:Xenon
D000777:Anesthetics; D018685:Anesthetics, Inhalation; D005741:Noble Gases; D006371:Helium; D014978:Xenon; D009356:Neon; D007726:Krypton; D001128:Argon; D000077335:Desflurane; D007530:Isoflurane; D009584:Nitrogen; D013459:Sulfur Hexafluoride