Nitrous Oxide As A Gas Anesthetic:
Recommendations from the IACUC at Case Western Reserve University
The IACUC STRONGLY RECOMMENDS that nitrous oxide NOT be used for any procedure that requires the subject to be unconscious.
Nitrous Oxide is often used as a gas anesthetic during dental procedures and other clinical procedures that require mild sedation. Based on these clinical results, nitrous oxide has also been used for pre-clinical procedures. To maintain a sufficient depth of unconsciousness, nitrous oxide must be mixed with a volatile anesthetic such as isoflurane (Aerrane), and must also be mixed with oxygen to prevent hypoxia.
Published results have shown that the effects of nitrous oxide and a volatile anesthetic are ADDITIVE or SLIGHTLY ANTAGONISTIC. Therefore, there is NO BENEFIT to maintaining the animal’s unconscious state when nitrous oxide is used with a volatile anesthetic, relative to using a higher dose of the volatile anesthetic.1
More importantly, the mixing of nitrous oxide and a volatile anesthetic can lead to three practical problems in the laboratory. First, the use of nitrous oxide requires a lower percentage of volatile anesthetic, which can be difficult to regulate. Unintended under- or over-regulation of the volatile anesthetic leads to unexpected consciousness or death. Second, a supply of both nitrous oxide and the volatile anesthetic must be monitored and resupplied when empty, which can add to the lab procedure and adds to the chemical inventory in the lab. Nitrous oxide is normally supplied in a compressed gas tank, which takes some care in transporting and securing to a permanent fixture. Third, nitrous oxide has a weak, slightly sweet odor that can be difficult to recognize. An overdose of nitrous oxide can often occur before the victim is aware of the odor. Other anesthetics, such as isoflurane, have distinctive odors especially at concentrations required without nitrous oxide.
Other volatile anesthetics can cause respiratory depression and/or cardiovascular depression.2 The use of nitrous oxide can reduce the amount of volatile anesthetic that is required to maintain unconsciousness, and therefore can reduce these respiratory and cardiovascular effects. The IACUC acknowledges that nitrous oxide may need to be used in some cases. BEFORE receiving approval from the IACUC for a protocol that uses nitrous oxide, the PI must contact DOES to:
- Receive safety training
- Undergo employee exposure monitoring
- Receive guidance for developing a laboratory infrastructure for scavenging of nitrous oxide
Lastly, nitrous oxide is a greenhouse gas, and has 296 times more impact on global warming than that per mass unit of carbon dioxide.3 Eliminating nitrous oxide from your laboratory complies with the conditions of the Kyoto Protocol to the United Nations Framework Convention on Climate Change.
References
1. Ropcke H, Wirz S, Boullion T, Bruhn J, Hoeft A. Pharmacodynamic interaction of nitrous oxide with sevoflurane, desflurane, isoflurane, and enflurane in surgical patients: measurements by effects on EEG median power frequency. Euro. J. Anaesthesiology 2001, 18:440-449.
2. Lukasik VM, Gillies RJ. Animal anesthesia for in vivo magnetic resonance. NMR Biomed 2003, 16:459-467.
3. Mennerick S, Jevtovic-Todorovic V, Todorovic SM, Shen W, Olney JW, Zorumski CF. Effect of nitrous oxide on excitatory and inhibitory synaptic transmission in hippocampal cultures. J Neurosci 1998, 18:9716-26.
|
