Nitrous oxide concentrations ambient

Entonox is a 50% mixture of nitrous oxide and oxygen which remains gaseous under pressure unless the ambient temperature falls below -5.5°C. In these circumstances the contents may separate into liquid nitrous oxide and gaseous oxygen. In such a situation there is a risk that at the start high percentage concentrations of oxygen could be delivered followed by almost pure nitrous oxide. 

Adverse effects. The incidence of nausea and vomiting increases with the duration of anaesthesia. Nitrous oxide interferes with the synthesis of methionine, deoxythymidine and DNA. Exposure of to nitrous oxide for more than 4 hours can cause megaloblastic changes in the bone marrow. Because prolonged and repeated exposure of staff as well as of patients may be associated with bone-marrow depression and teratogenic risk, scavenging systems are used to minimise ambient concentrations in operating theatres. 

For United States Pharmacopeia (USP) quality verification, perform the verification tests in the sequence listed (after the filled container has warmed to ambient temperature) a gas/liquid equilibrium must be established in the container. For a vapor sample, test nitrous oxide gas from the vapor phase of the container for a liquid sample, a representative vaporized sample of the liquid phase must be obtained. The sequence listed minimizes concentration changes and allows for maximum detection of toxic contaminants on the assumption that the usage is inhalation. 

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