From the Guidelines
Nitrous oxide should be avoided in various patient populations due to its specific properties and potential complications, and its use is generally not recommended for anesthetic maintenance in low-middle-income countries due to its high risk of postoperative nausea and vomiting (PONV) and delayed return of bowel function, as stated in the most recent guidelines 1.
Indications and Contraindications
The use of nitrous oxide for anesthetic maintenance has several indications and contraindications that must be considered. Some of the key points to consider include:
- Nitrous oxide provides moderate analgesia and rapid onset and offset of action, making it a useful agent in certain situations.
- However, it should be avoided in patients with pneumothorax, bowel obstruction, middle ear surgery, or recent vitreoretinal surgery due to its ability to expand gas-filled spaces.
- Patients with vitamin B12 deficiency, methylenetetrahydrofolate reductase deficiency, or homocystinuria should avoid nitrous oxide as it inactivates vitamin B12, potentially causing megaloblastic anemia and neurological complications with prolonged exposure.
- Nitrous oxide should also be avoided in pregnant women during the first trimester due to potential teratogenic effects and in patients with pulmonary hypertension as it can increase pulmonary vascular resistance.
- Additionally, nitrous oxide contributes to postoperative nausea and vomiting, so it may be best avoided in patients at high risk for these complications.
Evidence-Based Recommendations
The most recent guidelines recommend avoiding the use of nitrous oxide for anesthetic maintenance due to its high risk of PONV and delayed return of bowel function 1. Instead, propofol has become the standard medication for induction of general anesthesia due to its rapid onset and recovery and reduced nausea and vomiting. Other intravenous anesthetic agents, such as dexmedetomidine and ketamine, may be used in combination with propofol to provide effective total intravenous anesthesia.
Key Considerations
When considering the use of nitrous oxide, it is essential to weigh the potential benefits against the potential risks and complications. The mechanism behind the contraindications relates to nitrous oxide's physical properties (gas expansion) and its interference with methionine synthase, which requires vitamin B12 as a cofactor for DNA synthesis and myelin formation. Overall, the use of nitrous oxide should be approached with caution, and alternative agents should be considered whenever possible, especially in patient populations at high risk for complications.
From the Research
Indications for Nitrous Oxide (N2O) Use
- Nitrous oxide can be used as part of a technique using other anaesthetic gases, intravenous agents, or both for the induction and maintenance of general anaesthesia 2.
- Its low tissue solubility, low cost, and low rate of cardiorespiratory complications make nitrous oxide a commonly used general anaesthetic 2.
- Nitrous oxide reduces the cost of anaesthesia and limits cardiorespiratory side effects by enabling reduced doses of more potent anaesthetics 3.
- The use of nitrous oxide is associated with decreased odds of 30-day mortality and decreased odds of in-hospital mortality/morbidity 4.
Contraindications for Nitrous Oxide (N2O) Use
- Patients with pre-existing poor pulmonary function or at high risk of postoperative nausea and vomiting may need to avoid nitrous oxide 2.
- Nitrous oxide should not be used for patients with bowel obstruction, pneumothorax, middle ear and sinus disease, and following cerebral air-contrast studies due to its effects on the pressure and volume characteristics of air-containing spaces 5.
- Use of nitrous oxide is not recommended during the first two trimesters of pregnancy because of its effects on DNA production and the experimental and epidemiological evidence that N2O causes undesirable reproductive outcomes 5.
- Nitrous oxide should not be administered to immunosuppressed patients or to patients requiring multiple general anaesthetics due to its effects on white blood cell production and function 5.
Special Considerations
- The use of nitrous oxide increases the incidence of pulmonary atelectasis, but has no effects on the inhospital case fatality rate, the incidence of pneumonia, myocardial infarction, stroke, severe nausea and vomiting, venous thromboembolism, wound infection, or the length of hospital stay 2.
- Nitrous oxide-free anaesthesia may be associated with a reduced incidence of postoperative nausea and vomiting (PONV) 6.
- The ecological effects, ozone depleting potential, immune depression, and the proven factor of PONV have questioned the routine use of nitrous oxide in patients undergoing surgical procedures in general anaesthesia 6.