What is the concentration effect of nitrous oxide (N2O)?

From the Guidelines

The concentration effect of nitrous oxide is a critical consideration in anesthesia, as it can cause expansion of air-filled spaces within the body, leading to potential complications. When nitrous oxide is administered, it diffuses into air-filled cavities about 34 times faster than nitrogen diffuses out, leading to increased pressure and volume in these spaces. This occurs because nitrous oxide is more soluble in blood than nitrogen 1. Some key points to consider about the concentration effect of nitrous oxide include:

• Clinically, this effect becomes important in situations involving closed air spaces such as pneumothorax, bowel obstruction, middle ear surgeries, or air embolism, where the expanding gas can cause tissue damage or compromise organ function.
• The concentration effect develops rapidly during the first 30 minutes of nitrous oxide administration and reverses when the gas is discontinued.
• Anesthesiologists must be aware of this property when selecting anesthetic agents for patients with pre-existing air-filled spaces, often avoiding nitrous oxide in such cases to prevent complications like tympanic membrane rupture, increased intracranial pressure, or bowel distension.
• Understanding this physical property helps guide appropriate anesthetic management for patients with various clinical conditions, as noted in studies such as those by Saunders et al 1 and Maslekar et al 1. However, it is essential to note that the provided evidence does not directly discuss the concentration effect of nitrous oxide, but rather its use as an anesthetic agent and its benefits and risks in various clinical settings. Therefore, the information on the concentration effect is based on general knowledge of the properties of nitrous oxide, rather than the specific studies cited 1.

From the Research

Concentration Effect of Nitrous Oxide (N2O)

The concentration effect of nitrous oxide (N2O) has been studied in various settings, including pediatric procedural sedation and analgesia. The following points summarize the key findings:

• High-concentration continuous-flow nitrous oxide (50%-70%) has been found to be a safe agent for procedural sedation and analgesia in children 2.
• The depth of sedation and incidence of adverse events associated with various concentrations of nitrous oxide have been characterized in a pediatric emergency department setting 2.
• Nitrous oxide concentration, adverse events, and sedation depth were recorded, and moderate or deep sedation with scores of ≤ 2 occurred in 3% of patients who had received nitrous oxide 70% and no patients who had received nitrous oxide 50% 2.
• The end-organ effects of N2O have been well described, including its effects on the central nervous system, ventilation, hemodynamics, and neurologic and hematologic function 3.
• Nitrous oxide has been shown to be effective for a variety of minor surgical procedures, with demonstrated advantages to parenteral sedation including a more rapid onset and a shorter recovery time 3.
• The safety of high-concentration nitrous oxide by nasal mask for pediatric procedural sedation has been evaluated, with no adverse events recorded for 95.7% of cases 4.
• Adverse events were observed in 9% and 22% of children who received 60% and 70% N2O concentrations, respectively, in a pediatric dentistry setting 5.
• The combination of oral midazolam and inhaled nitrous oxide caused mild ventilatory depression in some children and resulted in a progression from conscious to deep sedation beginning at 30% N2O 6.

Key Findings by Concentration

• 50% N2O concentration:
  • Associated with lower sedation scores and fewer adverse events compared to higher concentrations 2, 5.
  • May not achieve satisfactory cooperation to complete pediatric dental treatment in some cases 5.
• 60% N2O concentration:
  • Appears to be more effective than 50% and safer than 70% for pediatric procedural sedation 5.
  • Associated with higher sedation scores and more adverse events compared to 50% N2O concentration 5.
• 70% N2O concentration:
  • Associated with higher sedation scores and more adverse events compared to lower concentrations 2, 5.
  • May be necessary to achieve adequate sedation and cooperation in some cases, but with increased risk of adverse events 5.