Nitrous oxide and the inhalation anesthetics

Abstract

Nitrous oxide is the most commonly used inhalation anesthetic in dentistry and is commonly used in emergency centers and ambulatory surgery centers as well. When used alone, it is incapable of producing general anesthesia reliably, but it may be combined with other inhalation and/or intravenous agents in deep sedative/general anesthetic techniques. However, as a single agent, it has impressive safety and is excellent for providing minimal and moderate sedation for apprehensive dental patients. To gain a full appreciation of the pharmacology, physiologic influences, and proper use of nitrous oxide, one must compare it with other inhalation anesthetics. The purpose of this CE article is to provide an overview of inhalation anesthetics in general and to address nitrous oxide more specifically in comparison.

Figure 1

Relative Onset of Effect. When gas tensions throughout body tissues equilibrate, the inspired gas tension (F_I) will equal that in the alveoli (F_A). Notice from this graph that nitrous oxide achieves approximately 90% equilibration within 10 minutes. For each gas illustrated in this graph, the speed of onset correlates with partition coefficients provided in Table 1.

Figure 2

Concentration Delivered Versus That Reaching Alveoli. The concentration of nitrous oxide delivered by the typical dental machine is drastically reduced when compared with the concentration that actually reaches the patient. (Adapted from Sher et al9)