In this tutorial we take a practical, evidence-based look at nitrous oxide—one of the oldest drugs in anaesthesia and still the only anaesthetic gas in routine clinical use. We explore its unique pharmacology, including the concentration effect, second gas effect and reverse second gas effect, explain why it remains useful during inhalational induction, and examine its true contribution to anaesthesia. The tutorial also reviews the evidence from major clinical trials, dispels common misconceptions, and discusses the important complications of nitrous oxide, including expansion of closed gas spaces, diffusion hypoxia, postoperative nausea and vomiting, vitamin B₁₂-related toxicity, and its environmental impact. By the end, you’ll understand when nitrous oxide adds real value to modern anaesthetic practice—and when it is better avoided.
This tutorial explains why emergence from volatile anesthesia depends on more than simply turning off the vaporizer. It reviews how blood gas partition coefficients influence onset, how oil gas partition coefficients relate to potency and MAC, and then focuses on tissue blood partition coefficients as a key determinant of recovery. The tutorial describes anesthetic uptake into blood, muscle, and fat during short, intermediate, and long cases, showing how tissue storage increases with time and with agent solubility. It also explains tissue back diffusion, where anesthetic stored in tissues continues to return to the blood and brain after the vaporizer is turned off, delaying wake-up. Finally, it compares volatile agents such as nitrous oxide, desflurane, sevoflurane, isoflurane, halothane, and methoxyflurane, emphasizing how lower tissue solubility produces faster, more predictable emergence.
Part 2 – Other Factors that Impact Emergence from Anesthesia
This tutorial examines the additional factors that determine how quickly a patient wakes after volatile anesthesia. It covers the concentration-flow ramp, fresh gas flow, alveolar ventilation, and cardiac output, explaining how these influence washout of anesthetic from the lungs and circulation. It discusses the effects of poor gas exchange, atelectasis, duration of surgery, higher inspired concentrations, and obesity on tissue loading and delayed emergence. The tutorial also reviews hysteresis and MAC awake, showing why patients can remain asleep at concentrations lower than those required for induction. Other important contributors such as hypothermia, opioids, benzodiazepines, propofol, dexmedetomidine, clonidine, ketamine, and nitrous oxide are included, along with a discussion of spontaneous ventilation versus intermittent positive pressure ventilation. The overall message is that emergence depends on both how efficiently the lungs clear anesthetic and how much anesthetic the body gives back
ORtoICU 