Nitrous oxide (medication)

Nitrous oxide, often called "gas and air," is a medical gas used to manage pain. It is an inhaled analgesic, which is a substance that reduces pain. This gas is highly valued because it works very quickly and leaves the body just as fast. Because of its importance in medical care, the World Health Organization includes it on its List of Essential Medicines. It is commonly used during childbirth, after a person experiences trauma, and during end-of-life care. It is also being researched as a potential treatment for certain types of depression.

The way nitrous oxide works in the body is quite fascinating. The gas is active on its own and does not need to change inside the body to work. When a patient breathes it in, the gas moves from the lungs to the brain through the blood circulation. This process is very fast, with peak action occurring about 30 seconds after administration. The analgesic effect is quite strong, which is roughly equivalent to 15 mg of morphine given through a subcutaneous route. Because the gas is removed unchanged via the lungs, the effects usually wear off in about 60 seconds.

While scientists do not fully understand every detail of its mechanism, they know it affects the brain's communication system. Nitrous oxide modulates many ligand-gated ion channels, which are proteins that allow ions to pass through cell membranes. Specifically, it blocks NMDAR channels and certain nicotinic acetylcholine channels. It also interacts with GABA and glycine receptors. Most of its effects, such as its ability to reduce pain or cause euphoria, likely come from inhibiting these NMDA receptor-mediated currents. It may also act by imitating nitric oxide within the central nervous system.

In modern medicine, nitrous oxide is typically administered as a mixture. A very common setup is a 50/50 mix of nitrous oxide and oxygen. This mixture is created using the Poynting effect, named after the English physicist John Henry Poynting. This effect allows oxygen to dissolve when it is bubbled through liquid nitrous oxide. This process creates a homogeneous mixture, meaning the gases are blended perfectly throughout the cylinder. This ensures that the patient receives a consistent 50/50 ratio even as the cylinder empties. However, if a cylinder becomes very cold, below −7 °C, some gas might turn back into a liquid.

There are different ways to deliver this gas depending on the setting. In a hospital, doctors may use a relative analgesia machine. These machines are complex and include parts like flowmeters, constant-flow regulators, and medical ventilators. They also use a scavenger system to manage the gas. In dental offices, the equipment is much simpler. Patients often use a demand-valve inhaler over their nose. This device is clever because it only releases gas when the patient actively inhales. If a patient becomes too sedated, they will naturally drop the valve, which stops the gas flow.

History shows how much our understanding of this gas has evolved. It was discovered between 1772 and 1793. In December 1844, Horace Wells performed the first dental operations using the gas in Hartford. Later, in 1863, Gardner Quincy Colton introduced it more broadly in New York City and New Haven. Early doctors used simple rubber cloth breathing bags, but breathing pure gas was dangerous. This could cause hypoxia, which is a lack of oxygen, or even death. By 1911, Arthur Ernest Guedel described how patients could administer the gas themselves. Later, in 1970, Peter Baskett and Alan Withnell helped bring pre-mixed gas to ambulances.

Safety is the most important part of using nitrous oxide. It must always be mixed with at least 21% oxygen, which is the same amount found in the air we breathe. There are several situations where the gas should not be used. It is not recommended for people with a bowel obstruction or a pneumothorax, which is a collapsed lung. It is also unsafe for people who have been scuba diving in the last 24 hours. This is because nitrous oxide is 30 to 40 times more soluble than nitrogen, so it can expand in air spaces in the body. While short-term use has few side effects, long-term use can lead to anemia or numbness.