Modern Uses

Medical Uses

After 168 years of its first anaesthetic use, nitrous oxide is the oldest anaesthetic gas, and is still in use as an inhaling agent by anaesthetists. As mentioned above Horace Wells was the pioneer in the usage nitrous oxide as an anaesthetic, but its introduction as widely accepted method only happened during 1863 by the hand of Gardner Quincy Colton. He brought nitrous oxide into a more wide use at the Colton Dental Association practices, of which we was a founding member. The first equipment utilized in dentistry, named at the time “Nitrous Oxide inhalers”, had a very simple design. This equipment administered nitrous oxide with the gas kept and inhaled through a sack composed of rubber, without a scavenger system or component for the measuring of the gas flow, and with no mixing of oxygen/air.  The recent analgesia machine, called relative because of the mixing of gases, has superseded these simple devices, built to deliver an exact stream of a mix of nitrous oxide with oxygen, for the patient to breathe in a safe, automated way. In clinical facilities, it usually is used a larger model of the machine used in dentist offices, as these usually lack features like the added anaesthetic vaporizer and medical ventilator. These features are not needed in models used in dentistry, as the objective is only to diminish the sense of pain without the patient losing consciousness.

The models used at the hospitals, the relative analgesia machine, usually feature a continual supply flow-measuring device. This enables the individual adjustment of the flow ratio and the share of the nitrous oxide and the other gas mixed in. Due to the low metabolizing of nitrous oxide by humans, at a ratio of 0.0004%, it remains potent when exhaled by the patient, requiring a special care with ventilation in order avoid intoxication and other hazards associated with exposure to nitrous oxide.

Given that nitrous oxide is mild general anaesthetic, it is used in conjunction with other anaesthetics in general anaesthesia. In this cases, nitrous oxide is used as carrier gas with oxygen in a 2 per 1 ration with more potent general anaesthetic drug as sevoflurane, desflurane, or others similar drugs. The minimum alveolar concentration (MAC) of nitrous oxide is of 105% and has a blood to gas partition coefficient of 0.46.

Nitrous oxide is regularly used to ease the pain related with acute coronary syndrome, which includes heart attacks, childbirth, oral surgery and trauma. As for the case of the usage during labour it has been demonstrated to safe and helpful in adding the women wanting to go through labour without the aid of an epidural, on the other hand its use in the case of acute coronary syndrome is yet of indefinite value. In other fields, it has been demonstrated that nitrous oxide can be useful in treating various addictions, for example alcohol withdrawal.

Rocket motors

Nitrous oxide is also utilized as an oxidizing agent in rocket engines. The advantages of its use is because of its low toxicity, when compared to other oxidizing agents; It is easy to store, stable at room temperature and comparatively safe to carry during a flight. Another advantage commonly noted is that during decomposition it can release breathable air. The high density and low pressure needed for storage allow it to be competitive with other pressurized gas storage systems. In 1914, it was issued the first patent on nitrous oxide and gasoline as rocket propellant by Robbert Goddard. Nitrous oxide is still used today in rockets that use a mixture of solid fuel combined with liquid or gas propellant, which are called hybrid rockets. One example of this kind of rockets is SpaceShipOne, which uses nitrous oxide as an oxidizing agent.

Nitrous oxide has a large following in model rocket enthusiasts, who use it for the same reasons outline above, namely safety of use.

Although nitrous oxide is better known for its use in hybrid rockets, it can be utilized in monopropellant rockets, which are rocks using only one propellant. When nitrous oxide is in the presence of a heated catalyst, it will decompose, releasing heat (exothermically), into oxygen and nitrogen at around 1300º Celsius. Due to this enormous heat release thermal auto-decomposition becomes secondary to the catalytic function. This can deliver monopropellant specific impulse of up to 180s and, while nitrous oxide power, as a monopropellant, is lower than other monopropellant alternatives, is low toxicity make it an interesting possibility. Other fact that make nitrous an interesting alternative is that it is a chemically stable substance, and as such does not pose the threat of spontaneous ignition.



Combustion Engines

Nitrous oxide is popularly in the auto world as nitrous. Nitrous oxide can be used in internal combustion engines with objective of obtaining a boost in power. Working in a similar way to turbocharging, the injection of nitrous oxide in the combustion chambers has the objective of raising the mass of oxygen injected. In this particular case, nitrous oxide has the objective of lowering the heating of the combustion chamber, enabling a bigger mixture of air-fuel to be injected into the chamber. This allows for burning of bigger quantity of fuel in the same combustion chamber.

Nitrous oxide can enhance the engine’s power through three physical/chemical mechanisms. The main effects occurs due to the increase of mass in the oxidizing agent present in the combustion chamber, allowing for a bigger injection of fuel, given that the power of an engines is related to the amount of heat produced during the combustion.

Simultaneously, the injection of nitrous oxide at low temperatures reduces the total density of the mixture, also enabling a bigger flow of air. In conclusion, this low temperature helps with cooling the engine, which can work at a bigger power output without the risk of overheating.  The cooling of the nitrous oxide can be explained general theory of gases. In the same instant that the nitrous oxide exits the cylinder, through the nitrous oxide injection system, moving from a high-pressure environment (cylinder) to a low-pressure environment (generally close to atmospheric pressure), the gas undergoes a quick expansion, which provokes as extreme cooling of the gas. As nitrous oxide is usually expelled into the vehicle’s admission system, it cools the system in a significant way. This, as explained above, leads to air entering the engine to become denser. At a second stage, a mixture of air, nitrous oxide and fuel enters the engine’s cylinders. As the cylinders work at a high pressure and a high pressure (generally over 400º Celsius and above 100 bar), the N2O molecule, through a chemical process, divides into N2 molecules (nitrogen) and O2 molecules (oxygen). The oxygen formed from this chemical reaction adds to the oxygen admitted into the engine, forming the total mass of oxidizing agent that to be burned.  Additional fuel is already present in the cylinders as the nitrous oxide injection system has already the function of injection more fuel, together with the nitrous oxide, in the adequate proportion of the increase of oxidizing agent and fuel. This is the main way in that nitrous oxide allows for an increase in power, which can be as much as 70% to 80% more.

The nitrogen resulting from the separation of the nitrous oxide stays inert (meaning inactive in chemical terms) during the burning of the fuel and the oxidizing agent and, at the same time lowering by a significant amount the cylinders internal temperature, which simultaneously allows for greater security and better possibilities of increases in power. Nitrogen, acting as regulatory agent by cooling the cylinders, complements the increase in power of engine, without the need for changes in the structure of the engine to sustain the increase of pressure and temperature.  Although there are other gas injection systems for cars, nitrous oxide is the one the provides the greatest advantage with the least downsides. This said the usage of nitrous oxide is not without problems. Extremely large increases in power output are possible but require and appropriate reinforcement of the engine, and the operating temperature and fuel levels should be monitored closely to avoid “pre-ignition”, or “detonation” (commonly referred as “knock” or “pinking”).

As a historical note, this technique to improve engine power was utilized during World War II by the Luftwaffe in planes equipped with the GM-1 system to increase the power of the aircraft’s engines. Due limitations in the technology available, its usage was limited to extremely high altitudes, failing to provide standard Luftwaffe planes with increased high-altitude performance. Due to this fact, its usage was limited to specialized aircrafts.

Liquid nitrous oxide used in cars is marginally different from the nitrous oxide used in medical applications, as to prevent substance abuse a minor amount of sulphur dioxide is added to it.

Aerosol propellant

Many times, in order to obtain food products with the appearance of foam, sprays or liquids, there is the use of canisters with pressurized aerosols. The use of propellants provides the needed pressure to force the liquid food out of the aerosol canister. One of the most common propellants is nitrous oxide, with nitrogen and carbon dioxide also being used to this end. As a food additive, nitrous oxide is referred as E942, its European code. Nitrous oxide is used in, for example, whipped cream, cheeses, mustard and cooking sprays. Another food related use of nitrous oxide is replacing oxygen when filling snack food packages, to prevent bacterial growth. An import fact, which explain it usefulness as a propellant for aerosol whipped cream, is that nitrous oxide is highly soluble in fatty composites. This means that when the nitrous oxide leaves the canister, becoming gaseous, it creating foam. Other propellants would not be as good in dealing with whipped cream. For example, if air were utilized as propellant it would not be able to create the volume that nitrous oxide can, as well as it would hasten rancidification of the butterfat, something that nitrous oxide would delay. As for carbon dioxide with would not be used in whipped cream as carbon dioxide is acidic when in contact with water, curdling the milk.

Recreational use

Nitrous oxide has a series of effects on the human body when inhaled, the main being:

  • Analgesia
  • Euphoria
  • Depersonalization
  • Derealisation
  • Dizziness
  • Auditory distortion

Apart from these effects, researchers have also found that it increases suggestibility and imagination. As noted above, recreational use was perhaps the first use given to nitrous oxide, namely by the upper class in Britain during 1799, in events know at the time as “laughing gas parties”.  Due to the low accessibility to the equipment required to create nitrous oxide, up until 1863 it was a rare occurrence, which happened mostly with students at medical universities.  However, when equipment became more readily available, to dental and medical practices, so was legislation restricting legal access to pure nitrous oxide in those areas. This was though to limit the recreational use, although studies show that nitrous was and still is a popular recreational drug. Due to that fact, the nitrous oxide used in cars has added sulphur dioxide, to discourage other than is intended use, namely recreational use.

Legal Questions

Nitrous oxide is a controlled substance in most countries, in order to prevent substance abuse. For this reason, liquid nitrous oxide used in cars has a minor amount of sulphur dioxide is added to it. As for auto nitrous oxide systems (NOS), they are illegal in some countries.