Nitrous Oxide Administration

Nitrous Oxide Administration

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Nitrous oxide (N2 O), commonly known as laughing gas or happy gas, was first discovered in 1793 by the English scientist Joseph Priestly and has been used for more than 150 years. It has remained one of the most widely used anesthetics in both dental and medical applications. [1]

Nitrous oxide is small inorganic chemical molecule and may also be known as dinitrogen oxide or dinitrogen monoxide. It is a colorless and nonflammable gas with a slightly sweet odor. [2]

Nitrous oxide also has some illicit recreational uses and abuse potential. It is widely used in multiple nonmedical areas. Some of the nonmedical uses of nitrous oxide include the semiconductor industry, car racing, and food processing. [1]

Nitrous oxide is administered by inhalation, absorbed by diffusion through the lungs, and eliminated via respiration. The elimination half life of nitrous oxide is approximately 5 minutes. [3] It is excreted essentially unchanged (ie, nonmetabolized) via the lungs; less than 0.004% is actually metabolized in humans.

As a general anesthetic, it is very weak and is generally not used as a single agent. It may be used as a carrier gas with oxygen in combination with more potent general inhalational gases for surgical anesthesia. [3] In dentistry, it is commonly used as a single agent (with oxygen) for partial sedation, most commonly in pediatric dental populations.

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General anesthesia, in combination with other anesthetics

Nitrous oxide is a weak inhalational anesthetic. Because 105% alveolar concentration is needed to induce general anesthesia when nitrous oxide is used as a sole anesthetic agent, it is ineffective as a single agent for general anesthesia. As a result, nitrous oxide is most commonly used in combination with other more potent inhalational anesthetics for general anesthesia. [1]

One of the most common uses of nitrous oxide in anesthesia is during mask induction of general anesthesia in pediatric patients. It is combined with oxygen and incrementally increasing doses of a more potent inhalational anesthetic (eg, sevoflurane) and delivered via mask inhalation.


In dentistry, nitrous oxide is indicated to decrease the pain and anxiety associated with procedures. It is commonly delivered by a nasal mask in combination with oxygen. [1] The specially designed nasal mask fully covers the nose, allowing the mixture of nitrous oxide with oxygen to flow while the dentist works on the patient’s mouth.

Nitrous oxide is commonly offered by pediatric dentists to assist in inducing amnesia, as well as increasing analgesia, relaxation, and cooperation in younger patients. [1]

Indications in adult dental patients include anxiety, low pain tolerance, underlying psychiatric disorders, and mental retardation. [1, 4]

Nitrous oxide may also be useful for prolonged or more involved dental procedures as well as in patients with hyperresponsive gag reflexes. [5]

Other indications

Although not standard practice, additional described uses may include colonoscopy, sigmoidoscopy, laser procedures, obstetrical labor pain, ophthalmic procedures, emergency medical care of patients in accidents and during ambulance transport, and minor invasive medical procedures, including joint injections. [6]

Less commonly, self-administered nitrous oxide is reported for chronic pain from terminal illness and pain associated with cancer treatment. [6]

Nitrous oxide use in children undergoing basic procedures including lumbar puncture, venous cannulation, or dressing changes has demonstrated a significant reduction in pain levels, allowing for a shorter recovery. [7, 8] The children who were administered nitrous oxide displayed less anxiety and distress during medical procedures. [7] A 2009 prospective, randomized study showed that a 70:30 mix of nitrous oxide in oxygen, administered for 3 minutes, was effective in reducing pain in children undergoing venipuncture. [8]

Nitrous oxide has been proven beneficial in young children receiving injections for juvenile arthritis. [9] Additionally, nitrous oxide has been used successfully as an anesthetic for children undergoing minor surgeries such as cyst surgery and abscess drainage. [5]

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Absolute contraindications

Overall, nitrous oxide is a very safe drug with few absolute contraindications.

Nitrous oxide is contraindicated in patients with significant respiratory compromise. [10]

The blood:gas partition coefficient of nitrous oxide is 34 times greater than that of nitrogen. This differential solubility means that nitrous oxide can leave the bloodstream and enter air-filled cavities 34 times faster than nitrogen. As a result, nitrous is contraindicated in patients in whom expansion of these air-filled cavities could compromise patient safety. This includes patients with pneumothorax, pulmonary blebs, air embolism, bowel obstruction, and those undergoing surgery of the middle ear.

Nitrous oxide is absolutely contraindicated in patients who have had eye surgery that uses an intraocular gas. [11, 12, 13, 14, 15]

Relative contraindications

Caution must be exercised in individuals with a history of stroke, hypotension, and known cardiac conditions.

Nitrous oxide is known to interfere with vitamin B12 and folate metabolism. In patients with these preexisting conditions, nitrous oxide should only be used with full precautionary consideration and close monitoring. Particular precautions should be taken in pediatric patients with underlying vitamin B12 deficiency (genetic or environmental) and conditions related to vitamin B12 deficiency. [16]

Nitrous oxide is relatively contraindicated in pregnancy. It is known to have potential teratogenic and fetal toxic effects, particularly with chronic use.

Dental contraindications

Dental nitrous oxide may be contraindicated in patients with severe nasal congestion, those who breathe through their mouths, or those unable to wear a nasal mask.

Some patients, especially children experiencing severe anxiety or extreme uncooperativeness, may not be good candidates for this milder therapy and may require more potent sedating intravenous or general anesthesia.

See the list below:

Since its discovery, nitrous oxide has been used widely by practitioners without an extensive comprehension of the complete functions of the gas. Nitrous oxide is a weak general anesthetic and is generally not used alone. It may be used in general anesthesia in a 70% concentration (in combination with 30% oxygen) or as a carrier gas with more potent general anesthetic agents. It has a blood:gas partition coefficient of 0.46 and a minimum alveolar concentration (MAC) of 105%. Its use as an anesthetic is appealing because of its ability to initiate a timely and brisk emergence from anesthesia (generally < 3 min). [3] Nitrogen gas is known to assist in prevention of atelectasis via splinting of the alveoli. [1]

Debate regarding the safety and efficacy of this commonly used inhalant anesthetic is ongoing among anesthesiologists. [3] Some anesthesiologists advocate abandonment of the drug and others use it routinely.

Nitrous oxide use in westernized countries seems to have decreased and is being replaced with other more potent, safe, and short-acting inhalation anesthetics (eg, sevoflurane, desflurane). However, nitrous oxide is still widely used in developing countries because it is inexpensive, readily available, easily administered, and has a long-standing safety record.

Nitrous oxide is reported to be safe in patients with a history of malignant hyperthermia. Since it is metabolized by the lungs, it does not have any associated nephrotoxicity or hepatotoxicity.

Nitrous oxide has been used for obstetric analgesia (primarily outside of the United States). Nitrous oxide is often times mixed in a 1:1 ratio with oxygen; the mixture is otherwise known as Entonox. [17] Labor pains have been shown to significantly decrease with the use of Entonox.

The mechanism of action of nitrous oxide is trifold and includes analgesia, anxiolysis, and anesthesia.

Its analgesic mechanism of action is described as opioid in nature and may involve a number of spinal neuromodulators.

The anxiolytic effect is similar to that of benzodiazepine and may involve gamma aminobutyric (GABA) receptors.

The anesthesia mechanism may involve GABA and possibly N-methyl-D-aspartate receptors as well. [6] In general, the effect of nitrous oxide ceases as soon as the inhalation stops, with no residual effect.

In a retrospective review by Wu et al of the use of nitrous oxide pneumoperitoneum in conjunction with laparoscopic peritoneal dialysis insertion in 87 patients, nitrous oxide was well tolerated by 94% of the patients. Five patients required conversion to general anesthesia. [18]

Myles et al conducted a randomized, single-blind trial to examine whether the use of nitrous oxide increases perioperative cardiovascular risk in patients with known or suspected coronary artery disease who undergo major noncardiac surgery. Of 7,112 patients, 3,543 were assigned to receive nitrous oxide, and 3,569 were assigned not to receive nitrous oxide. The primary outcome measure, a composite of death and cardiovascular complications (nonfatal myocardial infarction, stroke, pulmonary embolism, or cardiac arrest) within 30 days of surgery, occurred in 283 patients (8%) receiving nitrous oxide and in 296 patients (8%) not receiving nitrous oxide. Surgical site infection occurred in 321 patients (9%) receiving nitrous oxide and in 311 patients (9%) who did not receive nitrous oxide. Severe nausea and vomiting occurred in 506 patients (15%) receiving nitrous oxide versus 378 patients (11%) not receiving nitrous oxide. The investigators concluded that it is safe to use nitrous oxide in at-risk cardiac patients undergoing major noncardiac surgery; that nitrous oxide does not increase the risk for death, cardiovascular complications, or surgical site infections; and that through the use of nitrous oxide, it is possible to reduce the use of more volatile anesthetic agents. [19]

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Nitrous oxide is stored in closed gas cylinders. Oxygen and nitrous oxide, shown in the images below, are part of the required equipment.

Attached flow meters like the one shown below restrict the proportion as well as the flow rate of nitrous oxide in order to keep a minimum oxygen concentration. This minimum concentration is usually 21% (room air).

Dental administration uses a partial mask that covers the nose but allows access to the mouth.

Surgical anesthesia uses a full face mask that covers the nose and mouth. Alternatively, nitrous oxide may be administered via an endotracheal (ET) tube.

For each method of administration, proper equipment, monitoring, and storage unit integrity are necessary in order to avoid unintended gas leakage or excessive exposure. An example is shown in the image below.

See the list below:

For general anesthesia, most patients are placed in the supine position.

For dental anesthesia, patients are reclined in a seated position.

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Position the patient as described above.

Secure the mask and start the flow of nitrous oxide, as in the image below.

Most commonly, nitrous oxide gas is delivered in a 70:30 mix with oxygen. The 2:1 ratio of nitrous oxide to oxygen is also used in medical anesthesia. The typically administered mix is comparable to the 21% of oxygen present in natural atmospheric air. Less commonly, nitrous oxide may also be safely given in a 50:50 mix with oxygen. [20]

Frequently, patients receive 100% oxygen for 5 minutes once the nitrous oxide flow diminishes. This reduces occurrences of nausea and facilitates clearing of the euphoric and other effects of the nitrous oxide gas. [5]

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Ideally, proper ventilation should include a fresh air ventilation system, a nitrous oxide scavenging system, or both. Because nitrous oxide is not heavily metabolized during inhalation, it may build up in the treatment area, particularly if the room is poorly ventilated. Staff may be affected by the exhaled nitrous oxide and experience some of the same effects as the patient undergoing treatment.

Occupational contact with nitrous oxide has raised some concern regarding potential reproductive hazards of miscarriage, decreased fertility, or increased incidence of cervical cancer in female staff subject to chronic or prolonged exposure. This has been described among dental assistants and the wives of dentists. [7] Animal testing has led to further concern of similar health hazards. [17]

Proper security and safety precautions for the nitrous oxide cylinders may be advised to decrease potential risk of after-hours access and abuse by medical and dental staff.

See the list below:

When used properly, nitrous oxide is a very safe inhalational anesthetic gas. [21] Complications up to and including death have been described. They are relatively uncommon with standard medical and dental use but have arisen from chronic use or recreational abuse. The described adverse effects profile below may be very uncommon and not of primary concern to standard medical practitioners. [22]

Adverse effects that may be associated with nitrous oxide include gagging, coughing, hypotension, asthma attack, involuntary tracheal closure (spasm), lung damage, neuropathy, tinnitus, extremity numbness, anoxia and general respiratory distress, cardiac events (including myocardial infarcts), seizures, misperception of time, and vision-altering perceptions. [23] Additional adverse effects include possible exacerbation of vitamin B12 deficiency, anemia, and decreased hematopoiesis. Further studies may be needed to elucidate these observations.

Postoperative nausea and vomiting (PONV) is described with nearly all inhaled anesthetics including nitrous oxide. [3]

A study by Tsze et al that examined 1634 N20 administrations reported adverse events in 6.5% of administrations with vomiting as the most common (2.4%). Only 3 (0.2%) serious adverse events were reported. The administration of concomitant opioids and nils per os clear fluids 24</ref>

Inadvertent use of nitrous oxide in pregnancy may result in teratogenic and fetal toxic effects. While decreased fertility, spontaneous abortion, and congenital abnormalities possibly associated with nitrous oxide exposure have been reported in the dental literature, the clinical significance and causation of these findings remain unknown. [2]

Short-term impairment in mental performance, manual dexterity, and audiovisual senses has been described with nitrous oxide use. [25] Postoperative neurological symptoms have been described, particularly in patients with known or documented preoperative folate deficiencies. [3] While most adverse effects are reversible, peripheral neuropathies and limb spasms may become nonreversible manifestations. Symptoms of nitrous oxide and B12 deficiency may not appear for days or weeks after known exposure. [16]

Nitrous oxide has been shown to potentially inhibit methionine synthetase and cause an increase in homocysteine (Hcy) levels. Elevated Hcy levels have been correlated with increased postoperative complications, including possible cardiovascular morbidity. [26] The clinical implications of these limited studies may require further confirmation and evaluation.

Nitrous oxide may have neurotoxic effects of unknown significance on both infantile and senescent central nervous systems. [16] The clinical relevance or significance of these effects requires investigation.

Vitamin B12 deficiency should be considered in the differential diagnosis of patients who present with psychiatric or neurological manifestations, especially in those with a clear history of nitrous oxide exposure. [27] Pertinent laboratory testing should include B12, homocysteine, and methylmalonyl coenzyme A (CoA) levels. Although levels of B12 may be low to normal, levels of methylmalonyl CoA and homocysteine may be elevated.

Because of the potential delay in the appearance of clinical symptoms, the history of nitrous oxide exposure may be days to weeks prior to the presentation date. [27] Intramuscular administration of cobalamin may be curative in these cases. Recovery may be slow even with high doses of vitamin B12.

As a commonly abused inhalant drug, it can be habit-forming. Long-term exposure or use has been associated with anemia and other adverse effects related to vitamin B12 deficiency. [2]

Potentially dangerous adverse effects include overdose, hypoxia, severe hypotension, unconsciousness, or death. High nitrous oxide concentrations have been associated with severe hypoxia and death from asphyxiation.

Emmanouil DE, Quock RM. Advances in understanding the actions of nitrous oxide. Anesth Prog. 2007 Spring. 54(1):9-18. [Medline].

Sethi NK, Mullin P, Torgovnick J, Capasso G. Nitrous oxide “whippit” abuse presenting with cobalamin responsive psychosis. J Med Toxicol. 2006 Jun. 2(2):71-4. [Medline].

Browne DR, Rochford J, O’Connell U, Jones JG. The incidence of postoperative atelectasis in the dependent lung following thoracotomy: the value of added nitrogen. Br J Anaesth. 1970 Apr. 42(4):340-6. [Medline].

Coke JM, Edwards MD. Minimal and moderate oral sedation in the adult special needs patient. Dent Clin North Am. 2009 Apr. 53(2):221-30, viii. [Medline].

American Academy of Pediatric Dentistry Council on Clinical Affairs. Guideline on appropriate use of nitrous oxide for pediatric dental patients. Pediatr Dent. 2005-2006. 27(7 Suppl):107-9. [Medline].

Parlow JL, Milne B, Tod DA, Stewart GI, Griffiths JM, Dudgeon DJ. Self-administered nitrous oxide for the management of incident pain in terminally ill patients: a blinded case series. Palliat Med. 2005 Jan. 19(1):3-8. [Medline].

Rosen MA. Nitrous oxide for relief of labor pain: a systematic review. Am J Obstet Gynecol. 2002 May. 186(5 Suppl Nature):S110-26. [Medline].

Furuya A, Ito M, Fukao T, et al. The effective time and concentration of nitrous oxide to reduce venipuncture pain in children. J Clin Anesth. 2009 May. 21(3):190-3. [Medline].

Divatia JV, Vaidya JS, Badwe RA, Hawaldar RW. Omission of nitrous oxide during anesthesia reduces the incidence of postoperative nausea and vomiting. A meta-analysis. Anesthesiology. 1996 Nov. 85(5):1055-62. [Medline].

Sun R, Jia WQ, Zhang P, Yang K, Tian JH, Ma B, et al. Nitrous oxide-based techniques versus nitrous oxide-free techniques for general anaesthesia. Cochrane Database Syst Rev. 2015 Nov 6. CD008984. [Medline].

Tanchyk A, Tanchyk A. The absolute contraindication for using nitrous oxide with intraocular gases and other dental considerations associated with vitreoretinal surgery. Gen Dent. 2013 Sep-Oct. 61 (6):e6-7. [Medline].

Vote BJ, Hart RH, Worsley DR, Borthwick JH, Laurent S, McGeorge AJ. Visual loss after use of nitrous oxide gas with general anesthetic in patients with intraocular gas still persistent up to 30 days after vitrectomy. Anesthesiology. 2002 Nov. 97 (5):1305-8. [Medline].

Hart RH, Vote BJ, Borthwick JH, McGeorge AJ, Worsley DR. Loss of vision caused by expansion of intraocular perfluoropropane (C(3)F(8)) gas during nitrous oxide anesthesia. Am J Ophthalmol. 2002 Nov. 134 (5):761-3. [Medline].

Lee EJ. Use of nitrous oxide causing severe visual loss 37 days after retinal surgery. Br J Anaesth. 2004 Sep. 93 (3):464-6. [Medline].

Nitrous oxide may be a hazard after retinal surgery. BMJ. 2002. 325(7363):[Full Text].

Olfert SM. Reproductive outcomes among dental personnel: a review of selected exposures. J Can Dent Assoc. 2006 Nov. 72(9):821-5. [Medline].

Cleary AG, Ramanan AV, Baildam E, Birch A, Sills JA, Davidson JE. Nitrous oxide analgesia during intra-articular injection for juvenile idiopathic arthritis. Arch Dis Child. 2002 Jun. 86(6):416-8. [Medline].

Wu R, Okrainec A, Penner T. Laparoscopic Peritoneal Dialysis Catheter Insertion Using Nitrous Oxide under Procedural Sedation. World J Surg. 2014 Sep 5. [Medline].

Myles PS, Leslie K, Chan MT, Forbes A, Peyton PJ, Paech MJ, et al. The safety of addition of nitrous oxide to general anaesthesia in at-risk patients having major non-cardiac surgery (ENIGMA-II): a randomised, single-blind trial. Lancet. 2014 Aug 14. [Medline].

Baum VC. When nitrous oxide is no laughing matter: nitrous oxide and pediatric anesthesia. Paediatr Anaesth. 2007 Sep. 17(9):824-30. [Medline].

Zier JL, Liu M. Safety of high-concentration nitrous oxide by nasal mask for pediatric procedural sedation: experience with 7802 cases. Pediatr Emerg Care. 2011 Dec. 27(12):1107-12. [Medline].

Kavanagh T, Buggy DJ. Can anaesthetic technique effect postoperative outcome?. Curr Opin Anaesthesiol. 2012 Jan 19. [Medline].

Zier JL, Doescher JS. Seizures temporally associated with nitrous oxide administration for pediatric procedural sedation. J Child Neurol. 2010 Dec. 25(12):1517-20. [Medline].

Tsze DS, Mallory MD, Cravero JP. Practice Patterns and Adverse Events of Nitrous Oxide Sedation and Analgesia: A Report from the Pediatric Sedation Research Consortium. J Pediatr. 2016 Feb. 169:260-5.e2. [Medline].

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Rowland AS, Baird DD, Shore DL, Weinberg CR, Savitz DA, Wilcox AJ. Nitrous oxide and spontaneous abortion in female dental assistants. Am J Epidemiol. 1995 Mar 15. 141(6):531-8. [Medline].

Burnweit C, Diana-Zerpa JA, Nahmad MH, et al. Nitrous oxide analgesia for minor pediatric surgical procedures: an effective alternative to conscious sedation?. J Pediatr Surg. 2004 Mar. 39(3):495-9; discussion 495-9. [Medline].

Myles PS, Chan MT, Leslie K, Peyton P, Paech M, Forbes A. Effect of nitrous oxide on plasma homocysteine and folate in patients undergoing major surgery. Br J Anaesth. 2008 Jun. 100(6):780-6. [Medline].

Myles PS, Leslie K, Chan MT, et al. Avoidance of nitrous oxide for patients undergoing major surgery: a randomized controlled trial. Anesthesiology. 2007 Aug. 107(2):221-31. [Medline].

Freed WJ, Cannon-Spoor HE, Rodgers CR. Attenuation of the behavioral response to quisqualic acid and glutamic acid diethyl ester by chronic haloperidol administration. Life Sci. 1989. 44 (18):1303-8. [Medline].

Ally N Alai, MD, FAAD Medical Director, The Skin Center at Laguna; Former Professor, Department of Dermatology, Clinical Faculty and Preceptor, Department of Family Practice, University of California, Irvine, School of Medicine; Former Professor and Preceptor, Department of Family Practice Residency Training, Downey Medical Center; Expert Medical Reviewer, Medical Board of California; Expert Consultant, California Department of Consumer Affairs; Expert Reviewer, California Department of Registered Nursing

Ally N Alai, MD, FAAD is a member of the following medical societies: American Academy of Dermatology, American Society for MOHS Surgery

Disclosure: Nothing to disclose.

Karina R Ritter, RN University of California at Irvine

Disclosure: Nothing to disclose.

Siamak T Nabili, MD, MPH Assistant Clinical Professor, Department of Internal Medicine, University of California Irvine, School of Medicine; Hospitalist, Saddleback Memorial Hospital, Mission Hospital, South Coast Medical Center; Vice Chairman, Department of Internal Medicine, South Coast Medical Center

Siamak T Nabili, MD, MPH is a member of the following medical societies: American Academy of Hospice and Palliative Medicine, American College of Physicians-American Society of Internal Medicine

Disclosure: Nothing to disclose.

Arash M Saemi, MD Resident Physician, Department of Radiology, Dartmouth-Hitchcock Medical Center

Arash M Saemi, MD is a member of the following medical societies: American College of Physicians, Radiological Society of North America, Sigma Xi, Society of Interventional Radiology

Disclosure: Nothing to disclose.

Ghada Aluzri, MD President, West Coast Anesthesia; Anesthesiologist, Pacific Hills Surgical Center, Huntington Reproductive Center

Ghada Aluzri, MD is a member of the following medical societies: American Society of Anesthesiologists

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Jeff Burgess, DDS, MSD (Retired) Clinical Assistant Professor, Department of Oral Medicine, University of Washington School of Dental Medicine; (Retired) Attending in Pain Center, University of Washington Medical Center; (Retired) Private Practice in Hawaii and Washington; Director, Oral Care Research Associates

Disclosure: Nothing to disclose.

Muna Soltan, DDS, FAGD Consulting Staff, Riverside Kaiser Permanente Hospital

Disclosure: Nothing to disclose.

Shahriar Alikhani, MD Attending Anesthesiologist, Mission Hospital Regional Medical Center and Children’s Hospital of Orange County

Shahriar Alikhani, MD is a member of the following medical societies: American Society of Anesthesiologists, International Anesthesia Research Society, Phi Beta Kappa, Society for Pediatric Anesthesia

Disclosure: Nothing to disclose.

The authors would like to extend their appreciation to Dr. Muna Soltan, Dr. Shahriar Alikhani, Dr. Ally Alai, and The Skin Center at Laguna for their contribution of clinical photos for this topic.

Nitrous Oxide Administration

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