Nitrous Oxide, From Discovery to Now - IneedCE.com

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For example, in those with sinus problems and blocked eustachian tubes, nitrous oxide can cause increased pressure in the middle ear cavity, producing painful distention of the tympanic membrane. Certain ophthalmology surgeries inject gas into the ocular orbit; here, nitrous oxide should be turned off. Further, in cases of abdominal obstruction or those with colostomy bags, nitrous oxide can inflate either the bowel or the bag and prove problematic. Although nitrous oxide is inhaled and exhaled with negligible metabolism, it can affect certain enzyme systems and, in cases of chronic exposure, cause irreversible changes. It is well known that nitrous oxide inactivates the Vitamin B-12-dependent enzyme methionine synthetase. Long or repeated exposures to high concentrations can lead to megaloblastic changes, bone marrow depression and possible neurologic dysfunction. Recent studies, however, have revealed that when nitrous oxide is used during routine clinical practice, these effects on patients, if measurable at all, are very short-lived. Usually the changes correct to normal within 24–48 hours, and the occurrence of clinical symptoms is a very rare occurrence, even in patients with mild folate deficiency. As with any mood-altering substance, nitrous oxide can be abused. Chronic, long-term abuse can lead to more prolonged inactivation of the methionine synthetase enzyme. This, in turn, can lead to more severe megaloblastic changes, peripheral cytopenia, and bone marrow depression. A resultant pernicious anemia-like state may develop causing peripheral numbness, paresthesias, and lack of coordination. In extreme cases, death can ensue. With this in mind, one must consider the effect on healthcare workers of chronic exposure to trace amounts of nitrous oxide. Currently, the United States National Institute for Occupational Safety and Health (NIOSH) arbitrarily sets a safe trace value of nitrous oxide at 25 ppm. Recent studies would suggest that this value is very low. Workers exposed to trace amounts of 450 ppm nitrous oxide showed no adverse effects or measurable laboratory changes. Some have recommended to split the difference and increase the safe, accepted limit to 200 ppm; however, this will probably not happen until a number of studies corroborate these findings. Indications Nitrous oxide is a very safe and popular agent utilized by many dental practices. In this setting, its use is usually as a mild sedative and analgesic. It helps to allay anxiety many patients may have toward dental treatment, and it offers some degree of analgesia. As such, its use for phobic patients has been well established and remains its primary indication. However, other benefits of nitrous oxide can be utilized. For patients with a hyperactive gag reflex, nitrous oxide can be administered to help minimize this problem. For patients with certain medical disorders in which stress and the release of endogenous catecholamines can have a deleterious effect, the sedative effects of nitrous oxide can prove beneficial. Some of these disorders include hypertension, angina, previous myocardial infarction, previous cerebrovascular accidents, seizure disorders, diabetes, and, in some cases, asthma. Both the sedative and analgesic properties can be utilized for those procedures that tend to be more pain-inducing, or where local anesthetic effectiveness is diminished. Examples include oral surgery, periodontal surgery, procedures in areas of infection or procedures where access to the pulp is necessary. In the pediatric population, nitrous oxide can be used to help aid behavior management in those children in whom more conventional measures have proven unsuccessful. As mentioned earlier, nitrous oxide is also indicated as an adjunct agent during general anesthesia. Here, its additive effects can help minimize the doses and concentrations of other more potent intravenous and inhalational agents. Contraindications As appropriately stated in Malamed’s text on sedation, there are virtually no absolute contraindications to the use of nitrous oxide; however, there are some relative contraindications. Some of these relative contraindications include those patients with mental or psychiatric disorders in whom mood alteration may not produce the desired effect. Further, prior to the use of nitrous oxide, the practitioner should explain to the patient what effects to anticipate, including those that are beneficial and those that are not. As such, this can prove problematic in those patients in whom communication is limited due to mental or developmental disabilities or cultural or language barriers. In dentistry, since nitrous oxide is usually administered via a nasal hood, patients with blocked sinuses or mouth breathers garner little benefit. Further, patients with blocked eustachian tubes, as mentioned earlier, can experience ear pain due to distention of the tympanic membrane. This can be relieved by merely discontinuing the administration of nitrous oxide. Related to this cavity expanding phenomenon, nitrous oxide can prove problematic in those patients with bowel obstruction, colostomy bags, gas in the ocular orbit, large tubercular lesions in the lung, etc. Although nitrous oxide can be safely administered to most asthmatics and those with other forms of chronic obstructive pulmonary disease (COPD), there is a small subset of these patients in whom its use is not prudent. Those patients with severe pulmonary disease who utilize hypoxic drive (lack of oxygen) to stimulate breathing, rather than the normal mechanisms mediated by carbon dioxide accumulation, reflect a relative contraindication to the use of nitrous oxide. This is due to two reasons. First, these patients are usually more sensitive to the sedative effects of nitrous oxide. Second, supplemental oxygen is also administered with nitrous oxide, increasing the patient’s oxygen uptake, thereby removing the stimulus to breathe. 4 www.ineedce.com
Past reports of possible increased rates of spontaneous abortion related to nitrous oxide exposure exist. Although these early claims rely more on anecdotal evidence rather than scientifically reproducible fact, this still remains an area of controversy. As such, until definitively proven, elective nitrous oxide use in the pregnant population (especially in the first trimester) is best discouraged. In this situation, consultation with the patient’s obstetrician is strongly advised. Administration The newer flowmeters used in dental practice administer nitrous oxide and oxygen simultaneously and do not allow more than approximately a 75 to 25% ratio, respectively, to be administered. Also, when oxygen pressure ceases, most flowmeters cut nitrous oxide administration. These are current safeguards in place to enhance the safety of nitrous oxide administration. Older machines may not have these safeguards. Also, there should be no fewer than two office personnel (the doctor and an assistant, preferably of opposite sex) present with the patient while nitrous oxide is being administered. This is because, while under the influence of nitrous oxide, some patients can experience sexual dream states that they cannot distinguish from reality. This has led to erroneous allegations by patients, and it is a situation that is very easy to avoid. When administering nitrous oxide to patients, some simple points should be remembered. First, nitrous oxide is not a potent agent. It will not be successful all the time; therefore, expect some failures. Second, nitrous oxide works best in those situations where its use is planned and discussed with the patient beforehand. An attempt to use it as a rescue agent after an unpleasant situation has developed will have little chance of being effective. Third, patients should be informed as to what sensations they will experience when adequately sedated. These can include light-headedness, euphoria, tingling of extremities, and decrease in anxiety. They should also be informed as to what sensations they will experience if the clinical endpoint has been exceeded. These may include auditory changes, profuse sweating, crying, excessive dreaming or nausea. For dental use, nitrous oxide has some unique advantages. The onset time is very rapid and it is easily titrated up or down by adjusting the administered concentrations. It does not require an injection or venipuncture. Also, it is usually not necessary for the patient to be NPO (although Quick Reference Nitrous Oxide/Oxygen Sedation Administration Considerations & Recommendations 1. To help decrease patient anxiety and stress, schedule sedation appointments early in the day and do not keep the patient waiting for an extended time in the reception area. 2. Consider making patient NPO or recommend only a light meal prior to sedation. Consider a patient escort if necessary. 3. Obtain either patient, parental or legal guardian consent prior to any sedative procedure. 4. Take preoperative and postoperative vital signs on day of the appointment. 5. Position patient where treatment will take place to minimize motion after sedation is initiated. 6. Estimate flow rates based on the patient’s ventilation and adjust up or down based on expansion of the reservoir bag. (Ventilation may be approximated by estimating Tidal Volume [TV] as 10 cc/kg. of body weight with a respiratory rate of 10–12 breaths per minute [adult] or 16–24 breaths per minute [child]). 7. Begin sedation with 100% oxygen and titrate nitrous oxide upward by 10% every 60 seconds or so until desired endpoint achieved. If signs of over-sedation occur, decrease nitrous oxide concentration by 5% increments until patient comfort is achieved. 8. Administer 100% oxygen after cessation of nitrous oxide for at least 5 minutes. 9. Discharge patient when fully clinically recovered. 10. Expect and be prepared for occasional failures and complications! Day Of Appointment 1. Seat patient and obtain preoperative vital signs. 2. Adjust chair to working position. 3. Apply nasal hood, administer 100% oxygen, and adjust flows to patient’s ventilation. Titrate nitrous oxide 10% every 60 seconds to endpoint. 4. Begin treatment. 5. Discontinue nitrous oxide toward end of procedure and administer 100% oxygen for at least 5 minutes. 6. Obtain postoperative vital signs. 7. Discharge patient when fully clinically recovered. (a.) For pediatric behavior management, consider initiating sedation with 70% nitrous oxide to 30% oxygen until control is obtained and local anesthetic is administered, then titrate nitrous oxide concentration downward to maintenance levels of 25–40% until procedure is completed. (b.) Most patients will respond appropriately at 25–40% nitrous oxide. If not appropriately sedated by 50% nitrous oxide, then higher concentrations will probably be ineffective or cause unwanted side effects. www.ineedce.com 5
Page 1 and 2: Earn 4 CE credits This course was w
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