Aiding in the administration of nitrous oxide-oxygen analgesia

Preanesthetic Preparation

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Preanesthetic Preparation

The first step to preparing for administration of nitrous oxide is turning on the main tanks containing nitrous oxide and oxygen. Tanks should always be turned on slowly to avoid a

build-up of heat, and cylinders and gauges should be checked to be certain that both tanks are full. Procedure for this will vary, therefore, manufacturer’s instructions should be read carefully prior to operating any equipment.
The patient is seated comfortably and, as discussed previously, medical history and vital signs are checked. The analgesic machine should be positioned behind the patient with controls readily visible and easily accessible to the operator. The appropriate size nosepiece is selected to fit snuggly over the patient’s nose without causing an inability to breath or leakage around the sides. The nosepiece should be cleaned with a cold sterilizing agent rather than alcohol, since alcohol dries out the rubber and causes it to crack.
Prior to administration of nitrous oxide, the operator should discuss the procedure with the patient. The number one rule is to ALWAYS BE POSITIVE when discussing techniques and effects with patients. Describe expected results in positive terms. Tell the patient that they will feel relaxed, warm, and comfortable. Answer any questions they may have honestly; yet, do not use negative terminology. For example, a patient might ask, “Does this N2O make you feel drunk or nauseous?” You can respond that, “With proper administration, both of these side effects are rare; you should feel very relaxed.” At the same time that you are honestly answering the question, you are also reassuring the patient. It is important that you review all of the clinical manifestations of each plane of analgesia at this time in order to become familiar with each one so that you are capable of answering questions for the patient.
Once the patient had been informed of all procedures and effects, consent to the administration of nitrous oxide can be obtained. If the patient agrees to proceed, administration of nitous oxide is begun.

Techniques for Administration

The traditional nosepiece has an air valve in the center which should be opened about halfway prior to placing the nosepiece on the patient’s face. When using a scavenging mask, there is no valve that needs adjustment. Oxygen flow is begun at this time. The reason for completing these two procedures prior to placement of the nosepiece is to avoid causing a feeling of suffocation when covering the patient’s nose. Be certain that the tubing from the machine to the nosepiece is not tangled to provide for a smooth, even flow of gases. Place the nosepiece over the patient’s nose and ask him/her to breath normally while only oxygen is flowing in order to provide a period of adjustment to breathing out of the nosepiece.

At placement time, the oxygen is set at 8 liters. As mentioned earlier, the gauge in the nitrous oxide-oxygen machine will have numbers which represent liters of gaseous flow. Often lines between the numbers will indicate half liters. A small ball will rise and fall by turning the knob marked green for oxygen. Turn this knob until the ball reaches 8 liters on the gauge. After placing the nasal mask, ask the patient if this volume is comfortable for their respiration. It may need to be adjusted up or down for their needs. (5-10 L./min.).
After the patient has had a few minutes to adjust to breathing normally, flow of nitrous oxide can be begun. Stress that the patient should continue to breath through the nose since mouth breathing will cause an additional intake of oxygen from the room air, thereby, changing the ratio of gases. Patients can be informed that breathing through the mouth causes increased oxygen inhalation; therefore, they can regulate the effects of nitrous oxide by taking in room air if they feel that the nitrous oxide is a little stronger than desired. Request that they inform you if this should happen, so that you can adjust the flow of the gases accordingly. Talking will have the same effect as mouth breathing; therefore, patients should not talk in excess or the nitrous oxide will be diluted with room air. Observe the reservoir bag to be sure that the patient is breathing at a normal rate through the nose hood.
When the patient is breathing normally through the nosepiece, nitrous oxide flow can be started. At this time, the air valve on the nosepiece is closed slightly to prevent leakage of nitrous oxide into the room air. In the trituration techniques described in this module, the total flow of gas(es) will always remain constant. Thus, if the clinician begins with 8 lpm (liters per minute) the total amount of N2O and O2 administered will always equal 8 lpm. The first adjustment to begin N2O administration should equal about 20% N2O and 80 % O2. Since 20% of 8 lpm is appropriately 1.5 lpm, the nitrous oxide would be started at 1.5 lpm and the oxygen would be reduced

(from 8 lpm) to 6.5 lpm. Note that 1.5 l and 6.5 l equals the eight liters total flow with which the administration was started. Each time the nitrous oxide is increased ½ liter, the oxygen is decreased ½ liter. (Note: After each adjustment, wait one minute before adjusting these levels again, observing the patient’s reactions.) In this way, a total flow of 8 liters is maintained continuously. The oxygen is begun at 8 liters; 1 ½ liters of nitrous oxide (N2O) is administered and the oxygen (O2) is decreased to 6 ½ liters; therefore, a total of 8 liters is maintained. Continue decreasing the oxygen by ½ liter followed by increasing the nitrous oxide by ½ liter and observing the patient’s response, (i.e., 6 liters O2 and 2 liters N2O then observe; 5 ½ liters O2 and 2 ½ liters N2O then observe; and so on). The last adjustment of N2O should be made when the oxygen and the nitrous oxide are each at 4 liters, again totaling 8 liters. At this point, 50 percent O2 and 50 percent N2O are being administered. This is the highest ratio of nitrous oxide recommended for safe administration without special consideration. The importance of maintaining an appropriate ratio of oxygen to nitrous oxide cannot be over-stressed. Remember that detrimental effects of nitrous oxide are caused by hypoxia. This is why oxygen is administered simultaneously with nitrous oxide.

In order to compute the ratio of oxygen to nitrous oxide, divide the total flow of combined gases (in this case, 8 liters) into the liters of nitrous oxide being administered. For example, if your gauges are set at 5 liters O2 and 3 liters N2O, you would divide 8 (total liters) into 3 (N2O liters) to find that .37 or 37 percent nitrous oxide was being administered. Next, subtract the percentage of nitrous oxide from 100 percent (total flow) to determine the percentage of oxygen being administered. In this example, 37 percent (N2O) from 100 percent equals 63 percent oxygen. The ultimate ratio of nitrous oxide to oxygen should be recorded for each administration.
Remember, it takes one minute for any change in dosage to become evident. For this reason, the patient should be observed closely before readjusting the knobs. Carefully monitor the signs and symptoms of the patient. You can communicate with your patients to determine level of analgesia as long as they are not required to talk excessively, thereby inhaling too much room air. Be sure to use direct, specific questions while monitoring the patient. Ask, “What are you feeling?” rather than “How are you feeling?” Ask, “Are you breathing comfortably?” or “Do you feel warm and relaxed?” It is a good idea to tell patients you will use their name when speaking to them. Patients may drift in and out of the environment and should be able to relax. With these instructions, they will not feel forced to attempt to stay alert, listening to the operators. They will, however, be able to respond and cooperate when addressed by name.
Another suggestion is to inform the patient of the time frame occasionally, since time is often distorted under the effects of nitrous oxide. Tell the patient how long they have been there in relation to time remaining. For example, you might say, “You have been here for 20 minutes and we are about half-way through your treatment.”
When the patient reaches the appropriate level (generally, plane two of the analgesia), the dental treatment planned can be begun. The patient will feel relaxed and comfortable; and may feel drowsy and warm; or may drift in and out of the environment, but will still be able to cooperate. Clinical signs and symptoms should continue to be monitored closely for any change so further adjustments can be made if necessary.
If patients become irritated or they can no longer cooperate and their mouth tends to close, plane three is being approached. This is an indication that the nitrous oxide level is too high. Also, changes in physical symptoms, such as dilation of pupils or nausea, would be an indication of too much nitrous oxide. At this point, the clinician should take three steps to rectify the situation:
1. Reduce the level of nitrous oxide or turn it off depending upon severity of the side effect or reaction;
2. Increase the level of oxygen; and
3. Reassure the patient
All models of nitrous oxide-oxygen analgesia machines have a device called an oxygen “flush valve.” When turned on, the breathing bag fills with oxygen rapidly at a flow of about 50 liters per minute. Any time that pure oxygen is needed quickly, the flush mechanism can be employed. This may become important in an emergency situation.
Since emergencies occur without notice and analgesia levels fluctuate, it is important to monitor the patient continuously while nitrous oxide is being administered. NEVER leave a patient unattended while under the effects of nitrous oxide. Some references suggest retaking vital signs during dental treatment to compare baseline data. Remember, vital signs will remain normal with proper levels of analgesia. The ratio of oxygen to nitrous oxide should be maintained at a comfortable level according to the patient’s response. Table 5 presents a few common clinical findings with appropriate procedures to follow in each.

T A B L E 5
Clinical Findings during Maintenance Period

and Appropriate Procedures to Follow



  1. Reduced activity of the eyes (either closed or comfortably fixed toward the ceiling).

Means good sedation. No changes needed.

  1. Increased activity of the eyes.

Usually too light. Best to ascertain status by direct questioning. Probably needs positive verbal support and an increased N2O-O2 ratio.

  1. Fixed, hard stare of the eyes (possibly with dilation of pupils).

Too deep; approaching excitation stage. Reduce N2O to O2 ratio. Supply verbal and physical contact.

  1. Arms and legs crossed.

Patient is not relaxed yet. Needs more N2O and suggestions designed to achieve relaxation. (“As you feel your arms becoming more and more relaxed, let them rest naturally and comfortably by your side, and as you feel your legs becoming more and more relaxed, let them uncross and rest naturally and comfortably.”)



  1. Patient talks too much.

Too light due to mouth-breathing. Place rubber dam or cotton rolls and holder. Be aware of too much N2O when patient finally stops talking. May bring on sedation frighteningly fast.

  1. Patient talks too much.

Too light. May need to improve fit of nosepiece or prevent dilution with air or increase N2O or both.

  1. Patient answers slowly and deliberately.

Good sedation. No changes needed.

  1. Patient does not answer.

May be: 1) tired and asleep or 2) too deep. If no pre-medication was used and ratio of gases is such that anesthesia could not be produced (i.e., 30% N2O), either no change or reduced N2O. If in doubt, arouse patient by physically prodding and check verbally.

  1. Perspiration appears on face.

Indicates onset of peripheral vasodilation. No change in ratio of gases needed. Reassure patient that this is expected and will pass. Remove outer garments for use after the appointment and cover with light blanket to reduce rate of evaporation and loss of body heat.

  1. Paraesthesia (numbness or tingling) of extremities.

Indicates early phase of Stage 1 and is closely related to peripheral vasodilation phenomenon. Reassure patient that this is “just as it should be.” If no other changes occur in one or two minutes, increase ratio of N2O to O2 to achieve Plane 2.

  1. Paraesthesia (numbness or tingling) of lips, tongue or oral tissues.

Indicates more profound depth, probably achieving analgesia, and permits injections of local anesthetic to be given comfortably. After the injections, the N2O may be reduced or turned off unless needed to control apprehension.

Adapted from: Langa, Harry, D.D.S. Relative Analgesia in Dental Practice.

After dental treatment is completed, pure oxygen is administered to stabilize the patient before dismissal. Turn the nitrous oxide completely off and increase the oxygen to 8 liters to “oxygenate” or “flush” the patient with oxygen. Pure oxygen should be administered for a minimum of 3-5 minutes following nitrous oxide analgesia. Oxygen should be administered until the patient regains “normalcy.” It may take longer for some patients to return to normal than others. When oxygenating the patient, inform him/her that you are turning off the nitrous oxide and that, while breathing pure oxygen, the symptoms will disappear. An estimated 38 percent of the effects of nitrous oxide are psychological.
Once the patient feels normal again, vital signs should be taken again and compared to the baseline data. An operator who releases a patient who has not regained normalcy can be held legally liable for any harm that results. For this reason, oxygenation is essential. Also, if a patient is permitted to breath room air immediately after inhalation of nitrous oxide-oxygen, “diffusion anoxia” can result. If the patient is adequately flushed with oxygen, this condition can be prevented. Once the patient is oxygenated and reports that he/she feels normal, the patient can be dismissed. Some sources suggest administering a connect-the-dots test to patients to test their coordination prior to dismissal. After the patient is dismissed, a legal chart entry should be recorded.
Legal Chart Entries and Other Legal Considerations
There are two major reasons for being certain to record administration of nitrous oxide completely and accurately. First, in the event of a complaint by the patient or a malpractice suit, the dental chart will be considered a primary source of evidence. Second, dosage levels vary from patient to patient and even with the same patient on a day-to-day basis. Factors contributing to the variance include: amount of food or drink consumed prior to the appointment; mental and/or emotional state of the patient at any specific point in time; amount of sleep or physical condition of the patient; and increased tolerance with repeated administration. This is why the trituration technique presented in this module suggests beginning with pure oxygen and increasing nitrous oxide slowly at each patient appointment. It is not safe to assume that the previous analgesic level will be appropriate on sequential visits. A very rapid induction also might cause nausea or other adverse reactions.
A complete and accurate chart recording included the following information:
1. patient’s vital signs (pre and post-op);
2. consent of the patient was granted;
3. routine information including date, procedure performed, and information given to the patient;
4. maximum levels of nitrous oxide and oxygen stated in terms of percentages of each gas administered and total volume used;
5. length of administration;

6. any other anesthetics, premedication, or post medication administered.

7. length of oxygenation and patient’s report of feeling normal prior to dismissal;
8. any side effects or complications incurred, or the fact that none occurred.
A sample chart entry follows:
9/15/90 MH reviewed; pulse 75, PB 125/82, resp. 16; consent for N2O obtained; 73% O2, 27% N2O for 20 min.; 3% Carboncaine 1.2 ml inf. alv.; amalgam #30 MOD; 8 liter O2 for 5 min. until patient reported normalcy; no complications, post-op vital 70, 120/80, 16.
Additional considerations necessary for the ethical and legal administration of nitrous oxide should be made. Emergency equipment must be readily available at all times. Be certain to follow all previously discussed precautionary measures including: taking a thorough medical history including vital signs; making sure that the patient has regained normalcy prior to dismissal; obtaining consent of the patient before administration of nitrous oxide; and documenting the procedures thoroughly.
It is essential that any clinicians involved in the administration of nitrous oxide complete specific training prior to use. This is important for safety of the patient as well as legal protection for the operator. The dentist, dental hygienist and/or assistant can be held liable in any civil or malpractice suits filed by the patient.
Idaho State Board of Dentistry Rules and Regulations state that dental assistants who have completed training and obtained certification can “aid in the administration of nitrous oxide.” This rule has been interpreted to mean that dental assistants can monitor the patient and adjust levels of nitrous oxide to lower concentrations after nitrous oxide-oxygen analgesia has been administered by a licensed dentist. Dental assistants are not certified to legally administer nitrous oxide to patients or to begin induction.
A related consideration is liability insurance. Prior to utilizing nitrous oxide in the dental office, the liability policy must be cleared with the insurance carrier. Cost might be increased by a minimal amount; however, the increased cost is balanced by increased ability in patient management.
This completes instruction in the procedure for administration of nitrous oxide. Since the discussion presented was lengthy including explanations and justifications for each step, Table 6 presents a summary of steps to follow. Be certain to become totally familiar with the procedure prior to continuing.

T A B L E 6
Summary of Steps in the

Procedure for Administration of N2O



Pre-anesthetic Preparation

  1. Have patient visit the restroom.

  2. Check all equipment.

  3. Turn on main tanks and analgesic machine.

  4. Review medical history and take vital signs.

  5. Explain procedure and effects to patient and obtain consent.

  6. Select appropriate size nosepiece and clean with cold sterilizing agent.

During Administration

  1. Open air valve in nosepiece.

  2. Begin flow of O2 at 8 liters.

  3. Place nosepiece over patient’s nose allowing breathing adjustment time.

  4. Slightly close air valve in nosepiece.

  5. Begin N2O at 20% concentration (1.5 lpm) and O2 at 80% 6.51 lpm).

  6. Observe patient for one minute prior to changing dosage.

  7. Increase N2O by ½ liter and decrease O2 by ½ liter until desired effect is obtained.

  8. Monitor clinical manifestations, closely adjusting levels as needed after waiting one minute.

  9. Oxygenate patient until normalcy is regained (minimum 3 to 5 minutes).

Legal Chart Entry and Considerations

  1. Record a complete and accurate legal entry.

  2. Have emergency equipment readily available.

  3. Complete proper training prior to administration.

  4. Check with liability insurance carrier.



Many references state that nitrous oxide is the safest of all anesthetic gases. Some literature states that there is no harm associated with nitrous oxide at all. There are also many studies which show detrimental effects due to nitrous oxide. Problems with these studies leave some question relevant to their validity. Often, nitrous oxide is not isolated for study. It is tested in operating rooms where other anesthetic gases are employed simultaneously. Most results from studies which do isolate nitrous oxide have consisted of laboratory investigations on animals. Finally, extremely high levels and prolonged administration have been utilized for testing purposes.

Levels and length of administration seem to contribute to a significant difference in results. The lower level of nitrous oxide employed and less prolonged administrations have shown lesser or no detrimental side effects. In addition, nitrous oxide had been shown to exhibit addictive properties and to increase susceptibility to suggestion. Literature has documented some detrimental effects related to occupational exposure to trace amounts of nitrous oxide.

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