chapter 15 Inhalation Sedation: Techniques of Administration
The administration of nitrous oxide-oxygen (N2O-O2) for pharmacosedation is a very easy and straightforward procedure. It requires an approved sedation unit, a trained administrator, and a patient desiring sedation. Proper training conveys confidence to the patient and, as a result, an expectation of a successful outcome. Training, as defined by the American Dental Association guidelines, requires instruction in pain and anxiety control consisting of 14 hours of course content, including a clinical component during which competency in inhalation sedation technique is achieved.1 Even though N2O-O2 is considered a very safe drug, a number of unpleasant and potentially dangerous complications can still develop. Therefore the person responsible for the administration of N2O-O2 must be aware of these potential problems; know how to prevent them from occurring and how to recognize and manage them.
Some operators insist in turning on a sedation unit to a fixed percentage of N2O. This fixed percentage is either arbitrary or the one that was used at a previous appointment. This concept clearly violates the principle of titration, which allows for the correct amount (percentage) of N2O-O2 for the desired level of sedation. Titration, an important concept in the administration of any drug to a patient, is the primary guiding principle along with monitoring the patient for depth of sedation. Titration for each appointment is necessary both to compensate for individual variation in patient response to N2O and because patients may respond differently at each appointment and may not require the same level of sedation for different procedures. The ability to quickly increase or decrease flow of N2O permits every patient to achieve the level of sedation that he or she and the administrator are seeking. It allows for comfortable sedation for those who are difficult to sedate and those who are easily affected by the gas.
The techniques described emphasize titration as the guiding principle to successful N2O-O2 administration for both the patient and the administrator. This will result in fewer adverse side effects (e.g., nausea, vomiting, or poor behavioral reactions) and an overall normal pleasant experience.
The technique of inhalation sedation for the cooperative adult patient (an apprehensive patient who willingly accepts the nasal hood) is as follows. Management of the more difficult patient, such as the child or adult with a disability or the pediatric patient, is described in Chapters 35 and 38.
The following description of the administration of N2O-O2 applies to the adult patient (teenager included) who willingly accepts the nasal hood, is able to breathe through the nose, and is able to sit in the dental chair without involuntary muscular movements interfering with the procedure. The technique of administration will differ slightly for a patient who has never before received N2O-O2. At appropriate points in the technique, these differences are explained.
A patient who has a deep fear or phobia of dentistry may not be a candidate for N2O-O2 administration. N2O-O2 is not effective in patients with severe fear and/or phobias. Whether the patient has a deep fear or phobia is best determined through an appointment for discussion and possible demonstration of the use of N2O-O2. Because fear of the unknown often leads to phobias, an appointment to discuss N2O-O2 procedures in advance can help identify potential candidates for its use. The ideal time to introduce an apprehensive patient to inhalation sedation for the first time is not at an appointment at which actual dental or surgical treatment is scheduled. A further increase in anxiety can occur if the dentist or hygienist attempts to use N2O-O2 without having previously described the technique. Even the first sight of the nasal hood might remind the patient of unpleasant experiences that have occurred in the past, such as nausea and vomiting following general anesthesia or a sense of suffocation produced by the nasal hood.
In the ideal situation, the dentist, recognizing the patient’s need for N2O-O2 sedation (e.g., anxiety, medically compromised states, gagging), will discuss with the patient the reasons for selecting this technique and the benefits to be gained from its use both for the dentist and for the patient. This appointment can be used for a “demonstration” of the N2O-O2 equipment and to allow the patient the opportunity to ask questions about the upcoming procedure. It is remarkable how this familiarization can help relieve fear and promote a positive interaction between the clinician and the patient.
It is unusual to find an adult patient who has not heard of or been given N2O-O2. Laughing gas, or so-called sweet air, is a common term to the lay public. Some may have had a previous unpleasant experience with it. It is important for these patients to know that they are not obligated to experience it again, but it may be worthwhile to explain that they could have been easily overdosed (they were not titrated) and that you are confident you can provide a better experience. In any event, this time spent with the patient without the concern of an actual procedure is often all that is needed to get the partnership with the patient that you are seeking. These patients can be and often are your best practice ambassadors.
In discussing with the patient what he or she can expect from the experience, it is crucial to present honesty and clarity in the preoperative and the operative appointment. Do not tell the patient what he or she will or will not feel during this experience because each patient may respond differently. Instead of informing the patient that “you will feel tingling in your fingers or toes,” use a more open-ended statement such as “you should feel more relaxed and at ease.” Some patients who do not experience the suggested signs, such as tingling, will think that the N2O-O2 is not working for them or that something is wrong. It is better to be more vague and general. In a patient who, for religious, medical, or other personal reasons, does not use or like the effects of alcohol, comparing the actions of N2O with those of alcohol or other drugs will make the patient less willing to try and accept it. For the sake of these patients and the patient who has had a personal negative experience with substance abuse, the comparison of N2O and alcohol should be avoided.
At the conclusion of this initial visit, preoperative medications, such as prophylactic antibiotics, antianxiety drugs, or sleeping medication, may be prescribed. Oral antianxiety drugs are useful in the patient who becomes increasingly fearful as the dental appointment nears. Oral drugs help reduce these fears. However, care should be taken, especially in children, when giving concomitant sedation agents because synergistic effects with subsequent possibly dangerous levels of sedation may occur. Once in the dental office, the patient may then receive N2O-O2 for any additional sedation required during the dental treatment. Postoperative instructions can be given and financial matters handled before the patient is released.
Patients may have a light meal a few hours before an appointment for N2O-O2 administration. A heavy meal, particularly with children, should be avoided because this can often lead to nausea and vomiting. Conversely a patient who has had nothing to eat can also become nauseous.
Other monitors, such as the pretracheal stethoscope and the electrocardiogram (ECG), are considered optional in both the adult and pediatric patient whenever inhalation sedation is used as a sole technique. Pulse oximetry, although not mandatory or required, is relatively inexpensive and an excellent way to ensure that the patient is in fact adequately O2 saturated. This is the surest way to confirm that all N2O-O2 equipment and anatomic systems are functioning properly.
Experts in the use of N2O-O2 met in 1995 at the request of the American Dental Association to consider the then-current use of N2O-O2 in the dental office.2 One outgrowth of that meeting was the development of guidelines for equipment inspection and use. They are as follows.
On the day of the scheduled appointment, the dental assistant prepares the unit by opening one O2 and one N2O cylinder. The cylinders are opened by turning the knob on the top of the cylinder in a counterclockwise direction. Start by turning the knob only slightly, just barely opening the cylinder, permitting the pressure gauge to rise slowly. Once the pressure reaches its maximum level, the knob may be turned freely until fully open. The purpose of slowly opening the cylinder is to minimize any increase in internal temperature within the reducing valve as gas under high pressure rushes from the cylinder into the reducing valve.
COMMENT: Patients receiving N2O-O2 sedation do not urinate any more frequently than other persons; however, more urine is produced when a person is in the supine position than when standing. In addition, the patient who has to urinate while receiving N2O-O2 must be unsedated (given 100% O2), permitted to visit the restroom, and then resedated, a process requiring approximately 10 minutes. This time may be saved by requesting the patient to void, if necessary, before treatment.
COMMENT: Vital signs to be recorded include blood pressure, heart rate and rhythm, and respiratory rate. Vital signs may be recorded by the dentist, the dental hygienist, the dental assistant, or a nurse.
COMMENT: The preferred position (Figure 15-1) is first a consideration of patient comfort. The partially reclined position may be used, if necessary, for the patient’s comfort or the convenience of the dentist during the procedure. The upright position is not recommended unless essential for the procedure, such as when taking impressions or radiographs.
COMMENT: This procedure applies only to the use of the portable inhalation sedation unit (Figure 15-2), as opposed to the fixed, central systems commonly found in dental offices. The N2O-O2 unit should always be placed behind the patient, out of his or her line of sight. A positive placebo response will occur in a some patients receiving N2O-O2, but if the patient can see the unit and watch as the administrator adjusts the controls, this response can be negated.
COMMENT: Placing the nasal hood on the patient (Figure 15-3) after starting the flow of O2 will prevent the patient from feeling suffocated when breathing through the nose if the O2 flow is not begun before placement of the nasal hood.
Although it may appear ridiculous to remind a patient to breathe through the nose once the nasal hood has been positioned, this is a very important part of the procedure. Many persons will continue to breathe through their mouths unless they are specifically reminded not to do so, and this contaminates the environment.
COMMENT: The nasal hood usually has two hoses coming from the N2O-O2 unit. These are placed around the sides of the dental chair, and the nasal hood is secured by adjusting the slip ring behind the headrest (Figure 15-4). The patient is asked to hold the nasal hood in a comfortable position as this is done. Care must be taken in adjusting the nasal hood because one of the tubes is often pulled more than the other, making the nasal hood tilt to one side.
If the nasal hood has only one hose, it is placed over the patient’s forehead and secured. The nasal hood should not be too tight or too loose. The patient should have some lateral and up-and-down movement of the head. The patient serves as the final check as to whether the nasal hood is secure.
Leaks develop on occasion around an ill-fitting mask. Nasal hoods are available in a variety of sizes. The size is checked before the start of the procedure. The nasal hood used should fit the patient’s nose. An overly small or overly large mask will leak. Leaks may also develop with masks of the appropriate size. Most often, these leaks occur around the bridge of the nose, with the patient complaining of “air” exhaled into his or her eyes. Permitting the patient to adjust the nasal hood is often all that is needed to correct this situation. If this simple solution is ineffective, the hood is removed, a folded 2-inch square gauze pad is placed over the bridge of the nose, and the nasal hood is replaced. This usually seals the leak (Figure 15-5).
When a scavenging nasal hood (recommended) is used, the exhalation tubes must be connected to the vacuum system. It is important to adjust the vacuum so that the patient is able to exhale and inhale comfortably.2 If the vacuum is too weak, the patient may experience difficulty in breathing out, and if the vacuum is too forceful, the patient may not receive any N2O-O2 because the gases are rapidly sucked from the nasal hood into the overly efficient vacuum system.
COMMENT: This is one of the most important steps in the successful use of N2O-O2 sedation. The patient must be able to breathe comfortably at this point, before the start of N2O flow, to be comfortable throughout the procedure.
At the onset of the procedure, a 6-L/min flow of 100% O2 is initiated for the adult (3 or 4 L/min for smaller pediatric patients), the nasal hood is placed on the patient, and the patient instructed to breathe only through the nose. In most adult patients (and virtually all children), this minute volume will be more than adequate for the patient to breathe comfortably. Breathing comfortably implies that the patient is able to take a normal breath and feel as though the volume of “air” is adequate, as opposed to the patient who states that the machine is not delivering enough “air,” causing him or her difficulty in breathing. I have never seen the opposite situation, in which the patient states that there is too much “air” delivered.
It is impossible to predict which patient will require a minute volume greater than 6 L/min. Larger patients may be quite comfortable at 6 L/min, whereas petite patients may require higher flow rates. Persons who participate in endurance sports, such as marathon running, swimming, and bicycle racing, are more likely to require larger minute volumes. In addition, persons with chronic obstructive pulmonary disease (COPD), heart failure (HF), or partial nasal obstruction may also require larger volumes.
The patient is asked, “Can you breathe normally?” or “Are you comfortable?” If the answer is Yes, the flow rate is left at 6 L/min; if the patient requests a greater volume, the O2 flow rate is increased to 7 L/min and allowed to remain there for a minute, and the same question is asked. This process is repeated until the patient becomes comfortable. The appearance of the reservoir bag is a reliable indicator of appropriate flow rate.
It is not uncommon for a patient to require a higher flow rate at the beginning of N2O-O2 sedation. This is especially so for the patient receiving N2O-O2 sedation for the first time. Placing the nasal hood on the patient’s nose may pose a subconscious threat, and the individual may overcompensate by breathing more deeply and/or rapidly until satisfied that he or she will not suffocate. This same phenomenon is seen in early training of scuba (self-contained underwater breathing apparatus) divers. After the N2O-O2 provides sedation at this elevated flow rate, the dentist might return the flow rate to the original 6 L/min (without telling the patient). In almost all cases, the patient will be unable to detect the change.
Establishing the minimal flow rate is important because if it is assumed that the patient can tolerate 6 L/min comfortably but actually cannot, then the individual will probably never become comfortably sedated with N2O-O2 during the procedure. This step is always carried out with the patient receiving 100% O2 (Figure 15-6).
COMMENT: The appearance of the reservoir bag indicates the respiratory depth and rate. The reservoir bag on the sedation unit will provide an indication of the seal on the nasal hood in addition to allowing a determination of the adequacy of the minute volume of gas delivered to the patient. However, the patient is always the most reliable indicator of the signs and symptoms of inhalation sedation, including the seal of the hood and the adequacy of minute volume.
The reservoir bag that remains partially inflated (deflated) (Figure 15-7, A) and deflates and inflates partially with each breath usually indicates that the minute volume is adequate (the bag remains partially inflated throughout the procedure) and that the seal of the nasal hood is tight (inflates and deflates with each breath).
Figure 15-7 A, Partially inflated reservoir bag usually indicates adequate seal and minute volume. B, Deflated reservoir bag usually indicates either a leak around the nasal hood or a deficient minute volume. C, Distended reservoir bag indicates either an overly large minute volume or occluded breathing tubes.
COMMENT: Once an adequate minute volume of gas flow for the patient has been determined, the administration of N2O may begin. Two methods of administering N2O to the patient are presented, both of which are quite acceptable. In the first, the total liter flow of gases (N2O and O2) per minute is kept constant throughout the procedure (the constant liter flow technique). In the second method, the liter flow of O2 remains constant (the constant O2 flow technique), and the volume of N2O is adjusted. Advantages and disadvantages of both techniques are discussed. These techniques are used with inhalation sedation units that possess separate control knobs for the N2O and the O2 flows. On inhalation sedation units with a mixing dial, the operator needs only to adjust the dial to the desired concentration of N2O or O2. These units operate by keeping the total volume of gas flow constant throughout the procedure (constant liter flow technique).
In all situations, regardless of the type of unit or the technique used, the initial percentage of N2O should be approximately 20%. With the mixing dial units, the administrator needs merely to adjust the percentage dial to either 20% N2O or 80% O2. Flows of the individual gases are automatically adjusted. If a 6-L/min O2 flow is adequate for the patient, when the dial is adjusted to 20% N2O, the N2O flowmeter will read 1.2 L/min and the O2 flowmeter will decrease from 6 to 4.8 L/min.
When operating a unit with individual control knobs for N2O and O2 and using the constant liter flow technique, the administrator increases the N2O flow to 1 L/min and then decreases the O2 flow rate to 5 L/min (Figure 15-8). This produces an N2O percentage of 16.6% (1 L/min N2O/6 L/min total gas flow). In the constant O2 flow technique, the O2 flow is left at its initial rate (6 L/min in this case) and the N2O flow is increased to 1 L/min. The N2O concentration is 14.3% (Figure 15-9).
In my experience, many persons learning to use N2O-O2 inhalation sedation have difficulty determining the concentrations of the gases delivered. One of the most common misconceptions is that the liter flow of the N2O is equal to the percentage of the gas delivered. For example, a 2-L/min flow of N2O actually does not equal 20%. The only situation in which this would be the case is when the total gas flow (O2 + N2O) is 10 L/min. The percentage of a gas delivered through the N2O-O2 unit can readily be determined by dividing the liter flow per minute of the gas by the total volume of both gases delivered:
Table 15-1 provides an easy method of determining the percentage of N2O delivered at common flow rates.
COMMENT: The patient breathes this concentration of N2O for approximately 60 to 90 seconds. During this time, the administrator should observe the patient, looking for signs and symptoms of sedation. At the end of the 60- to 90-second period, the patient is asked, “What are you feeling?” It is important to ask open-ended questions that require the patient to respond with more than a simple Yes or No. “What are you feeling?” requires the patient to answer in sentences, stating “I feel no different from before,” or “I feel a little lightheaded.” The question, “Do you feel good?” brings responses of only Yes or No.