Aiding in the administration of nitrous oxide-oxygen analgesia

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Breathing Apparatus

Three types of breathing apparatus can be used for inhalation sedation: the full face mask, the nasal hood, or the nasal cannula. The full mask covers both the nose and the mouth, so it is impractical for use in dentistry. It is recommended, however, for administration of forced oxygen in cases of medical emergencies requiring oxygen for management. The nasal cannula is made of soft plastic tubing with two short prongs which fit into the nostrils for breathing. It is not recommended for routine use with nitrous oxide due to concerns about long-term exposure of dental personnel to trace elements of nitrous oxide in the operatory. Thus, a nasal hood is most frequently employed in dental practices.

The nasal hood fits comfortably, yet snuggly, over the patient’s nose. Two types are available. The traditional nosepiece had one hose on each side that is used for inhalation and exhaled gases are eliminated through an exhaling valve located on the top of the nasal hood. Again, this exhaling valve creates concerns for occupational exposure; thus, a scavenging nasal hood is recommended. The scavenging nasal hood typically has four tubes (two on each side) connected to it. Two of the tubes contain gas(es) flowing from the nitrous oxide machine. The other two tubes carry exhaled gases through a controlled ventilation system which deposits them outside of the building or to a safe repository away from the dental operatory.
When selecting a nasal hood, the clinician should be sure that it fits the patient’s nose properly in order to prevent discomfort, but to ensure minimal or no leakage into the treatment room. Autoclavable nasal hoods, or disposable hoods, are recommended in order to prevent disease transmission. Nasal hoods and tubing also should be checked frequently for cracks which might allow leakage and replaced as needed.

Safety Features

All inhalation sedation units marketed in the United States contain certain safety features to prevent accidents from occurring. They are designed so that a minimum of 21% oxygen will always be administered through the system. Any mechanical device can fail, however, so visual and verbal monitoring of a patient is always critical.

A brief description of these safety features follows:

  1. Pin index and diameter index safety systems – make it virtually impossible to attach N2O tanks to O2 yokes and vice versa.

  1. Minimum oxygen liter flow – assures that 2.5-3 L./min. of oxygen is the minimum amount that can be administered; thus a maximum of 75-79% nitrous oxide can be administered.

  1. Oxygen fail-safe system –designed so that the nitrous oxide will automatically turn off when oxygen is depleted before the N2O tank is empty.

  1. Emergency air inlet – designed to remain closed as long as gas(es) are being administered to the patient; however, when the oxygen fail safe system turns gases off, room air is allowed to enter the system so that the patient can continue to breath through the nasal hood.

  1. Fail-safe alarm – when the fail-safe system turns off the gases, an audible alarm sounds to alert the clinician that the patient is no longer receiving N2O-O2.

  1. Oxygen flush button – this flush mechanism allows for 100% oxygen to be administered through the reservoir bag in the event of an emergency. For forced oxygen delivery, however, a full face mask is required.

  1. Color coding – all parts (knobs, tanks, and sometimes tubing) are color-coded blue for N2O and green for O2.

  1. Texture of knobs – the knobs used to regulate liters of gas flowing into each tube are often textured differently to differentiate between adjusting the flow of N2O and the flow of O2.



Prior to administration of nitrous oxide, the clinician must complete a thorough medical history review and record vital signs of the patient. The medical history should be reviewed thoroughly with all new patients and updated at each reappointment or recall appointment. Special consideration should be given to all indications and contraindications prior to the administration of nitrous oxide.

Vital sign must also be recorded for each new patients or recall patient. Three basic vital signs including pulse rate, blood pressure, and respiration are indicated. The first measurement of each vital sign is recorded as the baseline for any particular patient. This baseline data will be used as that patient’s normal and all other future measurements will be compared to it to determine if any change has occurred. This comparison becomes particularly important in an emergency situation.
The measurement and recording of pulse, blood pressure, and respiration is simple to complete. Instructions for each procedure follows.

Vital Signs

The pulse rate is obtained by placing the pads of two (or more) fingers over the radial artery which is located on the wrist, below the hand, on the same side as the thumb. The pulse should be obtained utilizing the index finger and middle finger since the thumb has a pulse of its own which might be confused with the patient’s pulse. Feel around the designated area, applying gentle pressure until a beat can be detected. Once the pulse is located, begin counting the beats for a 60 second period. Record the pulse rate, (which is how many beats occur during the total 60 second period) and compare it to normal rates. In an adult patient, 60-100 beats/minute is considered normal; whereas in a child patient, 80-120 beats/minute is average. An anxious patient might have a higher pulse rate due to fear of dental procedures. If this is noted, wait 5 minutes and take the pulse again. It will usually subside during this resting period. An abnormal pulse rate should be drawn to the dentist’s or physician’s attention prior to proceeding with any dental treatment.

Next, the blood pressure is taken. Blood pressure measures how much air pressure is needed to close off an artery. A cuff is inflated on the upper arm until the blood going though the artery is stopped. This first measurement is called the “systolic” reading. The cuff is then slowly deflated until the artery is completely open and the blood flows freely through it. This second measurement is called the “diastolic” reading. It is the most important since it represents the constant pressure in the artery when the heart is beating at a normal rate and the artery is in its normal, open position.
Items needed for measuring the blood pressure include a sphygmomanometer and a stethoscope. The sphygmomanometer consists of a gauge, to measure air pressure in millimeters, connected by two hoses to an inflatable cuff. This cuff is wrapped around the patient’s bare upper arm one inch above the bend of the elbow. The patient’s arm should be resting on the arm of the dental chair. The positioned cuff should allow enough room for two fingers to be inserted between the cuff and the arm. The gauge should be positioned so that it is easily visible to the operator and the tubing should hang freely. A bulb is located at the end of the tubing. Turn the knob on the bulb until it is closed completely. Begin inflating the cuff by squeezing and releasing the bulb at the end of the tubing while palpating the radial artery (taking the pulse as previously described). Keep inflating the cuff until the pulse stops and continue inflating until the gauge rises 30 millimeters beyond that point. Then, begin deflating the cuff slowly by turning the knob counter-clockwise until the pulse can be detected again. This level represents the approximate systolic reading. Be certain that the cuff is completely deflated before placing the stethoscope. This may require you to squeeze the cuff to force all of the air out. The two ear plugs on the stethoscope should be placed in the operator’s ears. The round, flat portion of the stethoscope is centered on the bend of the arm just below the cuff. Close the knob on the bulb again. Inflate the cuff 30mm above the previously determined approximate systolic reading. Deflate the cuff slowly while listening for changes in the pulse. At the point when pulse first appears, read the number on the gauge. This is the systolic pressure. Continue deflating the cuff slowly and listening until the pulse completely disappears. At this point, read the number on the gauge again. This is the diastolic pressure. The blood pressure is recorded as a fraction with the systolic reading over the diastolic reading. The patient’s blood pressure should be compared to normal rates. Normal blood pressure is approximately 120/80 (or 120 systolic and 80 diastolic); however, systolic pressure less than 140 and diastolic pressure less than 90 is acceptable for an average adult patient. Clinical evaluation of blood pressure may lead to discovery of abnormal rates. The appropriate steps to follow with each reading are outlined in Table 4.
T A B L E 4
Clinical Evaluation of Blood Pressure




Less than 140 systolic and

Less than 90 diastolic

Routine dental management; recheck in six months.

140 to 160 systolic and

90 to 95 diastolic

Recheck blood pressure prior to dental therapy for three consecutive appointments. If all exceed these guidelines, medical consultation is indicated.

160 to 200 systolic and/or

95 to 115 diastolic

Recheck blood pressure in five minutes. If still elevated, medical consultation is indicated.

Greater than 200 systolic and/or

Greater than 115 diastolic

Recheck blood pressure in five minutes. If still elevated, immediate medical consultation is indicated. No dental therapy.

Adapted from: Malamed, Stanley F. Medical Emergencies in the Dental Office.

The third routine vital sign to be recorded is the respiratory rate. This should be noted when the patient is unaware of observation; since it if often difficult for a patient to breath normally when being watched. Some operators choose to observe respiration immediately after taking pulse for 60 seconds, leaving their fingers over the radial artery so the patient is unaware of observation. Respirations are counted by observing the rise and fall of the patient’s chest for 60 seconds. Normal respiratory rate for an adult is 16 to 18 breaths per minutes; whereas, a child will take 40-45 breaths per minute. Any significant variation in respiratory rate should be evaluated by the dentist prior to dental therapy. If within normal range, the respiratory rate is recorded with other vital signs and utilized as baseline data.
Any abnormality in medical history or vital signs should be drawn to the dentist’s attention prior to proceeding with treatment. This is particularly important when nitrous oxide is going to be administered. If all signs are normal, the operator should note each consideration mentally, as well as on the chart, so that the information is readily available in the event of an emergency. Once this has been completed, nitrous oxide can be administered.

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