Pre-administration Preparations

Before proceeding with the administration of nitrous oxide/oxygen analgesia/anxiolysis, a preoperative assessment must be performed. The assessment consists of a medical history and measurement of the patient’s vital signs. The medical history provides information regarding the patient’s:

  • Allergies and previous allergic or adverse drug reactions
  • Current medications including dose time, route, and site of administration
  • Diseases, disorders, or physical abnormalities and pregnancy status
  • Previous hospitalizations including dates and reasons

Vital sign measurements include:

  • Blood pressure
  • Pulse
  • Oxygen saturation (patients’ receiving greater than 50% nitrous oxide/oxygen concentration should be monitored)
  • Respiratory rate
  • Lungs - clear or congested
  • Nasal airway – clear or obstructed, nasal or mouth breather. Nitrous oxide/oxygen is inhaled through the nose. Any obstructions or tendencies that interfere with nasal breathing will reduce the amount of gas reaching the lungs and ultimately the brain.

The use of nitrous oxide/oxygen analgesia/anxiolysis should be well documented. Before administration a written informed consent should be obtained from the parent or guardian. Pretreatment dietary precautions, if indicated, should be recorded. Unless the patient has a history of vomiting, there are no fasting requirements for patients. It is recommended patients be instructed not eat for two hours before nitrous oxide administration to minimize the possibility of vomiting and aspiration.

Additional information recorded in the chart includes:

  • Reasons for recommendation of nitrous oxide/oxide analgesia/anxiolysis (poor behavior, anxiety, extensive treatment)
  • The percent of nitrous oxide/oxygen ratio and the flow rate
  • Duration of the procedure
  • Duration of post-treatment oxygenation
  • Status of patient upon discharge (active and alert, lethargic, accompanied by adult)
  • Pulse oximeter readings – pulse rate, oxygen saturation (for concentrations greater than 50% nitrous oxide/oxygen)
  • Clinical observations of the patient's reaction to nitrous oxide/oxygen analgesia/anxiolysis:
    • Response to commands
    • Skin color
    • Respiratory rate and rhythm
    • Musculo-skeletal changes
    • Behavior

Chart 1 and Chart 2 provide a summary of characteristic patient responses to nitrous oxide/oxygen analgesia/anxiolysis.

Chart 1. Characteristic Body Responses During N2O/O2 Administration.
State of Consciousness Age Levels Muscles of Facial Expressions Muscles of Mastication Extremities
Active Alert Consciousness (AAC)

Induction Non-operating phase
Adult No changes in these muscles. Patient can elevate and depress mandible normally. Parasthesia of toes, fingertips, thighs in approximately 40% of patients. Warm feeling in body.
Child There are no subjective somatic changes in children.
Altered State of Consciousness (ASC)

Maintenance Operating phase
Adult Facial expressions take on two forms.
  1. If the eyes are closed the patient will exhibit a sleep-like expression.
  2. If eyes remain open there is a "trance-like" appearance due to reduced blink responses.
Mandible tends to elevate and the mouth closes more easily. However, mouth props are generally not needed for dental procedure. Extremities feel heavy and relaxed. Arm and hand may rotate laterally and roll out of chair arm rests. Fingers may take on various positions for long periods of time. Feet may abduct.
Child Trance expression is profound. Mouth tends to close easily. Feet abduct.
Loss of Consciousness (LC)

Non-operating Phase
Adult and Child May exhibit an expression of pain due to contraction of Corrugator Supercili producing the furrowed brow. Obicularis Oculiicontraction produces the “crows-feet” effect around the eyes. Contraction of Temporalis, Masseter and Pterygoid closes mouth so that it cannot be forced open. Patient displays a clenched jaw appearance. Arm and leg muscles may contract and take on a stiffened appearance.
Chart 2. Characteristic Sensory Responses During N2O/O2 Administration.
State of Consciousness Age Levels Descriptive Olfactory Ocular Auditory Mouth, Throat, Voice
Active Alert Consciousness (AAC)

Induction Non-operating phase
Adult Tingling of fingers and toes.

Warm sensations.
Some patients describe a sweet odor to N2O. Occasional lacrimation. At times tear will roll down sides of face. Normal Occasional paresthesia of the lower and upper lip.
Child There are no subjective somatic changes in children.
Altered State of Consciousness (ASC)

Maintenance Operating phase
Adult Floating

Dreaming

Relaxed
Normal Sclera of eye may show prominent blood vessels. Pupils react to light normally. Peripheral vision is blurred. Blink reflex is normal. Variety of auditory hallucinations. Distant sounds may appear louder. Occasionally patient hears a buzzing or a humming sound. Speaks more slowly and quietly. Speaks with hesitation. Gag reflex is reduced. Cough reflex is normal.
Child Normal Sclera does not show prominent blood vessels. No auditory hallucinations. Reluctant to speak. Gag reflex is reduced.
Loss of Consciousness (LC)

Non-operating Phase
Adult and Child Fading away.

Blacking out.
Undetermined because of communication barrier. Eyes closed. Cannot hear. Does not speak, may laugh, grunt or groan. Approximately 10% of patients will laugh with intensity.

There are three states or levels of consciousness during nitrous oxide/oxygen administration.

The first level is the Active Alert Consciousness or Induction stage. The patient is beginning to experience the sensations felt during the initial administration of nitrous oxide/oxygen analgesia. This is an introductory or preoperative stage and the patient is not ready to undergo treatment.

The second level is the Altered State of Consciousness or Maintenance stage. The patient is correctly titrated and is receiving the ideal concentration of nitrous oxide/oxygen. This is the stage the patient is most comfortable. Once the patient describes the body and sensory responses associated with this level, treatment may commence.

The third level is the Loss of Consciousness stage. In this stage the nitrous oxide/oxygen concentration administered to the patient is too high and the patient expresses discomfort verbally and through bodily responses. If the patent exhibits these responses, treatment is stopped, the concentration of the nitrous oxide/oxygen concentration reduced and the patient is instructed to breathe though the mouth, to enhance nitrous oxide/oxygen by dilution with room air. Once the patient elicits positive responses again, treatment is continued at the reduced nitrous oxide/oxygen level.