Step 3 - Commencing with Treatment

Once the patient exhibits the responses described in the Altered State of Consciousness section of Chart 1, treatment may be commenced. Every effort should be made to maximize nasal breathing to maintain a steady level of nitrous oxide/oxygen. This includes minimal conversation with the patient and the use of rubber dam to minimize oral breathing.

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.
Image: Dental treatment.
Image: Dental treatment.

Monitoring of the patient’s level of consciousness is accomplished by observation of the patient’s facial expression, body position, response to questions as described in Charts 1 and 2 and the use of the pulse oximeter. Care must be taken to maintain the patient in the Altered State of Consciousness stage and avoid reverting back to the Active Alert Consciousness stage or advancing into the Loss of Consciousness stage. However, constant adjustments in the nitrous oxide/oxygen concentration can cause a “bouncing” effect in the patient resulting in post-operative nausea and headache.

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.