Clinical evaluation of the efficacy of three nitrous oxide scavenging units during dental treatment - [N.sub.2]O

Dental Assistant, The, March-April, 2003 by Fred Certosimo, Martin Walton, David Hartzell, Jennifer Farris

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The study population consisted of 12 volunteers, 7 men and 5 women, who ranged in age from 22-44 (mean = 25 [ or -] 3.5). The subjects were selected at random from a population of dental school volunteers. All subjects met the criteria for Class I of the American Society of Anesthesiology. None used tobacco products; none of the female subjects were pregnant.

The subjects participated in four clinical sessions at one-week intervals. During these sessions, each volunteer was exposed to either one of the three [N.sub.2]O) scavenger units or to a control that used no scavenger unit. The order of exposure to each of the variables was determined by a randomized computer-generated schedule established by an investigator not associated with the clinical portion of the study. Informed consent was obtained prior to subject participation in this investigation. A pilot study was performed to minimize variation between subjects, calibrate the instruments and the procedures, and expedite reproducibility.

Operatory preparation

All testing was conducted in the same ventilated operatory with an air flow rate that produced six air exchanges per hour. The [N.sub.2]O delivery machine was evaluated for proper connections and protection against gas leakage immediately before each experimental session, in accordance with ADA-recommended protocol. (1,11,24-26) Prior to each session, room air was evaluated using an infrared spectrophotometer to determine the baseline value of [N.sub.2]O in the operatory.

Patient preparation and Clinical monitors

Before each clinical session, each patient was given oral and written instructions including pretreatment and posttreatment dietary restrictions, activity limitations following the study, and a 24-hour contact telephone number. On the day of the study, the subject was seated in a standard dental operatory chair. Inhalation mask application and nose breathing technique were explained to each patient. The patient was encouraged to remain still and to minimize talking and mouth breathing. The room ambient temperature was recorded. Patient blood pressure (BP), pulse, and blood oxygen saturation were recorded electronically by the Passport XG (Datascope Corp., Montvale, NJ; 800/288-2121). The patient's respiratory rate was recorded to establish baseline measurements.

The door to the operatory was closed, the patient was placed in a semi-supine position, and a nasal hood was applied. Oxygen was delivered at a rate of 9.0 L/min. The hood was adjusted for both fit and comfort (Figure 2). The patient was asked to relax and reminded again to breathe only through the nose. Respiratory rates were recorded again at minutes 3 and 12 of the procedure. A pulse oximeter was used to continually monitor the patient's oxygen saturation; readings were taken at 3, 12, and 16 minutes.

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[N.sub.2]O TITRATION

As soon as the patient reported being comfortable with the position of his or her body and the position of the nasal hood, the investigator began titration of [N.sub.2]O. A constant gas volume technique was used. [N.sub.2]O was adjusted to a 1.0 L/min flow while oxygen flow was reduced to 8.0 L/min. The patient breathed this 11% [N.sub.2]O mixture for three minutes. If there were no untoward events and the patient still was comfortable, the flow of [N.sub.2]O was increased to 2.0 L/min and the oxygen flow was reduced to 7.0 L/min (22% [N.sub.2]O). The patient breathed this new mixture for six minutes, at which time a rubber dam was applied to isolate the maxillary anterior teeth. The dam was held away from the patient's face using a Young's frame. The [N.sub.2]O flow was increased to 3.0 L/min with a concomitant oxygen flow rate of 6.0 L/min (33% [N.sub.2]O). This final [N.sub.2]O/[O.sub.2] ratio was maintained for nine minutes, during which a sham operative dental procedure was conducted. At the completion of this sham treatment, the [N.sub.2]O was secured and the oxygen flow was increased to 9.0 L/min for at least four minutes to purge the [N.sub.2]O from the patient. The total length of exposure to [N.sub.2]O per subject was 18 minutes.