In the following cases, administration of nitrous oxide is not recommended. A careful review of the health history should be made to rule out these contraindications.
1. Nasal Obstruction
Patients with nasal obstruction cannot sufficiently inhale the N2O-O2 gases administered. Conditions which might lead to nasal blockage include:
the common cold
upper respiratory infections (URI) or bronchitis
allergies or hay fever
deviated nasal septum
In conditions such as the common cold, bronchitis or URI, the nasal hood will be contaminated during use. If nitrous oxide administration is attempted, a disposable nosepiece should be used or the nosepiece should be sterilized before cross-contamination of personnel or other patients can occur.
2. Chronic Obstruction Pulmonary Diseases (COPD)
COPD will prevent the sedative effect of N2O and contraindicate its use. Patients with emphysema, tuberculosis, eustachian tube blockage, and other chronic respiratory disorders should not receive nitrous oxide. It can result in immunosuppression, abnormal pulmonary function, secondary bacterial infections, or hypoxia.
3. Debilitating cardiac or cerebrovascular disease
If heart disease or valvular damage limits a person’s daily activities, N2O is not recommended. Patients who report cyanosis (blue coloring), dyspnea (shortness of breath), need for increased pillows when sleeping, or artery blockage should avoid all CNS depressants including N2O.
Nitrous oxide does cross the placenta to the fetus and it affects the baby’s CNS. Studies in animals show that a single dose of N2O is usually safe when administered in proper concentrations. Nitrous Oxide also has been shown to be the most highly recommended sedation agent when one must be employed during pregnancy. In the opinion of this author, however, administration of all drugs should be avoided whenever possible during pregnancy and particularly during the first trimester. If a sedative is absolutely essential for dental treatment, a medical consultation should be made prior to administration.
5. Patients with psychiatric disorders or compulsive personalities
It is difficult to predict the effects of N2O-O2 in patients with psychiatric disorders or compulsive personalities. Drugs given to psychiatric patients, such as mood-altering antidepressants, also should be carefully evaluated. Altering the consciousness of patients with psychiatric disorders or patients who fear “losing control” may result in negative reactions.
6. Claustrophobic patients
Some patients are not able to tolerate the nasal mask without a feeling of suffocation. The nasal cannula can be used in these cases; however, this technique is not routinely recommended because of the risk of exposure of trace elements to dental personnel.
7. Children with severe behavioral problems
Nitrous oxide can be used to control fear and anxiety in most pedodontic patients. A severely disruptive child, however, cannot give the degree of cooperation needed for administration of N2O-O2 inhalation sedation. Forced administration is never recommended.
8. The patient who does not want N2O-O2
Patients should never be forced or coerced to receive N2O (or any other drug) against their will. Doing so can result in negative side effects or legal repercussions.
There are many types of inhalation sedation units. This module discusses the most common apparatus used. A brief review of the central storage system, the nitrous oxide-oxygen machine, the breathing apparatus and safety features follows.
The Central Storage System
The central storage system is where the large tanks of nitrous oxide and oxygen are stored. It is usually separated from the treatment rooms. As mentioned previously, the nitrous oxide tanks are always marked blue for identification, and the oxygen tanks are green. A Pin Index Safety System prevents attaching the wrong cylinder to the yokes during installation. Cylinders should be handled with care, stored upright and kept intact.
A pressure gauge monitors the pressure within each cylinder. The nitrous oxide is stored at approximately 750 psig (pounds per square inch of gas) and the oxygen has approximately
1800-2150 psig. N2O and O2 are stored as a liquid under pressure which is released as a gas.
Pressure regulators are usually mounted inside of a box frame. They act to reduce cylinder pressure to about 50 psig to be used in the system.
When turning on the tanks in the control storage system, it is important to open the valves slowly in a counter-clockwise direction. No grease, oil, or lubricant of any type should be used on any of the valves, regulators, gauges, or tanks. It can be extremely dangerous if these lubricants come in contact with the gases because an explosion could result.
When the nitrous oxide and oxygen are turned on, the operator should check each pressure gauge and pressure regulator to be sure that the gases are flowing properly. Manufacturer’s instructions should be read to ascertain proper readings.
Several types of machines are available for use in nitrous oxide-oxygen inhalation sedation. The gases generally are transported to the machine at chairside through a series of copper tubings from the central storage area. Some offices have portable nitrous oxide-oxygen machines which house small tanks of N2O and O2. The portable units usually are employed when nitrous oxide is administered infrequently.
The most common machine used in dentistry has ball-type flow meters which indicate the amount of gas being administered. The machine has an on-off knob which allows the gases to flow into the tubing and nasal mask. Two additional knobs are used to regulate the amount of nitrous oxide or oxygen flow which is displayed in two separate glass tubings. As each knob is turned to a more open position, more gas enters the glass tubing in the flow meter and a ball floats to indicate how much gas is being dispensed. The flow tubes have markings that are numbered to show how many liters per minute are being dispensed. These two “ball flow meters” (one for N2O and one for O2) enable the clinician to regulate the flow up to a maximum of 10 liters per minute (L./min.). The nitrous oxide can be turned off to 0 L./min., but the minimum oxygen flow permitted is about 2.5-3 L./min. This safety feature prevents administration of pure nitrous oxide.
A reservoir bag, or breathing bag is located beneath the flowmeter. This bladder-type bag, made of rubber or silicone, holds a portion of the gas(es) that are available to be delivered into the flowmeter system. The main purpose of this bag is to store additional gas(es) in case the patient’s respiratory demands exceed the amount being delivered through the flowmeter. During normal respiration, nitrous oxide and oxygen are delivered directly into the flowmeter and none is taken from the reservoir bag. It also expands and contracts when a patient breathes so that respiration can be monitored during administration of nitrous oxide. Conducting tubes, or hoses, connect the nitrous oxide machine to the copper tubing leading to the central storage area. They also connect the machine to the nasal mask, or hood, used to administer nitrous oxide to the patient.