Kept on Wikipedia:Inhalation sedation

Inhalation sedation a form of conscious sedation where an inhaled drug should:

1. Depress the central nervous system (CNS) to an extent that allows operative treatment to be carried out with minimal physiological and psychological stress
2. Modify the patient's state of mind such that communication is maintained and the patient can respond to verbal command
3. Carry a margin of safety wide enough to render the unintended loss of consciousness and loss of protective reflexes unlikely.

History

"Laughing gas" was often used as entertainment in the early 1800s.

Nitrous oxide was first discovered by Joseph Priestly in 1772. In 1795, Sir Humphrey Davy and surgeon J. B. Borlase experimented with nitrous oxide and the effects of its inhalation. Davy then published a book in 1799 hinting the possible role of nitrous oxide in achieving mild anaesthesia during surgical procedures. In 1824, Henry Hill Hickman used carbon dioxide to achieve a state of "suspended animation" in animals; successfully diminishing pain during the surgical procedure. In 1831, chloroform was discovered by Justus von Liebig in Germany, Samuel Guthrie in New York and Eugène Soubeiran in France, all of whom worked independently. In 1842, a chemist in Rochester, William Edward Clarke provided Dr. Elijah Pope with ether prior to a tooth extraction of his patient. In the same year, a doctor in Georgia, Dr. Crawford W. Long administered ether to John Venable for the removable of a neck tumour. In 1844, Dr. Horace Wells carried out an experiment on himself where he had Professor Gardner Quincy Colton administer nitrous oxide to himself prior to a wisdom tooth extraction by Dr. John Riggs. Wells discovered that he was unaware of the procedure and experienced absolutely no pain during the procedure.

Indications

In the United Kingdom, the Scottish Dental Clinical Effectiveness Programme lists the following as indications for conscious sedation:

• Dental anxiety and phobia;
• A need for prolonged or traumatic dental procedures;
• Medical conditions potentially aggravated by stress, such as ischaemic heard disease, hypertension, asthma and epilepsy;
• Medical or behavioural conditions affecting the patient's ability to cooperate;
• Special care requirements.

Contraindications

The British Association of Oral Surgeons states that there are few absolute contraindication for conscious sedation however, relative contra-indications are important and can only be considered following a full assessment. Special care is required in the assessment and choice of sedation technique for children and elderly patients.

• Medical conditions which would compromise the inhalation of the sedation medication, such as the common cold, tonsillitis, severe COPD or nasal blockage;
• Neuromuscular diseases affecting the respiratory system, such as multiple sclerosis and myasthenia gravis;
• Women in the first trimester of pregnancy;
• Medical or behavioural conditions which would limit the patient's ability to understand the procedure;
• Claustrophobia or "fear of the mask".

Patient Assessment and Selection

It is recommended that a full assessment is carried out to inform the need for sedation and, if indicated, the technique most suited to the individual patient. Preferably, assessment should be done at a separate pre-treatment visit prior to the treatment session under sedation to allow the patient time to consider other treatment options available to them. All relevant anxiety management techniques including, where necessary, general anaesthesia must be explored with the patient to ensure that when conscious sedation is required, the most suitable form is selected on each occasion and administered in the correct environment by the appropriate practitioner. It is not a requirement for one conscious sedation technique to have been tried and failed before advancing to an alternative technique; a properly conducted patient assessment should aim to help inform what method of sedation, or otherwise, is most appropriate for the individual patient on each particular occasion.

Patient History:

A thorough medical, dental and social history must be taken and recorded to ensure that the conscious sedation technique chosen is the most appropriate to enable successful treatment outcomes for each individual, taking into account factors such as the patient’s age, state of health, social circumstances and any special needs they may have. The medical history should also include the patient’s use of both prescribed and non-prescribed drugs (including recreational or illicit drugs).

Examination:

Oral examination and treatment planning should be undertaken as part of the assessment. The practitioner should also assess the patient’s general appearance, skin colour, pulse and respiration. Recording of blood pressure is an essential part of the risk-assessment process for all patients having intravenous, oral or trans-mucosal sedation. The American Society of Anaesthesiologists (ASA) physical status classification system should be determined and recorded. Only patients in ASA classes I and II should normally be considered suitable for sedation in the primary care dental setting. Patients in ASA class III or IV should be referred to an appropriate secondary care (i.e. hospital) establishment which has critical care facilities.

ASA physical status classification system definitions relating to patients in assessment for conscious sedation:

• ASA I — A normal health patient;
• ASA II — A patient with mild systemic disease;
• ASA III — A patient with severe systemic disease;
• ASA IV — A patient with severe systemic disease that is a constant threat to life.

Equipment & Safety Features

Nitrous oxide gas cylinder

In UK, machines used for the administration of inhalation sedation should follow the British Standards and be well-maintained according to the manufacturer's guidance.

Equipment:

Equipment used for inhalation sedation for dentistry include:

1. Gas cylinders
2. Flowmeter — an important safety feature of the sedation unit. The device sits on top of the yoke assembly (metal framework adjoining the stand to the attached cylinders). It indicates the amount of gas being administered to the patient.
3. Reservoir bag
4. Conduction Tubing
5. Breathing apparatus (Nasal hood or face mask)

Safety Features:

All nasal hoods should have scavenging ability— provide fresh gas to the patient through one or two hoses and one or two extra hoses dissipate exhaled gas by the patient via a vacuum system.

Incorporated safety features ensure the ultimate responsibility for the safe use of the machine and the anaesthesia provider. The most important safety feature of the unit is oxygen fail safe mechanism. Nitrous oxide flow is only allowed via an opened valve when there is flow of oxygen to the system. In any circumstances when oxygen flow is less than 30%, nitrous oxide stops flowing. This prevents the potential delivery of 100% nitrous oxide and it becomes a standard on every sedation unit made today.

A pin index safety system is in place in order to prevent inadvertent incorrect fitting of the two cylinders in the wrong position, where metal pins are specifically arranged to protrude from the yoke onto the fitted cylinder. This specific mechanism prevents wrong cylinder being attached in the wrong fitting. In addition, the cylinders are colour coded which further reduces the risk of incorrect cylinder placement.

A diameter index system is also in place in order to prevent incorrect linking of hoses and stems as the attachment couplings as well as hoses and stems are different in diameter.

Pressure relief devices which dissipate contents of the cylinder to the atmosphere prevent explosion of cylinder due to over-filling. In an emergency, an oxygen flush or emergency oxygen system passes a high flow of high pressure oxygen direct from the source bypassing intermediate meters.

Several alarm systems are used to indicate a depleting oxygen supply. Audible alarms are required in Europe and are recommended in the United States.

Method

A single titratable drug is preferred in UK. The standard technique used in UK for inhalation sedation is nitrous oxide with oxygen.

All equipment are set up including scavenging system (accurate flowmeter, scavenging masks and vacuum system) to minimize trace gas contamination. The room and area ventilation are checked to ensure waste gases are not circulated elsewhere within the building. Absence of leaks at pressure connections on the unit is confirmed prior to the procedure.

Both oxygen and nitrous oxide cylinders are opened and activated. Patient's health history is reviewed and informed consent is taken once again at this stage. Patient's baseline vital signs of blood pressure, pulse rate and respirations are measured and recorded.

The operator selects the appropriate size and type of nasal hood for the patient. The breathing apparatus is connected to the tubing. Oxygen flow to the nasal hood begins at 100%. For an average-sized adult, begin with 6 to 7L/min while most children have it begin with 4 to 5L/min. Make sure the nasal hood is secured on patient.

Appropriate gas flow in liters per minute is determined before titrating nitrous oxide. Patient is asked if the flow is adequate to breathe comfortably and whether the patient feels any gas leakage from the mask. Reservoir bag is a good indicator for appropriate flow. If reservoir bag collapses, increase the gas flow. If the reservoir bag overinflates, the flow is decreased until the bag is two-thirds full.

There are slight variations in the administration technique of nitrous oxide depending on the type of machine. The suggested regimen is to start titrating with approximately 10-15% nitrous oxide and add subsequent increments with time in between. Recommended increments may varies from 5% to 10%. It is preferable to have at least 1 minute in between the increments. Instruct the patient to breathe through nose to allow a more accurate level of sedation.

Patient is assessed for signs and symptoms of adequate sedation. Nitrous oxide is titrated to desired level and stopped when patient is ready for the treatment. Operative procedures are performed while monitoring patient.

When operative procedures are done, nitrous oxide flow is terminated and postoperative 100% oxygen is delivered for 5 minutes. Patient's recovery is assessed using vital signs and subjective questioning. If necessary, postoperative oxygenation is continued. Patient is dismissed after recovery is ensured. Sedation record is completed and sedation equipment is sterilized and/or disinfected.

Signs of Adequate Sedation

Certain desired physical, physiologic and psychological effects are seen when an appropriate level of sedation is accomplished.

During an adequate and appropriate inhalation sedation, patient should be comfortable and relaxed but still aware of surroundings and responds to direction and conversation. Relaxation may be expressed through body movements such as shoulders dropping, legs uncrossing and arms positioned looser on arm rests.

Another good indicator of the level of sedation is the activity of patient's eyes. Patient's eyes become less active and glazed look appears. Some patients may experience tingling in extremities, body warmth, light feeling and heaviness in legs and arms.

Complications

Complications arising in inhalation sedation are termed as are those which require intervention in order to correct adverse physiological consequences that can inadvertently accompany the sedation technique.

Sedation-related complications include:

• Over-sedation;
• Respiratory depression/apnoea;
• Unconscious patient;
• Airway obstruction;
• Vomiting;
• Idiosyncratic responses;
• Delayed recovery;
• Failure of conscious sedation.

References

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