Conscious Sedation in Dentistry: Selecting the Right Patient

Conscious sedation

Conscious sedation is ‘A technique in which the use of a drug or drugs produces a state of depression of the nervous system enabling treatment to be carried out, but during which verbal contact with the patient is maintained throughout the period of sedation. The drugs and techniques used to provide conscious sedation for dental treatment should carry a margin of safety wide enough to render loss of consciousness unlikely.’^2,3 Sedation provides anxiolysis and amnesia for patients. Conscious sedation can be achieved with a single drug or multiple drugs using various different routes.

According to the sedation continuum, there are three stages of sedation: minimal, moderate and deep (Table 1). When patients are further down the sedation continuum and are unconscious, general anaesthesia is achieved. Patients are unarousable and might require airway and ventilation support. For the duration of a specific treatment, it is ideal to reach and maintain moderate sedation, which is also known as conscious sedation. During conscious sedation, patients are able to respond to verbal commands, ventilation and the cardiovascular system remains unaffected.⁴

Intravenous sedation can be achieved with a single drug or multiple drugs, using various different routes. In a dental setting, using single drug technique is recommended with midazolam. Midazolam is a benzodiazepine that is safe, fast acting and has a short half life. It can be administered via several routes, oral, intramuscular, intravenous, submucosal, intranasal, without the risk of cardiopulmonary depression.⁵ Regardless of how sedation is achieved, the ultimate goal is for the patient to be conscious and respond to verbal commands throughout the procedure.⁶

The main indications and contra-indications of conscious sedation in a primary setting for dental procedures are shown in Table 2.⁷

Pre-assessment

The main purpose of pre-assessment for sedation is to establish a baseline health status of the patient and recognize factors that may present a risk for the patient during sedation.⁶ Thorough assessment is required to assess patient suitability for sedation with respect to airway, fasting, venous access, intra-operative and post-operative monitoring, drug pharmacokinetics and pharmacodynamics, appropriately trained staff and a well equipped recovery room. SDCEP standards state that detailed patient assessment should be carried out at a different day to the day of the procedure, to allow sufficient time for the dentist to consider all the information required and the patient to comprehend all the given information and consider all the options available without the added pressure of the treatment on the same day. Operator/Sedationist will be responsible to carry out a thorough patient history and assessment and must have the appropriate knowledge, skill and training to carry out sedation.⁸ Pre-sedation assessment must include:

Medical history;

Dental history;

Weight, BMI;

ASA status;

Baseline vital signs;

Conscious sedation and general anaesthetic history;

Dental treatment plan;

The selected conscious sedation technique;

Any individual patient requirement;

Provision of pre- and post-operative written instructions provided before treatment;

Written consent for conscious sedation and dental treatment.

A thorough and full medical assessment must be carried out, including prescribed and non-prescribed medication and use of any recreational drugs. An assessment of sedation need must also be carried out to choose the appropriate technique and assess patient suitability.⁹

The American Society of Anesthesiologists' classification is to categorize patients according to their health status.¹⁰ ASA I and ASA II patients can be treated in a primary care setting under conscious sedation. Patients in ASA III and above category must be referred for treatment in the secondary care. Each patient that is pre-assessed for sedation must have an ASA grade to indicate their suitability for sedation (Table 3).

Table 3. Adapted from American Society of Anesthesiologists' classification.10

ASA Classifcation
ASA 1	Healthy person, fit, BMI under 30
ASA 2	Patient with mild systemic, well-controlled disease, eg controlled hypertension, diabetes
ASA 3	Patient with severe systemic disease, significant functional limitations, eg COPD – poorly controlled diabetes, hypertension, obesity
ASA 4	Severe systemic disease constantly threatening life, myocardial infarction, stroke, unstable angina
ASA 5	Moribund – not expected to live beyond 24 hours
ASA 6	Braindead

Physical and clinical examination consists of the assessing patient compliance as well as assessing and identifying the common predictors of a difficult airway. The pneumonic (LEMON) is used to assess and predict the difficulty of airway:

L – Look externally: craniofacial abnormalities, facial trauma, beard, moustache, tongue, large tongue and large incisors.

E – Evaluate 3-3-2 rule

Jaw opening: patient's mouth is fully open and allows three fingers between the upper and lower teeth;¹¹

Hyomental distance: three finger breadths space;

Thyromental distance: two finger breadths space.

M – Mallampati score is a simple grading system which consists of the ability to visualize the faucial pillars, soft palate and base of uvula when the patient protrudes the tongue as far out as possible and is a way of assessing the airway difficulty specifically in sedation (Figure 1).¹² The higher the Mallampati score, the more difficult the airway.

O – Obstruction. Anything that could potentially obstruct the airway, for example tumours, limited mouth opening, abscess, foreign body, dentures, haematoma, etc.

N – Neck mobility. Patients must be able to extend their neck and able to move it around. This is particularly important for clearing airway obstruction.

Obesity and obstructive sleep apnoea

One of the most prominent challenges when selecting patients for conscious sedation is obesity. Obesity is defined as having excess fat and generally those with BMI of over 30. Management of airways in obese patients is difficult due to the possibility of rapid oxygen desaturation as a result of excess fat narrowing the airway. There is also increased vulnerability to respiratory depression due to the effects of sedatives.¹⁸ Obese individuals tend to metabolize drugs differently compared to non-obese individuals. Pharmacokinetics and pharmacodynamics of drugs are unpredictable in obese patients. High BMI can result in high adipose tissues, reduced total body water, higher glomerular filtration rate and reduced hepatic clearance. These factors may mean that higher doses of sedative drugs might be required, thus leading to unpredictable sedative risks and patient reaction.¹⁹ Organs involved in drug metabolism and elimination can be affected by other co-morbidities caused by obesity and thus may result in a prolonged drug elimination process.²⁰

Obesity is a risk factor for developing obstructive sleep apnoea (OSA). OSA is a disorder where there is ‘partial or complete obstruction of the upper airway during sleep’. When sleeping, the muscle tones are relaxed, the soft palate and tongue obstructs the airway, resulting in sudden awakening from sleep.

All obese individuals and those with suspected OSA should go through a concise pre-operative assessment, including filling out a STOP-BANG questionnaire. A STOP-BANG questionnaire consists of a series of questions about snoring, tiredness, daytime sleepiness, blood pressure and body mass index. The score helps assess the probability of having obstructive sleep apnoea. Those with sleep apnoea are classified as ASA III and therefore are unsuitable for treatment under conscious sedation at a dental surgery, and must be referred to hospital.²¹

Monitoring

All patients selected for conscious sedation must have baseline vital signs including blood pressure, saturation levels, heart rate recorded pre-operatively, intra-operatively and post-operatively. Monitoring equipment such as ECG, Pulse oximeter, End tidal CO2, NIBP (non invasive blood pressure), defibrillator should be readily available.²² For those patients (ASA I and ASA II) having inhalation sedation, this baseline monitoring is usually not required.

The clinic where sedation is taking place must be fully equipped with medical emergency kit, resuscitation and airway management equipment. Reversal agent must be available and should be easily accessed. There must also be a dedicated recovery room. The staff involved in sedation must check that all equipment and drugs are up to date and within easy access prior to starting sedation procedure.

Consent

To comply with legal requirements and GDC standards, informed written consent must be obtained from each patient undergoing any type of dental treatment with or without conscious sedation.

Consent must be obtained on a different day to the procedure. The Sedationist must ensure that all steps of the procedure have been explained to the patient thoroughly including:

Staffing

All staff providing conscious sedation must be adequately trained. In a dental setting there may be a dedicated Sedationist or Operator-Sedationist. There must be an appropriately trained nurse present at all times to assist the Operator-Sedationist and to monitor the patient continuously. For advanced technique, there must be a dedicated Sedationist. All members of staff involved in providing sedation must have knowledge, skill and immediate life support training to deal with complications arising during sedation.

Conclusion and take away points

Conscious sedation in dentistry has gained greater popularity in recent years as an alternative to general anaesthesia. Its safety and efficacy in a primary setting means that it is an attractive technique to use both from the dentist and patient perspective. Patients are becoming more educated about the choices available and dentists are obligated to provide effective pain and anxiety control. Conscious sedation is not without its challenges in a primary setting. Strict guidelines and standards must be adhered to, to reduce risks and prevent complications and promote good clinical practice. Consequently, a thorough patient assessment is essential, taking into consideration every patient's individual needs and requirements.

Patient selection is paramount in the provision of dental care under conscious sedation. It is the duty of the sedation provider to ensure the safety of the patient and his/her environment.