Dolly FR, Block AJ. Effect of flurazepam on sleep-disordered breathing and nocturnal oxygen desaturation in asymptomatic subjects. Am J Med. 1982; 73:239-243 https://doi.org/10.1016/0002-9343(82)90185-1
Bonora M, John WM, Bledsoe TA. Differential elevation by protriptyline and depression by diazepam of upper airway respiratory motor activity. Am Rev Respir Dis. 1985; 131:41-45 https://doi.org/10.1164/arrd.1985.131.1.41
Nozaki-Taguchi N, Isono S, Nishino T Upper airway obstruction during midazolam sedation: modification by nasal CPAP. Can J Anaesth. 1995; 42:685-690 https://doi.org/10.1007/BF03012665
Oshima T, Masaki Y, Toyooka H. Flumazenil antagonizes midazolam-induced airway narrowing during nasal breathing in humans. Br J Anaesth. 1999; 82:698-702 https://doi.org/10.1093/bja/82.5.698
Bogunovic OJ, Greenfield SF. Practical geriatrics: use of benzodiazepines among elderly patients. Psychiatr Serv. 2004; 55:233-25 https://doi.org/10.1176/appi.ps.55.3.233
Senaratna CV, Perret JL, Lodge CJ. Prevalence of obstructive sleep apnea in the general population: a systematic review. Sleep Med Rev. 2017; 34:70-81 https://doi.org/10.1016/j.smrv.2016.07.002
Rosenthal LD, Dolan DC. The Epworth sleepiness scale in the identification of obstructive sleep apnea. J Nerv Ment Dis. 2008; 196:429-431 https://doi.org/10.1097/NMD.0b013e31816ff3bf
Chung F, Yegneswaran B, Liao P STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology. 2008; 108:812-821 https://doi.org/10.1097/ALN.0b013e31816d83e4
Phero JC, Rosenberg MB, Giovannitti JA Adult airway evaluation in oral surgery. Oral Maxillofac Surg Clin North Am. 2013; 25:385-399 https://doi.org/10.1016/j.coms.2013.04.005
Murphy PJ, Erskine R, Langton JA. The effect of intravenously administered diazepam, midazolam and flumazenil on the sensitivity of upper airway reflexes. Anaesthesia. 1994; 49:105-110 https://doi.org/10.1111/j.1365-2044.1994.tb03363.x
Practice Guidelines for Moderate Procedural Sedation and Analgesia 2018: a report by the American Society of Anesthesiologists Task Force on moderate procedural sedation and analgesia, the American Association of Oral and Maxillofacial Surgeons, American College of Radiology, American Dental Association, American Society of Dentist Anesthesiologists, and Society of Interventional Radiology. Anesthesiology. 2018; 128:437-479 https://doi.org/10.1097/ALN.0000000000002043
Khan ZH, Kashfi A, Ebrahimkhani E. A comparison of the upper lip bite test (a simple new technique) with modified Mallampati classification in predicting difficulty in endotracheal intubation: a prospective blinded study. Anesth Analg. 2003; 96:595-599 https://doi.org/10.1097/00000539-200302000-00053
Reed MJ, Dunn MJ, McKeown DW. Can an airway assessment score predict difficulty at intubation in the emergency department?. Emerg Med J. 2005; 22:99-102 https://doi.org/10.1136/emj.2003.008771
The ability to manage an airway is an essential skill for the safe provision of intravenous conscious sedation. A systematic airway assessment will allow identification of risk factors pre-operatively, flagging potential airway problems and aiding case selection. If difficulties arise, the practitioner will be able to act efficiently having anticipated the risk factors. Importantly, cases unsuitable for primary care can be readily identified and referred appropriately. In the interest of patient safety, this article aims to present methods of airway assessment that can be incorporated into the pre-sedation assessment.
CPD/Clinical Relevance: This article discusses airway assessment methods relevant to intravenous conscious sedation to promote patient safety.
Article
The use of midazolam for intravenous sedation in primary dental care has been proven safe and effective. The safety of conscious sedation is dependent on a thorough pre-operative assessment, careful administration and monitoring throughout. The Intercollegiate Advisory Committee for Sedation in Dentistry (IACSD) guidelines1 state that sedation dentists must be able to ‘carry out airway assessment and anticipate potential difficulties during sedation or if ventilation is required’. The Scottish Dental Clinical Effectiveness Programme (SDCEP) guidelines2 echo this requirement and state that potential airway difficulties should be assessed and documented at the pre-sedation assessment.
The Airway, Breathing, Circulation, Disability, Exposure (ABCDE) approach towards medical emergencies is well known and highlights the primary importance of the patient's airway. Nevertheless, guidance for airway assessment within dental sedation is limited.
Conscious sedation is defined as: ‘a technique in which the use of a drug or drugs produces a state of depression of the central 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.’1,2 Consequently, a patient should be able to maintain their airway reflexes throughout dental conscious sedation. Midazolam can be titrated until the desired clinical effect is achieved and it has a wide margin of safety, making it the drug of choice for dentist-led intravenous conscious sedation.
However, there are risks associated with intravenous sedation that include loss, obstruction or difficulty maintaining the patient's airway.3 Apnoea and airway obstruction have been reported following administration of IV midazolam in dentistry.4 Benzodiazepines (such as midazolam) can depress upper airway muscle motor activity, increasing the risk of upper airway obstruction resulting in apnoea (temporary cessation of breathing) and hypopnoea (a reduction of air flow).5,6,7 One study concluded that midazolam can also act to impair nasal patency and the ability to change breathing route in response to an obstruction.8 This finding is particularly profound because dental procedures can impact on the airway and carry an inherent risk of obstruction and aspiration, confounding difficulties when performing procedures under sedation.
A dental sedationist must be able to maintain an airway and perform satisfactory ventilation to maintain a patient's oxygenation in the event of over-sedation.9 A thorough pre-operative assessment of the patient's airway is essential to identify risk factors that may increase the likelihood of airway problems or difficulties with airway interventions such as bag-mask-valve ventilation. An ability to assess, anticipate and manage any difficulties will ensure patient safety.10
This article aims to provide practitioners with a framework to perform a thorough pre-operative airway assessment. Many of the recommendations are drawn from anaesthetic guidelines, but will help to draw the sedationist to important patient factors that can be assessed in the dental setting.
Assessment of a patient's airway
The assessment of a patient's airway consists of two main components: a history and examination.
Airway history
Past treatment
A thorough history is important to identify previous problems with sedation and general anaesthesia. Patients may report difficulties with general anaesthesia, such as the need for fibre-optic awake intubations or unexpected admissions to an intensive care unit. They may also report difficulties associated with previous sedation or the use of a reversal agent.
Age
Older patients may be more sensitive to benzodiazepines.11 Increased sensitivity may result in greater depression of upper airway neuromuscular mechanisms with potential to cause obstruction.7 This emphasizes the importance of carefully titrating a sedative drug to its desired effect. Another consideration is the mobility of a patient's temporomandibular joint and cervical spine, which can decrease with age.12 This may hinder a clinician's ability to provide a head tilt, chin lift, jaw thrust or place airway adjuncts to maintain a patient's airway.
ASA physical status
The American Society of Anesthesiologists (ASA) Physical Status Classification System categorizes patients according to their health (Table 1).13 Conscious sedation in primary care should normally be limited to ASA I and II patients.2,14 The ASA classification provides a useful reference for clinicians and can be easily documented. Those with an ASA greater than II are likely to require a referral to secondary care where they can be managed in a more appropriate environment.
ASA PS Classification
Definition
Adult examples (including but not limited to):
ASA I
A healthy patient
Healthy, non-smoking, no or minimal alcohol use
ASA II
A patient with mild systemic disease
Obesity (30<BMI<40), current smoker, social alcohol drinker, well-controlled diabetes and hypertension, mild lung disease, such as well-controlled asthma
ASA III
A patient with severe systemic disease
Morbid obesity (BMI >40), poorly controlled diabetes or hypertension, COPD, alcohol dependence or abuse, implanted pacemaker, ESRD undergoing regularly scheduled dialysis, history (>3 months) of MI, CVA, TIA, or CAD/stents
ASA IV
A patient with severe systemic disease that is a constant threat to life
Recent (< 3 months) MI, CVA, TIA, or CAD/stents, ongoing cardiac ischemia or severe valve dysfunction, sepsis
ASA V
A moribund patient who is not expected to survive without the operation
Ruptured abdominal/thoracic aneurysm, massive trauma, intracranial bleed with mass effect
Snoring and obstructive sleep apnoea (OSA) are risk factors for a difficult airway.12 They are suggestive of the presence of collapsible soft tissues within the airway. Prevalence estimates vary, a recent systematic review that primarily analysed data from Europe and North America found the prevalence of OSA to range from 9% to 38% in the general adult population, with the prevalence of clinically important OSA ranging from 6% to 17%. A higher prevalence was found in males, older people and those with a high BMI.15 Not all those who snore have OSA, but a common symptom of OSA is snoring.16 Clinical tools to help determine which patients may require further assessment and input from a medical practitioner is therefore useful. The Epworth Sleepiness scale (ESS) and STOP-Bang questionnaire (SBQ) are screening tools that have been suggested to help determine risk of OSA and are freely available online. Daytime sleepiness is one of the most common behavioural morbidities associated with OSA.17 The ESS asks users to state chance of dozing or falling asleep in various situations from which a score can be calculated.17 The SBQ assesses clinical features of OSA by asking a series of eight ‘yes’ or ‘no’ questions from which a score can be calculated based on the total number of ‘yes’ responses. There are four subjective questions (STOP – Snoring, Tiredness, Observed cessation of breathing, high blood Pressure) and four clinical characteristics (Bang – BMI, Age, Neck circumference and Gender).18 An SBQ score >3 indicates a higher risk for OSA.18 The outcome of the SBQ and/or the ESS may warrant referral to the patient's general medical practitioner for further investigation. Patients with OSA are classified as ASA III, and are not suitable for sedation in a primary care environment.19
Gastro-oesophageal reflux disease
Gastro-oesophageal reflux disease (GORD) may increase a patient's risk of aspiration.20 This emphasizes the importance of adhering to strict fasting requirements on the day of sedation.
Fasting requirements are controversial within dental sedation because the patient should maintain their airway reflexes. However, oversedation could lead to loss of, or decreased, airway reflexes.21 As a precaution, it is therefore advisable to follow fasting requirements, particularly for those with GORD due to the increased risk of aspiration. The common ‘2-4-6’ rule is endorsed by the IACSD and SDCEP guidelines.1,2 This involves fasting clear fluids for 2 hours and solids for 6 hours.9
Congenital diseases
The association of congenital diseases with significant comorbidities may place patients into at least an ASA III category. It is advisable to liaise with their medical practitioner should there be any doubt. Certain syndromes may be associated with unfavourable anatomy of the head, neck and upper airway. For example, those with Pierre Robin and Treacher Collins syndrome may exhibit macroglossia in combination with a small retrognathic mandible. Consequently, these patients may have a smaller upper airway, which is more prone to obstruction. Those with severe anomalies will be best sedated in a secondary care environment.10
Airway examination
Body mass index, weight distribution, and neck circumference
Body mass index (BMI) should form part of a patient's pre-sedation assessment.1,2 BMI is derived from the mass and height of a person. A BMI greater than 30 is indicative of obesity. Patients with a BMI >40 are classified as ASA III and are therefore unsuitable for primary care conscious sedation.13
Although BMI is important, the dental practitioner should also consider the distribution of a patient's body fat. Those who have a thick neck or appear to be ‘top-heavy’ may be at greater risk of airway problems due to increased distribution of adipose tissue around the upper airway. As a result, a high BMI with predominant weight distribution around the lower abdomen and hips may be less concerning than patients with weight centred around the upper body.10
A neck circumference over 40 cm (16 inches) may be associated with an increased likelihood of OSA.18 This can be easily assessed by asking for an individual's collar size, or using a flexible tape measure and forms part of the STOP-Bang questionnaire.
Cervical spine mobility
Assessment of a patient's cervical spine mobility will allow the practitioner to assess how easily a patient's airway can be opened with manoeuvres such as a head tilt chin lift.10 This can be simply performed by checking for full range of movement when the patient moves their head side to side and up and down. This will give an indication of the ease of opening the airway to relieve issues.
Dentition
Removable dental prostheses may present a risk to the airway. The presence or absence of these should be recorded during the sedation pre-assessment. Prostheses should be removed prior to sedation to minimize risk of displacement and airway obstruction, particularly if poorly fitting. Adjacent teeth should also be examined: loose teeth and restorations could be displaced during procedures and risk airway obstruction. Where appropriate, practitioners may wish to consider methods of airway protection, such as rubber dam.
Another consideration is that the edentulous may be more difficult to ventilate in an emergency due to the loss of cheek and lip support resulting in a poor mask seal.10,12,20
Mouth opening, interincisal distance and mandibular protrusion
A smaller mouth is easier to occlude and the presence of trismus may hinder the ability to open the airway or place adjuncts in an emergency. An interincisal distance of less than 30 mm may be considered non-reassuring.22 The interincisal distance could therefore be measured and documented.
Classifications are also available that examine the patient's ability to protrude their mandible. Limited protrusion of the mandible may indicate difficulties with bag/mask ventilation or use of a jaw thrust to open the airway should any of these interventions be necessary. The upper lip bite test by Khan et al23 (Table 2a) and jaw protrusion classification presented by Bradley et al12 (Table 2b) may provide a useful indication of the patient's ability to protrude their jaw. An inability for a patient to bite their upper lip, or place their lower incisors in front of their upper incisors are non-reassuring features. These tests may be difficult or unsuitable for those who are edentulous or wear dentures.
a
Class
Position of the lower incisors
b
Class
Position of lower teeth in relation to the upper
1
Lower incisors can bite past the vermillion border of the upper lip
A
Lower incisors can be placed in front of upper incisors
2
Lower incisors can bite the upper lip (but not past the vermillion border)
B
Lower incisors can be placed in line with upper incisors
3
Unable to bite the upper lip
C
Lower teeth cannot be placed in line with the upper incisors
Thyromental distance
The thyromental distance is that measured between the thyroid notch and the mental prominence when the head is fully extended. A distance less than 6 cm has been cited as a risk factor for difficult mask ventilation and difficulty in placing supraglottic airway devices.12
The Modified Mallampati score
The Modified Mallampati score classifies the visibility of oropharyngeal structures when the patient opens their mouth maximally and extrudes their tongue. The score is simple to implement and is illustrated by Table 3. Debate exists regarding its usefulness as a predictor for airway difficulties and inter-operator variability is present. Also note, as illustrated by Table 3, how one patient may demonstrate a range of Mallampati scores. However, it allows the sedationist to appreciate the size, position and mobility of the tongue in relation to the oral cavity and oral access.12 The greater the score, the more difficult the airway is potentially considered to be.
Class
Structures visible
I
Faucial pillars, soft palate and uvula visible
II
Faucial pillars and soft palate visible Uvula obscured by tongue
III
Only soft palate is visible
IV
Soft palate not visible
The LEMON score
The LEMON score incorporates multiple factors into a single tool to identify potentially difficult airways (Table 4). A maximum score of 10 exists by assigning 1 point to each of the criteria, with a higher score indicating a more difficult airway.24 A higher LEMON score has been found to be associated with increased intubation difficulty.24 Difficulty exists regarding the interpretation of the score in the dental setting; however, it is a useful framework that directs practitioners towards valuable assessment criteria. Practitioners should apply their own judgement dependent upon the score. A lower LEMON score is more reassuring.
Criteria
Score
Look externally
Facial trauma
1
Large/prominent incisors
1
Large tongue
1
Moustache or beard
1
Evaluate the 3-3-2 rule
Interincisal distance <3 finger widths
1
Hyoid to mental prominence distance <3 finger widths
1
Thyroid to floor of mouth distance <2 finger widths
1
Mallampati score
3 or 4
1
Obstruction
Evidence of airway obstruction, ie stridor
1
Neck mobility
Poor neck mobility
1
Conclusion
A thorough pre-sedation airway assessment must be conducted and documented for every patient to comply with published guidance. This article highlights important factors to consider when assessing a patient's airway, which may be incorporated into existing pre-sedation assessments to aid the decision-making process. It is important to remember that these tools are not diagnostic in themselves, and every patient must be assessed on an individual basis. An appreciation of the parameters discussed should increase confidence in identifying patients with an increased risk of airway difficulties. Practitioners should be able to identify suitable cases for management in primary care, and confidently refer where secondary care input is required. This is essential for patient safety. However, unexpected airway complications may arise regardless of the outcome of the pre-sedation assessment, highlighting the need for practitioners to be diligent.
