February 4, 2020
by Rob Matsui; Paul Azzopardi, HBSc, MSc, DDS
Pre-operative airway assessment and management is essential to successful dental treatment under procedural sedation. In the event of oversedation, defined as the transition from an intended level of sedation to an unintended deeper level of sedation, the patient’s ability to independently maintain ventilatory function may be impaired. This can result from an inability for the patient to maintain a patent airway, which may require the operator to intervene with assistive maneuvers to help stent the airway open and may include ventilatory support via a bag-valve-mask device.
For the non-anesthetist, intervention may seem daunting and operators inexperienced in managing an airway may find great difficulty in resolving an airway emergency if bag-mask-ventilation (BMV) is required. In addition to an accurate medical history, risk factors that should be considered during pre-sedation consultation should also include assessment of patient-specific factors related directly to predicted ease or difficulty with BMV.1,2,3
Assessing these risk factors can help predict the ability to maintain an adequate mask seal and the ability to maintain airway patency, both of which can be evaluated by adequate chest rise once positive pressure ventilation is applied. The overall clinical goal of mask ventilation is to maintain adequate blood oxygenation (as monitored via pulse oximetry readings above 90%).3
A number of factors can significantly affect mask seal and therefore the ability to provide BMV. Specific factors such as the presence of a beard,1,4,5 edentulism (especially in the maxillary and mandibular anterior segment), sunken cheeks,3 tongue protrusion, retrognathia and limited mandibular protrusion can affect the ability to obtain an adequate mask seal conducive to positive pressure ventilation. Although not a risk factor for difficult ventilation in and of itself, the elderly population (over age 55) may portray a number of these risk factors and therefore should carry special consideration.
With concern to mandibular protrusion, simple chairside tests can be performed to evaluate this predictor including the upper lip bite test (ULBT) or the upper lip catch test (ULCT).2,6 The basis for the ULBT is the position of the incisal edges of lower anterior teeth in relation to the vermillion border of the upper lip and is divided into three classes (Figure 1): Class I = at or above the vermillion line, Class II = below vermillion line and Class III = inability to bite the upper lip. For patients who are edentulous, the ULCT can be applied and follows similar designations as follows with regard to the lower lip (Fig. 1): Class 0 = glides or rolls over the upper lip as high as the rhinion (lower point of median suture that joins nasal bones) or any point midway between the vermillion line and the rhinion, Class I = catches the upper lip, between a point 2 mm above vermillion line and a point midway between vermillion line or just above it, Class II = catches the upper lip at the level of vermillion line or just above it (2 mm), Class III = caresses the upper lip but falls short of obliterating the vermillion line. The finding of a Class I ULBT has a negative predictive value of 86% for difficult mask ventilation, thus suggesting but not guaranteeing that mask ventilation should be easy.7 The finding of a class II or III in either the ULBT and ULCT may be indicative of a difficult BMV.2,6,7
Upper Lip Tests: Catch Test Bite Test
Airway patency is a critical component in predicting ease of BMV. Factors that can predict complications include obesity (BMI> 26) which can decrease lung compliance due to increased body mass, sleep apnea, a history of snoring, limited neck mobility and pregnancy.1,3,4,5 Patients with these associated risk factors can be challenging for BMV as a result of upper airway obstruction, because sedation reduces airway muscle tone. Airway obstruction is most commonly caused by the tongue drifting posteriorly and severely limiting or completely impeding airflow. For those providers trained in airway manipulation, improving head position via a head-tilt and chin-lift maneuver with or without a jaw thrust can restore airway patency in most situations. For situations where this does not relieve airway obstruction, more advanced interventions such as two-handed mask ventilation that requires trained support staff and/or airway adjuncts such as an oropharyngeal/nasopharyngeal airway, supraglottic devices such as a laryngeal mask airway (LMA) or even endotracheal intubation. Further description of the technical aspects required to perform BMV exceed the scope of this discussion, however sedation providers are required to obtain and maintain current basic life support (BLS) and possibly advanced cardiac life support training, depending on the sedation depth/modality used. Further practice with BMV, a lifesaving skill, can be arranged and is encouraged when participating in these courses.
It should be made clear that the aforementioned factors in assessing the difficulty of BMV should be interpreted by the clinician as a collection of observations, assessments and inquiries to obtain an overall picture of the sedation candidate prior to treatment initiation.1,2,3,4 In order to remember these predictors, a helpful acronym that has clinical relevance is BONES.8
B – Beard. Does the patient have a beard?
O – Obesity/OSA. Is the patient obese (BMI >26)? Have they been diagnosed with obstructive sleep apnea? Does the patient snore (flaccid tongue, possible macroglossia)?
N – Neck/Tongue/Chin Mobility – Does the patient have limited neck mobility <80o (arthritis/trauma)? Do they have a retrognathic mandible or soft tissue profile, is their ULBT>1 or ULCT>0? Can they protrude their tongue?
E – Elderly/Edentulism. Is the patient elderly (>55 years)? Are they edentulous (sunken cheeks)?
S – Stiff Lungs/Subglottic Stenosis. Does the patient have any form of restrictive lung disease (pulmonary fibrosis/scoliosis)? Do they have an upper respiratory tract infection resulting in stridor (or history of laryngomalacia, laryngeal paralysis, or presence of an airway mass/lesion)? Do they have a history of obstruction due to abnormal airway anatomy (subglottic stenosis)?
If the answer is yes to any of the above questions, in the event of an over-sedation, a provider should anticipate difficulty with BMV and prepare accordingly in an effort to avoid life-threatening complications that may arise. For the moderate sedation provider, prompt identification of a deeper sedation state and subsequent administration of reversal agent(s) should occur simultaneously with BMV or any form of airway support.
In order to further emphasize the importance of this discussion to the procedural sedationist, the authors would like to present the following scenario: Imagine a seemingly routine case at your office where meticulous consideration on BMV predictors may have been overlooked. You have completed a thorough medical history and have deemed the patient suitable for moderate sedation to complete the necessary dental treatment. The patient is scheduled for the complicated extraction of teeth 46 and 47. The patient is anxious about the procedure but agrees to moderate parenteral sedation with midazolam. There are no contraindications to procedure start (e.g. no changes in medical history, no changes in medications and no violation of npo status) and you administer a standard initial dose of 2 mg of midazolam. Despite waiting for appropriate onset of effect, the patient still seems uncomfortable and you confirm her depth of sedation as moderate via purposeful response to verbal commands. You decide to administer another 1 mg bolus of midazolam and she tolerates local anesthetic (LA) administration. You perform an IAN block and supplemental buccal and lingual infiltration without incident and begin the extraction of tooth 47. Upon luxation with an elevator, the patient grimaces. You feel confident that your LA is sufficient and instruct your nurse to administer another bolus of 2 mg of midazolam. After several minutes, tooth 47 has been extracted and you begin to prepare to extract tooth 46. As you are preparing to elevate, you hear a tonal shift in the pulse oximeter and your nurse points out that the SpO2 value is trending down below 93%. You provide tactile stimulation to the patient while instructing them to take a deep breath, however the patient’s breathing appears impaired and their response to your repeated verbal commands is not purposeful. You attempt to increase the inspired fraction of oxygen by providing supplemental oxygen via nasal cannula. Despite your efforts the oxygen saturation decreases to 88%. You perform a head-tilt chin-lift but the patient’s SpO2 continues to trend downwards, now at 84%. You call for the bag-valve-mask and attempt to ventilate the patient, but you do not see adequate chest rise. The pulse oximeter now reads 80%. You continue to attempt BMV by pushing the mask into the patients face and squeezing the bag harder and faster. You hear a hissing sound around the mask. SpO2 is now 77%. You ask for an oropharyngeal airway and continue attempting BMV without much success. The oxygen saturation level continues to drop; the pulse oximeter now reads 73%. The oropharyngeal airway arrives and is immediately inserted, which significantly improves airway patency and you obtain a mask seal with a two-handed jaw thrust. The oxygen saturation reading begins trending upwards, and now reads 92%. You decide to administer flumazenil to reverse the sedation as this patient is unable to maintain a patent airway without support. After two 0.2 mg IV doses of flumazenil, the patient gags on and then coughs out the oropharyngeal airway. Once suitably recovered, the patient is unhappy that tooth 46 has not been extracted. By contrast, you are relieved that your patient has recovered from this airway complication.
Upon debrief with your team, you realize that critical steps could have been taken in advance of the treatment in anticipation of a potentially difficult airway that couldhave been better managed by the team. On re-review of the medical history and dental examination you are suddenly conscious of this 66-year-old female’s retrognathic soft tissue profile and the additional impact of her missing maxillary anterior teeth for which she wore a partial denture. She had reported mild snoring. Her BMI is 27 and her ULCT was class II. Assessing this patient using BONES would have anticipated the difficult BMV and although the event was resolved without sequelae, the prudent practitioner would take these factors into account in determining if this patient is suitable for moderate sedation and judiciously titrate parenteral sedative agent to avoid over-sedation.
A helpful philosophy to maintain for any sedation procedure is to presume that any patient you treat, even if it is the same individual on subsequent visits, may be an outlier to standard dosing regimens and that each patient has the potential to be over-sedated to the extent that an unintended deep sedation is reached that may require ventilatory support. As with any other dental procedure performed on our patients, each intervention has its associated risks and complications and the same applies to administering sedative agents. The major difference however between the two interventions is that a complication in sedation may be a life-threatening event. It may be beneficial to create and review a pre-appointment checklist to ensure that you, your team, and your operatory is adequately prepared to manage foreseeable complications.
In closing, in order to complete the discussion on management of over-sedation, the following should be considered prior to the start of treatment:
1. Take a thorough medical history;
2. Perform a specific airway assessment with a focus on BONES as a predictor for difficult BMV;
3. Upon recognition of a potentially difficult airway, have airway adjuncts immediately available and make your team aware of their locations;
4. Determine your reversal agent doses and have knowledge of their onset to peak clinical effect and duration of action.
For reversal of benzodiazepines via antagonism at GABA/benzodiazepine receptors. Administer slowly in 0.2 mg increments over 15-30 seconds. IV onset time: 1-2 minutes with peak effect at 6-10 min. Re-sedation can occur and may require repeat doses up to every 20 minutes. Do not exceed 1 mg/dose or 3 mg/hour.
For reversal of opioids via antagonism at all opioid receptors. Administer cautiously, titrating slowly in 0.1-0.2 mg increments to desired effect. IV onset time: 1-2 minutes with peak effect at 5-15 min. Repeat doses may be required every 2-5 minutes.
5. Use the lowest effective dose of a sedative agent to perform the necessary procedure (“Start low and go slow”).
6. Continuously assess the depth of sedation throughout the procedure via verbal command and tactile stimulation.
7. When indicated, verify profound anesthesia via LA administration and utilize supplemental LA techniques to ensure profound anesthesia before administering additional sedative bolus doses
8. If the depth of sedation progresses to a state deeper than the intended level of sedation, provide supplemental oxygen and ventilatory support if required, and promptly administer reversal agent(s).
9. Report event within 24 hours if this is mandated by your regulatory body.
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About the Author
Dr. Robert Matsui completed his MSc degree in Oral Microbiology in 2009 and his DDS degree in 2013 both at the University of Toronto, Faculty of Dentistry. He is expected to complete his specialty training in Dental Anesthesia at the University of Toronto in 2020. Upon graduation, Dr. Matsui would like to practice in Northern Ontario servicing our First Nations populations.
Dr. Paul Azzopardi completed his MSc degree in Biochemistry in 2009 and his DDS degree in 2013 at Western University. He subsequently completed a general practice residency at the University of Alberta in 2014. He is currently in his second-year of the Graduate Dental Anaesthesia program at the University of Toronto.