Anesthesia

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© Springer Nature Switzerland AG 2021

R. Reti, D. Findlay (eds.)Oral Board Review for Oral and Maxillofacial Surgerydoi.org/10.1007/978-3-030-48880-2_11

11. Outpatient Anesthesia

Robert Reti1  , David V. Valauri2, Michael H. Schiffman3, Andre H. Montazem4 and Jason E. Portnoff5
(1)

Southwest Oral Surgery, St. Louis, MO, USA
(2)

The Mount Sinai Hospital, Icahn School of Medicine, Oral & Maxillofacial Surgery/Otalaryngology, New York, NY, USA
(3)

Schiffman Oral Surgery, Woodmere, NY, USA
(4)

Elmhurst Hospital Center, Oral/Maxillofacial Surgery, Elmhurst, NY, USA
(5)

Nova Southeastern University College of Dental Medicine, Department of Oral and Maxillofacial Surgery, Boca Raton, FL, USA
 
Keywords

Minimal sedationModerate sedationDeep sedationThyromental distanceUpper lip bite testBody mass indexNil per OSCricothyrotomyTranstracheal needle ventilationPediatric airwayOxygenationVentilationCirculationModified Aldrete scorePharmacodynamicsPharmacokineticsMinimal alveolar concentration (MAC)Propofol (Diprivan®)Ketamine (Ketalar®)Midazolam (Versed®)Fentanyl (Sublimaze®)Succinylcholine (Anectine®)Rocuronium (Zemuron®)

It should be no surprise that it is expected that you will perform safe outpatient anesthesia in your office. Per the AAOMS parameters of care, all patients whom are an ASA class II and above should be considered for consultation with a physician for medical clarification of the patient’s medical condition and clearance to assist in making appropriate decisions for the setting and depth of anesthesia.

Accepted Definitions of Sedation and Anesthesia (AAOMS Parameters of Care 2017) [1] (Table 11.1)

Minimal Sedation (Anxiolysis) is a drug-induced state during which patients respond normally to verbal commands. Although cognitive function and physical coordination may be impaired, airway reflexes and ventilatory and cardiovascular functions are unaffected.

Table 11.1

Continuum of depth of sedation: definition of general anesthesia and levels of sedation/analgesia

 

Minimal sedation (anxiolysis)

Moderate sedation/analgesia (conscious sedation)

Deep sedation/analgesia

General anesthesia

Responsiveness

Normal response to verbal stimulation

Purposeful response to verbal or tactile stimulation

Purposeful response after repeated or painful stimulation

Unarousable, even with painful stimulus

Airway

Unaffected

No intervention required

Intervention may be required

Intervention often required

Spontaneous ventilation

Unaffected

Adequate

May be inadequate

Frequently inadequate

Cardiovascular function

Unaffected

Usually maintained

Usually maintained

May be impaired

Modified from Gross et al. [2]

Moderate Sedation/Analgesia (Conscious Sedation) is a drug-induced depression of consciousness during which patients respond purposefully1 to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained.

Deep Sedation/Analgesia is a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully1 following repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.

General Anesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. The ability to maintain ventilation function is often impaired. Patients often require assistance in maintaining a patent airway, and positive pressure ventilation may be required because of depressed spontaneous ventilation or drug-induced depression of neuromuscular function. Cardiovascular function may be impaired. Because sedation is a continuum, it is not always possible to predict how an individual patient will respond. Hence, practitioners intending to produce a given level of sedation should be able to rescue2 patients whose level of sedation becomes deeper than initially intended. Individuals administering moderate sedation/analgesia should be able to rescue2 patients who enter a state of deep sedation/analgesia, whereas those administering deep sedation/analgesia should be able to rescue2 patients who enter a state of general anesthesia.

Airway Assessment

The goal of the evaluation is to predict the difficulty of mask ventilation and endotracheal intubation, should either be required during surgery. Critical components of the airway assessment include the patient’s general appearance, dental exam, Mallampati score, maximum incisal opening, thyromental distance, mandibular protrusion, and BMI.

  • Dental Exam – look for mobile/carious teeth, edentulism, crowns, dentures, orthodontic appliances, and large tongue/tonsils.

  • Mallampati Score (See Fig. 11.1) – Original classification scheme was first described in 1985 as a clinical sign to predict difficult intubation and included 3 classes. In the modified Mallampati (by Samsoon and Young) a 4th class is included. Score of 3 or 4 indicates potential difficult intubation. Assessment of patient seated upright with head in neutral position, mouth open, tongue protruded without phonation.

    • Class I: soft palate, uvula, tonsillar pillars, and fauces are visible.

    • Class II: superior 2/3 of uvula and soft palate are visible.

    • Class III: <1/3rd of uvula and soft palate are visible.

    • Class IV: soft palate not visible.

  • Maximum Incisal Opening (MIO) – normal is >40 mm, <35 mm should be considered limited. Be cautious of patients with a history of temporomandibular joint disorders or a history of head and neck radiation. The ability to perform specific airway maneuvers depends in part on the degree that a patient is able to maximally open. At a MIO of 20 mm, it is possible to insert an oral or nasal airway, GlideScope ™, and perform a fiberoptic intubation. As the MIO increases to 30 mm, insertion of a laryngeal mask airway (LMA) becomes possible. At a MIO of 40 mm, direct laryngoscopy (DL) intubation may be performed.

  • Thyromental Distance – the distance between the top of the thyroid cartilage and the menton of the mandible. It is an indicator of the ability to displace the tongue during direct laryngoscopy. A distance of <6.5 cm (three finger breadths) may indicate difficulty with intubation.

  • Mandibular Protrusion – evaluate patient’s ability to protrude the lower jaw so that the mandibular incisors are in front of the maxillary incisors. This maneuver correlates with the clinician’s ability to sublux the mandible during laryngoscopy.

  • Upper Lip Bite Test (ULBT) – assesses a patient’s ability to reach and cover their upper lip with their mandibular incisors (similar to mandibular protrusion test).

    • Grade 1: fully covers the upper lip with lower incisors.

    • Grade 2: partially covers the upper lip with lower incisors.

    • Grade 3: cannot reach the upper lip with lower incisors.

  • Body Mass Index (BMI) and Obesity – patients often have increased parapharyngeal fat which can cause difficulty with airway maneuvers and these patients are more prone to desaturation during sedation. On the opposite spectrum, be extremely cautious of those with a BMI of <18.5, as they are at a higher rate of mortality with anesthetic challenges. Patients with a BMI of <18.5 are more prone to hypokalemia, dehydration, delayed gastric emptying, decreased GFR, and have a predisposition to aspiration.

    • BMI Scale (m/kg2):

      • Normal: 18.5–24.9

      • Overweight: 25–29.9

      • Obese: 30–39.9

      • Morbidly obese: 40–49.9

      • Super obese: >50

  • Neck Circumference – if greater than 43 cm (17 inches), associated with difficulty for intubation, more predictive than BMI.

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Fig. 11.1

Mallampati classification. (Reprinted with permission from Strauss and Noordhoek [11])

Laboratory Tests and Other Studies

  • Testing should be based on the history and physical of the patient and the nature of the surgical procedure.

  • An electrocardiogram (EKG) should be obtained in all adults over the age of 65, and any patient with a history of hypertension (HTN), cardiac disease, substance abuse, or eating disorder.

  • A fasting fingerstick glucose (FSG) should be obtained on all diabetics both prior to surgery and postoperatively prior to discharge.

  • Other lab tests that may be indicated depending on the patient’s reported history include Hematocrit (Hct), chest X-ray (CXR), urine pregnancy test (b-hCG), BMP, LFTs, coagulation studies, or echocardiogram.

Evaluation of Functional Status

  • During the preoperative evaluation, it is important to ask patients about their exercise capacity, as this is a significant determinant of perioperative risk. In general, patients with good exercise tolerance are at lower risk for cardiopulmonary complications during anesthesia. One commonly used measure of exercise tolerance is metabolic equivalent tasks (METs).

  • MET is a physiological measure that expresses the energy cost of performing various physical activities. It is expressed as the ratio of a patient’s metabolic rate during a specific physical activity over the reference metabolic rate, which is the resting or basal oxygen consumption of a 40-year-old, 70-kg man (3.5 mL O2/kg/min or MET 1) [3].

  • Perioperative risk is elevated in patients with <4 METs. Activities of <4 METs include watching TV, shopping, golfing with a cart, and walking slowly (2–3 mph).

  • Activities associated with >4 METs include climbing a flight of stairs, bicycling, walking >4 mph, and performing housework.

American Society of Anesthesiology (ASA) Classification

American Society of Anesthesiology Clinical Information [Internet]. Schaumburg, IL: American Society of Anesthesiologists; 2017. ASA physical status classification system; [approved 2014 Oct 15; Available from: www.ncbi.nlm.nih.gov/books/NBK441940/]

  • ASA Class I: A healthy patient (healthy, non-smoking, no or minimal alcohol use).

  • ASA Class II: mild systemic disease (WITHOUT substantive functional limitations).

    • For example, current smoker, social alcohol drinker, pregnancy, obesity (BMI 30–40), well-controlled DM/HTN, mild lung disease.

  • ASA Class III: severe systemic disease that limits activity but is not incapacitating (substantial functional limitations).

    • For example, poorly controlled DM/HTN, COPD, morbid obesity (BMI ≥40), active hepatitis, alcohol dependence or abuse, implanted pacemaker, moderate reduction of ejection fraction, ESRD undergoing regularly scheduled dialysis, history (>3 months) of MI, CVA, TIA, or CAD/stents.

  • ASA Class IV: severe systemic disease that is a constant threat to life.

    • For example, recent (< 3 months) MI, CVA, TIA, or CAD/stents, ongoing cardiac ischemia or severe valve dysfunction, severe reduction of ejection fraction, sepsis, DIC, ARD, or ESRD not undergoing regularly scheduled dialysis.

  • ASA Class V: moribund patient who is not expected to survive without operation.

  • ASA Class VI: declared brain-dead patient whose organs are being removed for donor purposes.

  • The addition of “E” denotes emergency surgery – added when a delay in treatment of the patient would lead to a significant increase in the threat to life or body part.

NPO Guidelines

In 2017, the American Society of Anesthesiology published a set of practice guidelines regarding preoperative fasting prior to anesthesia. These guidelines were meant to reduce the occurrence and severity of complications related to perioperative pulmonary aspiration of gastric contents [4].

The ASA’s preoperative fasting guidelines for elective procedures requiring general anesthesia, regional anesthesia, or sedation/analgesia are summarized as follows:

  • Clear liquids – at least 2 hours.

    • Examples of clear liquids include water, fruit juice without pulp, carbonated beverages, clear tea, plain gelatin, and black coffee. These liquids should NOT include alcohol. The volume of liquid ingested is less important than the type of liquid ingested.

  • Breast milk – at least 4 hours.

  • Infant formula – at least 6 hours.

  • Non-human milk – at least 6 hours.

  • Solids, light meals, non-clear liquids – at least 6 hours.

  • Heavy meal or fried/fatty foods – at least 8 hours.

Note: The routine use of preoperative gastrointestinal stimulants (e.g., metoclopramide), medications that block gastric acid secretion (e.g., H2 antagonists, PPIs), antacids (e.g., sodium citrate, magnesium trisilicate), antiemetics (e.g., droperidol, ondansetron), to decrease the risk of pulmonary aspiration in patients who have no apparent increased risk for pulmonary aspiration is NOT recommended. The use of anticholinergics (e.g., atropine, glycopyrrolate) is NOT recommended to reduce risk of pulmonary aspiration.

Airway Management

Oxygen Delivery Methods

Mouth to Mouth

  • Exhaled air contains 17% oxygen.

Nasal Cannula

  • Each increase liter per minute is approximately 4% above room air.

  • FiO2 = 20 + [4 L/min × L/min].

  • Flow greater than 4 L/min, although delivering 36%, may be uncomfortable.

Simple Facemask

  • Flow 8–12 L/min.

  • FiO2: 35–65%.

  • Increase approximately 4% per liter flow.

Non-Rebreather

  • Flow rate should be min 6–15 L/min.

  • FiO2: 60–100%.

  • Delivered oxygen ~60%, each L/min increase will raise FiO2 ~5%.

Mask Ventilation

  • Can be used for spontaneously breathing patients or apneic patients via positive pressure ventilation.

  • Uses:

    • Primary means of ventilation for a short procedure.

    • Bridge to establishing a more definitive airway.

    • Pre-oxygenation prior to GA induction.

    • Valuable rescue technique when intubation proves difficult.

  • Caution if full stomach, severe facial trauma or C-spine fracture.

  • Difficulty occurs when ventilating via the facemask is not possible because of an inadequate mask seal (e.g., beard hair), excessive gas leak, and/or excessive resistance to the ingress or egress of gas. This may be helped by oro/naso-pharyngeal airways.

  • Risk factors for bag mask ventilation difficulty include age greater than 55 years, BMI > 26 kg/m2, edentulism, presence of a beard, and history of snoring [5].

Oropharyngeal Airways

  • Follows the curvature of the tongue, pulling the tongue and epiglottis away from the posterior pharyngeal wall.

  • Not appropriate for use in conscious patients (can cause coughing, retching, or laryngospasm due to irritation at base of tongue). Best used in the deeply anesthetized patient.

  • Sized by measuring from the corner of a patient’s mouth to the angle of the jaw.

Nasopharyngeal Airways

  • Less stimulating than oropharyngeal airways, more appropriate for lightly anesthetized patients.

  • Lubricate prior to insertion and insert with the bevel facing the nasal septum.

Laryngeal Mask Airway (LMA)

  • Supraglottic airway that is blindly inserted into the pharynx.

  • Provides a patent conduit for ventilation, oxygenation, and delivery of anesthetic gases without tracheal intubation.

  • Less invasive than intubation but provides a more definitive airway than a facemask.

  • Can be used for either spontaneous ventilation or PPV.

  • Allows for delivery of O2 and inhaled anesthetics during spontaneous ventilation or via PPV at pressures up to 20 cmH2O.

  • Flexible LMA Tube allows the tube to be moved out of the surgical field without displacement of the cuff, or loss of seal for the anesthesiologist.

Endotracheal Intubation

  • Gold standard for airway management.

  • Establishes a definitive airway.

  • Maximal protection against aspiration of gastric contents.

  • Allows for delivery of O2, inhalational anesthetics and allows for PPV with higher airway pressures than with a facemask or supraglottic airway (LMA).

Emergency Percutaneous Airways

Cricothyrotomy

  • Invasive technique that provides access to the airway in situations when either noninvasive maneuvers have failed or when it is clinically indicated as a primary plan to secure the airway.

  • Not considered a permanent airway, and after placement plans should be made for either the removal or conversion to a formal tracheostomy.

  • Technique:

    • Step 1: Extend the head and neck and identify and immobilize the cricothyroid membrane. (Make an initial vertical incision if identification is not possible.)

    • Step 2: Make a horizontal stab incision through the skin and cricothyroid membrane and keep the blade in place.

    • Step 3: Use a tracheal hook to apply caudal and outward traction on the cricoid cartilage; remove the scalpel.

    • Step 4: Insert the ETT tube (6.0 cuffed mm) or tracheostomy tube (No.4 cuffed tracheostomy tube) and inflate the cuff.

    • Step 5: Ventilate with a low-pressure source.

    • Step 6: Confirm pulmonary ventilation.

  • Note: In children <6 years of age, cricothyrotomy is contraindicated because the cricoid cartilage is the narrowest portion of the airway and the isthmus of the thyroid gland typically reaches the level of the cricothyroid membrane. Needle cricothyrotomy with transtracheal jet ventilation is indicated in this pediatric population.

  • Conversion to tracheostomy is normally recommended within 72 hours to prevent subglottic stenosis [6].

Transtracheal Needle Ventilation

Jul 23, 2021 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Anesthesia
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