Introduction

• Anesthesia and sedation in dentistry can have several forms, including:

  • Local anesthesia alone.

  • Oral and/or intranasal sedation.

  • Intramuscular (IM) sedation.

  • Inhalation sedation (nitrous oxide).

  • Intravenous (IV) mild/moderate sedation.

  • IV deep sedation (used by oral and maxillofacial surgeons [OMSs]).

  • Total IV general anesthesia (used by OMSs).

  • Inhalation general anesthesia with/without endotracheal intubation.

• Each of these modalities requires complex training and performance by qualified practitioners, as well as a thorough understanding of pharmacology.

This chapter only discusses local anesthesia, nitrous oxide, and medications used for mild/moderate sedation.

Pharmacology

• The field of medical science which deals with the properties and effects of drugs as well as their interactions with living systems such as cells, organs, animals, and humans.

Drug Distribution

• Eventual placement of the drug within the body over a given period of time.

• Primary compartments include:

  • Brain.

  • Muscle.

  • Fat.

Metabolism

• Alteration of the drug by the body.

• Most drugs are metabolized in the liver.

  • Microsomal enzyme alteration (cytochrome [CYP] P-450).

  • Many drugs can inhibit the CYP isoforms of the P-450 drug metabolism system.

  • Two simultaneous doses of drugs normally metabolized in this manner may cause elevated blood levels of one or both medications, leading to toxic overdose effects.

    • Example: erythromycin causes elevated blood levels of theophylline, which results in theophylline toxicity.

    • Other drugs or foods, such as grapefruit juice, can inhibit the activity of the CYP isoforms resulting in a higher than usual blood level of drugs metabolized by the P-450 system.

Plasma Protein Binding

• Protein binding can enhance or detract from a drug’s performance.

• As a general rule, agents that are minimally protein bound penetrate tissues better, but are excreted much more rapidly.

• Drugs may bind to a wide variety of plasma proteins, including albumin.

• The concentration of several plasma proteins can be altered by many factors including stress, surgery, liver or kidney dysfunction, inadequate nutrition, and pregnancy.

• Drugs bound to plasma proteins will not enter the liver readily to be metabolized or excreted, resulting in a longer drug half-life and elevated blood levels in the elderly whose plasma albumin contents are lower.

  • Example: benzodiazepines can cause increased sedation and respiratory depression in the elderly.

Biotransformation

• The process that changes a drug to a different form that typically is more water-soluble.

Pathology

• Liver disease generally results in elevated levels of nonmetabolized drugs.

Absorption

• The route/initial process of the drug entering the body.

  • Gastrointestinal tract.

    • Oral ingestion.

    • Rectal (suppository).

  • Respiratory (inhaled medication into lungs, often via an inhaler).

  • Vascular (IV).

  • Skin (subcutaneous/intradermal).

  • Muscle (IM).

Excretion/Elimination

• The metabolized form of many drugs is more likely to stay in fluids and less likely to be reabsorbed by the kidney and back into the bloodstream.

• This facilitates excretion in urine.

• Elimination can also take place through the lungs, sweat, saliva, and feces.

Routes of Administration

• Oral.

  • Advantages:

    • Convenient access.

    • Painless route (no needles).

    • Economic—low cost.

  • Disadvantages:

    • Delayed onset (may take 30–45 minutes to show effect).

    • Unpredictable effects (same dosage may have different effects on different patients).

    • Patient compliance may be suboptimal (bad-tasting medications may be rejected by younger patients).

    • Difficult route of administration for patients with nausea.

• Topical.

  • Mucous membrane (e.g., topical anesthesia in dentistry).

  • Skin (e.g., nicotine patch).

  • Advantages:

    • Easily accessible.

    • More rapid absorption than via oral route.

    • Drugs enter systemic circulation without hepatic first pass.

  • Disadvantages:

    • Patient cooperation (patient might remove medication patch).

    • Slow onset.

    • Unpredictable effects.

    • Most drugs are poorly absorbed by this route.

• Intranasal: direct delivery to the brain may be facilitated by the incomplete blood–brain barrier in the olfactory region.

  • Advantages:

    • Rapid absorption.

    • Relatively minimal irritation.

    • Usually well tolerated by most patients.

    • Easily administered.

  • Disadvantages:

    • Patient cooperation could be an issue (pediatric patients).

    • Contraindicated for use in patients with upper respiratory infections.

Injection Routes

• Intramuscular (IM).

  • Advantages:

    • Good absorption due to vascularity of the muscle mass.

    • Easy access regardless of patient age, size, or nausea.

  • Disadvantages:

    • Variable and unpredictable onset of the drug effect.

    • Cannot titrate drug dosage.

    • Some drugs can be irritating to the muscle.

• Intravenous (IV).

  • Advantages:

    • Accurate dosage control.

    • Rapid onset.

    • Greater maximum volume of administration.

    • Greater dilution of the drug in normal saline or lactated Ringer’s solution.

  • Disadvantages:

    • Greater potential for complications including infection and damage of the vasculature.

    • Greater discomfort associated with exploration and puncture of a subsurface vessel.

    • Increased technique sensitivity.

Inhalational Anesthesia

• Advantages:

  • Easily administered by trained professionals.

  • Painless.

  • Easily titrated.

  • Notable compliance for anesthesia in children.

  • Rapid absorption into systemic circulation through the lungs.

  • Most inhalational agents are general anesthetics except nitrous oxide.

• Disadvantages:

  • Special equipment required.

  • Inhalational general anesthetics may require intubation and ventilatory support.

Anesthetic Techniques

• Local anesthesia.

• Oral and nasal sedation.

• IM injection.

• Inhalation sedation (including nitrous oxide).

• IV mild/moderate sedation.

• IV deep sedation.

• General anesthesia.

Medications Utilized in Anesthesia/Sedation for Dental Patients

• Benzodiazepines.

  • Anxiolytic.

  • Anticonvulsant.

  • Antispasmodic.

  • Sedative/hypnotic.

  • Amnesic (anterograde amnesia).

  • Enhances the binding of gamma-aminobutyric acid (GABA) to the GABA receptor complex.

    • Increases frequency of chloride channel opening, which decreases the intracellular voltage and thus decreases neuronal firing.

  • Often available in both oral (PO) and IV forms.

  • Short-acting (< 6 hours) agents:

    • Triazolam (Halcion^®) PO.

    • Midazolam (Versed^®) PO, IV.

  • Intermediate (6–10 hours) agent:

    • Alprazolam (Xanax^®) PO.

  • Long-acting (> 10 hours) agents:

    • Diazepam (Valium^®) PO, IV.

    • Lorazepam (Ativan^®) PO, IV.

  • Diazepam (Valium^®).

    • Reduces anxiety.

    • Relaxes patient.

    • Dose-dependent anterograde amnesia.

    • Dose: 2–20 mg IV.

    • Easy to titrate.

    • Sedation effects may be reversed with flumazenil.

    • Insoluble in water.

    • Dissolved in propylene glycol which can cause vein irritation (phlebitis).

    • Half-life 20 to 40 hours.

  • Midazolam (Versed^®).

    • Produces greater sedation than diazepam.

    • More profound anterograde amnesia than diazepam.

    • Shorter acting than diazepam.

    • Water soluble—less risk of thrombophlebitis than diazepam.

    • Dose: 1 to 5 mg IV.

    • Half-life: 1 to 4 hours.

    • Sedation effects may be reversed with flumazenil.

• Reversal agent for benzodiazepines.

  • Flumazenil (Romazicon^®).

    • Used to reverse the effects of benzodiazepines.

    • Competitive antagonist at the GABA receptor.

    • Dose: 0.2 to 1.0 mg IV.

    • Reverses sedation and respiratory depression.

    • Rapid onset (1–2 minutes).

    • Patients might need to be observed for up to 2 hours because of the relatively short-term effects of flumazenil.

    • Watch for resedation.

• Opioids.

  • Narcotics.

  • All are potent analgesics.

  • Act as agonist on mu, delta, kappa, and sigma receptors in the central nervous system (CNS).

  • Mu receptors (supraspinal).

    • Responsible for analgesia and euphoria.

  • Available in both oral (PO) and IV forms.

    • Fentanyl (IV, PO).

    • Morphine (IV, PO).

    • Codeine (PO).

    • Meperidine (IV, PO).

  • Adverse effects:

    • Pruritis (due to histamine release).

    • Nausea/vomiting.

    • Urinary retention.

    • Constipation.

    • Miosis.

    • Respiratory depression.

  • Signs of opioid withdrawal:

    • Hypertension.

    • Piloerection (“goose bumps”).

    • Chills.

    • Sweating.

    • Nausea/vomiting.

    • Abdominal cramping.

    • Restlessness.

    • Mydriasis.

    • Lacrimation and rhinorrhea.

    • Insomnia.

    • Manifestations not life-threatening unlike alcohol or benzodiazepine withdrawals.

  • All are respiratory depressants.

  • Minimal cardiovascular effects at normal doses.

  • Relieve pain without altering other senses (e.g., vision, hearing, touch).

  • All are reversible with naloxone (Narcan^®).

  • Fentanyl.

    • Synthetically modified morphine that is 100 times more potent.

    • Rapid onset (< 1 minute).

    • Short duration (30–60 minutes).

    • Cardiovascular system remains stable, but may see bradycardia.

    • No histamine release.

    • Best narcotic for asthmatic patients and patients with a history of nausea and vomiting.

    • Dose: 0.025 to 0.1 mg IV (25-100 µg).

    • Can cause profound respiratory depression with deeper but infrequent breaths.

    • Can cause chest wall rigidity if the administered dose is too potent and rapid.

    • Most commonly used in current practice.

  • Morphine.

    • A natural opioid.

    • Narcotic analgesic standard—the standard to which other narcotics are compared.

    • No longer commonly used for IV anesthesia in oral and maxillofacial surgery.

    • Important emergency medication for myocardial infarction (dose 2–10 mg IV).

    • High addiction potential.

• Narcotic antagonist.

  • Reverses the opioid’s sedation and respiratory depression effects.

  • Pure mu receptor antagonist.

    • No opioid receptor agonist activity.

  • Also reverses the opioid’s analgesic effects.

    • Can precipitate opioid withdrawal in patients with chronic pain on long-term opioids.

  • Example: Naloxone (Narcan^®).

    • Dose: 0.4 to 2.0 mg IV.

    • Rapid onset of action (1–2 minutes).

    • Short duration of action (45 minutes).

    • Patients may need to be observed for up to 2 hours following administration.

• Nitrous oxide/oxygen delivery system.

  • Must be capable of administering positive pressure oxygen.

  • Must have a scavenging system.

    • Two-tube system: (1) Scavenger tube removes exhaled nitrous oxide for the protection of the office staff. (2) Larger tube delivers nitrous oxide/oxygen gas mixture to patient.

• Oxygen.

  • Stored in green medical gas cylinder tanks of varying sizes.

  • Room air is approximately 21% oxygen.

  • Thirty percent or higher concentration of oxygen is recommended when delivering other pharmacologic agents to patients.

  • Recommended for all medical emergencies except hyperventilation (see Chapter 13, Management of Medical Emergencies).

  • May be used with all sedation cases.

  • Use with caution in patients with chronic obstructive pulmonary disease (COPD).

    • Flow should be no higher than 2 to 3 L/minute in patients with COPD.

• Nitrous oxide.

  • Indications for use:

    • Patients with mild apprehension undergoing dental procedures/extractions.

    • Anxious or hyperactive children.

  • Contraindications for use:

    • Absolute contraindications: (1) Pregnancy (may cause spontaneous abortion according to some studies, though controversial), (2) otitis media, (3) congenital pulmonary blebs, (4) sinus blockage, (5) bowel obstruction, (6) nasal obstruction, (7) cystic fibrosis, (8) COPD.

    • Relative contraindications: (1) Upper respiratory infection, (2) severe dental fear or anxiety, (3) patients with a prior bad experience or adverse reaction to nitrous oxide.

    • Asthma is not a contraindication for use of nitrous oxide.

  • Stored in blue medical gas cylinder tanks of varying sizes.

  • Is known by many as “laughing gas.”

  • Physiology of nitrous oxide:

    • Acts on the CNS.

    • Produces a generalized neurologic depression and inhibits mental focus.

    • Decreases all forms of sensory input.

  • Solubility of nitrous oxide:

    • Relatively insoluble in blood.

    • Requires high alveolar concentration to achieve its intended effects.

  • Concentration effect:

    • The higher the concentration of nitrous oxide inhaled, the more rapid the increase in arterial concentration.

  • Minimum of 30% oxygen delivery is required.

  • Most flowmeters allow delivery of 30 to 70% nitrous oxide concentrations.

  • Weak anesthetic.

  • Provides analgesia.

  • Produces euphoria and relaxation.

  • No biotransformation.

  • Side effects include:

    • Headaches.

    • Nausea/vomiting.

    • Lethargy.

    • Diffusion hypoxia.

  • Diffusion hypoxia:

    • May occur if the patient is permitted to recover from nitrous oxide sedation while breathing in only room air.

    • Nitrous oxide from the bloodstream diffuses into the alveoli in the lungs diluting the oxygen concentration in the alveoli more rapidly than it can be replaced.

    • This causes decreased oxygen blood saturation, resulting in hypoxia.

    • Preventable via administration of high-concentration oxygen (100%) for at least 5 minutes during the recovery from nitrous oxide sedation. (1) 100% oxygen is almost five times more concentrated than the oxygen in room air (21%). (2) Allows for maintenance of adequate oxygen concentration in the alveoli.

  • Complications of prolonged exposure to nitrous oxide:

    • Bone marrow suppression.

    • Megaloblastic anemia.

    • Leukopenia (low white blood cell numbers).

    • Neurological deficiencies: peripheral neuropathies.

    • Pernicious anemia.

  • Nonflammable gas.

  • May induce slight respiratory and myocardial depression.

  • Patients with obstructive sleep apnea are sensitive to nitrous oxide and may benefit from lower concentrations of nitrous oxide.

  • Not contraindicated for use in patients with asthma.

  • Slight odor.

  • Quick recovery once the gas has been discontinued.

• Technique for use of nitrous oxide:

  • Give verbal instructions prior to initiating nitrous oxide.

  • Confirm that female patients are not pregnant.

  • Inform patients that they “may feel like they are floating.”

  • Inform patients that they “may feel tingling in their fingers and toes.”

  • Total flow of air needed ≅ 6 to 8 L per minute typically.

    • Respiratory minute ventilation = tidal volume (amount of air per breath) × respiratory rate (usual is 12–16 breaths per minute).

  • Onset of effect is usually 2 to 3 minutes after initiating flow of nitrous oxide.

  • Low level nitrous oxide administration is usually sufficient for children.

    • Thirty-three percent nitrous oxide: 2 L per minute nitrous oxide: 4 L per minute oxygen.

  • Medium level nitrous oxide administration is usually sufficient for most adults; maximum dose recommended for children.

    • Fifty percent nitrous oxide: 3 L per minute nitrous oxide: 3 L per minute oxygen.

  • High level nitrous oxide administration (for certain adults who are unaffected at medium level).

    • 62.5% nitrous oxide: 5 L per minute nitrous oxide: 3 L per minute oxygen.

  • Maximum level nitrous oxide administration (for certain adults who are unaffected at high level).

    • Seventy percent nitrous oxide: 7 L per minute nitrous oxide:3 L per minute oxygen.

  • Procedure of administering nitrous oxide:

    • Place monitors: (1) Pulse oximeter—continuous, (2) blood pressure cuff set to every 5 to 10 minutes.

    • Apply shaded protective eyewear to patient.

    • Turn down brightness of ambient room lights.

    • Turn on pleasant music to drown out office noise.

    • Turn flowmeter on to 6 to 8 L per minute oxygen (100%) before placing the nasal hood on the patient.

    • Place the nasal hood on the patient ensuring that the size is appropriate and the fit is snug: (1) The patient should not feel air outflow on his/her eyes. (2) The patient should feel that he/she is getting enough air solely by breathing through their nose and nasal hood.

    • Ensure the scavenging system is turned on.

    • Slowly initiate administering nitrous oxide by incrementally adjusting the nitrous oxide dial on the flowmeter: (1) Allow 2 to 3 minutes to take effect. (2) If the nitrous oxide level is too low, the patient will not experience the relaxant effects. (3) If the nitrous oxide level is too high, the patient may experience nausea, dysphoria, sleepiness, disorientation, or sweating.

    • When the procedure is completed, turn off the nitrous oxide dial on the flowmeter and allow the patient to breathe 100% oxygen (6–8 L per minute) for at least 5 minutes: (1) This will prevent diffusion hypoxia and headache. (2) There is no need to slowly titrate down the nitrous oxide level when the procedure is completed.

  • Oxygen flow must be maintained at least at 3 L per minute.

  • If the oxygen tank is empty or the tubing is not properly connected, the nitrous oxide will shut off (fail-safe mechanism).

  • If the nitrous oxide tank is empty or the tubing is not properly connected, the oxygen will keep running (as long as there is oxygen in the tank).