nitrous oxide sedation william m clark m d m b a m s n.
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Nitrous Oxide Sedation William M. Clark, M.D.,M.B.A., M.S.

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  1. Nitrous Oxide SedationWilliam M. Clark, M.D.,M.B.A., M.S.

  2. Pain Terms • Allodynia – ordinary non-painful sensations are experienced as painful sensations • Hyperalgesia – pain sensations are intensified and amplified • Hypoalgesia – decrease sense of pain • Analgesia – a neurologic or pharmacologic state in which painful stimuli are so moderated that they are perceived but do not hurt. • Anesthesia – a loss of sensation due to pharmacologic depression of nerve function • Paresthesia – an abnormal sensation; such as burning, pricking, ticking or tingling • Dysesthesia- (1) impairment of sensation short of anesthesia (2) a condition in which a disagreeable sensation is produced by ordinary stimuli; caused by lesions of the sensory pathways, peripheral or central (3) abnormal sensation experienced in the absence of stimuli

  3. What are the Types of Anesthesia • General Anesthesia • Regional Anesthesia • Local Anesthesia • Sedation

  4. General (Inhalation or Intravenous) – produces an unconscious state. In this state the person is a. unaware of what is happening b. pain-free c. *immobile d. free from memory of the period of time during when her or she is anesthetized • * The skeletal muscle reflexes continue to work from an unconscious state – so must be paralyzed (Neuromuscular blocking)

  5. Neuromuscular Blocking • Due to reflex activity of skeletal muscles – certain blocking agents must be administered during general anesthesia. If no blocking agent is used the skeletal muscles will reflexively contract upon painful stimuli.

  6. Regional Anesthesia– A region of the body is anesthetized without the person becoming unconscious – for example a spinal block or epidural. • Local Anesthesia – numbing a small area by injecting a local anesthetic under the skin or mucous membrane where the incision or other procedure (extraction- cleaning) will occur.

  7. Sedation – analgesia produced pharmacologically by general anesthesia drugs given in smaller doses – twilight sleep (intravenous valium, Opioids and other agents).

  8. Opioids – Morphine was isolated from opium in 1805 and was quickly tried as a intravenous anesthetic. The morbidity and mortality associated with its use in high doses caused many to avoid its usage. In 1939 Meperidine (Demerol) was introduced and a concept of “balanced anesthesia” began. Thiopental was used for induction- nitrous oxide for amnesia- Meperidine (or any Opioid) for analgesia and curare for muscle relaxation. • Sodium thiopental, better known as Sodium Pentathol is a rapid-onset short-acting barbiturategeneral anaesthetic

  9. Nitrous Oxide is an Inhalation Anesthesia • Because it is – let’s review some respiratory anatomy and physiology • Because it is an anesthesia we also need to briefly review some neurological data

  10. Respiratory Anatomy

  11. General Respiratory Anatomy • Nose • Mouth • Pharynx • Trachea • Mainstem bronchi – primary bronchi (lung bronchi) • Secondary bronchi – lobar bronchi • Tertiary bronchi – segmental bronchi- goes to broncho-pulmonary segments • Bronchioles – no longer cartilage in the walls • Terminal bronchioles – last conduit – non- diffusion (exchange) region • Respiratory bronchioles – first diffusion (exchange) region • Alveolar Ducts • Alveolar Sacs • Alveolus

  12. Epicranius, frontal belly Root and bridge of nose Dorsum nasi Ala of nose Apex of nose Naris (nostril) Philtrum (a) Surface anatomy Figure 22.2a

  13. Upper lip Gingivae (gums) Superior labial frenulum Palatine raphe Palatoglossal arch Hard palate Palatopharyngeal arch Soft palate Uvula Posterior wall of oropharynx Palatine tonsil Tongue Sublingual fold with openings of sublingual ducts Lingual frenulum Opening of submandibular duct Gingivae (gums) Vestibule Inferior labial frenulum Lower lip (b) Anterior view Figure 23.7b

  14. Cribriform plate of ethmoid bone Frontal sinus Sphenoid sinus Nasal cavity Posterior nasal aperture Nasal conchae (superior, middle and inferior) Nasopharynx Pharyngeal tonsil Nasal meatuses (superior, middle, and inferior) Opening of pharyngotympanic tube Nasal vestibule Uvula Nostril Oropharynx Hard palate Palatine tonsil Soft palate Isthmus of the fauces Tongue Lingual tonsil Laryngopharynx Hyoid bone Larynx Epiglottis Vestibular fold Esophagus Thyroid cartilage Vocal fold Cricoid cartilage Trachea Thyroid gland (c) Illustration Figure 22.3c

  15. Respiratory Physiology

  16. Review of Terms • External Respiration versus Internal Respiration • Respiratory Volumes • Breath Rate • Minute Ventilation • Respiratory Zone • Gas Exchange Across the Respiratory Zone

  17. External Respiration versus Internal Respiration • External Respiration – taking oxygen from the atmosphere and putting it into the blood – also taking carbon dioxide from the blood and putting it into the atmosphere. • Internal Respiration – taking carbon dioxide (waste product made by cells) from the cell and putting it into the blood and taking oxygen from the blood and putting it into the cells.

  18. Respiratory Volumes • Used to assess a person’s respiratory status • Tidal volume (TV) – volume you normally breath in and out • Inspiratory reserve volume (IRV) – That extra amount of air you could breath in over that you brought in for tidal volume • Expiratory reserve volume (ERV) That extra amount of air you could breath out over that you breathed out for tidal volume • Residual volume (RV) – That air in your lungs you cannot breath out – unless some blow to the chest occurs (getting the wind knocked out of you)

  19. Maximum amount of air contained in lungs after a maximum inspiratory effort: TLC = TV + IRV + ERV + RV Total lung capacity (TLC) 6000 ml 4200 ml Maximum amount of air that can be expired after a maxi- mum inspiratory effort: VC = TV + IRV + ERV Vital capacity (VC) 4800 ml 3100 ml Respiratory capacities Maximum amount of air that can be inspired after a normal expiration: IC = TV + IRV Inspiratory capacity (IC) 3600 ml 2400 ml Volume of air remaining in the lungs after a normal tidal volume expiration: FRC = ERV + RV Functional residual capacity (FRC) 2400 ml 1800 ml (b) Summary of respiratory volumes and capacities for males and females Figure 22.16b

  20. Inspiratory reserve volume 3100 ml Inspiratory capacity 3600 ml Vital capacity 4800 ml Total lung capacity 6000 ml Tidal volume 500 ml Expiratory reserve volume 1200 ml Functional residual capacity 2400 ml Residual volume 1200 ml (a) Spirographic record for a male Figure 22.16a

  21. Breath Rate • Normal breath rates for an adult person at rest range from 12 to 20 breaths per minute. Respiration rates over 25 breaths per minute or under 12 breaths per minute (when at rest) may be considered abnormal.

  22. Minute Ventilation • Minute ventilation – the amount of air brought into and out of the lungs in one minute (breath rate per minute times tidal volume) – average breath rate per minute is 12 – 20 breaths per minute – for example 12 BPM x 500cc = 6 Liters/minute

  23. Respiratory System Zones • Conducting Zone – where no gas exchange can occur with the blood – membranes too thick to perform diffusion of gases • Conducting Zone Location– Nose and/or mouth down to end of terminal bronchioles • Respiratory (Exchange) Zone – where gas exchange can occur with the blood – membranes thin enough for diffusion • Respiratory Zone Location – starts at respiratory bronchioles and extends to the very bottom of the respiratory system (Alveoli)

  24. Gas Exchange Across Respiratory Zone • The respiratory zone is the total area in the respiratory system that exchange of air with the blood can occur. In the average person this is about 70 meters squared of surface area – or about the size of a tennis court. Under normal circumstances a person can diffuse oxygen at a rate of 21 ml/min/mm Hg Since the pressure across the respiratory membrane is around 11 mm Hg – the value is 11 x 21 = 230 ml of Oxygen diffusing through the area in one minute – this is equal to rate at which the body uses oxygen.

  25. Ideal Gas Equation PV = nRT • P – pressure • V- Volume • n – number of moles • R – gas rate constant • T - temp

  26. Boyle’s Law • There is an inverse Relationship between pressure and volume of a gas in a closed container • The larger the volume of the container with gas in it – the lower the pressure and vice-versa

  27. Dalton’s Lawof Partial pressures • A gas in a mixture of gases will exert a pressure independent of the other gases in the mixture and in accordance with the percent of the gas present • Thus to get the partial pressure of gases in our atmosphere you multiply the Atmospheric Pressure times the gas percent present in the atmosphere

  28. Partial Pressures of Gases in the Atmosphere • If we consider that we live at sea level the Atmospheric pressure is 760 mm of mercury pressure per cubic inch • The atmosphere is roughly 79% Nitrogen, 21% Oxygen and .04% Carbon Dioxide • .79 x 760 = 600 mm Hg partial pressure for N2 • .21 x 760 = 160 mm Hg partial pressure for O2 • .0004 x 760 = .30 mm Hg partial pressure for CO2

  29. Henry’s Law • The amount of a gas that will dissolve in a liquid depends on the partial pressure of the gas above the liquid and the solubility coefficient of that gas for that liquid. • Dissolved amount = PP of gas x *solubility coefficient

  30. Solubility coefficients of gases with relative comparison to O2 • Gas Solubility coefficient Relative Magnitude • with O2 • Oxygen 0.024 1 • Carbon Dioxide 0.57 23 • Nitrogen 0.012 0.53 • Nitrous Oxide 0.47 20 • Halothane 2.4 100 • Carbon Monoxide 0.018 0.81 Note – Nitrous Oxide gets into blood better than N2

  31. Neurobiology • What is a nucleus, tract, ganglion and nerve? • What is a brain Center? • What is a Cranial Nerve versus a Spinal Nerve? • What are some important brain centers in regards to the Dental Profession? • What are some important nerves in regards to the Dental Profession?

  32. A nucleus is a group of neuron cell bodies in the central nervous system – dedicated to a certain function. • A tract is a group of fibers (axons and/or dendrites) in the central nervous system. • A nerve is a group of neuron fibers in the peripheral nervous system. • A ganglion is group of neuron cell bodies in the peripheral nervous system. A brain center is a nucleus in the central nervous system – that performs the said function.

  33. Cranial Nerves versus Spinal Nerves • A cranial nerve originates from the brain. There are 12 of them on each side of the brain • A spinal nerve originates from the spinal cord. There are 31 of them on each side of the spinal cord.

  34. Some important Centers • The breathing center is composed of several nuclei in the Pons and medulla oblongata. • The gag reflex also termed the pharyngeal reflex is centered in the medulla and consists of reflexive motor response of pharyngeal elevation and constriction with tongue retraction in response to sensory stimulation of the pharyngeal wall, posterior tongue, tonsils or faucal pillars. The gag reflex involves afferent fibers from the glossopharyngeal nerve (IX) and some from the vagus (x) with efferent motor fibers to the pharynx, soft palate and tongue from the vagus.

  35. Nausea and Vomiting are coordinated by the brainstem and is effected by neuromuscular responses in the gut, pharynx, and thoraco-abdominal wall. The mechanisms underlying nausea are poorly understood but likely involve the cerebral cortex, as nausea requires conscious perception. • Coordination of Emesis – Several brainstem nuclei initiate emesis including the tractus solitarius, dorsal vagal and phrenic nuclei, and medullary nuclei that regulate respiration; nuclei that control pharyngeal, facial, and tongue movements coordinate the initiation of emesis. The neurotransmitters involved in this coordination are uncertain; however, roles for neurokinin, serotonin and vasopressin are postulated.

  36. Important Cranial Nerves in the Dental Professions • Cranial Nerve V – Sensory to Face • Cranial Nerve VII – Motor to Face

  37. Cranial Nerve V: The Trigeminal Nerves SENSORY TO THE FACE • Largest cranial nerves; fibers extend from pons to face • Three divisions • Ophthalmic (V1) passes through the superior orbital fissure • Maxillary (V2) passes through the foramen rotundum (Upper Teeth) • Mandibular (V3) passes through the foramen ovale (Lower teeth) • Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

  38. Table 13.2

  39. Table 13.2

  40. FACIAL NERVE (Cranial Nerve VII) Table 13.2

  41. Table 13.2

  42. Brief Discussion of Pain • Mechanical, thermal and chemical stimuli stimulate pain receptors. The fast pain receptors signal thermal and mechanical (tooth pulling and/or cleaning) stimuli. All three stimuli can stimulate the slow pain receptors. Chemical substances that stimulate pain receptors are bradykinin, serotonin, histamine, potassium ions, acids, acetylcholine and proteolytic enzymes. Fast pain is more of a localize pain that can be pin point located by the person – whereas slow pain is more diffuse.

  43. Review of Neural Anatomy as it relates to Pain • Local pain receptor – termed a nocioceptor • Afferent (sensory) neuron – fast pain travels via alpha (big myelinated neurons) into the dorsal horn of the spinal cord – slow pain travels via type C (thin and non-myelinated) neurons into the spinal cord • Spinal Cord – in the spinal cord the afferent neurons synapse at different regions of the dorsal horn depending on slow versus fast – slow fibers pick up a short interneuron – then synapse on a third order neuron which immediately crosses over the cord to the other side then travels up (ascending tract) the spinal cord terminating in a region of the brain. Fast fibers pick up a second order neuron that crosses the cord to the other side and then travels up (ascending tract) the spinal cord terminating in a region of the brain. The tract taking the signal to the brain (in both slow and fast) is termed the “lateral spinothalamic tract”. • Brainstem and Thalamus – for slow pain the spinothalamic tract neurons terminate in Reticular fibers in the brainstem and some ( ¼ to 1/10) go to the Thalamus – for fast fibers some go to the brainstem but most go directly to the Thalamus. • Cortex – Post central gyrus location – place in brain that give experience and location to the pain

  44. Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature receptors Lumbar spinal cord (b) Spinothalamic pathway Figure 12.34b (2 of 2)

  45. Perceptual level(processing in cortical sensory centers) 3 Motor cortex Somatosensory cortex Thalamus Reticular formation Cerebellum Pons Medulla Circuit level (processing in ascending pathways) 2 Spinal cord Free nerve endings (pain, cold, warmth) Muscle spindle Receptor level (sensory reception and transmission to CNS) 1 Joint kinesthetic receptor Figure 13.2