ANATOMY & PHYSIOLOGYfor NITROUS OXIDE
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Transcript of ANATOMY & PHYSIOLOGYfor NITROUS OXIDE
ANATOMY & PHYSIOLOGYANATOMY & PHYSIOLOGYfor NITROUS OXIDEfor NITROUS OXIDE
Respiratory SystemRespiratory System
Two functional partsTwo functional parts Conducting zoneConducting zone
Respiratory zoneRespiratory zone
Conducting ZoneConducting Zone
Transports gases from outside to respiratory Transports gases from outside to respiratory zonezone
Includes anatomic deadspace (150 ml)Includes anatomic deadspace (150 ml)
Conducting ZoneConducting Zone
Nasal passagesNasal passagesPharynxPharynx NasopharynxNasopharynx OropharynxOropharynx HypopharynxHypopharynx
Conducting Zone (cont.) Conducting Zone (cont.)
LarynxLarynxTracheaTracheaBronchi (left and right mainstem)Bronchi (left and right mainstem)BronchiolesBronchioles
Respiratory ZoneRespiratory Zone
Portion of lung where exchange of gases Portion of lung where exchange of gases occurs between blood and airoccurs between blood and air
Respiratory ZoneRespiratory Zone
Respiratory bronchiolesRespiratory bronchiolesAlveolar ductsAlveolar ductsAlveolar sacsAlveolar sacsAlveoliAlveoli
AlveolusAlveolus
Unit in which actual gas exchange occursUnit in which actual gas exchange occurs
Around 300 million totalAround 300 million total
A pocket of air surrounded by thin membrane A pocket of air surrounded by thin membrane (1-2 micrometers in thickness) containing (1-2 micrometers in thickness) containing capillariescapillaries
Alveolus Alveolus
Wall consists of 4 thin layersWall consists of 4 thin layers Mucinous coveringMucinous covering Alveolar epithelium (incomplete)Alveolar epithelium (incomplete) Interstitial layerInterstitial layer Endothelial cells (pulmonary capillaries)Endothelial cells (pulmonary capillaries)
Physiology of RespirationPhysiology of Respiration
Inhaled gases travel through conducting zone to Inhaled gases travel through conducting zone to respiratory zonerespiratory zone
Gases diffuse across alveolar membranes Gases diffuse across alveolar membranes according to pressure gradientsaccording to pressure gradients
Pulmonary capillaries are a pool of blood vessels Pulmonary capillaries are a pool of blood vessels (70 sq meters)(70 sq meters)
Respiratory MechanicsRespiratory Mechanics
Pre inspiration - resting - -5cm H2O pleuralPre inspiration - resting - -5cm H2O pleuralPeak inspiration - more negative pressuresPeak inspiration - more negative pressuresEnd inspiration - negative pleural, 0 alveolar End inspiration - negative pleural, 0 alveolar Peak expiration -positive alveolarPeak expiration -positive alveolarEnd expiration - -5cm pleural, 0 alveolarEnd expiration - -5cm pleural, 0 alveolar
Respiratory MechanicsRespiratory Mechanics
Muscles InvolvedMuscles Involved Primary - DiaphragmPrimary - Diaphragm IntercostalsIntercostals
Accessory - Abdominals, Scalenes,Accessory - Abdominals, Scalenes, SternocleidomastoidSternocleidomastoid Some back musclesSome back muscles
Respiratory MechanicsRespiratory Mechanics
Resting pleural cavity pressure = - 5 cm H20Resting pleural cavity pressure = - 5 cm H20Thorax expands, increasing negative pressureThorax expands, increasing negative pressure
Air flows into lungs/alveoli until positive pressure Air flows into lungs/alveoli until positive pressure develops and gas exchange occursdevelops and gas exchange occurs
Air flows out of lungs to return to resting pleural Air flows out of lungs to return to resting pleural pressure of negative 5 cm H20pressure of negative 5 cm H20
Nitrous Oxide Inhalational Sedation Nitrous Oxide Inhalational Sedation May Represent the Most Ideal May Represent the Most Ideal
Sedation TechniqueSedation Technique
PHARMACOLOGY OFPHARMACOLOGY OFNITROUS OXIDENITROUS OXIDE
Preparation of Nitrous OxidePreparation of Nitrous Oxide
Ammonium nitrate crystals heated to 240 Ammonium nitrate crystals heated to 240 degrees celsiusdegrees celsius
Decomposition to nitrous oxide and water Decomposition to nitrous oxide and water
Preparation of Nitrous OxidePreparation of Nitrous Oxide
heatheat
NHNH44NONO3 =======> 3 =======> NN22O + 2 HO + 2 H22OO 240 deg.240 deg.CC
Preparation of Nitrous OxidePreparation of Nitrous Oxide
N20 is chemically scrubbed 99.5% pureN20 is chemically scrubbed 99.5% pure
Stored in compressed form in metal cylindersStored in compressed form in metal cylinders30% in liquid form in full cylinder30% in liquid form in full cylinder
NitricNitric oxide (NO) is the most dangerous oxide (NO) is the most dangerous impurity (use only medical grade N2O) impurity (use only medical grade N2O)
Physical PropertiesPhysical Properties
N2O is a nonirritating, sweet-smelling, colorless N2O is a nonirritating, sweet-smelling, colorless gasgas
Only inorganic substance other than CO2 to have Only inorganic substance other than CO2 to have CNS depressant propertiesCNS depressant properties
Only inorganic gas used to produce anesthesia in Only inorganic gas used to produce anesthesia in humanshumans
Physical PropertiesPhysical Properties
N2O liquid requires heat for vaporization into N2O liquid requires heat for vaporization into gaseous stategaseous state
Relatively insoluble in the blood; Blood-gas Relatively insoluble in the blood; Blood-gas solubility coefficient is 0.47 at 37 deg. Csolubility coefficient is 0.47 at 37 deg. C
Potency of Nitrous OxidePotency of Nitrous Oxide
Least potent of anesthetic gasesLeast potent of anesthetic gases
35 more times soluble than N2 in plasma35 more times soluble than N2 in plasma100 times more soluble than O2 in plasma100 times more soluble than O2 in plasma
N2O + O2 can produce CNS depressionN2O + O2 can produce CNS depression
Potency of Nitrous OxidePotency of Nitrous Oxide
N2O in subanesthetic doses can produce N2O in subanesthetic doses can produce analgesiaanalgesia
N2O +O2 at 20%/80% is equal-analgesic to N2O +O2 at 20%/80% is equal-analgesic to 10 to 15 mg of morphine10 to 15 mg of morphine
Optimal concentration is 35%Optimal concentration is 35%
Pharmacology of Nitrous OxidePharmacology of Nitrous Oxide
N2O is rapidly absorbed into the CV system, N2O is rapidly absorbed into the CV system, due to large concentration gradient of N2O due to large concentration gradient of N2O between alveolar sacs and bloodbetween alveolar sacs and blood
N2O rapidly fills air-filled body cavitiesN2O rapidly fills air-filled body cavities
Pharmacology of Nitrous OxidePharmacology of Nitrous Oxide
Due to rapid uptake, two phenomena are seenDue to rapid uptake, two phenomena are seen Concentration effect Concentration effect - higher concentrations - higher concentrations
cause more rapid uptake of N2Ocause more rapid uptake of N2O Second gas effectSecond gas effect - a second anesthetic gas - a second anesthetic gas
will also be taken up more rapidly than usual will also be taken up more rapidly than usual when added to N2Owhen added to N2O
Concentration EffectConcentration Effect
Seen only when using high concentrations of a Seen only when using high concentrations of a gasgas
The higher the concentration inhaled, the more The higher the concentration inhaled, the more rapidly the arterial tension of the gas rapidly the arterial tension of the gas increasesincreases
The diffusion gradient from the lungs into The diffusion gradient from the lungs into blood results in a greater uptake of gas into blood results in a greater uptake of gas into lungslungs
Second Gas EffectSecond Gas Effect
Occurs when another inhalation anesthetic is Occurs when another inhalation anesthetic is used with N2Oused with N2O
Rapid uptake of N2O produces a vacuum in Rapid uptake of N2O produces a vacuum in alveoli alveoli
Second gas also undergoes rapid uptake along Second gas also undergoes rapid uptake along with N2Owith N2O
AbsorptionAbsorption
CNS saturation occurs by displacement of N2 CNS saturation occurs by displacement of N2 by N2O, usually in 3-5 minutes by N2O, usually in 3-5 minutes
Tissues with greater blood flow (brain, heart, Tissues with greater blood flow (brain, heart, liver, kidney) receive greater amounts of liver, kidney) receive greater amounts of N2ON2O
AbsorptionAbsorption
Tissues with poor blood supply (fat, muscle, Tissues with poor blood supply (fat, muscle, connective tissue) absorb small amountsconnective tissue) absorb small amounts
Slow absorption occurs once primary Slow absorption occurs once primary
saturation is completedsaturation is completedTherefore no body reservoir present to slow Therefore no body reservoir present to slow
recovery once N2O terminatedrecovery once N2O terminated
BiotransformationBiotransformation
N2O undergoes N2O undergoes nono biotransformation in the biotransformation in the bodybody
Majority of N2O is exhaled unchanged 3 to 5 Majority of N2O is exhaled unchanged 3 to 5 mins. following termination of deliverymins. following termination of delivery
1% eliminated via skin and lungs in 24 hours1% eliminated via skin and lungs in 24 hours
Diffusion HypoxiaDiffusion Hypoxia
Can occur following termination of N2O if Can occur following termination of N2O if patient is allowed to breathe only room airpatient is allowed to breathe only room air
““Hangover” effect (headache,nausea,lethargy) is Hangover” effect (headache,nausea,lethargy) is producedproduced
Prevented by having the patient breathe 100% O2 Prevented by having the patient breathe 100% O2 for minimum of 3 to 5 minutesfor minimum of 3 to 5 minutes
Diffusion HypoxiaDiffusion Hypoxia
Rapid diffusion of N2O from blood to lungs Rapid diffusion of N2O from blood to lungs results in decreased CO2 arterial tension results in decreased CO2 arterial tension with decreased stimulus for respirationwith decreased stimulus for respiration
Rapid diffusion of N2O back into lungs Rapid diffusion of N2O back into lungs dilutes alveolar O2 with resultant hypoxiadilutes alveolar O2 with resultant hypoxia
Pharmacology of Nitrous OxidePharmacology of Nitrous Oxide
N2O is non-allergenicN2O is non-allergenic
Least toxic of inhalational agentsLeast toxic of inhalational agents
Effects of Nitrous OxideEffects of Nitrous Oxideon Organ Systemson Organ Systems
Central Nervous SystemCentral Nervous System
Actual Actual mechanism unknownmechanism unknown Mild depression of CNS (cerebral cortex) in Mild depression of CNS (cerebral cortex) in
conjunction with physiological levels of O2 conjunction with physiological levels of O2 (greater than 20%)(greater than 20%)
Sensations depressed (sight, hearing, touch, Sensations depressed (sight, hearing, touch, pain) pain)
Cardiovascular SystemCardiovascular System
No changes in heart rate or cardiac outputNo changes in heart rate or cardiac output
Blood pressure remains stable with only slight Blood pressure remains stable with only slight decreasedecrease
Cutaneous vasodilationCutaneous vasodilation
Respiratory SystemRespiratory System
N2O is non-irritating to pulmonary epitheliumN2O is non-irritating to pulmonary epithelium
Changes (drop) in rate and depth more likely Changes (drop) in rate and depth more likely due to anxiolytic effectsdue to anxiolytic effects
Slight elevation of resting respiratory minute Slight elevation of resting respiratory minute volume at 50%/50%volume at 50%/50%
GI SystemGI System
No clinically significant effects, unless there No clinically significant effects, unless there is a closed space (obstruction)is a closed space (obstruction)
N/V rarely seen unless hypoxia presentN/V rarely seen unless hypoxia present
Can be used in hepatic dysfunctionCan be used in hepatic dysfunction
Hematopoietic SystemHematopoietic System
Long-term exposure (greater than 24 hours) Long-term exposure (greater than 24 hours) can produce transient bone marrow can produce transient bone marrow depressiondepression
Musculoskeletal SystemMusculoskeletal System
No direct relaxation of skeletal muscleNo direct relaxation of skeletal muscle
Anxiolytic effects help relaxationAnxiolytic effects help relaxation
Reproductive SystemReproductive System
Uterine contractions not inhibitedUterine contractions not inhibited
Pregnancy is a relative contraindication Pregnancy is a relative contraindication (avoid in first trimester)(avoid in first trimester)