practice of Anaesthesia
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The most commonly used anaesthetics-the inhalational agents- depend on the
lungs for uptake and elimination.
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The most important side effects of both
inhalational and intravenously
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administered anaesthetics are primarilyrespiratory.
FunctionsoftheRespiratory
System
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? Gas Exchange
? O2, CO2
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? Acid-base balance? CO2 +H2O H2CO3 H+ + HCO3-
? Phonation
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? Pulmonary defense? Pulmonary metabolism and handling of
bioactive materials
6
--- Content provided by FirstRanker.com ---
Respiration
? The term respiration includes 3 separate
--- Content provided by FirstRanker.com ---
functions:
? Ventilation:
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? Breathing.? Gas exchange:
? Between air and capillaries in the lungs.
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? Between systemic capillaries and tissues ofthe body.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? 02 utilization:
? Cellular respiration.
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Ventilation? Mechanical process that moves air
in and out of the lungs.
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? [O2] of air is higher in the lungs
Insert 16.1
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than in the blood, O2 diffuses fromair to the blood.
? C02 moves from the blood to the
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air by diffusing down its
concentration gradient.
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? Gas exchange occurs entirely bydiffusion:
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Diffusion is rapid because of the
large surface area and the small
--- Content provided by FirstRanker.com ---
diffusion distance.RespiratoryZone
--- Content provided by FirstRanker.com ---
? Region of gasexchange
between air
--- Content provided by FirstRanker.com ---
and blood.
? Includes
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respiratorybronchioles
and alveolar
--- Content provided by FirstRanker.com ---
sacs.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Must containalveoli.
--- Content provided by FirstRanker.com ---
Alveoli? Polyhedral in shape and clustered like units of honeycomb.
? ~ 300 million air sacs (alveoli).
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? Large surface area (60?80 m2).? Each alveolus is 1 cell layer thick.
? Total air barrier is 2 cells across (2 mm).
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? 2 types of cells:? Alveolar type I:
? Structural cells.
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? Alveolar type II:
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--- Content provided by FirstRanker.com ---
? Secrete surfactant.ConductingZone
? All the structures air
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passes through before
reaching the respiratory
--- Content provided by FirstRanker.com ---
Insert fig. 16.5zone.
? Warms and humidifies
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inspired air.
? Filters and cleans:
--- Content provided by FirstRanker.com ---
? Mucus secreted to trapparticles in the inspired air.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Mucus moved by cilia to be
expectorated.
TracheobronchialTree:
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a) Trachea- conduit for ventilation
? Clearance of tracheal &bronchial secretions
? Begins at the lower border of the cricoid cartilage
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and extends to the level of the carina? Average length of 10?13 cm
? The external diameters of the trachea is
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approximately 2.3 cm coronally and 1.8 cmsagitally in men and 2.0 cm & 1.4 cm,
respectively, in women
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? The trachea bifurcates at the carina into the right
and left main stem bronchi
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? Dichotomous division, starting with the tracheaand ending in alveolar sacs, is estimated to
involve 23 divisions.
--- Content provided by FirstRanker.com ---
? An estimated 300 million alveoli provide an
enormous membrane (50?100 m2 ) for gas
--- Content provided by FirstRanker.com ---
exchange in the average adult? Gas exchange can occur only across the flat
epithelium, which begins to appear on
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respiratory bronchioles
PulmonaryCirculation&
Lymphatics
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? The lungs are supplied by two circulations,pulmonary and bronchial
? The bronchial circulation arises from lt heart
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? Along their courses, the bronchial vesselsanastomose with the pulmonary arterial
circulation and continue as far as the alveolar
--- Content provided by FirstRanker.com ---
duct.
? The pulmonary circulation normally receives the
--- Content provided by FirstRanker.com ---
total output of the right heart via the pulmonaryartery, which divides into rt and lt branches to
supply each lung
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? Deoxygenated blood passes through the
pulmonary capillaries, where O2 is taken up and
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CO2 is eliminated? The oxygenated blood is then returned to the lt
heart by 4 main pulmonary veins (two from each
--- Content provided by FirstRanker.com ---
lung)
Innervation
? The diaphragm is innervated by the phrenic
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nerves, which arise from the C3?C5 nerve roots.
? U/L phrenic nerve palsy only modestly reduces
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most indices of pulmonary function (~ 25%).? B/L phrenic nerve palsies produce more severe
impairment
--- Content provided by FirstRanker.com ---
? The vagus nerves provide sensory innervation to
the tracheobronchial tree
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ThoracicCavity? Diaphragm:
? Sheets of striated muscle divides anterior body cavity
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into 2 parts.
? Above diaphragm: thoracic cavity:
--- Content provided by FirstRanker.com ---
? Contains heart, large blood vessels, trachea, esophagus,thymus, and lungs.
? Below diaphragm: abdominopelvic cavity:
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? Contains liver, pancreas, GI tract, spleen, and
genitourinary tract.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com? Intrapleural space:
? Space between visceral and parietal pleurae.
--- Content provided by FirstRanker.com ---
IntrapulmonaryandIntrapleuralPressures
? Visceral and parietal pleurae are flush against each other.
--- Content provided by FirstRanker.com ---
? The intrapleural space contains only a film of fluidsecreted by the membranes.
? Lungs normally remain in contact with the chest walls.
--- Content provided by FirstRanker.com ---
? Lungs expand and contract along with the thoracic cavity.? Intrapulmonary pressure:
? Intra-alveolar pressure (pressure in the alveoli).
--- Content provided by FirstRanker.com ---
? Intrapleural pressure:www.freelivedoctor.com
? Pressure in the intrapleural space.
--- Content provided by FirstRanker.com ---
? Pressure is negative, due to lack of air in the intrapleuralspace.
TranspulmonaryPressure
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? Pressure difference across the wall of the lung.
? Intrapulmonary pressure ? intrapleural pressure.
? Keeps the lungs against the chest wall.
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www.freelivedoctor.com
IntrapulmonaryandIntrapleural
Pressures(continued)
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? During inspiration:? Atmospheric pressure is > intrapulmonary
pressure (-3 mm Hg).
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? During expiration:
? Intrapulmonary pressure (+3 mm Hg) is >
--- Content provided by FirstRanker.com ---
atmospheric pressurewww.freelivedoctor.com
.
--- Content provided by FirstRanker.com ---
Boyle'sLaw
? Changes in intrapulmonary pressure occur as a
--- Content provided by FirstRanker.com ---
result of changes in lung volume.? Pressure of gas is inversely proportional to its volume.
? Increase in lung volume decreases intrapulmonary
--- Content provided by FirstRanker.com ---
pressure.
? Air goes in.
--- Content provided by FirstRanker.com ---
? Decrease in lung volume, raises intrapulmonarypressure above atmosphere.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Air goes out.
PhysicalPropertiesoftheLungs
? Ventilation occurs as a result of pressure
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differences induced by changes in lung
volume.
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? Physical properties that affect lungfunction:
? Compliance.
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? Elasticity.www.freelivedoctor.com
? Surface tension.
--- Content provided by FirstRanker.com ---
Compliance
? Distensibility (stretchability):
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? Ease with which the lungs can expand.? Change in lung volume per change in
transpulmonary pressure.
--- Content provided by FirstRanker.com ---
DV/DP
? 100 x more distensible than a balloon.
--- Content provided by FirstRanker.com ---
? Compliance is reduced by factors that produceresistance to distension.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
Elasticity? Tendency to return to initial size after
distension.
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? High content of elastin proteins.
? Very elastic and resist distension.
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? Recoil ability.? Elastic tension increases during inspiration
and is reduced by recoil during expiration.
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SurfaceTension
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? Force exerted by fluid in alveoli to resistdistension.
? Lungs secrete and absorb fluid, leaving a very thin film of fluid.
--- Content provided by FirstRanker.com ---
? This film of fluid causes surface tension.
? Fluid absorption is driven (osmosis) by Na+ active
transport.
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? Fluid secretion is driven by the active transport of Cl- out
of the alveolar epithelial cells.
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? H20 molecules at the surface are attracted towww.freelivedoctor.com
other H20 molecules by attractive forces.
--- Content provided by FirstRanker.com ---
? Force is directed inward, raising pressure in alveoli.
Surfactant
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? Phospholipid produced by
alveolar type II cells.
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? Lowers surface tension.Insert fig. 16.12
? Reduces attractive forces of
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hydrogen bonding by becoming
interspersed between H20
--- Content provided by FirstRanker.com ---
molecules.? Surface tension in alveoli is
reduced.
--- Content provided by FirstRanker.com ---
? As alveoli radius decreases,
surfactant's ability to lower
--- Content provided by FirstRanker.com ---
surface tension increases.www.freelivedoctor.com
? Disorders:
--- Content provided by FirstRanker.com ---
? RDS.
? ARDS.
QuietInspiration
--- Content provided by FirstRanker.com ---
? Active process:
? Contraction of diaphragm, increases thoracic volume
--- Content provided by FirstRanker.com ---
vertically.? Parasternal and external intercostals contract,
raising the ribs; increasing thoracic volume
--- Content provided by FirstRanker.com ---
laterally.
? Pressure changes:
--- Content provided by FirstRanker.com ---
? Alveolar changes from 0 to ?3 mm Hg.www.freelivedoctor.com
? Intrapleural changes from ?4 to ?6 mm Hg.
--- Content provided by FirstRanker.com ---
? Transpulmonary pressure = +3 mm Hg.Expiration
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? Quiet expiration is a passive process.? After being stretched by contractions of the diaphragm and
thoracic muscles; the diaphragm, thoracic muscles, thorax, and
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lungs recoil.
? Decrease in lung volume raises the pressure within alveoli
--- Content provided by FirstRanker.com ---
above atmosphere, and pushes air out.? Pressure changes:
? Intrapulmonary pressure changes from ?3 to +3 mm Hg.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
? Intrapleural pressure changes from ?6 to ?3 mm Hg.
? Transpulmonary pressure = +6 mm Hg.
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PulmonaryVentilation
Insert fig. 16.15
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www.freelivedoctor.comLung volumes and capacities
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4 lung volumes:tidal (~500 ml)
inspiratory reserve (~3100 ml)
expiratory reserve (~1200 ml)
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residual (~1200 ml)4 lung capacities
inspiratory (~3600 ml)
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functional residual (~2400 ml)vital (~4800 ml)
total lung (~6000 ml)
Terms Used to Describe Lung Volumes
--- Content provided by FirstRanker.com ---
and Capacities
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
AnatomicalDeadSpace
? Not all of the inspired air reached the alveoli.
? As fresh air is inhaled it is mixed with air in anatomical
--- Content provided by FirstRanker.com ---
dead space.
? Conducting zone and alveoli where [02] is lower than
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normal and [C02] is higher than normal.? Alveolar ventilation = F x (TV- DS).
? F = frequency (breaths/min.).
--- Content provided by FirstRanker.com ---
? TV = tidal volume.www.freelivedoctor.com
? DS = dead space.
--- Content provided by FirstRanker.com ---
RestrictiveandObstructiveDisorders
? Restrictive disorder:
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? Vital capacity isreduced.
? FVC is normal.
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Insert fig. 16.17
? Obstructive disorder:
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? Diagnosed by teststhat measure the rate
of expiration.
--- Content provided by FirstRanker.com ---
? VC is normal.
? FEV1 is < 80%.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
GasExchangeintheLungs
? Dalton's Law:
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? Total pressure of a gas mixture is = to the sum of the
pressures that each gas in the mixture would exert
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independently.? Partial pressure:
? The pressure that an particular gas exerts
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independently.
? PATM = PN
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+ P + P2 + P02
C02
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H20= 760 mm Hg.
? 02 is humidified = 105 mm Hg.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com? H20 contributes to partial pressure (47 mm Hg).
? P0 (sea level) = 150 mm Hg.
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2
? PC0 = 40 mm Hg.
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2PartialPressuresofGasesinInspiredAir
andAlveolarAir
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Insert fig. 16.20www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
PartialPressuresofGasesinBlood? When a liquid or gas (blood and alveolar air) are
at equilibrium:
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? The amount of gas dissolved in fluid reaches a
maximum value (Henry's Law).
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? Depends upon:? Solubility of gas in the fluid.
? Temperature of the fluid.
? Partial pressure of the gas.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
? [Gas] dissolved in a fluid depends directly on its
--- Content provided by FirstRanker.com ---
partial pressure in the gas mixture.SignificanceofBloodP0
2andPC02
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Measurements
? At normal P0 2
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arterial bloodis about 100
mm Hg.
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? P0 level in
2
--- Content provided by FirstRanker.com ---
the systemicveins is about
40 mm Hg.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
nPC0 is 46 mm Hg in the systemic veins.
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2nProvides a good index of lung function.
PulmonaryCirculation
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? Rate of blood flow through the pulmonarycirculation is = flow rate through the systemic
circulation.
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? Driving pressure is about 10 mm Hg.
? Pulmonary vascular resistance is low.
--- Content provided by FirstRanker.com ---
? Low pressure pathway produces less net filtration thanproduced in the systemic capillaries.
? Avoids pulmonary edema.
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? Autoregulation:
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--- Content provided by FirstRanker.com ---
? Pulmonary arterioles constrict when alveolar P02decreases.
? Matches ventilation/perfusion ratio.
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PulmonaryCirculation(continued)
? In a fetus:
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? Pulmonary circulation has a higher vascular resistance,because the lungs are partially collapsed.
? After birth, vascular resistance decreases:
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? Opening the vessels as a result of subatmospheric
intrapulmonary pressure.
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? Physical stretching of the lungs.? Dilation of pulmonary arterioles in response to
increased alveolar P0 .2
--- Content provided by FirstRanker.com ---
www.freelivedoctor.comLungVentilation/PerfusionRatios
--- Content provided by FirstRanker.com ---
? Functionally:Insert fig. 16.24
? Alveoli at
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apex are
underperfused
--- Content provided by FirstRanker.com ---
(overventilated).? Alveoli at the base are
underventilated
--- Content provided by FirstRanker.com ---
(overperfused).
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
BrainStemRespiratoryCenters? Neurons in the reticular
formation of the
--- Content provided by FirstRanker.com ---
medulla oblongata
form the rhythmicity
--- Content provided by FirstRanker.com ---
Insert fig. 16.25center:
? Controls automatic
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breathing.
? Consists of interacting
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neurons that fire eitherwww.freelivedoctor.com
during inspiration (I
--- Content provided by FirstRanker.com ---
neurons) or expiration
(E neurons).
BrainStemRespiratoryCenters(continued)
--- Content provided by FirstRanker.com ---
? I neurons project to, and stimulate spinal motor
neurons that innervate respiratory muscles.
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? Expiration is a passive process that occurs whenthe I neurons are inhibited.
? Activity varies in a reciprocal way.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
RhythmicityCenter
--- Content provided by FirstRanker.com ---
? I neurons located primarily in dorsal respiratory group(DRG):
? Regulate activity of phrenic nerve.
--- Content provided by FirstRanker.com ---
? Project to and stimulate spinal interneurons that
innervate respiratory muscles.
--- Content provided by FirstRanker.com ---
? E neurons located in ventral respiratory group (VRG):? Passive process.
? Controls motor neurons to the internal intercostal
--- Content provided by FirstRanker.com ---
muscles.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Activity of E neurons inhibit I neurons.? Rhythmicity of I and E neurons may be due to
pacemaker neurons.
--- Content provided by FirstRanker.com ---
PonsRespiratoryCenters
? Activities of medullary rhythmicity center is
--- Content provided by FirstRanker.com ---
influenced by pons.
? Apneustic center:
--- Content provided by FirstRanker.com ---
? Promotes inspiration by stimulating the Ineurons in the medulla.
? Pneumotaxic center:
--- Content provided by FirstRanker.com ---
? Antagonizes the apneustic center.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Inhibits inspiration.Chemoreceptors
? 2 groups of chemo-
--- Content provided by FirstRanker.com ---
receptors that monitor
changes in blood PC0 , P0 ,
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22
and pH.
--- Content provided by FirstRanker.com ---
Insert fig. 16.27
? Central:
--- Content provided by FirstRanker.com ---
? Medulla.? Peripheral:
? Carotid and aortic bodies.
--- Content provided by FirstRanker.com ---
? Control breathing indirectly via
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
sensory nerve fibers to themedulla (X, IX).
EffectsofBloodPC0 andpHon
--- Content provided by FirstRanker.com ---
2Ventilation
? Chemoreceptor input modifies the rate and depth
--- Content provided by FirstRanker.com ---
of breathing.
? Oxygen content of blood decreases more slowly
--- Content provided by FirstRanker.com ---
because of the large "reservoir" of oxygen attached tohemoglobin.
? Chemoreceptors are more sensitive to changes in PC0 .2
--- Content provided by FirstRanker.com ---
H
H
--- Content provided by FirstRanker.com ---
-20 + C02 2C03 H+ + HC03
? Rate and depth of ventilation adjusted to
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
maintain arterial PC02 of 40 mm Hg.
--- Content provided by FirstRanker.com ---
ChemoreceptorControl? Central chemoreceptors:
? More sensitive to changes in arterial PC0 .2
--- Content provided by FirstRanker.com ---
H
H
--- Content provided by FirstRanker.com ---
20 + CO2 2C03 H+? H+ cannot cross the blood brain barrier.
? C02 can cross the blood brain barrier and will form H2C03.
--- Content provided by FirstRanker.com ---
? Lowers pH of CSF.? Directly stimulates central chemoreceptors.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
ChemoreceptorControlofBreathing
--- Content provided by FirstRanker.com ---
EffectsofBloodP0 onVentilation
2
--- Content provided by FirstRanker.com ---
? Blood PO2 affected by breathing indirectly.? Influences chemoreceptor sensitivity to changes in PC02.
? Hypoxic drive:
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? Emphysema blunts the chemoreceptor response to PC02.
? Choroid plexus secrete more HC0 -3 into CSF, buffering the
fall in CSF pH.
--- Content provided by FirstRanker.com ---
? Abnormally high PC02 enhances sensitivity of carotid bodies
to fall in P02.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.comEffectsofPulmonaryReceptorson
Ventilation
--- Content provided by FirstRanker.com ---
? Lungs contain receptors that influence the brain stem
respiratory control centers via sensory fibers in vagus.
--- Content provided by FirstRanker.com ---
? Unmyelinated C fibers can be stimulated by:? Capsaicin:
? Produces apnea followed by rapid, shallow breathing.
--- Content provided by FirstRanker.com ---
? Histamine and bradykinin:
? Released in response to noxious agents.
--- Content provided by FirstRanker.com ---
? Irritant receptors are rapidly adaptive receptors.? Hering-Breuer reflex:
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
? Pulmonary stretch receptors activated during inspiration.
? Inhibits respiratory centers to prevent undue tension on lungs.
--- Content provided by FirstRanker.com ---
Hemoglobinand02Transport? 280 million
hemoglobin/RBC.
--- Content provided by FirstRanker.com ---
? Each hemoglobin has 4
polypeptide chains and
--- Content provided by FirstRanker.com ---
Insert fig. 16.324 hemes.
? In the center of each
--- Content provided by FirstRanker.com ---
heme group is 1 atom
of iron that can
--- Content provided by FirstRanker.com ---
combine with 1molecule 02.
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
Hemoglobin? Oxyhemoglobin:
? Normal heme contains iron in the reduced form (Fe2+).
--- Content provided by FirstRanker.com ---
? Fe2+ shares electrons and bonds with oxygen.? Deoxyhemoglobin:
? When oxyhemoglobin dissociates to release oxygen,
--- Content provided by FirstRanker.com ---
the heme iron is still in the reduced form.
? Hemoglobin does not lose an electron when it
--- Content provided by FirstRanker.com ---
combines with 02.www.freelivedoctor.com
Hemoglobin(continued)
--- Content provided by FirstRanker.com ---
? Methemoglobin:
? Has iron in the oxidized form (Fe3+).
--- Content provided by FirstRanker.com ---
? Lacks electrons and cannot bind with 02.? Blood normally contains a small amount.
? Carboxyhemoglobin:
--- Content provided by FirstRanker.com ---
? The reduced heme is combined with carbon
monoxide.
--- Content provided by FirstRanker.com ---
? The bond with carbon monoxide is 210 timeswww.freelivedoctor.com
stronger than the bond with oxygen.
--- Content provided by FirstRanker.com ---
? Transport of 02 to tissues is impaired.
Hemoglobin(continued)
--- Content provided by FirstRanker.com ---
? Oxygen-carrying capacity of blood determined by its
[hemoglobin].
--- Content provided by FirstRanker.com ---
? Anemia:? [Hemoglobin] below normal.
? Polycythemia:
--- Content provided by FirstRanker.com ---
? [Hemoglobin] above normal.
? Hemoglobin production controlled by erythropoietin.
--- Content provided by FirstRanker.com ---
? Production stimulated by PC0 delivery to kidneys.2
? Loading/unloading depends:
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
? P0 of environment.
--- Content provided by FirstRanker.com ---
2? Affinity between hemoglobin and 02.
OxyhemoglobinDissociationCurve
--- Content provided by FirstRanker.com ---
Insert fig.16.34
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
EffectsofpHandTemperature
? The loading and
--- Content provided by FirstRanker.com ---
unloading of O2influenced by the
affinity of
--- Content provided by FirstRanker.com ---
Insert fig. 16.35
hemoglobin for 02.
--- Content provided by FirstRanker.com ---
? Affinity is decreasedwhen pH is
decreased.
--- Content provided by FirstRanker.com ---
? Increased
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
temperature and2,3-DPG:
? Shift the curve to the
--- Content provided by FirstRanker.com ---
right.
Effectof2,3DPGon02Transport
--- Content provided by FirstRanker.com ---
? Anemia:? RBCs total blood [hemoglobin] falls, each RBC
produces greater amount of 2,3 DPG.
--- Content provided by FirstRanker.com ---
? Since RBCs lack both nuclei and
mitochondria, produce ATP through
--- Content provided by FirstRanker.com ---
anaerobic metabolism.? Fetal hemoglobin (hemoglobin f):
? Has 2 g-chains in place of the b-chains.
--- Content provided by FirstRanker.com ---
www.freelivedoctor.com
? Hemoglobin f cannot bind to 2,3 DPG.
--- Content provided by FirstRanker.com ---
? Has a higher affinity for 02.C02Transport
? C02 transported in the blood:
--- Content provided by FirstRanker.com ---
? HC0 -3 (70%).? Dissolved C02 (10%).
? Carbaminohemoglobin (20%).
--- Content provided by FirstRanker.com ---
--- Content provided by FirstRanker.com ---
ca
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
H20 + C02 H2C03
High PC02
--- Content provided by FirstRanker.com ---
ChlorideShiftatSystemicCapillaries? H
-
--- Content provided by FirstRanker.com ---
20 + C02 H2C03 H+ + HC03
? At the tissues, C02 diffuses into the RBC; shifts the
--- Content provided by FirstRanker.com ---
reaction to the right.? Increased [HC0 -3] produced in RBC:
? HC0 -
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3 diffuses into the blood.
? RBC becomes more +.
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? Cl- attracted in (Cl- shift).? H+ released buffered by combining with
www.freelivedoctor.com
--- Content provided by FirstRanker.com ---
deoxyhemoglobin.
? HbC02 formed.
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? Unloading of 02.CarbonDioxideTransportandChloride
Shift
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Insert fig. 16.38
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--- Content provided by FirstRanker.com ---
AtPulmonaryCapillaries? H
-
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20 + C02 H2C03 H+ + HC03
? At the alveoli, C02 diffuses into the alveoli;
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reaction shifts to the left.? Decreased [HC0 -
-
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3 ] in RBC, HC03 diffuses into the
RBC.
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? RBC becomes more -.? Cl- diffuses out (reverse Cl- shift).
? Deoxyhemoglobin converted to oxyhemoglobin.
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? Has weak affinity for H+.
? Gives off HbC02.
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www.freelivedoctor.comReverseChlorideShiftinLungs
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Insert fig. 16.39www.freelivedoctor.com
RespiratoryAcidosis
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? Hypoventilation.
? Accumulation of CO2 in the tissues.
? PCO2 increases.
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? pH decreases.? Plasma HCO -3 increases.
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RespiratoryAlkalosis
? Hyperventilation.
? Excessive loss of CO2.
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? PCO2 decreases.
? pH increases.
? Plasma HCO -3 decreases.
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www.freelivedoctor.comVentilationDuringExercise
? During exercise, breathing
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becomes deeper and more rapid.
? Produce > total minute volume.
? Neurogenic mechanism:
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Insert fig. 16.41
? Sensory nerve activity from
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exercising muscles stimulatesthe respiratory muscles.
? Cerebral cortex input may
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stimulate brain stem centers.
? Humoral mechanism:
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? PC0 and pH may be different at2
chemoreceptors.
--- Content provided by FirstRanker.com ---
? Cyclic variations in the values
that cannot be detected by
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blood samples.www.freelivedoctor.com
AcuteRespiratoryFailure
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? Results from inadequate gas exchange? Insufficient O2 transferred to the blood
? Hypoxemia
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? Inadequate CO2 removal
? Hypercapnia
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ClassificationofRF? Type 1
? Type 2
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? Hypoxemic RF
? Hypercapnic RF
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? PaO2 < 60 mmHg with ? PaCO2 > 50 mmHgnormal or PaCO2
? Hypoxemia is common
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qAssociated with acute ? Drug overdose,
diseases of the lung
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neuromuscular disease,qPulmonary edema
chest wall deformity,
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(Cardiogenic,
COPD, and Bronchial
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noncardiogenic (ARDS), asthmapneumonia, pulmonary
hemorrhage, and collapse
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PathophysiologiccausesofAcuteRFHypoventilation
V/P mismatch
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Shunt
Diffusion
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abnormalityClassificationofRespiratoryFailure
Fig. 68-2
--- Content provided by FirstRanker.com ---
Mechanismsofhypoxemia? Alveolar hypoventilation
? V/Q mismatch
? Shunt
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? Diffusion limitationAlveolarHypoventilation
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Restrictive lung disease
CNS disease
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Chest wall dysfunctionNeuromuscular disease
Perfusionwithoutventilation
(shunting)
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Intra-pulmonary
? Small airways occluded ( e.g asthma, chronic bronchitis)
? Alveoli are filled with fluid ( e.g pulm edema, pneumonia)
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? Alveolar collapse ( e.g atelectasis)
Deadspaceventilation
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? DSV increase:? Alveolar-capillary interface destroyed e.g
emphysema
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? Blood flow is reduced e.g CHF, PE? Overdistended alveoli e.g positive-
pressure ventilation
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Diffusionlimitation
?Severe emphysema
?Recurrent pulmonary emboli
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?Pulmonary fibrosis?Hypoxemia present during exercise
DiffusionLimitation
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Fig. 68-5Hypercarbia
? Hypercarbia is always a reflection of inadequate
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ventilation? PaCO2 is
? directly related to CO2 production
--- Content provided by FirstRanker.com ---
? Inversely related to alveolar ventilationPaCO2 = k x VCO2
VA
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Hypercarbia
? When CO2 production increases, ventilation
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increases rapidly to maintain normal PaCO2? Alveolar ventilation is only a fraction of total
ventilation
--- Content provided by FirstRanker.com ---
VA = VE ? VD
? Increased deadspace or low V/Q areas may
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adversely effect CO2 removal? Normal response is to increase total ventilation
to maintain appropriate alveolar ventilation
--- Content provided by FirstRanker.com ---
HypercapnicRespiratoryFailure? Imbalance between ventilatory supply
and demand
--- Content provided by FirstRanker.com ---
EtiologyandPathophysiology
? Airways and alveoli
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? Asthma? Emphysema
? Chronic bronchitis
? Cystic fibrosisS
EtiologyandPathophysiology
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? Central nervous system
? Drug overdose
? Brainstem infarction
--- Content provided by FirstRanker.com ---
? Spinal chord injuriesEtiologyandPathophysiology
? Chest wall
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? Flail chest
? Fractures
? Mechanical restriction
? Muscle spasm
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EtiologyandPathophysiology? Neuromuscular conditions
? Muscular dystrophy
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? Multiple sclerosisDiagnosisofRF
1?Clinical(symptoms,signs)
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? Hypoxemia? Hypercapnia
? Dyspnea, Cyanosis
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? Cerebral blood flow,
? Confusion, somnolence, fits and CSF Pressure
? Tachycardia, arrhythmia
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? Headache
? Tachypnea (good sign)
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? Asterixis? Use of accessory ms
? Papilloedema
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? Nasal flaring
? Warm extremities,
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collapsing pulse? Recession of intercostal ms ? Acidosis (respiratory, and
? Polycythemia
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metabolic)
? Pulmonary HTN,
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? pH, lactic acidCorpulmonale, Rt. HF
RespiratoryFailure
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Symptoms? CNS:
? Headache
? Visual Disturbances
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? Anxiety? Confusion
? Memory Loss
? Weakness
? Decreased Functional Performance
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RespiratoryFailure
Symptoms
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Cardiac:Orthopnea
Peripheral edema
Chest pain
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Other:Fever, Abdominal pain, Anemia, Bleeding
Clinical
? Respiratory compensation
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? Sympathetic stimulation? Tissue hypoxia
? Haemoglobin desaturation
Clinical
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? Respiratory compensation
? Tachypnoea RR > 35 Breath /min
? Accessory muscles
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? Recesssion? Nasal flaring
? Sympathetic stimulation
? Tissue hypoxia
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? Haemoglobin desaturationClinical
? Respiratory compensation
? Sympathetic stimulation
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? HR
? BP
? Sweating
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Tissue hypoxia? Altered mental state
? HR and BP (late)
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? Haemoglobin desaturation cyanosisRespiratoryFailure
LaboratoryTesting
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Arterial blood gas
PaO2
PaCO2
PH
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Chest imagingChest x-ray
CT sacn
Ultrasound
Ventilation?perfusion scan
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ManagementofARF
? ICU admission
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? 1 -Airway management? Endotracheal intubation:
? Indications
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? Severe Hypoxemia
? Altered mental status
? Importance
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? precise O2 delivery to the lungs
? remove secretion
? ensures adequate ventilation
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ManagementofARF? Correction of hypoxemia
? O2 administration via nasal
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prongs, face mask,
intubation and Mechanical
ventilation
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? Goal: Adequate O2delivery to tissues
? PaO2 = > 60 mmHg
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? Arterial O2 saturation>90%
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Indicationsforintubationandmechanicalventilation
? Innability to protect the airway
? Respiratory acidosis (pH<7.2)
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? Refractory hypoxemia? Fatigue/increased metabolic demands
? impending respiratory arrest
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? Pulmonary toiletManagementofARF
? Mechanical ventilation
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? Increase PaO2
? Lower PaCO2
? Rest respiratory ms
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(respiratory ms fatigue)? Ventilator
? Assists or controls the
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patient breathing
? The lowest FIO2 that
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produces SaO2 >90% andPO2 >60 mmHg should be
given to avoid O2 toxicity
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ManagementofARF
? PEEP (positive End-
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Expiratory pressure
? Used with mechanical ventilation
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? Increase intrathoracic pressure? Keeps the alveoli open
? Decrease shunting
? Improve gas exchange
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? Hypoxemic RF (type 1)? ARDS
? Pneumonias
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ManagementofARF? Noninvasive
Ventilatory support
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(IPPV)
? Mild to moderate RF
? Patient should have
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? Intact airway,
? Alert, normal airway
protective reflexes
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? Nasal or full face mask
? Improve oxygenation,
? Reduce work of breathing
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? Increase cardiac output? AECOPD, asthma, CHF
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ManagementofARF? Treatment of the
underlying causes
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? After correction of hypoxemia,
hemodynamic stability
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? Antibiotics? Pneumonia
? Infection
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? Bronchodilators (COPD, BA)? Salbutamol
? reduce bronchospasm
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? airway resistanceManagementofARF
? Treatment of the
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underlying causes
? Physiotherapy
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? Chest percussion to loosensecretion
? Suction of airways
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? Help to drain secretion? Maintain alveolar inflation
? Prevent atelectasis, help
lung expansion
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ManagementofARF? Weaning from mechanical ventilation
? Stable underlying respiratory status
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? Adequate oxygenation? Intact respiratory drive
? Stable cardiovascular status
? Patient is a wake, has good nutrition, able to cough and
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breath deeply