Bronchospasm

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Bronchospasm Successful Management

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Preoperative Considerations Pathophysiology of
bronchospasm - concept of smooth muscle
contraction as the cause of increased airway
resistance in patients with reactive airways is
overly simplistic. - bronchoconstrictor response
to trigger is characteristic of asthma reaction
- airway edema - increase secretion -
smooth muscle contraction
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Studies airway caliber in asthma patients -
marked thickening of submucosa - inflammation
--gt increase inflammatory cells in lung of
asthma - asthma clinically as airway obstruction
that improves with steroids - airway narrow by
constriction or secretion --gt marked increase
in resistance - bronchial hyperresponsiveness
increase by airway inflammation
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Role of recent infection - following upper
airway viral infection especially influenza --gt
normal subject increase airway reactivity -
asthma --gt most common viral exacerbration -
anesthesia following recent URI result in higher
incidence of problems with airway reflex
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Medications - B adrenergic agonist - mainstay
treatment chronic and acute in patient with mild
to moderate reactive airways - inhale B2
agonist - albuterol - pirbuterol -
terbutaline - salmeterol - fenoterol
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- have LD50 greater than therapeutic dose -
remain significant controversy as to whether
there are detrimental effect of chronic use of B
adrenergic agonist esp. high potency drug such
as fenoterol - inhaled corticosteroids as first
line therapy with B adrenergic agonist reserved
for PRN use
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- Theophylline - bronchodilating action - does
not add to therapeutic effects in acute attack -
very low toxic/therapeutic index - did not
provide bronchodilation in dogs anesthesized with
halothane when bronchospasm was provoked with
histamine - role --gt prophylaxis of acute
attack in chronic asthmatic prevention nighttime
episode of bronchospasm
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- chronic lung disease - theophylline beneficial
effects on improvement mucociliary clearance and
diaphragmatic contraction - theophylline
increase arrythmias during halothane anesthetic
induction, although similar effect are not seen
with enflurane or isofluranes - steroid few
hour preoperative useful in patients with
moderate to severe asthma and history of
required in past - one day of high dose
steroids should not significantly affect wound
healing
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- steroid course in the week(s) prior to surgery
maybe useful in case of ongoing wheezing -
steroids increase rate of wound healing problems
or infection are not well founded - 1991 NIH
Expert Panel recommendation that asthmatics with
an FEV1 less than 80 of predicted should
receive a preoperative course of oral
steroids - Leukotiene receptor anatagonists or
synthesis inhibitors are a recent addition to
the anti asthmatic -- mild benefits
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Choice Of Anesthesia RA GA mask LMA -
since instrumentation of airway is major trigger
for wheezing during anesthesia - avoid
intubation are useful - asthmatic patient have
wheezing 6.4 with intubation lt 2 without
intubation or RA
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- LMA insertion , airway resistance decrease less
than following ETT insertion - high spinal 48
reduction in expiratory reserve volume --gt
decrease cough - its a problem in chronic
bronchitis or current URI - most patients with
reactive airways, RA is ideal - high block
leading to sympathetic blockade and consequent
bronchospasm also appear to be unfounded
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- study - asthma no difference between
anesthetize with high epidural (T2-T4) and GA
with ketamine / isoflurane - volunteer -
document bronchial hyperreactivity found high
thoracic epidural did not alter airway resistance
and attenuate response to inhale acetylcholine
due to systemic absorption of LA rather than any
direct effect from epidural - survey Japan -
incidence asthmatic attack with epidural anesth
than GA - However, several case in ASA close
claim study with adverse outcome had received
RA - light anesthesia often used with subsequent
airway irritation
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Induction agents - thiopental rarely may cause
bronchospasm - airway instrumentation under
thiopental anesthesia alone may trigger
spasm - isolate sheep airway --gt thio caused
tracheal contraction and bronchial
relaxation - ketamine produce smooth muscle
relaxation via neural mechanism release of
cathecolamine
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- lidocaine - prevent reflex
bronchoconstriction - little effect toxicity at
dose 1.5 mg/kg 1-3 min prior intubation -
direct tracheal lidocaine spray carries hazard of
triggering airway reaction and should be avoid
in favor of IV route - induction of asthmatic
with 2.5 mg/kg propofol --gt significant lower
incidence of wheezing following tracheal
intubation when compared with 6 mg/kg thiamylal
or methohexital - propofol result in significant
lower respiratory resistance following tracheal
intubation than thiopental or etomidate
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Inhalation agents - study in dog with ascaris
antigen induce bronchospasm --gt halothane and
isoflurane were equally effective experimentally
in reducing bronchospasm - halothane better
bronchodilate than isoflurane at 1.7 MAC -
halothane induction less cough - bronchodilating
effect of inhale anesthetic following intubation
found that sevoflurane was effective
bronchodilator as halothane and more effective
than isoflurane
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Muscle relaxants - Rapacuronium --gt severe
bronchospasm - Mivacurium --gt release
significance amount of histamine and lead to
mast cell degranulation concern in patient
history atopy or asthma --gt rabbit --gt
significance increase airway resistance
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Analysis of a Bronchospastic crisis Why do peak
airway pressure rise ? - airway constrict -
coughing and bucking - secretion and mucosal
engorgement further contribute to the problem -
severe case --gt air trapping (auto-PEEP) may
occur chest become overdistend and less
compliance
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What is auto PEEP and why is it a problem ? -
increase resistance --gt require longer
inspiration time to deliver adequate TV --gt
shortened expiratory time combine with airway
compression during exhalation may result in
incomplete exhalation - in patient whose volume
status is marginal, an increase of just a few
cmH2O in intrathoracic pressure can greatly
decrease venous return and result in hypotension
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Why does the oximeter show a dropping saturation
? - secretion and spasm have result in airway
closure and underventilation of perfuse
airway - hypoxia is generally not a major
problem in pure reactive airway disease -
problem --gt inadequate perfusion resulting in
fasely low reading on oximeter - keep in mind
--gt if low saturation is accompanied by
hypotension - trying to treat low saturation
with PEEP could just make things worse
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Why does pCO2 go up and ETCO2 go down ? -
difference in resistance result in overdistention
of some lung units - V/Q mismatch -
overdistension alveoli may not be perfuse at all
especially hypotension --gt large increase in
dead space - if increase airway pressure --gt
decrease minute ventilation
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- the compressible volume of typical anesthesia
circuit is large enough that wasted ventilation
is often 7-10 cc/cmH2O --gt as pressure go to 60
--gt half liter of each set breath may actually
not be delivered to the patient - anesthesia
ventilator --gt increase respiratory
impedance --gt at high pressure, attempt to
increase MV are often unrewarding - changing to
a more powerful ICU type ventilator may be the
better approach
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Responding to the Crisis Deepen anesthesia -
even when there is drop in BP --gt deepening
anesthetic is useful especially since it may
lower intrathoracic pressure and improve venous
return - paralysis will decrease respiratory
impedance associated with bucking - halothane
and sevoflurane may be a better choice of
inhaled anesthetic than isoflurane especially at
lower level of MAC
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Dont spare the beta 2 agonists - very safe
agent - provide further bronchodilation during
halothane in animal model - study, mechanically
ventilate patient in ICU found that maximum
benefit occur after 15 puffs of albuterol via
spacer with no patient benefiting from more
puffs - terbutaline is available as subcutaneous
preparation but no evidence superior to inhale
route
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- salmeterol - long duration of action - use
asthmatic prophylactically - dont use in acute
episode because onset of action 20
min Ketamine - incremental dose - quick way
of maintaining BP - rapidly deepening
anesthesia - avoid problem of delivering an
inhale anesthetic to patient with poor
ventilation
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Bring in an ICU Ventilator - our anesthesia
ventilator are not design for patient with
respiratory failure, too much compressible volume
to make adequate ventilation in face of high
impedance - ICU ventilator - pressure as high
as 120 cmH2O are feasible - high flow allow for
shorter inspiratory time with adequate time for
greater exhalation and lower auto PEEP --gt
improve circulation - major disadvantage is need
to switch to intravenous from inhalation
anesthetic
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