Transcript No Slide Title

Inpatient
Management of
Asthma
Michael Bressack, M.D.
Definition
• Reversible airway
obstruction
• Airway inflammation
• Airway hyperresponsiveness
• Status asthmaticus =
unresponsive to initial
nebulized bronchodilator
Pathophysiology
• Airway inflammation- eosinophils,
polymorphonuclear cells, lymphocytes,
macrophages, mast cells
• Proinflammatory mediators
• Airway edema, smooth muscle hypertrophy,
exudation, mucous plugging
• Hypertrophy of goblet cells and mucous
glands
Cause of Asthma
Attack
• Infectious, usually viral
• Allergic
• Irritant
Symptoms / Signs
• Dyspnea / tachypnea / increased work
of breathing / difficulty speaking
• Cough
• Wheeze / rhonchi / rales / decreased
breath sounds
• Cyanosis
• Abnormal level of consciousness
• Pulsus paradoxus
Pulsus Paradoxus
• Increased pulmonary venous
capacitance
• Increased left ventricular afterload
• Leftward shift of the interventricular
septum
• Alterations in pulse oximetry tracings
Panel A: tracing during respiratory distress- pulsus paradoxus of 16
torr (RWV respiratory waveform variation) Panel B: tracing after
treatment / mild respiratory distress- pulsus paradoxus of 8 torr
Hartert T., Chest, 115:477, 1999
Criteria for ICU Admission
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Severe respiratory symptoms/exam
Worsening respiratory symptoms/exam
Abnormal neurologic status
Increasing pC02
Barotrauma
Past history of respiratory failure
Therapy
First-line therapy
Oxygen
Inhaled 2 catecholamine
Corticosteroids
Ipratropium inhalation
Inhaled 2 Catecholamine
• Albuterol- 2 selective bronchodilator of small and
large airways (0.15mg/kg/dose)
• 2 receptor polymorphism determining
responsiveness, desensitization, and
downregulation
• Continuous (more rapid response/cost effective)
(0.4-0.8mg/kg/hr up to 10-20mg/hr), intermittent
(MDI vs nebulizer)
• Side effects include tachycardia, tremor/ agitation,
hypoxemia, hypokalemia, arrhythmia, hypotension
• Consider subcutaneous epinephrine (0.01ml/kg
1/1000) acutely with poor aerosol delivery
Corticosteroids
• Suppresses underlying inflammation by blocking
proinflammation and activating antiinflammation
at the level of gene transcription
• Restores 2 receptor function by reversing
desensitization and downregulation
• Genetic polymorphism effects response
• Onset begins in 2-4 hours, peaks ~ 6-8 hrs
• Dose = solumedrol 2 - 4 mg/kg/day
• Risk of myopathy, especially when also receiving
paralytics
Ipratropium
• Anticholinergic quaternary derivative
of atropine
• Inhibits cholinergic-mediated
bronchospasm
• Primarily effects larger bronchi
• Use in conjunction with 2
bronchodilator
• Most beneficial as multiple doses (250500g Q20 min x3) in severe asthma
Therapy
Second-line therapy
Magnesium sulfate
Heliox
rhDNAse
Theophylline
Intravenous 2 catecholamine
Intravenous ketamine
Magnesium sulfate
• Direct inhibition of Ca-mediated smooth
muscle constriction
• Possibly useful to prevent hospitalization
and treat impending respiratory failure
• 25-75 mg/kg (max 2 gm) over 20 min
• Advantage is lack of cardiac stimulation
(tachycardia, 02 consumption)
• Side effects include nausea, vomiting, facial
flushing, hypotension, muscle weakness
Heliox
• Indication: treatment of increased airway resistance in
areas of turbulent gas flow (density-dependent)
• Characteristics: decreased gas density, ideally requires 6080% helium, no adverse effects, works immediately
• Goal: “therapeutic bridge”, changing the biophysical
characteristics of gas flow until other treatments (e.g.
steroids) take effect or until the disease improves
• Mechanisms:
– with turbulent flow, heliox’s low gas density causes less airflow
resistance and increased flow rate (decreased work of breathing,
decreased ventilatory pressures, less gas trapping)
– low gas density decreases the Reynolds number, which shifts some
flow from turbulent to laminar
– low gas density increases the C02 diffusion coefficient, improving
C02 elimination
– low gas density facilitates the delivery of inhaled medications into
the tracheobronchial tree
• Therapeutic targets: asthma, bronchiolitis, upper airway
obstruction (e.g. croup, postextubation stridor)
rhDNAse
• Recombinant
deoxyribonuclease
• Decreases the sputum viscosity
by degrading the extracellular
DNA released by neutrophils
Bronchial Cast
Aminophylline
• Phosphodiesterase inhibitor used to be first-line
therapy
• Relaxes airway smooth muscle, improves
diaphragm function, stimulates respiratory drive,
increases catecholamine release, has
antiinflammatory effect
• Studies show uncertain beneficial effects
• Low therapeutic index- side effects include
gastrointestinal (nausea, vomiting, abdominal
pain), neurologic (headache, agitation, seizures),
cardiovascular (arrhythmias, hypotension,
cardiac metabolic rate)
Intravenous 2 Catecholamine
(terbutaline)
• Direct systemic effect with increased
catecholamine side effects (load 10g/kg,
max 0.4-1.0mg, followed by 0.14.0g/kg/min, max 1.0mg/hr)
• Serious risks include hypotension,
arrhythmias, tachycardia, ischemia
• Risks of intravenous terbutaline are much
less than isoproterenol
• Maintain adequate cardiac output and blood
pressure
Intravenous Ketamine
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Dissociative anesthetic
Increases catecholamines
Direct airway smooth muscle relaxation
Inhibits vagal tone
0.5-2.0mg/kg/hr
Can be used as treatment with or without
mechanical ventilation
Mechanical Ventilation
• Avoid intubation if at all possible. Respiratory arrest is the
only absolute indication (decide clinically, not from
arterial blood gas).
• Consider a trial of Bipap, if tolerated, before intubation
• Use ketamine (propofol also has bronchodilatory
properties), paralysis, cuffed endotracheal tube
• Fluid bolus prior to intubation to prevent decreased cardiac
output (decreased venous return)
• Basic principles are to give adequate ventilation without
barotrauma and with minimal dynamic hyperinflation
– low minute ventilation (tidal volume, respiratory rate)
– prolonged expiratory time/shortened inspiratory time
– pressure-limited ventilation, limiting PIP to 35-40cmH20,
Pplateau 30cmH20, PEEP 0-5cmH20
– tolerate permissive hypercapnea (pH7.20)
– sedation/paralysis (minimizes dysynchrony and C02 production)
– monitor for dynamic hyperinflation/intrinsic PEEP
– consider extrinsic PEEP (<intrinsic PEEP)