Case 78 - Asthma Flashcards
What is asthma, how is it diagnosed?
Asthma
- reverisble airway obstruction
- obstructive disease
- airway hyperresponsiviness and inflammation
- s/sx = wheezing, SOB, cough
Dx
- history
- forced expiratory volumes (obstructive disease via PFTs)
What are PFTs, and what do they look like in obstructive vs restrictive lung disease?
PFT = comprise of spirometry and flow-volume loops
Obstructive
- decrease everything except TLC, FRC, RV
- FEV1 decreased more than FVC (hence V1/VC < 80%)
- increase in TLC 2/2 increase in RV and FRV
- **useful to obtain in COPD patients to assess degree of reversibility by using bronchodilators and measuring PFT response to it**
Restrictive
- decrease everything except FEV1/FVC, FEF 25-75%
- decrease FEV1 and FVC proportionely, therefore v1/vc ratio unchanged or > 80%
what are the PFTs for asthmatics?
- asthmastics have normal PFTs between exacerbations
- PFTs during exacerbations = obstructive disease
- sensitive marker = FEF 25-25% - Decreased
-
can give methacholine challenge
- assess airway reactivitiy in suspected asthma pts with borderline PFTS
- will trigger bronchospasm intentionally
What is FEF 25-75%?
- does not require patient effort
- sensntive marker for obstruction
- obtained by dividing volume expired between 25% and 75% of FVC by the time elasped between these two points
what are flow volume loops for obstructive vs restrictive lung disease?
Flow volume loops
- x axis is lung volume
- inspiratoin is below x axis
- expiration is above y axis
Obstruction
- associated with airway resistance with expiration
- normal inspiratory curve
- flattening of expiratory curve
Restriction
- not associated with airway resistance
- associated with reduced lung volumes
- curve = reduced lung volume with no airway resistance and no flow limitation
what are flow volume loops for intrathoracic vs extrathoracic vs fixed obstructions
Fixed obstructoins
- ex: tracheal stenosis
- decrease in inspiratory and expiratory flow
Intrathoracic obstruction
- ex: tracheal or endobronchial tumor
- inspiration - airway expands, chest wall rises, and pushes/lifts tumor away from lumen.
- expiration - tumor collapses airway –> airway narrowing during forced expiration
Extrathoracic obstruction
- ex: vocal cord paralysis, pharyngeal muscle weakness
- inspiratoin creates negative intrathoracic pressure –> transmitted into pharyngeal area which sucks lesions into airway lumen
- inspiration - lesion enters lumen airway, obstructs gas flow with inspiration, decrease inspiratory air flow
Which asthma medications are used to treat acute attacks, and long-term control?
Acute attack
- short acting B2 agonist (albuterol) + systemic steroids
Long term
- long acting B2 agonist - salmterol
- never used alone due to increase risk of death
- inhaled corticosteroid - fluticasone
- inhaled anticholinergics - ipratropium (better for copd)
- leukotriene antagonists - montelukast
- oral or IV steroids - prednisone, hydrocortisone, methylprednisolone
what tx regimens are used for intermittent asthma, mild, moderate persistnt, and sever persistent?
intermittent
- inhaled short acting b2 agonist prn
mild persistent
- low dose inhaled corticsteroid or leukotrine antagnost daily + short acting b2 agonist prn
moderate persistent
- medium dose inhaled cortisteroid + long acting b2 agonist
severe persistent
- high dose inhaled cortcosteroid + long acting b2 agonist + long term oral steroid
what are indications for mechanical ventialation in severe asthma (status asthmaticus) and waht are specific concerns?
status asthmaticus
- bronchial hyperresponsiveness and severe airway inflammation unresponsive to treatments
- intubation and mech ventilation should be initiated when patient is hypercapnic, physically exhuasted, absent breath sounds + no wheezing (sign of moving NO AIR)
concerns with mech ventilation
- bronchial hyperresponsiveness and inflammation –> intense bronchoconstrcition and severe reduction in expiratory flow
- Mech vent –> increased airway resistence, high peak inspiratory pressure, prolong expiration times, auto-PEEP, and breath “stacking”
- breath stacking = incomplete evacuation of air during expiration followed by new inspiratory volume
- Mgmt
- fio2 100%
- R 8 to 12 bpm
- TV 6-8 ml/kg
- increase expiratoty time (I:E 1 to 4 or 1 to 6)
- neuromuscular bloackade - increase chest wall compliance and make ventilation easier
How would you preop eval a patient with asthma?
History
- frequency and severity of attacks
- response to tx
- ED visits and previous intubations acute attack
- use of systemic steorid (dose, duration, last use)
- no benefit in obtaining preop PFT
PE
- lung exam, wheezing present?
- severe bronchospasm = absent breath sounds and no wheezing = moving NO AIR
- use of accessory muscles
- prolongation of expiratory phase
Meds
- asymptomatic & mild asthma
- continue meds as scheduled + inhaled B2 agonist DOS
- mod to severe asthma
- continue meds as scheduled
- periop steroid initiated prior to surgery, taper after uncomplicated surgical course
A patient with history of asthma comes for elective surgery. During your h & p, you discover the patient has an upper respiratory tract infection. Would you cancel the case?
URI
- known to increase airway reactivity
- known to trigger bronchospasm exacerbation in asthmatics
MGMT
- asymptomatic, clear sounding chest –> proceed
- asymptomatic, wheezing –> tx and proceed
- fever, erythematous throat, productive cough –> postpone surgery
Does regional anesthesia protect an asthmatic patient from intraop bronchospasm?
- airway instrumentation, light plane of anesthesia, secretions all lead to intraop bronchospasm
Regional Anes
- although avoids airway instrumentation, pulm function can still be affected:
- 1) high block –> affect pulm function
- 2) sympathetic blockade –> unopposed vagal tone –> bronchospasm
How would you administer general anesthesia in an asthmatic patient?
- bronchospasm exacerbation –> airway instrumentation, light plane of anesthesia, secretoins
- goals: deep anesthesia, bronchodilators nearby, ??glyco to dry secretions
general anes
- deep plane of anes prior to larygnoscopy and intubation
- consider ketamine as inductino agent (potent anesthetic with bronchodilating properites)
- LMA vs ETT
- LMA less stimulating than ETT, less increased airway reistance compared to ETT
- does not protect against aspiratoin
what are signs of periop bronchospasm?
Physical Exam
- auscultation = expiratory wheezing
- prolonged expiratory time
- awake patient = tachypnea, shortness of breath
Mech vent
- increased airway resistance with increase inspiratory pressure (higher pressure required to deliver gas through stentoic airways into alveoli)
- capnography = upslope of expiratory phase
DDx of bronchospasm?
- asthma exacerbation
- tracheal tube kinking
- tracheal tube secretions
- CHF
- anaphylaxis (medication, blood transfusion)
- increased histamine release (morphine)
- pneumothorax / PE (rare)
