Asthma Flashcards
Asthma: Alterations in PFTs/Lung Volumes
Decreased FEV1
extent of decrease reflects severity of expiratory obstuction
During asthma attack FEV1
Asthma: Blood Gas Alterations
In mild to moderate asthma FEV1 >50% predicted – PaO2 and PaCO2 normal
PaCO2 often decreased as a result of hyperventilation
With severe asthma (FEV1
Pharmacologic Management: Prophylactic Approach Treat Underlying Inflammation
Inhaled Corticosteroids
Decrease bronchial mucosa inflammation and hyper-responsiveness
Cromolyn
Leukotriene Inhibitors
Methylxanthines – phosphodiesterase inhibitors
Pharmacologic Management: Rescue Approach - Bronchodilators
Beta-2 Adrenergic Agonists – albuterol, terbutaline
B-2 receptor activation of adenylate cyclase with increased cAMP concentrations & bronchodilation
SNS side effects: tachycardia, dysrhythmias, potassium shifts
Anticholinergic Drugs – ipratropium
Block muscarinic receptors = bronchodilation
Less effective than B-2 in asthmatics
Pre Induction for the patient with asthma?
Assess Breath Sounds
PFTs before and after bronchodilator therapy for major elective operations (especially FEV1)
FEV1/FVC should be >70%-80% expected or personal best prior to surgery
FEV1/FVC
Peri-operative Prophylaxis of Bronchoconstriction
- Pre-operative bronchodilators – albuterol before induction
- Pre-operative steroids
- Inhaled – start 48 hours pre-op
- IV - hydrocortisone 100mg Q 8 hrs on day of surgery if FEV1
Anesthesia for the patient with asthma should consider?
Consider regional techniques GA should be designed to depress airway reflexes, avoid hyperactivity Bronchoconstriction Avoid histamine release
Induction and Maintenance in the Asthmatic Patient
Blunt airway reflexes and bronchoconstriction response during airway instrumentation
Regional Anesthesia a good option
IV induction – propofol & ketamine best
Avoid drug preparations with metabisulfites
IV opioids
Consider Lidocaine 1.5 mg/kg IV or intratracheal (LTA)
High concentration of volatile agent >1.5 MAC for bronchodilation and bronchial reflex inhibition…..need a strong CV system
Sevoflurane and Halothane less pungent – less coughing to trigger bronchospasm
Avoid NDMR that release histamine
Anticholinesterase drugs: neostigmine O.K. if given with anticholinergic (glycopyrrolate)
IV fluids – liberal hydration to decrease viscosity of secretions Intra-op bronchospasm – attach albuterol metered dose inhaler to T-piece of ETT Smooth emergence – ETT promotes reflex bronchoconstriction and airway resistance Deep extubation (in appropriate patients) and/or lidocaine 1-3mg/kg IV
When selecting medications used during general anesthesia for this case, what medications are attractive and not attractive – and why?
Induction agents
Thiopental – not attractive as releases histamine
Ketamine – bronchodilator (sympathetic nervous system stimulation) but also stimulates secretions
Etomidate, propofol – attractive as do not release histamine. Generic propofol contains sulfites – consider avoiding in the asthmatic.
Neuromuscular relaxant
Avoid those that trigger histamine release (succinylcholine, curare, mivacurium, atracurium – dose and speed of administration dependent)
Opioid
Avoid those that stimulate histamine release (morphine). Fentanyl and analogues are OK.
Consider avoiding ketorolac & other NSAIDs in the asthmatic.
Volatile anesthetics and the asthma patient?
All are potent bronchodilators however isoflurane and desflurane irritate the airways and may be bothersome, especially during induction and/or emergence.
Halothane is the classic volatile agent for the asthmatic but being supplanted by sevoflurane.
Ventilation Goals in the Asthmatic Patient
Decreased RR to 8-10 bpm
– need adequate exhalation times
Prolong I:E ratio
shorter inspiratory time compared to expiratory time
Increase tidal volume to maintain normal PaCO2 (within limits)
Tidal volume and inspiratory flow rate adjustments limited by excessive peak airway pressures (40 cmH2O upper limit)
What is in the differential diagnosis of intraoperative wheezing?
Foreign body (gastric tube in the lung) Partially blocked/kinked ETT Light anesthesia Aspiration Endobronchial intubation Pneumothorax Pulmonary embolus Pulmonary edema “cardiac asthma” Acute exacerbation of asthma
How to manage bronchospasm
If an episode of bronchospasm occurs during anesthesia
Administer 100% O2
Deepen the level of anesthesia as with a volatile agent or IV drugs
Administer B2 agonist
In severe cases administer Epinephrine IV (severe cases; infusion 2-8 mcg/min, subcutaneously 0.3-0.5 mg q20-30 min
Consider IV corticosteroids 1-2mg of cortisol
Consider IV Aminophylline
