asthma

Question 1

12 yr old presents for appendectomy. parents inform you she was admitted and treated 4 days ago for status asthmaticus. her lungs are currently clear to auscultation, but she is very nauseated. her current meds include dexamethasone, omalizumab, salmeterol. how would you treat her condition?

Answer 1

1. supplemental O2 to maintain SpO2 >90%
2. b-agonist (like albuterol)
3. corticosteroids (these can take 4-6 hours to reach therapeutic benefit)
4. aminophylline (bronchodilation, stimulate central respiratory cycle, reduce diaphragmatic ms fatigue, relax vascular sm ms)
5. empiric antibiotics
6. IV fluids
7. PFTs
8. ABG
9. consider IV mag for bronchodilation
10. consider mech vent

Question 2

when would you intubate this patient and what vent strategy would you use?

Answer 2

i would intubate when patient began to show signs of respiratory fatigue or compromise. this could be assessed by monitoring response to therapy with PFTs and ABGs.

if PFT showed FEV1 or peak exp flow rate 50 mmHg despite aggressive therapy, i would intubate and initiate mech vent.

my goals during mech vent are to decrease work of breathing, maintain oxygenation, and augment alveolar ventilation without causing intrinsic lung injury. i would use pressure control, recognizing the the decelerating flow pattern associated with this mode will more efficiently overcome the high airway resistance and minimize the peak pressures require to deliver a given TV. it will also improve the distribution of ventilation. i would establish a prolonged expiratory phase for complete exhalation to avoid auto-PEEP (breath-stacking) which can result in barotrauma.

when the patients FEV1 increased to >50% of normal, i would initiate weaning.

Question 3

how would you assess the patients status in preop?

Answer 3

careful history and physical.

focus on severity and characteristics of her pulmonary disease, along with the effectiveness of her current treatment. age of onset, triggers, allergies, recent rest infection, changes in symptoms, current meds, anesthetic history, recent hospital course.

auscultation for pulm wheezing or crepitation, check for accessory ms use

testing:
- PFTs before and after bronchodilator therapy
- ABG
- CXR

Question 4

how would you prepare her for emergency surgery?

Answer 4

optimize her asthma, reduce pain/anxiety, minimize risk of aspiration

reassure her family, continue current meds, consider chest PT

• administer fentanyl to reduce pulmonary splinting, decreased ability to cough, and bronchospasm associated with pain, keeping in mind to avoid narcotics that induce histamine release (morphine)
• diphenhydramine (H1-receptor blocker) to inhibit histamine-induced bronchoconstriction and reduce potential for anxiety-induced bronchospasm
• stress dose hydrocortisone (HPA suppression from chronic steroids)
• metoclopramide to facilitate stomach emptying
• ondansetron to treat nausea
• abuterol just prior to induction

Question 5

would you give atropine preoperatively?

Answer 5

anticholinergics may be beneficial to reduce mucous gland secretions and airway hyperactivity (reduces vagal tone and inhibits muscarinic cholinergic receptors)

however, its administration is controversial since it could result in increased inspissation (increased viscosity of airway secretions) leading to plugging and the initiation of an asthma attack.

given this risks and benefits, i would probably not administer this medication pre-operatively.

Question 6

you plan on general anesthesia. how will you induce her?

Answer 6

goals for asthmatic with full stomach/nausea are the achieve an adequate plane of anesthesia (avoid bronchoconstriction) while minimizing risk of aspiration

1. administer short-acting b2 agonist
2. denitrogenate her lungs with 100% oxygen
3. facilitate gastric emptying with meoclopramide
4. treat nausea with ondansetron
5. administer 2 mpg/kg of fentanyl 2-3 minute prior to induction to blunt response to laryngoscopy
6. give 1-2 mg/kg of lidocaine 1-2 min prior to induction to prevent reflex-induced bronchoconstriction
7. apply cricoid pressure
8. perform RSI using ketamine (bronchodilation), propofol (bronchodilation), and succinylcholine (potential for histamine-release but need for rapid paralysis for ETT placement)