Extra Topic 4.1 -- Status Asthmaticus

Question 1

If you had been the intensive care physician responsible for this patient with status asthmaticus four days ago, how would you have treated her condition?

(A 12-year-old female presents to the operating suite with acute appendicitis. Her parents inform you that she has severe asthma. They further report that their daughter was hospitalized and treated 4 days ago for status asthmaticus. Her lungs are currently clear to auscultation bilaterally, but she is extremely nauseous. Her current medications include dexamethasone, omalizumab, and salmeterol.)

Answer 1

When treating a patient with this life-threatening condition, I would:

1. provide supplemental oxygen to maintain the oxygen saturation above 90%;
2. administer B2-agonists (i.e. albuterol), corticosteroids (recognizing that it may take 4-6 hours to realize a therapeutic benefit), aminophylline (to induce bronchodilation, stimulate the central respiratory cycle, reduce diaphragmatic muscle fatigue, and relax vascular smooth muscles), empirical broad-spectrum antibiotics, and intravenous fluids (although the benefits of this treatment are limited);
3. order pulmonary function tests and arterial blood gases to monitor the adequacy of oxygenation, ventilation, and the patient’s response to treatment;
4. consider the addition of intravenous magnesium sulfate (for bronchodilatory affects), if the patient’s response to other bronchodilators is inadequate; and
5. consider mechanical ventilation, if the patient begins to show signs of respiratory fatigue and/or inadequate ventilation and oxygenation (PaCO2 > 50 mmHg).

Question 2

When would you intubate a patient with status asthmaticus, and what ventilator strategy would you employ?

(A 12-year-old female presents to the operating suite with acute appendicitis. Her parents inform you that she has severe asthma. They further report that their daughter was hospitalized and treated 4 days ago for status asthmaticus. Her lungs are currently clear to auscultation bilaterally, but she is extremely nauseous. Her current medications include dexamethasone, omalizumab, and salmeterol.)

Answer 2

I would consider intubation and the initiation of mechanical ventilation if the patient began to show signs of respiratory fatigue and/or inadequate ventilation and oxygenation.

Therefore, I would monitor the patient’s response to therapy using pulmonary function tests and arterial blood gases.

If pulmonary function testing showed a FEV₁ or peak expiratory flow rate = 25% of normal, or if arterial blood gases showed a PaCO2 > 50 mmHg, despite aggressive therapy, I would intubate the patient and initiate mechanical ventilation.

My goals during mechanical ventilation are to decrease the work of breathing, maintain adequate oxygenation, and augment alveolar ventilation without causing intrinsic lung injury.

Therefore, I would employ a pressure control mode of ventilation, recognizing that the decelerating flow pattern associated with this mode of ventilation will more efficiently overcome the high resistance of the asthmatic’s airways, minimize the peak pressures required to deliver a given tidal volume, and improve the distribution of ventilation.

Moreover, I would establish a prolonged expiratory phase to allow for complete exhalation and to avoid auto-PEEP (breath stacking), which can result in barotrauma.

When the patient’s FEV₁ or peak expiratory flow rates increased to >/= 50% of normal, I would initiate weaning from mechanical ventilation.

Question 3

Ok. Back to our current situation, with the patient having been discharged from the hospital several days ago and now presenting to the operating suite with acute appendicitis.

How would you assess this patient’s asthmatic condition, pre-operatively?

(A 12-year-old female presents to the operating suite with acute appendicitis. Her parents inform you that she has severe asthma. They further report that their daughter was hospitalized and treated 4 days ago for status asthmaticus. Her lungs are currently clear to auscultation bilaterally, but she is extremely nauseous. Her current medications include dexamethasone, omalizumab, and salmeterol.)

Answer 3

I would first perform a careful history, focusing on the severity and characteristics of her pulmonary disease, along with the effectiveness of her current therapy.

To this end, I would attempt to elicit information concerning the –

• age of onset,
• triggering events,
• allergies,
• recent respiratory infection,
• changes in symptomatology (cough, sputum, wheezing, etc.),
• current medications,
• anesthetic history, and
• her recent hospital course.

Next, I would perform a physical exam to identify any pulmonary wheezing or crepitations and/or the use of accessory muscle of respiration.

Considering the severity of her disease, I would order:

1. pulmonary function tests, before and after bronchodilator therapy, to more accurately assess the severity of obstruction and her response to therapy;
2. arterial blood gases, to evaluate the adequacy of ventilaton/oxygenation and to establish baseline levels (helpful in the event of subsequent respiratory dysfunction); and
3. chest x-rays, to identify or rule out pulmonary infection.

Question 4

How would you prepare her for emergent surgery?

(A 12-year-old female presents to the operating suite with acute appendicitis. Her parents inform you that she has severe asthma. They further report that their daughter was hospitalized and treated 4 days ago for status asthmaticus. Her lungs are currently clear to auscultation bilaterally, but she is extremely nauseous. Her current medications include dexamethasone, omalizumab, and salmeterol.)

Answer 4

My goals in preparing this patient for surgery are to optimize her asthma, control her pain, reduce her anxiety, and minimize the risk of aspiration.

Therefore, I would reassure the patient and family, continue her current medications, and consider chest physiotherapy.

Moreover, I would administer –

• fentanyl, to avoid the pulmonary splinting, decreased ability to cough, and bronchospasm potentially associated with pain (avoid narcotics that release histamine and carefully titrate to avoid respiratory depression);
• diphenhydramine (an H1-receptor blocker), to inhibit histamine-induced bronchoconstriction and reduce the potential for anxiety-induced bronchospasm; a
• stress dose of hydrocortisone (100 mg), given the potential for hypothalamic-pituitary-adrenal suppression with chronic steroid treatment (she is being treated with dexamethasone);
• metoclopramide, to facilitate stomach emptying; and
• ondansetron, to treat her nausea.

Just prior to induction, I would administer –

• a short acting B2-agonist (i.e. albuterol), to minimize the risk of bronchoconstriction during intubation.

Question 5

Would you give atropine, pre-operatively?

(A 12-year-old female presents to the operating suite with acute appendicitis. Her parents inform you that she has severe asthma. They further report that their daughter was hospitalized and treated 4 days ago for status asthmaticus. Her lungs are currently clear to auscultation bilaterally, but she is extremely nauseous. Her current medications include dexamethasone, omalizumab, and salmeterol.)

Answer 5

Anticholinergic medications may be beneficial for asthmatic patients secondary to reduced mucous gland secretions (possibly improving inflammation) and airway hyperreactivity (secondary to reduced vagal tone and inhibition of muscarinic cholinergic receptors).

However, their preoperative administration is controversial, since they could result in increased inspissation (increased viscosity and thickening of airway secretions), potentially leading to airway plugging and the initiation of an asthmatic attack.

Therefore, considering these potential complications, and recognizing that the intramuscular doses of anticholinergic medications typically used for pre-anesthetic medication are unlikely to significantly decrease her airway resistance (they would be sufficient to reduce airway secretions), I would NOT administer this medication pre-operatively.

If I wanted to administer an anticholinergic, preoperatively, to optimize his asthmatic condition, I would consider providing an inhaled medication, such as ipratropium.

Question 6

You are planning general anesthesia for the procedure. How will you induce her?

(A 12-year-old female presents to the operating suite with acute appendicitis. Her parents inform you that she has severe asthma. They further report that their daughter was hospitalized and treated 4 days ago for status asthmaticus. Her lungs are currently clear to auscultation bilaterally, but she is extremely nauseous. Her current medications include dexamethasone, omalizumab, and salmeterol.)

Answer 6

My goals when inducing this severely asthmatic patient with a full stomach and nausea, are to achieve an adequate plane of anesthesia to avoid bronchoconstriction in response to mechanical stimulation while, at the same time, minimizing the risk of aspiration.

Therefore, assuming her airway exam were reassuring, I would:

1. administer a short acting B2-agonist;
2. denitrogenate with 100% oxygen;
3. ensure that she had received metoclopramide and ondansetron to facilitate gastric emptying and treat her nausea, respectively;
4. administer 2 mcg/kg of fentanyl, 2-3 minutes prior to induction, to avoid light anesthesia during laryngoscopy;
5. give 1-2 mg/kg of intravenous lidocaine, 1-2 minutes prior to induction, to prevent reflex-induced bronchoconstriction
   
   • (Topical lidocaine may also be used, but the application may provoke bronchospasm if the depth of anesthesia is insufficient. Since there is significant risk for light anesthesia during a RSI, I would not employ this technique.);
6. apply cricoid pressure; and
7. perform a RSI using ketamine (induces bronchodilation), propofol (produces bronchdilation and a more reliable depth of anesthesia as compared to thiopental), and succinylcholine.
   
   • While succinylcholine could potentially result in significant histamine release (risk for histamine-induced bronchospasm), I believe that its ability to facilitate the rapid placement of an endotracheal tube is important to reduce the risk of aspiration in this patient presenting for emergent surgery (inadequate fasting), an acute abdominal process (delayed gastric emptying), and active nausea.