Asthma occurs when the main air passages of your lungs, the bronchial tubes, become inflamed. Asthma is characterized by increased responsiveness of the airways. The muscles of the bronchial walls tighten, and cells in the lungs produce extra mucus further narrowing your airways. This can cause minor wheezing to severe difficulty in breathing. Signs and symptoms can range from mild to very severe and are often similar to those of other conditions, including emphysema, early congestive heart failure or vocal cord problems. Two most common tools to measure lung function: Spirometer and Peak flow meter.
The indications for intubation include apnea, near apnea, a sustained respiratory rate of more than 40 breaths per minute (in an adult), depressed level of consciousness, changes in mental status, central cyanosis, or appearance of severe distress. The severity of asthma define in five step scale dependent upon the amount of treatment required to control symptoms:
1. Requires occasional use of a short acting Beta2-agonist.
2. Being the addition of inhaled steroid at up to 400 mcg of beclomethasone dipropionate or equivalent per day.
3. Addition of a third therapy such as a long acting Beta 2-agonist or leukotriene-receptor antagonist.
4. Suggests a cautious increase of inhaled steroids, to maximum of 800mcg per day.
5. Introduction of oral steroids, high dose of inhaled steroid > 1000 mcg per day or other systemic steroid sparing agents such as aminohpylline.
Anesthesiologist must be extra cautious when anesthetizing children on steps four and five.
Premedication : Mild sedation before entering OT, short-acting benzodiazepine midazolam IV (0.05 to 0.1 mg/kg IV) or, in small children, orally (0.5 to 1 mg/kg, with maximum of 15 mg). Bronchodilators should be given just prior to induction. Patients use their inhalers as usual on the day of surgery, but also to take inhaled Beta 2-agonist prior to admission to the operating room. Corticosteroids may help to prevent perioperative bronchospasm although evidence is limited. Intravenous hydrocortisone is recommended to avoid adrenal crisis.
Choice of the anesthesia: Regional anesthesia vs general vs mask vs LMA. Most patient with reactive airways, regional anesthesia is ideal. Ketamine, agent of choice: bronchodilator effect, possibly mediated by direct relaxation of airway smooth muscles. Inhabits vagal pathways and augments catecholamine release, should be accompanied by an anticholinergic agent
Volatile agents used are well known as bronchodilating drugs. Halothane was the agent of choice in the past. Sevoflurane is the most commonly used agent now. LMA may be useful but have not been fully investigated in children. The use of LMA, instead of laryngoscopy and endotracheal intubation, should be considered in patients undergoing minor surgery, as airway reflexes are stimulated less significantly. LMA does not protect the airway from aspiration and is not effective in ventilating patients who have a significant elevation in airway pressure. The best approach to anesthetizing a child might be the use of face mask but only in the presence of good airway and the suitability of the surgical procedures.
Maintenance of anesthesia can be achieved by either IV infusion of hypnotic agents (propofol 50 to 200 mg/kg/min) or the administration of volatile anesthetics, which induce bronchodilatation in a dose-dependent fashion. Opioids and muscle relaxants are frequently administered during surgery. Fentanyl (1 to 3 mcg/kg) and its derivatives do not release histamine (the preferred choices among opioids)
Various muscle relaxants including vecuronium bromide (0.08 to 0.12 mg/kg) and rocuronium bromide (0.6 to 1.2 mg/kg) are devoid of histamine release and are the preferred choices for muscle relaxant (asthma patient). Muscle relaxant should be administered only for the duration of surgery. Asthmatics who are steroid-dependent should be given additional therapy perioperatively in order to avoid adrenal insufficiency during surgery. Perioperative epidural analgesia has been shown to be important in pain relief and in decreasing pulmonary complication.
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