Treatment may be described under three categories. Treatment of the acute attacks; treatment in between attacks; and treatment of status asthmaticus (Severe acute asthma).
Treatment of the acute attack
Sypathomimetic drungs
Acute asthma readily responds to sympathomimetic drugs. The time-honored drug used to be adrenaline 0.5 to 1ml of 1:1000 aqueous solution given subcutaneously. It promptly relieves bronchospams, brings about expectoration, opens up the airways, and terminates the paroxysm within minutes. Adverse side effects of sympathomimetic drugs include rise in blood pressure, tachycardia, palpitation, and precipitation of angina in those with coronary artery diseases. Aquaeous adrenaline is effective for 4 hours after which the dose may have to be repeated. Oily preparations with a longer duration of action are available. Hurts's method of administration is to deliver adrenaline subcutaneously in a does of 1 drop every minute till the bronchospasm is relieved. This helps in minimizing the dose to the optimum without causing unpleasant side effects. With the advent of safer drugs, the use of adrenaline has been reduced but still in some cases where other drugs fail, adrenaline may be necessary to give immediate relief.
Another sympathomimetic drug employed for the relief of the paroxysm is ephedrine in a dose of 25-50 mg orally every 6 hours, It is often combined with one of the xanthine derivatives. Its effect is slower but more sustained. In elderly subjects it produces urinary retention, which may precipitate prostratic symptoms. Other side effects include palpitation, excitement, and insomnia. Isoprenaline given in a dose of 20 mg subcutaneously, sublingually or as an aerosol (1/100 solution) is also effective in relieving bronchospasm during an acute attack. Sympathomimetic drugs should be used with caution in hypertensives and elderly subjects with coronary artery disease or urinary obstruction. Fatal arrhythmias may be precipitated by repeated doses of these drugs in those cases with status asthmaticus.
Beta-adrenergic agonists
Salbutamol is a selective beta-2-adrenergic agonist with less of cardiovascular side effects. It is commonly used orally in doses of 2-4 mg every 6-8 hours. It can be used parenterally in an intramuscular or intravenous dose or 500/ microgram. It is prompt in action and relatively safe. Several other beta-2-agonists such as terbutaline, isoetharine etc, are also available.
Methyl xanthines
Theophylline is the prototype of this group of drugs. Several later derivatives are available for oral use. Though the effects are not dramatic. Mild cases do respond to these drugs when given orally in doses of 150-200mg every 6 hours. Aminophylline is one of the ingredients of several commercial anti-asthmatic preparations along with ephedrine and phenobarbitone. The oral dose ranges from 200-300mg and it has to be given every 6 hours. The more effective route of administration of aminophylline is intravenous. The does is 240mg diluted in 20ml of 25% glucose and given intravenously over a period of 3-5 minutes. The effect is dramatic relief of the asthmatic paroxysm. This drug is particularly useful in cases unresponsive to or unsuitable for sympathomemetric drugs. It is one of the common drugs used in management of status asthmaticus. In patients with cardiovascular disease and in conditions where the possibility of left ventricular failure cannot be ruled out, this is the drug of choice. Adverse side effects are rare, but sometimes sudden vasomotor collapse or allergic manifestations may develop
Corticosteroids
These are indicated for the prompt relief of acute severe asthma and also as maintenance dosage in recurrent and chronic disease. For the acute attack, hydrocortisone,e in a dose of 100-200mg or its analogues (dexamethasone 4-8 mg or betamethasone 4-8 mg) are given intravenously as a bolus dose or in a slow drip. The effect is very obvious within 30-60 minutes. Oral preparations such as prednisolone or the other derivatives are preferred for maintenance dose. They are given for short periods to time over a period of exacerbation. The minimum effective dose is to be employed. Some cases may become steroid-dependent and the smallest dose required to be given for symptomatic relief can be determined by trial and error.
Aerosols of beclomethason are being increasingly used to abort or prevent an attack. This route of medication is convenient and the dosage can be kept to a minimum. The aerosol should be taken before bronchospasm is severe to ensure that the drug reaches the bronchi. Once severe bronchospasm develops, the patient cannot take an effective inspiration to deliver the drug at the site of action.
Anticholinergic agents
Atropine used to be given in asthma since it is effective in relieving bronchospasm but it seldom used now on account of its troublesome side effects. Another anticholinergic agent, ipratropium bromide is used at times as an aerosol with success in a dose of 36 mg 6 hours.
Prevention of recurrence
It is important to avoid known allergens which can be identified, especially in the case of some allergens like hose dust and pollen. Desensitization can be achieved by repeated challenges. Disodium cromoglycate administered as an inhalation in a dose of 20mg has the property of preventing mediator release from the mast cells. The inhalation has to be repeated every 6 hours. This drug should not be used during an acute attack since it may cause aggravation of the symptoms.
Respiration and other systemic infections should receive prompt attentions. The appropriate antibiotic should be selected based on microbiological tests. Tranquilisers, psycho-therapy or suggestion under hypnosis may be useful adjuncts in persons with prominent emotional everlay.
Management of acute severe asthma
Status asthmaticus has to be managed as a medical emergency. This condition is generally unresponsive to conventional drugs administered in the usual manner. Clinical assessment of the severity can be made from the intensity of dyspnea. Cyanosis and inability of the patient to speak uninterruptedly. Estimation of peak expiratory flow rate gives an objective assessment of the condition.
General measures:
These involve putting the patient to bed rest propped up with a back-rest; starting an intravenous infusion of normal saline. This aids in the administration of drugs and fluid replacement is essential to correct dehydration; and administering oxygen under supervision.
• Aminophylline is given as slow intravenous injection in a dose of 4-6mg/kg every 6 hours. Many cases get at least partial relief. Aminophylline can also be given as an intravenous infusion at the rate of 0.5-0.7mg/kg/hr.
• Corticosteriods should be given intravenously in high dosage. Hydrocortisone 100-300mg, betamethasone 8mg or dexamethasone 8mg are the preparations of choice. Sedatives which do not depress the respiratory centre are indicated if the patient is restless. Diazepam 5mg is suitable in most cases.
If the condition does not respond to treatment or the respiratory embarrassment is increasing, ventilation should be assisted. If the secretions are tenacious and difficult to be expectorated, throat suction or bronchoscopic aspiration may be required.
Indications for ventilatory assistance
1. Pa CO2 above 44mm Hg,
2. Pa O2 below 50mm Hg,
3. FEV1 or PEFR less than 10% of predicted value
4. extreme physical exhaustion, and
5. clouding of consciousness.
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