Physical Therapy In Bronchial Asthma
Chronic inflammatory process characterized by increased susceptibility of the trachea
and bronchi to various stimuli, manifested by diffuse narrowing of the airways, whose intensity varies either spontaneously as a result of treatment.
The course of the disease has a characteristic intermittent nature, with periods of symptoms of variable duration, alternating with phases devoid of symptoms, there are often allergic factors, but these can not always be proven.
Pathophysiology
The dynamic expression of asthma is given for why paroxysmal bronchospasm, reversible and repeatable, but airway obstruction is still ongoing edema of the bronchial walls, and the consequent hypersecretion of forced expiration, which further restricts the light of the bronchus.
There is a reduction in vital capacity, increased residual volume and hyperventilation requiring increased respiratory effort and increased need for air, giving the sensation of dyspnea. The bronchial obstruction is not uniform, some areas are completely obstructed during expiration, the markedly distended alveoli, reducing the capillary bed and damaging the infusion.
In others, there is no interruption of blood flow, but reduction of ventilation, so more than ventilation perfusion, but as there is low oxygen tensoalveolar appears a final reduction in arterial oxygen tension, a major cause of hypoxemia in asthma. Furthermore, when promoting the catecholamine or aminophylline bronchodilation, vasodilation occurs capillary parallel, increasing the flow was reduced and thereby pass more poorly oxygenated blood, paradoxically increasing hypoxia.
As a result of anxiety, dyspnea and excessive respiratory effort, there is an increased minute ventilation and alveolar ventilation, leading to hypocapnia and mild excessive loss of water that sometimes not associated with fluid intake, can lead to dehydration.
When the obstruction reaches over 75% of the pulmonary ventilation is unable to eliminate the excess gas and then rises arterial pCO2, assuming an emergency. Despite hyperventilation, hypoxemia is very common because the excessive ventilation of perfused alveoli, although offset by alveolar hypercapnia subventilados, fails to compensate for hypoxia caused by poorly ventilated areas infusion. Hypoxemia did not should cause concern and can be easily corrected by the administration of oxygen at low concentrations.
Arterial blood gas analysis revealed the fact that, invariably, hypoxemia, hypocapnia and increased arterial pH in patients with mild or moderate, can not be requested, since the therapist minister oxygen in these cases without the risk of respiratory arrest. Usually the asthmatic experiences in crises, remarkable VAD, which is attributed to nervous reflexes (stretch receptors and irritation) and hypoxemia.
Arterial blood gas analysis, however, can provide two important insights to the characterization of the crisis:
1) as hypoxemia reflects the nonuniform intensity distribution of the index V / Q, it allows us to infer the intensity of the functional impairment of the airways;
2) a normal or elevated PaCO2, which is exceptional, denotes diaphragmatic fatigue and failure in compensatory mechanisms of hypoxia. It is thought that justifies admission to the ICU, given the imminent need for mechanical ventilation.
Pharmacological Treatment
The sympathomimetic or adrenergic drugs can stimulate various receptors, or both (epinephrine, ephedrine), or with selectivity over the predominant beta-1 and beta-2 (isopropilnoradrenalina or isoproterenol), with selective or more punctiform receptors on beta -2, which allows control of bronchoconstriction (salbutamol, fenoterol, terbutaline and metaproterenol). Pharmacologically, adrenaline and isoproterenol are catecholamines, the metaproterenol, terbutaline and fenoterol are resorcinols, and salbutamol is a saligenina.
Adrenaline or epinephrine is exclusively parenteral and its effect is ephemeral. When used in acute attacks, is by the subcutaneous injection (0.2 to 0.5 ml of aqueous solution 1:1000). Ephedrine has mild bronchodilator effect, usually associated to theophylline and marketed a sedative (Tedral, Franol, Marax etc..).
The isoproterenol (Isuprel) is endowed with potent selective beta-adrenergic effect, and its most common use by inhalation. It is a drug that has fallen into disuse progressive for its transient effect and subject to refractoriness, and also the great benefits of drugs with selective beta-2 current.
The beta-2 agonists are very effective, which resulted in its widespread use in the treatment and prevention of bronchial asthma. Their actions are manifold: relaxation of bronchial smooth muscle (and preventing its contracture), acceleration of mucociliary removal and prevention of release of mediators. There are several drugs in this group of commercially available, including: mataproterenol, terbutaline, salbutamol or albuterol and fenoterol.
Of methylxanthine, both aminophylline (theophylline associated etilenodramina), commonly used intravenously in the emergency department, the simple theophylline, used with attendance increasing, thanks to the introduction of numerous repairs prolonged effect, act by inhibiting phosphodiesterase for potentiation of diaphragmatic contractility and by stimulating regulatory centers of ventilation.
Steroids basically has its extraordinary effect of its anti-inflammatory. They stabilize lysosomal membranes, reducing the storage of histamine and leukotrienes (SRS-A) and restore the responsiveness of the smooth muscle to beta-agonists. By inhibiting the inflammatory response presumptively delayed, corticosteroids constitute the best feature where the control of asthma is insufficient by combining and bronchodilators, and in cases where there is a progressive worsening of crisis.
Disodium cromoglycate seems to be able to reduce the release of mediators by acting on the membrane of mast cells and basophils. This is a prophylactic drug should not be used during crises.
Side effects:
- Adrenergic: Most studies showed a small change in airway smooth muscle to beta stimulation, after prolonged treatment with beta-agonist drugs, but a well-controlled study that showed that regular inhalation of formoterol was associated with a slight worsening of symptoms asthma and bronchial reactivity compared with the use of the agent with the criterion of "only when necessary."
The arterial oxygen tension (PaO 2) may decrease after administration of beta agonists, where the grounds ventilation / perfusion lung worsen. However, this effect is usually small, can occur with any bronchodilator medication and their clinical significance depends on the patient's initial PaO2.
There are concerns about the toxicity secondary to myocardial propellants based on freon contained in all commercially available inhalers batchers. Although fluorocabonetos can sensitize the heart to the toxic effects of catecholamines, such an effect only occurs at very high concentrations myocardium that are not achieved if the inhalers are used as recommended. In general, b2 adrenoceptor agonist bronchodilators are safe and effective when administered in doses which avoid the systemic side effects.
- Methylxanthines:
1) Effect on central nervous system: at low doses and moderate, methylxanthines, particularly caffeine, cause a slight increase in cortical stimulation and alertness removal of fatigue. At very high doses, there may be spinal cord stimulation and convulsions. Anxiety and tremor are the main side effects in patients who ingest large doses of aminophylline for asthma.
2) Cardiovascular effects: The methylxanthines have positive chronotropic and inotropic effects directly to the heart. At low concentrations, such effects appear to result from increased release of catecholamines is caused by inhibition of presynaptic receptors adenosinicos ..
At high concentrations, the influx of calcium daily can be increased by increasing cAMP resulting from the inhibition of phosphodiesterase. In high concentrations, there is a decrease of calcium sequestration by the sarcoplasmic reticulum. In unusually sensitive individuals, consuming a few cups of coffee can cause arrhythmias, but in most people, the parenteral administration of high doses of methylxanthines produces only a sinus tachycardia and increased cardiac output.
In large doses, these agents also relax vascular smooth muscle, except in cerebral blood vessels, where they cause contraction. However, the routine consumption of coffee and other beverages containing methylxanthines in general slightly increases peripheral vascular resistance and blood pressure, probably through the release of catecholamines. Methylxanthines decrease blood viscosity and can improve the blood flow in certain circumstances.
- Steroids: The main drawbacks of prolonged use of steroids are: psychogenic disorders; Cushingoid effect, suppression of hypothalamic-pituitary-adrenal; hypertension; diabetogeno effect, growth arrest, peptic ulcer, spontaneous fractures, opportunistic infections, reactivation of tubercular process.
- Cromoglycate: How is poorly absorbed from the gastrointestinal tract, the adverse effects of cromolyn are smaller and are located at the injection site. Include symptoms such as sore throat, cough, dry mouth, chest tightness and wheezing. Some of these symptoms can be prevented by the inhalation of a medicament prior to agonist treatment with cromolyn. Adverse effects are rare. The dermatitis, myositis, and gastroenteritis reversible, occurs in about 2% of patients have been few reported cases of pulmonary infiltration with eosinophilia and anaphylaxis.
- Anticholinergics: The systemic adverse effects limit the amount of atropine sulfate may be administered, but the development of a quaternary ammonium derivative with atropine more selective, ipratropium bromide, allows high doses for muscarinic receptors in the airways , because the compound is poorly absorbed immediately and does not penetrate the central nervous system.
Non-pharmacological treatment
- Physical therapy: The physical therapy consist of the phase in which the patient will meet, or in a crisis during or intercritical. In the intercritical period, the respiratory exercise preceded by nebulization (hydrate the airways) aims to improve gradually the ventilatory capacity of the individual, to correct defects of posture and respiratory muscle reeducation.
Avoid shortening of the chest muscles as well as deformities through postural patterns, stretching is very important.
The care given to patients in crisis will be to support drug and, if possible, noninvasive ventilatory support (NIV). The use of NIV is to minimize respiratory effort determined and thus avoid endotracheal intubation and subsequent mechanical ventilation. The adoption of bilevel mode (two pressure levels: IPAP and EPAP) in the NIV is recommended, macaras via nasal or facial.
However, signs of severe physical examination such as tachypnea (RR> 35), tachycardia (HR> 120), use of accessory muscles, presence of pulsus paradoxus greater than 12 mmHg, orthopnea, sweating when associated with the presence of hypercapnia, hypoxia or acidosis lactic guide to the need for endotracheal intubation. Cyanosis, altered level of consciousness and hypotension are late signs of respiratory failure and should not be expected to be instituted mechanical ventilation.
Patients whose peak flow is less than 30% predicted or FEV1 is less than 1 liter are at risk for respiratory failure. The presence of hypercapnia alone. Then the patient will be referred to the intensive care unit due to respiratory care, measurement of arterial blood gases, hemodynamic monitoring.
The mechanical ventilation must meet the needs rest to respiratory muscles and promote adequate oxygenation and especially the reduction of dynamic hyperinflation. Then the volume controlled modes or pressure controlled can be adopted provided they meet a low minute volume and prolonged expiratory time. The presence of bronchospasm and / or mucous should be opposed to there form a pressure positive end-expiratory pressure (autoPEEP) and thus alveolar overdistension.
To achieve adequate oxygenation without increasing the dynamic hyperinflation, must use a tidal volume of 5-8 ml / kg and a respiratory rate of 10-14 minutes, the fraction of inspired O2 (FIO2) starting at 100% and a 80-100L/min inspiratory flow. Subsequently, adjustments of these parameters must be made for an SpO2> 92% and maintain the plateau pressure of less than or equal to 30. The plateau pressure must be used as a measure of hyperinflation, since it reflects more reliable alveolar than just measuring the self PEEP.
The peak pressure usually kept below 40. The difference PIP - Pplateau, in turn, may be useful in monitoring the degree of airflow limitation.
In asthmatics, the initial PEEP should be zero (ZEEP), since in asthmatics the addition of extrinsic PEEP appears to increase slightly the PaO2 increased at the expense of hyperinflation.
by: Stiven Benson
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