Asthma oxygen therapy

Patients with acute severe asthma should receive supplemental oxygen therapy to maintain arterial oxygen saturation above 90% (above 95% in pregnant women and patients with heart disease). Significant dehydration should be corrected urine specific gravity may help guide therapy in young children, in whom assessment of hydration status may be difficult. 

High concentration oxygen therapy is reserved for a state of low PaOj in association with a normal or low PaCO (type I respiratory failure), as in pulmonary embolism, pneumonia, pulmonary oedema, myocardial infarction, and young patients with acute severe asthma. Concentrations of up to 100% may be used for short periods, since there is little risk of inducing hypoventilation and CO retention. 

Determining appropriate use of supplemental oxygen therapy Assessment of the effect of a rehabil itation program Evaluation of specific disease states or conditions (e.g., asthma COPD interstitial lung disease pulmonary vascular disorders coronary artery disease other vascular disorders neuromuscular disorders obesity anxiety-induced hyperventilation)... 

The low breathing resistance of helium—oxygen mixtures is of therapeutic advantage for patients suffering from asthma and other obstmctive respitatory difficulties. The mixtures have also been used for hyperbaric therapy. 

Treatment of severe acute asthma includes the use of oxygen for the rapid reversal of hypoxemia, a short-acting P2-agonist to reverse airway constriction, and a systemic corticosteroid to attenuate the inflammatory response.1 Close monitoring of objective measures such as FEVi or PEF is important to quantify the response to therapy. Because recovery from exacerbations is often gradual, intensified therapy should be continued for several days. 

Certain forms of dyspnea yield only to opiates. Especially in this category is the dyspnea of acute left ventricular failure and pulmonary edema. Most authorities agree that morphine is contraindicated in patients with pulmonary edema caused by chemical respiratory irritants. If needed in such cases for severe pain, its use should be combined with oxygen inhalation and positive-pressure therapy. In bronchial asthma, morphine is usually contraindicated because there is danger of addiction, the drug tends to depress respiration and to constrict bronchioles, and patients with asthma may be allergic to the drug. Deaths have occurred from the use of morphine in asthma. 

Table 2.1. Drag application routes. Note that inhalation of gases is very different from inhalation of aerosols. Gases will, like oxygen, be sy stemically distributed, whereas the droplets of aerosols will be deposited on the mucous membranes of the bronchi. Accordingly, aerosols are mostly used for topical therapy of asthma.

Beta-adrenoceptor agonists can prodnce or worsen hypoxia acutely in patients with asthma by increasing ventilation-perfusion inequality. It is not known whether this effect is clinically important in patients with asthma not severe enough to require hospital treatment (where supplementary oxygen is standard therapy). 

Routine modern therapy of severe exacerbations of asthma includes oxygen in addition to frequent inhalation of p -selective bronchodilators and. frequently, systemic corticosteroids. Therapy of status asthmaticus is more complicated, requiring intubation and respiratory assistance, sedation, parenteral corticosteroids, and bronchodilators. 

Air enriched with 40 % oxygen is necessary for medical treatment of asthma. For this kind of therapy, poly(4-methylpentene-l) and poly(2,6-dimethylphenylene oxide) are applied, for which the FO2 and o values are, 3.23xl0-9cm3(STP) cm/cm2-sec.cmHg, 4.1 1.58xl0-9cm3 (STP)-cm/cm2-sec-cmHg, 4.2, respectively. 

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