Mechanical Ventilation

When in spite of the emergency physician's best effort to treat an acute asthma exacerbation, when the patient begins to exhibit signs of acute ventilatory failure, noninvasive positive-pressure ventilation may be attempted.30 However, if the patient manifests progressive hypercarbia and acidosis or becomes exhausted or confused, intubation and mechanical ventilation are necessary to prevent respiratory arrest. Mechanical ventilation does not relieve the airflow obstruction; it merely eliminates the work of breathing and enables the patient to rest while the airflow obstruction is resolved. Fortunately, fewer than 1 percent of asthmatics ever require mechanical ventilation. Direct oral intubation is preferred over the nasotracheal route.

The potential complications of mechanical ventilation in asthmatic patients are numerous. Increased airway resistance may lead to extremely high peak airway pressures, barotrauma, and hemodynamic impairment. Mucous plugging is frequent, often leading to increased airway resistance, atelectasis, and pulmonary infection. Due to the severity of airflow obstruction during the early phases of treatment, the tidal volume may be larger than the returned volume, leading to air trapping and increased residual volume [intrinsic positive end-expiratory pressure (intrinsic PEEP)]. These effects may be partially avoided by utilizing rapid inspiratory flow rates at a reduced respiratory frequency (12 to 14/min), and allowing adequate time for the expiratory phase. one can achieve the goal of ventilatory support—maintenance of an adequate arterial oxygen saturation (90 percent or more)—without concern for "normalizing" the hypercarbic acidosis. 31 This approach is called controlled mechanical hypoventilation or permissive hypoventilation. All patients requiring mechanical ventilation must be admitted to an intensive care unit.

Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

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