Respiratory failure may be defined as impairment of normal gas exchange severe enough to require acute therapeutic intervention. Definitions based on arterial blood gases (see Table 57–1) may not apply to patients with chronic pulmonary diseases. For example, dyspnea and progressive respiratory aci-dosis may be present in patients with chronic CO2 retention. Arterial blood gases typically follow one of several patterns in patients with respiratory fail-ure (Figure 57–7). At one extreme, the derangement
primarily affects oxygen transfer from the alveoli into blood, giving rise to hypoxemia (hypoxic respi-ratory failure); unless severe ventilation/perfusion mismatching is present, CO2 elimination in these instances is typically normal or even enhanced. At the other extreme, the disorder primarily affects CO2 elimination (pure ventilatory failure), resulting in hypercapnia; mismatching of ventilation to perfusion is typically absent or minimal. Hypoxemia, however, can occur with pure ventilatory failure when arte-rial CO2 tension reaches 75–80 mm Hg in patients breathing room air (see the alveolar gas equation). Few patients with respiratory failure display a pattern as “pure” as these extreme examples.
Regardless of the disorder, the treatment of respi-ratory failure is primarily supportive while the reversible components of underlying disease are treated. Hypoxemia is treated with oxygen therapy and positive airway pressure (if FRC is decreased), whereas hypercarbia (ventilatory failure) is treated with mechanical ventilation. Other general mea-sures may include using aerosolized bronchodila-tors, intravenous antibiotics, and diuretics for fluid overload, therapy to improve cardiac function, and nutritional support.
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